patch, 19 partsCleanup merge API

diff --git a/merge-recursive.c b/merge-recursive.c
index 12300131fc..1163508811 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -934,9 +934,11 @@ static int update_file_flags(struct merge_options *opt,
 		}
 
 		buf = read_object_file(&contents->oid, &type, &size);
-		if (!buf)
-			return err(opt, _("cannot read object %s '%s'"),
-				   oid_to_hex(&contents->oid), path);
+		if (!buf) {
+			ret = err(opt, _("cannot read object %s '%s'"),
+				  oid_to_hex(&contents->oid), path);
+			goto free_buf;
+		}
 		if (type != OBJ_BLOB) {
 			ret = err(opt, _("blob expected for %s '%s'"),
 				  oid_to_hex(&contents->oid), path);

diff --git a/merge-recursive.c b/merge-recursive.c
index 1163508811..37bb94fb4d 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -3571,8 +3571,11 @@ int merge_recursive(struct merge_options *opt,
 		repo_read_index(opt->repo);
 
 	opt->ancestor = "merged common ancestors";
-	clean = merge_trees(opt, get_commit_tree(h1), get_commit_tree(h2),
-			    get_commit_tree(merged_common_ancestors),
+	clean = merge_trees(opt,
+			    repo_get_commit_tree(opt->repo, h1),
+			    repo_get_commit_tree(opt->repo, h2),
+			    repo_get_commit_tree(opt->repo,
+						 merged_common_ancestors),
 			    &mrtree);
 	if (clean < 0) {
 		flush_output(opt);

merge-recursive.c, sequencer.c

diff --git a/merge-recursive.c b/merge-recursive.c
index b762ecd7bd..7f56cb0ed1 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -3583,9 +3583,6 @@ static int merge_recursive_internal(struct merge_options *opt,
 	flush_output(opt);
 	if (!opt->call_depth && opt->buffer_output < 2)
 		strbuf_release(&opt->obuf);
-	if (show(opt, 2))
-		diff_warn_rename_limit("merge.renamelimit",
-				       opt->needed_rename_limit, 0);
 	return clean;
 }
 
@@ -3606,7 +3603,9 @@ static int merge_start(struct merge_options *opt, struct tree *head)
 
 static void merge_finalize(struct merge_options *opt)
 {
-	/* Common code for wrapping up merges will be added here later */
+	if (show(opt, 2))
+		diff_warn_rename_limit("merge.renamelimit",
+				       opt->needed_rename_limit, 0);
 }
 
 int merge_trees(struct merge_options *opt,
diff --git a/sequencer.c b/sequencer.c
index 34ebf8ed94..c85e594704 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -617,7 +617,6 @@ static int do_recursive_merge(struct repository *r,
 	if (is_rebase_i(opts) && clean <= 0)
 		fputs(o.obuf.buf, stdout);
 	strbuf_release(&o.obuf);
-	diff_warn_rename_limit("merge.renamelimit", o.needed_rename_limit, 0);
 	if (clean < 0) {
 		rollback_lock_file(&index_lock);
 		return clean;

diff --git a/merge-recursive.c b/merge-recursive.c
index 37bb94fb4d..b762ecd7bd 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -3381,21 +3381,14 @@ static int process_entry(struct merge_options *opt,
 	return clean_merge;
 }
 
-int merge_trees(struct merge_options *opt,
-		struct tree *head,
-		struct tree *merge,
-		struct tree *common,
-		struct tree **result)
+static int merge_trees_internal(struct merge_options *opt,
+				struct tree *head,
+				struct tree *merge,
+				struct tree *common,
+				struct tree **result)
 {
 	struct index_state *istate = opt->repo->index;
 	int code, clean;
-	struct strbuf sb = STRBUF_INIT;
-
-	if (!opt->call_depth && repo_index_has_changes(opt->repo, head, &sb)) {
-		err(opt, _("Your local changes to the following files would be overwritten by merge:\n  %s"),
-		    sb.buf);
-		return -1;
-	}
 
 	if (opt->subtree_shift) {
 		merge = shift_tree_object(opt->repo, head, merge, opt->subtree_shift);
@@ -3499,11 +3492,11 @@ static struct commit_list *reverse_commit_list(struct commit_list *list)
  * Merge the commits h1 and h2, return the resulting virtual
  * commit object and a flag indicating the cleanness of the merge.
  */
-int merge_recursive(struct merge_options *opt,
-		    struct commit *h1,
-		    struct commit *h2,
-		    struct commit_list *ca,
-		    struct commit **result)
+static int merge_recursive_internal(struct merge_options *opt,
+				    struct commit *h1,
+				    struct commit *h2,
+				    struct commit_list *ca,
+				    struct commit **result)
 {
 	struct commit_list *iter;
 	struct commit *merged_common_ancestors;
@@ -3555,7 +3548,7 @@ int merge_recursive(struct merge_options *opt,
 		saved_b2 = opt->branch2;
 		opt->branch1 = "Temporary merge branch 1";
 		opt->branch2 = "Temporary merge branch 2";
-		if (merge_recursive(opt, merged_common_ancestors, iter->item,
+		if (merge_recursive_internal(opt, merged_common_ancestors, iter->item,
 				    NULL, &merged_common_ancestors) < 0)
 			return -1;
 		opt->branch1 = saved_b1;
@@ -3571,12 +3564,12 @@ int merge_recursive(struct merge_options *opt,
 		repo_read_index(opt->repo);
 
 	opt->ancestor = "merged common ancestors";
-	clean = merge_trees(opt,
-			    repo_get_commit_tree(opt->repo, h1),
-			    repo_get_commit_tree(opt->repo, h2),
-			    repo_get_commit_tree(opt->repo,
-						 merged_common_ancestors),
-			    &mrtree);
+	clean = merge_trees_internal(opt,
+				     repo_get_commit_tree(opt->repo, h1),
+				     repo_get_commit_tree(opt->repo, h2),
+				     repo_get_commit_tree(opt->repo,
+							  merged_common_ancestors),
+				     &mrtree);
 	if (clean < 0) {
 		flush_output(opt);
 		return clean;
@@ -3596,6 +3589,58 @@ int merge_recursive(struct merge_options *opt,
 	return clean;
 }
 
+static int merge_start(struct merge_options *opt, struct tree *head)
+{
+	struct strbuf sb = STRBUF_INIT;
+
+	assert(opt->branch1 && opt->branch2);
+
+	if (repo_index_has_changes(opt->repo, head, &sb)) {
+		err(opt, _("Your local changes to the following files would be overwritten by merge:\n  %s"),
+		    sb.buf);
+		return -1;
+	}
+
+	return 0;
+}
+
+static void merge_finalize(struct merge_options *opt)
+{
+	/* Common code for wrapping up merges will be added here later */
+}
+
+int merge_trees(struct merge_options *opt,
+		struct tree *head,
+		struct tree *merge,
+		struct tree *common,
+		struct tree **result)
+{
+	int ret;
+
+	if (merge_start(opt, head))
+		return -1;
+	ret = merge_trees_internal(opt, head, merge, common, result);
+	merge_finalize(opt);
+
+	return ret;
+}
+
+int merge_recursive(struct merge_options *opt,
+		    struct commit *h1,
+		    struct commit *h2,
+		    struct commit_list *ca,
+		    struct commit **result)
+{
+	int ret;
+
+	if (merge_start(opt, repo_get_commit_tree(opt->repo, h1)))
+		return -1;
+	ret = merge_recursive_internal(opt, h1, h2, ca, result);
+	merge_finalize(opt);
+
+	return ret;
+}
+
 static struct commit *get_ref(struct repository *repo, const struct object_id *oid,
 			      const char *name)
 {

builtin/merge-recursive.c, builtin/stash.c, t/t3030-merge-recursive.sh

diff --git a/builtin/merge-recursive.c b/builtin/merge-recursive.c
index 5b910e351e..a4bfd8fc51 100644
--- a/builtin/merge-recursive.c
+++ b/builtin/merge-recursive.c
@@ -1,3 +1,4 @@
+#include "cache.h"
 #include "builtin.h"
 #include "commit.h"
 #include "tag.h"
@@ -63,6 +64,9 @@ int cmd_merge_recursive(int argc, const char **argv, const char *prefix)
 	if (argc - i != 3) /* "--" "<head>" "<remote>" */
 		die(_("not handling anything other than two heads merge."));
 
+	if (repo_read_index_unmerged(the_repository))
+		die_resolve_conflict("merge");
+
 	o.branch1 = argv[++i];
 	o.branch2 = argv[++i];
 
diff --git a/builtin/stash.c b/builtin/stash.c
index fde6397caa..bec011c1bb 100644
--- a/builtin/stash.c
+++ b/builtin/stash.c
@@ -427,6 +427,8 @@ static int do_apply_stash(const char *prefix, struct stash_info *info,
 				return error(_("could not save index tree"));
 
 			reset_head();
+			discard_cache();
+			read_cache();
 		}
 	}
 
diff --git a/t/t3030-merge-recursive.sh b/t/t3030-merge-recursive.sh
index ff641b348a..a37bcc58a0 100755
--- a/t/t3030-merge-recursive.sh
+++ b/t/t3030-merge-recursive.sh
@@ -667,15 +667,22 @@ test_expect_success 'merging with triple rename across D/F conflict' '
 test_expect_success 'merge-recursive remembers the names of all base trees' '
 	git reset --hard HEAD &&
 
+	# make the index match $c1 so that merge-recursive below does not
+	# fail early
+	git diff --binary HEAD $c1 -- | git apply --cached &&
+
 	# more trees than static slots used by oid_to_hex()
 	for commit in $c0 $c2 $c4 $c5 $c6 $c7
 	do
 		git rev-parse "$commit^{tree}"
 	done >trees &&
 
-	# ignore the return code -- it only fails because the input is weird
+	# ignore the return code; it only fails because the input is weird...
 	test_must_fail git -c merge.verbosity=5 merge-recursive $(cat trees) -- $c1 $c3 >out &&
 
+	# ...but make sure it fails in the expected way
+	test_i18ngrep CONFLICT.*rename/rename out &&
+
 	# merge-recursive prints in reverse order, but we do not care
 	sort <trees >expect &&
 	sed -n "s/^virtual //p" out | sort >actual &&

cache-tree.c, cache-tree.h, merge-recursive.c, merge-recursive.h

diff --git a/cache-tree.c b/cache-tree.c
index 706ffcf188..d2baf6baf5 100644
--- a/cache-tree.c
+++ b/cache-tree.c
@@ -659,6 +659,36 @@ int write_index_as_tree(struct object_id *oid, struct index_state *index_state,
 	return ret;
 }
 
+struct tree *write_tree_from_memory(struct repository *repo)
+{
+	struct tree *result = NULL;
+	struct index_state *istate = repo->index;
+
+	if (unmerged_index(istate)) {
+		int i;
+		fprintf(stderr, "BUG: There are unmerged index entries:\n");
+		for (i = 0; i < istate->cache_nr; i++) {
+			const struct cache_entry *ce = istate->cache[i];
+			if (ce_stage(ce))
+				fprintf(stderr, "BUG: %d %.*s\n", ce_stage(ce),
+					(int)ce_namelen(ce), ce->name);
+		}
+		BUG("unmerged index entries in merge-recursive.c");
+	}
+
+	if (!istate->cache_tree)
+		istate->cache_tree = cache_tree();
+
+	if (!cache_tree_fully_valid(istate->cache_tree) &&
+	    cache_tree_update(istate, 0) < 0) {
+		BUG("error building trees");
+	}
+
+	result = lookup_tree(repo, &istate->cache_tree->oid);
+
+	return result;
+}
+
 static void prime_cache_tree_rec(struct repository *r,
 				 struct cache_tree *it,
 				 struct tree *tree)
diff --git a/cache-tree.h b/cache-tree.h
index 757bbc48bc..4d67c237ba 100644
--- a/cache-tree.h
+++ b/cache-tree.h
@@ -47,6 +47,8 @@ void cache_tree_verify(struct repository *, struct index_state *);
 #define WRITE_TREE_PREFIX_ERROR (-3)
 
 int write_index_as_tree(struct object_id *oid, struct index_state *index_state, const char *index_path, int flags, const char *prefix);
+struct tree *write_tree_from_memory(struct repository *repo);
+
 void prime_cache_tree(struct repository *, struct index_state *, struct tree *);
 
 int cache_tree_matches_traversal(struct cache_tree *, struct name_entry *ent, struct traverse_info *info);
diff --git a/merge-recursive.c b/merge-recursive.c
index 1a3c6ab7f3..937a816288 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -412,36 +412,6 @@ static void unpack_trees_finish(struct merge_options *opt)
 	clear_unpack_trees_porcelain(&opt->unpack_opts);
 }
 
-struct tree *write_tree_from_memory(struct repository *repo)
-{
-	struct tree *result = NULL;
-	struct index_state *istate = repo->index;
-
-	if (unmerged_index(istate)) {
-		int i;
-		fprintf(stderr, "BUG: There are unmerged index entries:\n");
-		for (i = 0; i < istate->cache_nr; i++) {
-			const struct cache_entry *ce = istate->cache[i];
-			if (ce_stage(ce))
-				fprintf(stderr, "BUG: %d %.*s\n", ce_stage(ce),
-					(int)ce_namelen(ce), ce->name);
-		}
-		BUG("unmerged index entries in merge-recursive.c");
-	}
-
-	if (!istate->cache_tree)
-		istate->cache_tree = cache_tree();
-
-	if (!cache_tree_fully_valid(istate->cache_tree) &&
-	    cache_tree_update(istate, 0) < 0) {
-		BUG("error building trees");
-	}
-
-	result = lookup_tree(repo, &istate->cache_tree->oid);
-
-	return result;
-}
-
 static int save_files_dirs(const struct object_id *oid,
 			   struct strbuf *base, const char *path,
 			   unsigned int mode, int stage, void *context)
diff --git a/merge-recursive.h b/merge-recursive.h
index 33f3d53c09..973f2729a8 100644
--- a/merge-recursive.h
+++ b/merge-recursive.h
@@ -97,7 +97,6 @@ int merge_recursive_generic(struct merge_options *o,
 
 void init_merge_options(struct merge_options *o,
 			struct repository *repo);
-struct tree *write_tree_from_memory(struct repository *repo);
 
 int parse_merge_opt(struct merge_options *out, const char *s);
 

diff --git a/merge-recursive.c b/merge-recursive.c
index 937a816288..104c70b787 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -681,7 +681,9 @@ static void add_flattened_path(struct strbuf *out, const char *s)
 			out->buf[i] = '_';
 }
 
-static char *unique_path(struct merge_options *opt, const char *path, const char *branch)
+static char *unique_path(struct merge_options *opt,
+			 const char *path,
+			 const char *branch)
 {
 	struct path_hashmap_entry *entry;
 	struct strbuf newpath = STRBUF_INIT;
@@ -915,7 +917,8 @@ static int update_file_flags(struct merge_options *opt,
 		}
 		if (S_ISREG(contents->mode)) {
 			struct strbuf strbuf = STRBUF_INIT;
-			if (convert_to_working_tree(opt->repo->index, path, buf, size, &strbuf)) {
+			if (convert_to_working_tree(opt->repo->index,
+						    path, buf, size, &strbuf)) {
 				free(buf);
 				size = strbuf.len;
 				buf = strbuf_detach(&strbuf, NULL);
@@ -3392,7 +3395,8 @@ static int merge_trees_internal(struct merge_options *opt,
 		 * opposed to decaring a local hashmap is for convenience
 		 * so that we don't have to pass it to around.
 		 */
-		hashmap_init(&opt->current_file_dir_set, path_hashmap_cmp, NULL, 512);
+		hashmap_init(&opt->current_file_dir_set, path_hashmap_cmp,
+			     NULL, 512);
 		get_files_dirs(opt, head);
 		get_files_dirs(opt, merge);
 
@@ -3498,7 +3502,8 @@ static int merge_recursive_internal(struct merge_options *opt,
 		struct tree *tree;
 
 		tree = lookup_tree(opt->repo, opt->repo->hash_algo->empty_tree);
-		merged_common_ancestors = make_virtual_commit(opt->repo, tree, "ancestor");
+		merged_common_ancestors = make_virtual_commit(opt->repo,
+							      tree, "ancestor");
 	}
 
 	for (iter = ca; iter; iter = iter->next) {
@@ -3609,7 +3614,8 @@ int merge_recursive(struct merge_options *opt,
 	return ret;
 }
 
-static struct commit *get_ref(struct repository *repo, const struct object_id *oid,
+static struct commit *get_ref(struct repository *repo,
+			      const struct object_id *oid,
 			      const char *name)
 {
 	struct object *object;
@@ -3644,7 +3650,8 @@ int merge_recursive_generic(struct merge_options *opt,
 		int i;
 		for (i = 0; i < num_base_list; ++i) {
 			struct commit *base;
-			if (!(base = get_ref(opt->repo, base_list[i], oid_to_hex(base_list[i]))))
+			if (!(base = get_ref(opt->repo, base_list[i],
+					     oid_to_hex(base_list[i]))))
 				return err(opt, _("Could not parse object '%s'"),
 					   oid_to_hex(base_list[i]));
 			commit_list_insert(base, &ca);

merge-recursive.c, merge-recursive.h

diff --git a/merge-recursive.c b/merge-recursive.c
index 104c70b787..0a90546824 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -3356,24 +3356,26 @@ static int process_entry(struct merge_options *opt,
 static int merge_trees_internal(struct merge_options *opt,
 				struct tree *head,
 				struct tree *merge,
-				struct tree *common,
+				struct tree *merge_base,
 				struct tree **result)
 {
 	struct index_state *istate = opt->repo->index;
 	int code, clean;
 
 	if (opt->subtree_shift) {
-		merge = shift_tree_object(opt->repo, head, merge, opt->subtree_shift);
-		common = shift_tree_object(opt->repo, head, common, opt->subtree_shift);
+		merge = shift_tree_object(opt->repo, head, merge,
+					  opt->subtree_shift);
+		merge_base = shift_tree_object(opt->repo, head, merge_base,
+					       opt->subtree_shift);
 	}
 
-	if (oid_eq(&common->object.oid, &merge->object.oid)) {
+	if (oid_eq(&merge_base->object.oid, &merge->object.oid)) {
 		output(opt, 0, _("Already up to date!"));
 		*result = head;
 		return 1;
 	}
 
-	code = unpack_trees_start(opt, common, head, merge);
+	code = unpack_trees_start(opt, merge_base, head, merge);
 
 	if (code != 0) {
 		if (show(opt, 4) || opt->call_depth)
@@ -3401,7 +3403,7 @@ static int merge_trees_internal(struct merge_options *opt,
 		get_files_dirs(opt, merge);
 
 		entries = get_unmerged(opt->repo->index);
-		clean = detect_and_process_renames(opt, common, head, merge,
+		clean = detect_and_process_renames(opt, merge_base, head, merge,
 						   entries, &re_info);
 		record_df_conflict_files(opt, entries);
 		if (clean < 0)
@@ -3468,11 +3470,11 @@ static struct commit_list *reverse_commit_list(struct commit_list *list)
 static int merge_recursive_internal(struct merge_options *opt,
 				    struct commit *h1,
 				    struct commit *h2,
-				    struct commit_list *ca,
+				    struct commit_list *merge_bases,
 				    struct commit **result)
 {
 	struct commit_list *iter;
-	struct commit *merged_common_ancestors;
+	struct commit *merged_merge_bases;
 	struct tree *mrtree;
 	int clean;
 
@@ -3482,31 +3484,31 @@ static int merge_recursive_internal(struct merge_options *opt,
 		output_commit_title(opt, h2);
 	}
 
-	if (!ca) {
-		ca = get_merge_bases(h1, h2);
-		ca = reverse_commit_list(ca);
+	if (!merge_bases) {
+		merge_bases = get_merge_bases(h1, h2);
+		merge_bases = reverse_commit_list(merge_bases);
 	}
 
 	if (show(opt, 5)) {
-		unsigned cnt = commit_list_count(ca);
+		unsigned cnt = commit_list_count(merge_bases);
 
 		output(opt, 5, Q_("found %u common ancestor:",
 				"found %u common ancestors:", cnt), cnt);
-		for (iter = ca; iter; iter = iter->next)
+		for (iter = merge_bases; iter; iter = iter->next)
 			output_commit_title(opt, iter->item);
 	}
 
-	merged_common_ancestors = pop_commit(&ca);
-	if (merged_common_ancestors == NULL) {
+	merged_merge_bases = pop_commit(&merge_bases);
+	if (merged_merge_bases == NULL) {
 		/* if there is no common ancestor, use an empty tree */
 		struct tree *tree;
 
 		tree = lookup_tree(opt->repo, opt->repo->hash_algo->empty_tree);
-		merged_common_ancestors = make_virtual_commit(opt->repo,
-							      tree, "ancestor");
+		merged_merge_bases = make_virtual_commit(opt->repo, tree,
+							 "ancestor");
 	}
 
-	for (iter = ca; iter; iter = iter->next) {
+	for (iter = merge_bases; iter; iter = iter->next) {
 		const char *saved_b1, *saved_b2;
 		opt->call_depth++;
 		/*
@@ -3522,14 +3524,14 @@ static int merge_recursive_internal(struct merge_options *opt,
 		saved_b2 = opt->branch2;
 		opt->branch1 = "Temporary merge branch 1";
 		opt->branch2 = "Temporary merge branch 2";
-		if (merge_recursive_internal(opt, merged_common_ancestors, iter->item,
-				    NULL, &merged_common_ancestors) < 0)
+		if (merge_recursive_internal(opt, merged_merge_bases, iter->item,
+					     NULL, &merged_merge_bases) < 0)
 			return -1;
 		opt->branch1 = saved_b1;
 		opt->branch2 = saved_b2;
 		opt->call_depth--;
 
-		if (!merged_common_ancestors)
+		if (!merged_merge_bases)
 			return err(opt, _("merge returned no commit"));
 	}
 
@@ -3542,7 +3544,7 @@ static int merge_recursive_internal(struct merge_options *opt,
 				     repo_get_commit_tree(opt->repo, h1),
 				     repo_get_commit_tree(opt->repo, h2),
 				     repo_get_commit_tree(opt->repo,
-							  merged_common_ancestors),
+							  merged_merge_bases),
 				     &mrtree);
 	if (clean < 0) {
 		flush_output(opt);
@@ -3585,14 +3587,14 @@ static void merge_finalize(struct merge_options *opt)
 int merge_trees(struct merge_options *opt,
 		struct tree *head,
 		struct tree *merge,
-		struct tree *common,
+		struct tree *merge_base,
 		struct tree **result)
 {
 	int ret;
 
 	if (merge_start(opt, head))
 		return -1;
-	ret = merge_trees_internal(opt, head, merge, common, result);
+	ret = merge_trees_internal(opt, head, merge, merge_base, result);
 	merge_finalize(opt);
 
 	return ret;
@@ -3601,14 +3603,14 @@ int merge_trees(struct merge_options *opt,
 int merge_recursive(struct merge_options *opt,
 		    struct commit *h1,
 		    struct commit *h2,
-		    struct commit_list *ca,
+		    struct commit_list *merge_bases,
 		    struct commit **result)
 {
 	int ret;
 
 	if (merge_start(opt, repo_get_commit_tree(opt->repo, h1)))
 		return -1;
-	ret = merge_recursive_internal(opt, h1, h2, ca, result);
+	ret = merge_recursive_internal(opt, h1, h2, merge_bases, result);
 	merge_finalize(opt);
 
 	return ret;
@@ -3636,8 +3638,8 @@ static struct commit *get_ref(struct repository *repo,
 int merge_recursive_generic(struct merge_options *opt,
 			    const struct object_id *head,
 			    const struct object_id *merge,
-			    int num_base_list,
-			    const struct object_id **base_list,
+			    int num_merge_bases,
+			    const struct object_id **merge_bases,
 			    struct commit **result)
 {
 	int clean;
@@ -3646,14 +3648,14 @@ int merge_recursive_generic(struct merge_options *opt,
 	struct commit *next_commit = get_ref(opt->repo, merge, opt->branch2);
 	struct commit_list *ca = NULL;
 
-	if (base_list) {
+	if (merge_bases) {
 		int i;
-		for (i = 0; i < num_base_list; ++i) {
+		for (i = 0; i < num_merge_bases; ++i) {
 			struct commit *base;
-			if (!(base = get_ref(opt->repo, base_list[i],
-					     oid_to_hex(base_list[i]))))
+			if (!(base = get_ref(opt->repo, merge_bases[i],
+					     oid_to_hex(merge_bases[i]))))
 				return err(opt, _("Could not parse object '%s'"),
-					   oid_to_hex(base_list[i]));
+					   oid_to_hex(merge_bases[i]));
 			commit_list_insert(base, &ca);
 		}
 	}
diff --git a/merge-recursive.h b/merge-recursive.h
index 973f2729a8..a96c8ad50f 100644
--- a/merge-recursive.h
+++ b/merge-recursive.h
@@ -74,14 +74,14 @@ static inline int merge_detect_rename(struct merge_options *o)
 int merge_recursive(struct merge_options *o,
 		    struct commit *h1,
 		    struct commit *h2,
-		    struct commit_list *ancestors,
+		    struct commit_list *merge_bases,
 		    struct commit **result);
 
 /* rename-detecting three-way merge, no recursion */
 int merge_trees(struct merge_options *o,
 		struct tree *head,
 		struct tree *merge,
-		struct tree *common,
+		struct tree *merge_base,
 		struct tree **result);
 
 /*
@@ -91,8 +91,8 @@ int merge_trees(struct merge_options *o,
 int merge_recursive_generic(struct merge_options *o,
 			    const struct object_id *head,
 			    const struct object_id *merge,
-			    int num_ca,
-			    const struct object_id **ca,
+			    int num_merge_bases,
+			    const struct object_id **merge_bases,
 			    struct commit **result);
 
 void init_merge_options(struct merge_options *o,

diff --git a/merge-recursive.c b/merge-recursive.c
index 0a90546824..61faa26c4f 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -3475,7 +3475,7 @@ static int merge_recursive_internal(struct merge_options *opt,
 {
 	struct commit_list *iter;
 	struct commit *merged_merge_bases;
-	struct tree *mrtree;
+	struct tree *result_tree;
 	int clean;
 
 	if (show(opt, 4)) {
@@ -3545,14 +3545,15 @@ static int merge_recursive_internal(struct merge_options *opt,
 				     repo_get_commit_tree(opt->repo, h2),
 				     repo_get_commit_tree(opt->repo,
 							  merged_merge_bases),
-				     &mrtree);
+				     &result_tree);
 	if (clean < 0) {
 		flush_output(opt);
 		return clean;
 	}
 
 	if (opt->call_depth) {
-		*result = make_virtual_commit(opt->repo, mrtree, "merged tree");
+		*result = make_virtual_commit(opt->repo, result_tree,
+					      "merged tree");
 		commit_list_insert(h1, &(*result)->parents);
 		commit_list_insert(h2, &(*result)->parents->next);
 	}

diff --git a/merge-recursive.h b/merge-recursive.h
index a96c8ad50f..e27c2a05bb 100644
--- a/merge-recursive.h
+++ b/merge-recursive.h
@@ -64,21 +64,21 @@ struct collision_entry {
 	unsigned reported_already:1;
 };
 
-static inline int merge_detect_rename(struct merge_options *o)
+static inline int merge_detect_rename(struct merge_options *opt)
 {
-	return o->merge_detect_rename >= 0 ? o->merge_detect_rename :
-		o->diff_detect_rename >= 0 ? o->diff_detect_rename : 1;
+	return opt->merge_detect_rename >= 0 ? opt->merge_detect_rename :
+		opt->diff_detect_rename >= 0 ? opt->diff_detect_rename : 1;
 }
 
 /* merge_trees() but with recursive ancestor consolidation */
-int merge_recursive(struct merge_options *o,
+int merge_recursive(struct merge_options *opt,
 		    struct commit *h1,
 		    struct commit *h2,
 		    struct commit_list *merge_bases,
 		    struct commit **result);
 
 /* rename-detecting three-way merge, no recursion */
-int merge_trees(struct merge_options *o,
+int merge_trees(struct merge_options *opt,
 		struct tree *head,
 		struct tree *merge,
 		struct tree *merge_base,
@@ -88,16 +88,16 @@ int merge_trees(struct merge_options *o,
  * "git-merge-recursive" can be fed trees; wrap them into
  * virtual commits and call merge_recursive() proper.
  */
-int merge_recursive_generic(struct merge_options *o,
+int merge_recursive_generic(struct merge_options *opt,
 			    const struct object_id *head,
 			    const struct object_id *merge,
 			    int num_merge_bases,
 			    const struct object_id **merge_bases,
 			    struct commit **result);
 
-void init_merge_options(struct merge_options *o,
+void init_merge_options(struct merge_options *opt,
 			struct repository *repo);
 
-int parse_merge_opt(struct merge_options *out, const char *s);
+int parse_merge_opt(struct merge_options *opt, const char *s);
 
 #endif

merge-recursive.c, merge-recursive.h

diff --git a/merge-recursive.c b/merge-recursive.c
index 0a944f51ae..0f8d451f2e 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -385,8 +385,7 @@ static int add_cacheinfo(struct merge_options *opt,
 
 static inline int merge_detect_rename(struct merge_options *opt)
 {
-	return opt->merge_detect_rename >= 0 ? opt->merge_detect_rename :
-		opt->diff_detect_rename >= 0 ? opt->diff_detect_rename : 1;
+	return (opt->detect_renames != -1) ? opt->detect_renames : 1;
 }
 
 static void init_tree_desc_from_tree(struct tree_desc *desc, struct tree *tree)
@@ -1885,9 +1884,7 @@ static struct diff_queue_struct *get_diffpairs(struct merge_options *opt,
 	 */
 	if (opts.detect_rename > DIFF_DETECT_RENAME)
 		opts.detect_rename = DIFF_DETECT_RENAME;
-	opts.rename_limit = opt->merge_rename_limit >= 0 ? opt->merge_rename_limit :
-			    opt->diff_rename_limit >= 0 ? opt->diff_rename_limit :
-			    1000;
+	opts.rename_limit = (opt->rename_limit != -1) ? opt->rename_limit : 1000;
 	opts.rename_score = opt->rename_score;
 	opts.show_rename_progress = opt->show_rename_progress;
 	opts.output_format = DIFF_FORMAT_NO_OUTPUT;
@@ -3711,14 +3708,14 @@ static void merge_recursive_config(struct merge_options *opt)
 {
 	char *value = NULL;
 	git_config_get_int("merge.verbosity", &opt->verbosity);
-	git_config_get_int("diff.renamelimit", &opt->diff_rename_limit);
-	git_config_get_int("merge.renamelimit", &opt->merge_rename_limit);
+	git_config_get_int("diff.renamelimit", &opt->rename_limit);
+	git_config_get_int("merge.renamelimit", &opt->rename_limit);
 	if (!git_config_get_string("diff.renames", &value)) {
-		opt->diff_detect_rename = git_config_rename("diff.renames", value);
+		opt->detect_renames = git_config_rename("diff.renames", value);
 		free(value);
 	}
 	if (!git_config_get_string("merge.renames", &value)) {
-		opt->merge_detect_rename = git_config_rename("merge.renames", value);
+		opt->detect_renames = git_config_rename("merge.renames", value);
 		free(value);
 	}
 	if (!git_config_get_string("merge.directoryrenames", &value)) {
@@ -3741,11 +3738,9 @@ void init_merge_options(struct merge_options *opt,
 	opt->repo = repo;
 	opt->verbosity = 2;
 	opt->buffer_output = 1;
-	opt->diff_rename_limit = -1;
-	opt->merge_rename_limit = -1;
+	opt->rename_limit = -1;
 	opt->renormalize = 0;
-	opt->diff_detect_rename = -1;
-	opt->merge_detect_rename = -1;
+	opt->detect_renames = -1;
 	opt->detect_directory_renames = 1;
 	merge_recursive_config(opt);
 	merge_verbosity = getenv("GIT_MERGE_VERBOSITY");
@@ -3797,16 +3792,16 @@ int parse_merge_opt(struct merge_options *opt, const char *s)
 	else if (!strcmp(s, "no-renormalize"))
 		opt->renormalize = 0;
 	else if (!strcmp(s, "no-renames"))
-		opt->merge_detect_rename = 0;
+		opt->detect_renames = 0;
 	else if (!strcmp(s, "find-renames")) {
-		opt->merge_detect_rename = 1;
+		opt->detect_renames = 1;
 		opt->rename_score = 0;
 	}
 	else if (skip_prefix(s, "find-renames=", &arg) ||
 		 skip_prefix(s, "rename-threshold=", &arg)) {
 		if ((opt->rename_score = parse_rename_score(&arg)) == -1 || *arg != 0)
 			return -1;
-		opt->merge_detect_rename = 1;
+		opt->detect_renames = 1;
 	}
 	/*
 	 * Please update $__git_merge_strategy_options in
diff --git a/merge-recursive.h b/merge-recursive.h
index 1454772528..e63483b8db 100644
--- a/merge-recursive.h
+++ b/merge-recursive.h
@@ -23,10 +23,8 @@ struct merge_options {
 	long xdl_opts;
 	int verbosity;
 	int detect_directory_renames;
-	int diff_detect_rename;
-	int merge_detect_rename;
-	int diff_rename_limit;
-	int merge_rename_limit;
+	int detect_renames;
+	int rename_limit;
 	int rename_score;
 	int needed_rename_limit;
 	int show_rename_progress;

merge-recursive.c, merge-recursive.h

diff --git a/merge-recursive.c b/merge-recursive.c
index 61faa26c4f..0a944f51ae 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -54,6 +54,24 @@ static unsigned int path_hash(const char *path)
 	return ignore_case ? strihash(path) : strhash(path);
 }
 
+/*
+ * For dir_rename_entry, directory names are stored as a full path from the
+ * toplevel of the repository and do not include a trailing '/'.  Also:
+ *
+ *   dir:                original name of directory being renamed
+ *   non_unique_new_dir: if true, could not determine new_dir
+ *   new_dir:            final name of directory being renamed
+ *   possible_new_dirs:  temporary used to help determine new_dir; see comments
+ *                       in get_directory_renames() for details
+ */
+struct dir_rename_entry {
+	struct hashmap_entry ent; /* must be the first member! */
+	char *dir;
+	unsigned non_unique_new_dir:1;
+	struct strbuf new_dir;
+	struct string_list possible_new_dirs;
+};
+
 static struct dir_rename_entry *dir_rename_find_entry(struct hashmap *hashmap,
 						      char *dir)
 {
@@ -92,6 +110,13 @@ static void dir_rename_entry_init(struct dir_rename_entry *entry,
 	string_list_init(&entry->possible_new_dirs, 0);
 }
 
+struct collision_entry {
+	struct hashmap_entry ent; /* must be the first member! */
+	char *target_file;
+	struct string_list source_files;
+	unsigned reported_already:1;
+};
+
 static struct collision_entry *collision_find_entry(struct hashmap *hashmap,
 						    char *target_file)
 {
@@ -358,6 +383,12 @@ static int add_cacheinfo(struct merge_options *opt,
 	return ret;
 }
 
+static inline int merge_detect_rename(struct merge_options *opt)
+{
+	return opt->merge_detect_rename >= 0 ? opt->merge_detect_rename :
+		opt->diff_detect_rename >= 0 ? opt->diff_detect_rename : 1;
+}
+
 static void init_tree_desc_from_tree(struct tree_desc *desc, struct tree *tree)
 {
 	parse_tree(tree);
diff --git a/merge-recursive.h b/merge-recursive.h
index e27c2a05bb..1454772528 100644
--- a/merge-recursive.h
+++ b/merge-recursive.h
@@ -39,36 +39,17 @@ struct merge_options {
 	struct repository *repo;
 };
 
-/*
- * For dir_rename_entry, directory names are stored as a full path from the
- * toplevel of the repository and do not include a trailing '/'.  Also:
- *
- *   dir:                original name of directory being renamed
- *   non_unique_new_dir: if true, could not determine new_dir
- *   new_dir:            final name of directory being renamed
- *   possible_new_dirs:  temporary used to help determine new_dir; see comments
- *                       in get_directory_renames() for details
- */
-struct dir_rename_entry {
-	struct hashmap_entry ent; /* must be the first member! */
-	char *dir;
-	unsigned non_unique_new_dir:1;
-	struct strbuf new_dir;
-	struct string_list possible_new_dirs;
-};
+void init_merge_options(struct merge_options *opt, struct repository *repo);
 
-struct collision_entry {
-	struct hashmap_entry ent; /* must be the first member! */
-	char *target_file;
-	struct string_list source_files;
-	unsigned reported_already:1;
-};
+/* parse the option in s and update the relevant field of opt */
+int parse_merge_opt(struct merge_options *opt, const char *s);
 
-static inline int merge_detect_rename(struct merge_options *opt)
-{
-	return opt->merge_detect_rename >= 0 ? opt->merge_detect_rename :
-		opt->diff_detect_rename >= 0 ? opt->diff_detect_rename : 1;
-}
+/* rename-detecting three-way merge, no recursion */
+int merge_trees(struct merge_options *opt,
+		struct tree *head,
+		struct tree *merge,
+		struct tree *merge_base,
+		struct tree **result);
 
 /* merge_trees() but with recursive ancestor consolidation */
 int merge_recursive(struct merge_options *opt,
@@ -77,16 +58,9 @@ int merge_recursive(struct merge_options *opt,
 		    struct commit_list *merge_bases,
 		    struct commit **result);
 
-/* rename-detecting three-way merge, no recursion */
-int merge_trees(struct merge_options *opt,
-		struct tree *head,
-		struct tree *merge,
-		struct tree *merge_base,
-		struct tree **result);
-
 /*
- * "git-merge-recursive" can be fed trees; wrap them into
- * virtual commits and call merge_recursive() proper.
+ * merge_recursive_generic can operate on trees instead of commits, by
+ * wrapping the trees into virtual commits, and calling merge_recursive().
  */
 int merge_recursive_generic(struct merge_options *opt,
 			    const struct object_id *head,
@@ -95,9 +69,4 @@ int merge_recursive_generic(struct merge_options *opt,
 			    const struct object_id **merge_bases,
 			    struct commit **result);
 
-void init_merge_options(struct merge_options *opt,
-			struct repository *repo);
-
-int parse_merge_opt(struct merge_options *opt, const char *s);
-
 #endif

merge-recursive.c, merge-recursive.h

diff --git a/merge-recursive.c b/merge-recursive.c
index a5049b06a3..c572d37b21 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -29,6 +29,15 @@
 #include "revision.h"
 #include "commit-reach.h"
 
+struct merge_options_internal {
+	int call_depth;
+	int needed_rename_limit;
+	struct hashmap current_file_dir_set;
+	struct string_list df_conflict_file_set;
+	struct unpack_trees_options unpack_opts;
+	struct index_state orig_index;
+};
+
 struct path_hashmap_entry {
 	struct hashmap_entry e;
 	char path[FLEX_ARRAY];
@@ -309,7 +318,8 @@ static inline void setup_rename_conflict_info(enum rename_type rename_type,
 
 static int show(struct merge_options *opt, int v)
 {
-	return (!opt->call_depth && opt->verbosity >= v) || opt->verbosity >= 5;
+	return (!opt->priv->call_depth && opt->verbosity >= v) ||
+		opt->verbosity >= 5;
 }
 
 __attribute__((format (printf, 3, 4)))
@@ -320,7 +330,7 @@ static void output(struct merge_options *opt, int v, const char *fmt, ...)
 	if (!show(opt, v))
 		return;
 
-	strbuf_addchars(&opt->obuf, ' ', opt->call_depth * 2);
+	strbuf_addchars(&opt->obuf, ' ', opt->priv->call_depth * 2);
 
 	va_start(ap, fmt);
 	strbuf_vaddf(&opt->obuf, fmt, ap);
@@ -335,7 +345,7 @@ static void output_commit_title(struct merge_options *opt, struct commit *commit
 {
 	struct merge_remote_desc *desc;
 
-	strbuf_addchars(&opt->obuf, ' ', opt->call_depth * 2);
+	strbuf_addchars(&opt->obuf, ' ', opt->priv->call_depth * 2);
 	desc = merge_remote_util(commit);
 	if (desc)
 		strbuf_addf(&opt->obuf, "virtual %s\n", desc->name);
@@ -403,43 +413,43 @@ static int unpack_trees_start(struct merge_options *opt,
 	struct tree_desc t[3];
 	struct index_state tmp_index = { NULL };
 
-	memset(&opt->unpack_opts, 0, sizeof(opt->unpack_opts));
-	if (opt->call_depth)
-		opt->unpack_opts.index_only = 1;
+	memset(&opt->priv->unpack_opts, 0, sizeof(opt->priv->unpack_opts));
+	if (opt->priv->call_depth)
+		opt->priv->unpack_opts.index_only = 1;
 	else
-		opt->unpack_opts.update = 1;
-	opt->unpack_opts.merge = 1;
-	opt->unpack_opts.head_idx = 2;
-	opt->unpack_opts.fn = threeway_merge;
-	opt->unpack_opts.src_index = opt->repo->index;
-	opt->unpack_opts.dst_index = &tmp_index;
-	opt->unpack_opts.aggressive = !merge_detect_rename(opt);
-	setup_unpack_trees_porcelain(&opt->unpack_opts, "merge");
+		opt->priv->unpack_opts.update = 1;
+	opt->priv->unpack_opts.merge = 1;
+	opt->priv->unpack_opts.head_idx = 2;
+	opt->priv->unpack_opts.fn = threeway_merge;
+	opt->priv->unpack_opts.src_index = opt->repo->index;
+	opt->priv->unpack_opts.dst_index = &tmp_index;
+	opt->priv->unpack_opts.aggressive = !merge_detect_rename(opt);
+	setup_unpack_trees_porcelain(&opt->priv->unpack_opts, "merge");
 
 	init_tree_desc_from_tree(t+0, common);
 	init_tree_desc_from_tree(t+1, head);
 	init_tree_desc_from_tree(t+2, merge);
 
-	rc = unpack_trees(3, t, &opt->unpack_opts);
+	rc = unpack_trees(3, t, &opt->priv->unpack_opts);
 	cache_tree_free(&opt->repo->index->cache_tree);
 
 	/*
-	 * Update opt->repo->index to match the new results, AFTER saving a copy
-	 * in opt->orig_index.  Update src_index to point to the saved copy.
-	 * (verify_uptodate() checks src_index, and the original index is
-	 * the one that had the necessary modification timestamps.)
+	 * Update opt->repo->index to match the new results, AFTER saving a
+	 * copy in opt->priv->orig_index.  Update src_index to point to the
+	 * saved copy.  (verify_uptodate() checks src_index, and the original
+	 * index is the one that had the necessary modification timestamps.)
 	 */
-	opt->orig_index = *opt->repo->index;
+	opt->priv->orig_index = *opt->repo->index;
 	*opt->repo->index = tmp_index;
-	opt->unpack_opts.src_index = &opt->orig_index;
+	opt->priv->unpack_opts.src_index = &opt->priv->orig_index;
 
 	return rc;
 }
 
 static void unpack_trees_finish(struct merge_options *opt)
 {
-	discard_index(&opt->orig_index);
-	clear_unpack_trees_porcelain(&opt->unpack_opts);
+	discard_index(&opt->priv->orig_index);
+	clear_unpack_trees_porcelain(&opt->priv->unpack_opts);
 }
 
 static int save_files_dirs(const struct object_id *oid,
@@ -454,7 +464,7 @@ static int save_files_dirs(const struct object_id *oid,
 
 	FLEX_ALLOC_MEM(entry, path, base->buf, base->len);
 	hashmap_entry_init(entry, path_hash(entry->path));
-	hashmap_add(&opt->current_file_dir_set, entry);
+	hashmap_add(&opt->priv->current_file_dir_set, entry);
 
 	strbuf_setlen(base, baselen);
 	return (S_ISDIR(mode) ? READ_TREE_RECURSIVE : 0);
@@ -585,7 +595,7 @@ static void record_df_conflict_files(struct merge_options *opt,
 	 * If we're merging merge-bases, we don't want to bother with
 	 * any working directory changes.
 	 */
-	if (opt->call_depth)
+	if (opt->priv->call_depth)
 		return;
 
 	/* Ensure D/F conflicts are adjacent in the entries list. */
@@ -597,7 +607,7 @@ static void record_df_conflict_files(struct merge_options *opt,
 	df_sorted_entries.cmp = string_list_df_name_compare;
 	string_list_sort(&df_sorted_entries);
 
-	string_list_clear(&opt->df_conflict_file_set, 1);
+	string_list_clear(&opt->priv->df_conflict_file_set, 1);
 	for (i = 0; i < df_sorted_entries.nr; i++) {
 		const char *path = df_sorted_entries.items[i].string;
 		int len = strlen(path);
@@ -613,7 +623,7 @@ static void record_df_conflict_files(struct merge_options *opt,
 		    len > last_len &&
 		    memcmp(path, last_file, last_len) == 0 &&
 		    path[last_len] == '/') {
-			string_list_insert(&opt->df_conflict_file_set, last_file);
+			string_list_insert(&opt->priv->df_conflict_file_set, last_file);
 		}
 
 		/*
@@ -680,8 +690,8 @@ static void update_entry(struct stage_data *entry,
 static int remove_file(struct merge_options *opt, int clean,
 		       const char *path, int no_wd)
 {
-	int update_cache = opt->call_depth || clean;
-	int update_working_directory = !opt->call_depth && !no_wd;
+	int update_cache = opt->priv->call_depth || clean;
+	int update_working_directory = !opt->priv->call_depth && !no_wd;
 
 	if (update_cache) {
 		if (remove_file_from_index(opt->repo->index, path))
@@ -724,16 +734,16 @@ static char *unique_path(struct merge_options *opt,
 	add_flattened_path(&newpath, branch);
 
 	base_len = newpath.len;
-	while (hashmap_get_from_hash(&opt->current_file_dir_set,
+	while (hashmap_get_from_hash(&opt->priv->current_file_dir_set,
 				     path_hash(newpath.buf), newpath.buf) ||
-	       (!opt->call_depth && file_exists(newpath.buf))) {
+	       (!opt->priv->call_depth && file_exists(newpath.buf))) {
 		strbuf_setlen(&newpath, base_len);
 		strbuf_addf(&newpath, "_%d", suffix++);
 	}
 
 	FLEX_ALLOC_MEM(entry, path, newpath.buf, newpath.len);
 	hashmap_entry_init(entry, path_hash(entry->path));
-	hashmap_add(&opt->current_file_dir_set, entry);
+	hashmap_add(&opt->priv->current_file_dir_set, entry);
 	return strbuf_detach(&newpath, NULL);
 }
 
@@ -775,7 +785,7 @@ static int dir_in_way(struct index_state *istate, const char *path,
 static int was_tracked_and_matches(struct merge_options *opt, const char *path,
 				   const struct diff_filespec *blob)
 {
-	int pos = index_name_pos(&opt->orig_index, path, strlen(path));
+	int pos = index_name_pos(&opt->priv->orig_index, path, strlen(path));
 	struct cache_entry *ce;
 
 	if (0 > pos)
@@ -783,7 +793,7 @@ static int was_tracked_and_matches(struct merge_options *opt, const char *path,
 		return 0;
 
 	/* See if the file we were tracking before matches */
-	ce = opt->orig_index.cache[pos];
+	ce = opt->priv->orig_index.cache[pos];
 	return (oid_eq(&ce->oid, &blob->oid) && ce->ce_mode == blob->mode);
 }
 
@@ -792,7 +802,7 @@ static int was_tracked_and_matches(struct merge_options *opt, const char *path,
  */
 static int was_tracked(struct merge_options *opt, const char *path)
 {
-	int pos = index_name_pos(&opt->orig_index, path, strlen(path));
+	int pos = index_name_pos(&opt->priv->orig_index, path, strlen(path));
 
 	if (0 <= pos)
 		/* we were tracking this path before the merge */
@@ -849,12 +859,12 @@ static int was_dirty(struct merge_options *opt, const char *path)
 	struct cache_entry *ce;
 	int dirty = 1;
 
-	if (opt->call_depth || !was_tracked(opt, path))
+	if (opt->priv->call_depth || !was_tracked(opt, path))
 		return !dirty;
 
-	ce = index_file_exists(opt->unpack_opts.src_index,
+	ce = index_file_exists(opt->priv->unpack_opts.src_index,
 			       path, strlen(path), ignore_case);
-	dirty = verify_uptodate(ce, &opt->unpack_opts) != 0;
+	dirty = verify_uptodate(ce, &opt->priv->unpack_opts) != 0;
 	return dirty;
 }
 
@@ -864,8 +874,8 @@ static int make_room_for_path(struct merge_options *opt, const char *path)
 	const char *msg = _("failed to create path '%s'%s");
 
 	/* Unlink any D/F conflict files that are in the way */
-	for (i = 0; i < opt->df_conflict_file_set.nr; i++) {
-		const char *df_path = opt->df_conflict_file_set.items[i].string;
+	for (i = 0; i < opt->priv->df_conflict_file_set.nr; i++) {
+		const char *df_path = opt->priv->df_conflict_file_set.items[i].string;
 		size_t pathlen = strlen(path);
 		size_t df_pathlen = strlen(df_path);
 		if (df_pathlen < pathlen &&
@@ -875,7 +885,7 @@ static int make_room_for_path(struct merge_options *opt, const char *path)
 			       _("Removing %s to make room for subdirectory\n"),
 			       df_path);
 			unlink(df_path);
-			unsorted_string_list_delete_item(&opt->df_conflict_file_set,
+			unsorted_string_list_delete_item(&opt->priv->df_conflict_file_set,
 							 i, 0);
 			break;
 		}
@@ -916,7 +926,7 @@ static int update_file_flags(struct merge_options *opt,
 {
 	int ret = 0;
 
-	if (opt->call_depth)
+	if (opt->priv->call_depth)
 		update_wd = 0;
 
 	if (update_wd) {
@@ -1001,7 +1011,7 @@ static int update_file(struct merge_options *opt,
 		       const char *path)
 {
 	return update_file_flags(opt, contents, path,
-				 opt->call_depth || clean, !opt->call_depth);
+				 opt->priv->call_depth || clean, !opt->priv->call_depth);
 }
 
 /* Low level file merging, update and removal */
@@ -1030,7 +1040,7 @@ static int merge_3way(struct merge_options *opt,
 	ll_opts.extra_marker_size = extra_marker_size;
 	ll_opts.xdl_opts = opt->xdl_opts;
 
-	if (opt->call_depth) {
+	if (opt->priv->call_depth) {
 		ll_opts.virtual_ancestor = 1;
 		ll_opts.variant = 0;
 	} else {
@@ -1164,7 +1174,7 @@ static int merge_submodule(struct merge_options *opt,
 	struct object_array merges;
 
 	int i;
-	int search = !opt->call_depth;
+	int search = !opt->priv->call_depth;
 
 	/* store a in result in case we fail */
 	oidcpy(result, a);
@@ -1385,7 +1395,7 @@ static int handle_rename_via_dir(struct merge_options *opt,
 	int mark_conflicted = (opt->detect_directory_renames == 1);
 	assert(ren->dir_rename_original_dest);
 
-	if (!opt->call_depth && would_lose_untracked(opt, dest->path)) {
+	if (!opt->priv->call_depth && would_lose_untracked(opt, dest->path)) {
 		mark_conflicted = 1;
 		file_path = unique_path(opt, dest->path, ren->branch);
 		output(opt, 1, _("Error: Refusing to lose untracked file at %s; "
@@ -1428,12 +1438,12 @@ static int handle_change_delete(struct merge_options *opt,
 	const char *update_path = path;
 	int ret = 0;
 
-	if (dir_in_way(opt->repo->index, path, !opt->call_depth, 0) ||
-	    (!opt->call_depth && would_lose_untracked(opt, path))) {
+	if (dir_in_way(opt->repo->index, path, !opt->priv->call_depth, 0) ||
+	    (!opt->priv->call_depth && would_lose_untracked(opt, path))) {
 		update_path = alt_path = unique_path(opt, path, change_branch);
 	}
 
-	if (opt->call_depth) {
+	if (opt->priv->call_depth) {
 		/*
 		 * We cannot arbitrarily accept either a_sha or b_sha as
 		 * correct; since there is no true "middle point" between
@@ -1508,14 +1518,14 @@ static int handle_rename_delete(struct merge_options *opt,
 				     opt->branch2 : opt->branch1);
 
 	if (handle_change_delete(opt,
-				 opt->call_depth ? orig->path : dest->path,
-				 opt->call_depth ? NULL : orig->path,
+				 opt->priv->call_depth ? orig->path : dest->path,
+				 opt->priv->call_depth ? NULL : orig->path,
 				 orig, dest,
 				 rename_branch, delete_branch,
 				 _("rename"), _("renamed")))
 		return -1;
 
-	if (opt->call_depth)
+	if (opt->priv->call_depth)
 		return remove_file_from_index(opt->repo->index, dest->path);
 	else
 		return update_stages(opt, dest->path, NULL,
@@ -1552,7 +1562,7 @@ static int handle_file_collision(struct merge_options *opt,
 	/*
 	 * In the recursive case, we just opt to undo renames
 	 */
-	if (opt->call_depth && (prev_path1 || prev_path2)) {
+	if (opt->priv->call_depth && (prev_path1 || prev_path2)) {
 		/* Put first file (a->oid, a->mode) in its original spot */
 		if (prev_path1) {
 			if (update_file(opt, 1, a, prev_path1))
@@ -1581,10 +1591,10 @@ static int handle_file_collision(struct merge_options *opt,
 	/* Remove rename sources if rename/add or rename/rename(2to1) */
 	if (prev_path1)
 		remove_file(opt, 1, prev_path1,
-			    opt->call_depth || would_lose_untracked(opt, prev_path1));
+			    opt->priv->call_depth || would_lose_untracked(opt, prev_path1));
 	if (prev_path2)
 		remove_file(opt, 1, prev_path2,
-			    opt->call_depth || would_lose_untracked(opt, prev_path2));
+			    opt->priv->call_depth || would_lose_untracked(opt, prev_path2));
 
 	/*
 	 * Remove the collision path, if it wouldn't cause dirty contents
@@ -1626,12 +1636,12 @@ static int handle_file_collision(struct merge_options *opt,
 	null.mode = 0;
 
 	if (merge_mode_and_contents(opt, &null, a, b, collide_path,
-				    branch1, branch2, opt->call_depth * 2, &mfi))
+				    branch1, branch2, opt->priv->call_depth * 2, &mfi))
 		return -1;
 	mfi.clean &= !alt_path;
 	if (update_file(opt, mfi.clean, &mfi.blob, update_path))
 		return -1;
-	if (!mfi.clean && !opt->call_depth &&
+	if (!mfi.clean && !opt->priv->call_depth &&
 	    update_stages(opt, collide_path, NULL, a, b))
 		return -1;
 	free(alt_path);
@@ -1671,7 +1681,7 @@ static int handle_rename_add(struct merge_options *opt,
 				    &ci->ren1->src_entry->stages[other_stage],
 				    prev_path_desc,
 				    opt->branch1, opt->branch2,
-				    1 + opt->call_depth * 2, &mfi))
+				    1 + opt->priv->call_depth * 2, &mfi))
 		return -1;
 	free(prev_path_desc);
 
@@ -1689,7 +1699,7 @@ static char *find_path_for_conflict(struct merge_options *opt,
 				    const char *branch2)
 {
 	char *new_path = NULL;
-	if (dir_in_way(opt->repo->index, path, !opt->call_depth, 0)) {
+	if (dir_in_way(opt->repo->index, path, !opt->priv->call_depth, 0)) {
 		new_path = unique_path(opt, path, branch1);
 		output(opt, 1, _("%s is a directory in %s adding "
 			       "as %s instead"),
@@ -1720,17 +1730,17 @@ static int handle_rename_rename_1to2(struct merge_options *opt,
 	       "rename \"%s\"->\"%s\" in \"%s\"%s"),
 	       o->path, a->path, ci->ren1->branch,
 	       o->path, b->path, ci->ren2->branch,
-	       opt->call_depth ? _(" (left unresolved)") : "");
+	       opt->priv->call_depth ? _(" (left unresolved)") : "");
 
 	path_desc = xstrfmt("%s and %s, both renamed from %s",
 			    a->path, b->path, o->path);
 	if (merge_mode_and_contents(opt, o, a, b, path_desc,
 				    ci->ren1->branch, ci->ren2->branch,
-				    opt->call_depth * 2, &mfi))
+				    opt->priv->call_depth * 2, &mfi))
 		return -1;
 	free(path_desc);
 
-	if (opt->call_depth) {
+	if (opt->priv->call_depth) {
 		/*
 		 * FIXME: For rename/add-source conflicts (if we could detect
 		 * such), this is wrong.  We should instead find a unique
@@ -1845,12 +1855,12 @@ static int handle_rename_rename_2to1(struct merge_options *opt,
 				    &ci->ren1->src_entry->stages[ostage1],
 				    path_side_1_desc,
 				    opt->branch1, opt->branch2,
-				    1 + opt->call_depth * 2, &mfi_c1) ||
+				    1 + opt->priv->call_depth * 2, &mfi_c1) ||
 	    merge_mode_and_contents(opt, b,
 				    &ci->ren2->src_entry->stages[ostage2],
 				    c2, path_side_2_desc,
 				    opt->branch1, opt->branch2,
-				    1 + opt->call_depth * 2, &mfi_c2))
+				    1 + opt->priv->call_depth * 2, &mfi_c2))
 		return -1;
 	free(path_side_1_desc);
 	free(path_side_2_desc);
@@ -1891,8 +1901,8 @@ static struct diff_queue_struct *get_diffpairs(struct merge_options *opt,
 	diff_setup_done(&opts);
 	diff_tree_oid(&o_tree->object.oid, &tree->object.oid, "", &opts);
 	diffcore_std(&opts);
-	if (opts.needed_rename_limit > opt->needed_rename_limit)
-		opt->needed_rename_limit = opts.needed_rename_limit;
+	if (opts.needed_rename_limit > opt->priv->needed_rename_limit)
+		opt->priv->needed_rename_limit = opts.needed_rename_limit;
 
 	ret = xmalloc(sizeof(*ret));
 	*ret = diff_queued_diff;
@@ -3022,13 +3032,13 @@ static int handle_content_merge(struct merge_file_info *mfi,
 		reason = _("add/add");
 
 	assert(o->path && a->path && b->path);
-	if (ci && dir_in_way(opt->repo->index, path, !opt->call_depth,
+	if (ci && dir_in_way(opt->repo->index, path, !opt->priv->call_depth,
 			     S_ISGITLINK(ci->ren1->pair->two->mode)))
 		df_conflict_remains = 1;
 
 	if (merge_mode_and_contents(opt, o, a, b, path,
 				    opt->branch1, opt->branch2,
-				    opt->call_depth * 2, mfi))
+				    opt->priv->call_depth * 2, mfi))
 		return -1;
 
 	/*
@@ -3044,7 +3054,7 @@ static int handle_content_merge(struct merge_file_info *mfi,
 
 		output(opt, 3, _("Skipped %s (merged same as existing)"), path);
 		if (add_cacheinfo(opt, &mfi->blob, path,
-				  0, (!opt->call_depth && !is_dirty), 0))
+				  0, (!opt->priv->call_depth && !is_dirty), 0))
 			return -1;
 		/*
 		 * However, add_cacheinfo() will delete the old cache entry
@@ -3052,8 +3062,8 @@ static int handle_content_merge(struct merge_file_info *mfi,
 		 * flag to avoid making the file appear as if it were
 		 * deleted by the user.
 		 */
-		pos = index_name_pos(&opt->orig_index, path, strlen(path));
-		ce = opt->orig_index.cache[pos];
+		pos = index_name_pos(&opt->priv->orig_index, path, strlen(path));
+		ce = opt->priv->orig_index.cache[pos];
 		if (ce_skip_worktree(ce)) {
 			pos = index_name_pos(opt->repo->index, path, strlen(path));
 			ce = opt->repo->index->cache[pos];
@@ -3074,7 +3084,7 @@ static int handle_content_merge(struct merge_file_info *mfi,
 
 	if (df_conflict_remains || is_dirty) {
 		char *new_path;
-		if (opt->call_depth) {
+		if (opt->priv->call_depth) {
 			remove_file_from_index(opt->repo->index, path);
 		} else {
 			if (!mfi->clean) {
@@ -3332,7 +3342,7 @@ static int process_entry(struct merge_options *opt,
 			conf = _("directory/file");
 		}
 		if (dir_in_way(opt->repo->index, path,
-			       !opt->call_depth && !S_ISGITLINK(a->mode),
+			       !opt->priv->call_depth && !S_ISGITLINK(a->mode),
 			       0)) {
 			char *new_path = unique_path(opt, path, add_branch);
 			clean_merge = 0;
@@ -3341,7 +3351,7 @@ static int process_entry(struct merge_options *opt,
 			       conf, path, other_branch, path, new_path);
 			if (update_file(opt, 0, contents, new_path))
 				clean_merge = -1;
-			else if (opt->call_depth)
+			else if (opt->priv->call_depth)
 				remove_file_from_index(opt->repo->index, path);
 			free(new_path);
 		} else {
@@ -3406,7 +3416,7 @@ static int merge_trees_internal(struct merge_options *opt,
 	code = unpack_trees_start(opt, merge_base, head, merge);
 
 	if (code != 0) {
-		if (show(opt, 4) || opt->call_depth)
+		if (show(opt, 4) || opt->priv->call_depth)
 			err(opt, _("merging of trees %s and %s failed"),
 			    oid_to_hex(&head->object.oid),
 			    oid_to_hex(&merge->object.oid));
@@ -3425,7 +3435,7 @@ static int merge_trees_internal(struct merge_options *opt,
 		 * opposed to decaring a local hashmap is for convenience
 		 * so that we don't have to pass it to around.
 		 */
-		hashmap_init(&opt->current_file_dir_set, path_hashmap_cmp,
+		hashmap_init(&opt->priv->current_file_dir_set, path_hashmap_cmp,
 			     NULL, 512);
 		get_files_dirs(opt, head);
 		get_files_dirs(opt, merge);
@@ -3462,7 +3472,7 @@ static int merge_trees_internal(struct merge_options *opt,
 		string_list_clear(entries, 1);
 		free(entries);
 
-		hashmap_free(&opt->current_file_dir_set, 1);
+		hashmap_free(&opt->priv->current_file_dir_set, 1);
 
 		if (clean < 0) {
 			unpack_trees_finish(opt);
@@ -3474,7 +3484,8 @@ static int merge_trees_internal(struct merge_options *opt,
 
 	unpack_trees_finish(opt);
 
-	if (opt->call_depth && !(*result = write_tree_from_memory(opt->repo)))
+	if (opt->priv->call_depth &&
+	    !(*result = write_tree_from_memory(opt->repo)))
 		return -1;
 
 	return clean;
@@ -3538,7 +3549,7 @@ static int merge_recursive_internal(struct merge_options *opt,
 
 	for (iter = merge_bases; iter; iter = iter->next) {
 		const char *saved_b1, *saved_b2;
-		opt->call_depth++;
+		opt->priv->call_depth++;
 		/*
 		 * When the merge fails, the result contains files
 		 * with conflict markers. The cleanness flag is
@@ -3557,14 +3568,14 @@ static int merge_recursive_internal(struct merge_options *opt,
 			return -1;
 		opt->branch1 = saved_b1;
 		opt->branch2 = saved_b2;
-		opt->call_depth--;
+		opt->priv->call_depth--;
 
 		if (!merged_merge_bases)
 			return err(opt, _("merge returned no commit"));
 	}
 
 	discard_index(opt->repo->index);
-	if (!opt->call_depth)
+	if (!opt->priv->call_depth)
 		repo_read_index(opt->repo);
 
 	opt->ancestor = "merged common ancestors";
@@ -3579,14 +3590,14 @@ static int merge_recursive_internal(struct merge_options *opt,
 		return clean;
 	}
 
-	if (opt->call_depth) {
+	if (opt->priv->call_depth) {
 		*result = make_virtual_commit(opt->repo, result_tree,
 					      "merged tree");
 		commit_list_insert(h1, &(*result)->parents);
 		commit_list_insert(h2, &(*result)->parents->next);
 	}
 	flush_output(opt);
-	if (!opt->call_depth && opt->buffer_output < 2)
+	if (!opt->priv->call_depth && opt->buffer_output < 2)
 		strbuf_release(&opt->obuf);
 	return clean;
 }
@@ -3603,6 +3614,8 @@ static int merge_start(struct merge_options *opt, struct tree *head)
 		return -1;
 	}
 
+	opt->priv = xcalloc(1, sizeof(*opt->priv));
+	string_list_init(&opt->priv->df_conflict_file_set, 1);
 	return 0;
 }
 
@@ -3610,7 +3623,9 @@ static void merge_finalize(struct merge_options *opt)
 {
 	if (show(opt, 2))
 		diff_warn_rename_limit("merge.renamelimit",
-				       opt->needed_rename_limit, 0);
+				       opt->priv->needed_rename_limit, 0);
+	free(opt->priv);
+	opt->priv = NULL;
 }
 
 int merge_trees(struct merge_options *opt,
@@ -3748,8 +3763,6 @@ void init_merge_options(struct merge_options *opt,
 
 	opt->renormalize = 0;
 
-	string_list_init(&opt->df_conflict_file_set, 1);
-
 	merge_recursive_config(opt);
 	merge_verbosity = getenv("GIT_MERGE_VERBOSITY");
 	if (merge_verbosity)
diff --git a/merge-recursive.h b/merge-recursive.h
index d57fce0daa..a1bb29dc33 100644
--- a/merge-recursive.h
+++ b/merge-recursive.h
@@ -1,13 +1,15 @@
 #ifndef MERGE_RECURSIVE_H
 #define MERGE_RECURSIVE_H
 
-#include "string-list.h"
-#include "unpack-trees.h"
+#include "strbuf.h"
 
 struct commit;
-
+struct commit_list;
+struct object_id;
 struct repository;
+struct tree;
 
+struct merge_options_internal;
 struct merge_options {
 	struct repository *repo;
 
@@ -40,13 +42,8 @@ struct merge_options {
 	const char *subtree_shift;
 	unsigned renormalize : 1;
 
-	/* internal fields used by the implementation (do NOT set these) */
-	int call_depth;
-	int needed_rename_limit;
-	struct hashmap current_file_dir_set;
-	struct string_list df_conflict_file_set;
-	struct unpack_trees_options unpack_opts;
-	struct index_state orig_index;
+	/* internal fields used by the implementation */
+	struct merge_options_internal *priv;
 };
 
 void init_merge_options(struct merge_options *opt, struct repository *repo);

merge-recursive.c, merge-recursive.h

diff --git a/merge-recursive.c b/merge-recursive.c
index 32889a2f0d..0f689095d9 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -1046,10 +1046,10 @@ static int merge_3way(struct merge_options *opt,
 		ll_opts.variant = 0;
 	} else {
 		switch (opt->recursive_variant) {
-		case MERGE_RECURSIVE_OURS:
+		case MERGE_VARIANT_OURS:
 			ll_opts.variant = XDL_MERGE_FAVOR_OURS;
 			break;
-		case MERGE_RECURSIVE_THEIRS:
+		case MERGE_VARIANT_THEIRS:
 			ll_opts.variant = XDL_MERGE_FAVOR_THEIRS;
 			break;
 		default:
@@ -1359,15 +1359,15 @@ static int merge_mode_and_contents(struct merge_options *opt,
 							&b->oid);
 		} else if (S_ISLNK(a->mode)) {
 			switch (opt->recursive_variant) {
-			case MERGE_RECURSIVE_NORMAL:
+			case MERGE_VARIANT_NORMAL:
 				oidcpy(&result->blob.oid, &a->oid);
 				if (!oid_eq(&a->oid, &b->oid))
 					result->clean = 0;
 				break;
-			case MERGE_RECURSIVE_OURS:
+			case MERGE_VARIANT_OURS:
 				oidcpy(&result->blob.oid, &a->oid);
 				break;
-			case MERGE_RECURSIVE_THEIRS:
+			case MERGE_VARIANT_THEIRS:
 				oidcpy(&result->blob.oid, &b->oid);
 				break;
 			}
@@ -3779,9 +3779,9 @@ int parse_merge_opt(struct merge_options *opt, const char *s)
 	if (!s || !*s)
 		return -1;
 	if (!strcmp(s, "ours"))
-		opt->recursive_variant = MERGE_RECURSIVE_OURS;
+		opt->recursive_variant = MERGE_VARIANT_OURS;
 	else if (!strcmp(s, "theirs"))
-		opt->recursive_variant = MERGE_RECURSIVE_THEIRS;
+		opt->recursive_variant = MERGE_VARIANT_THEIRS;
 	else if (!strcmp(s, "subtree"))
 		opt->subtree_shift = "";
 	else if (skip_prefix(s, "subtree=", &arg))
diff --git a/merge-recursive.h b/merge-recursive.h
index a1bb29dc33..c4e6fb85f1 100644
--- a/merge-recursive.h
+++ b/merge-recursive.h
@@ -28,9 +28,9 @@ struct merge_options {
 	/* xdiff-related options (patience, ignore whitespace, ours/theirs) */
 	long xdl_opts;
 	enum {
-		MERGE_RECURSIVE_NORMAL = 0,
-		MERGE_RECURSIVE_OURS,
-		MERGE_RECURSIVE_THEIRS
+		MERGE_VARIANT_NORMAL = 0,
+		MERGE_VARIANT_OURS,
+		MERGE_VARIANT_THEIRS
 	} recursive_variant;
 
 	/* console output related options */

diff --git a/merge-recursive.c b/merge-recursive.c
index c572d37b21..32889a2f0d 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -4,30 +4,31 @@
  * The thieves were Alex Riesen and Johannes Schindelin, in June/July 2006
  */
 #include "cache.h"
-#include "config.h"
+#include "merge-recursive.h"
+
 #include "advice.h"
-#include "lockfile.h"
-#include "cache-tree.h"
-#include "object-store.h"
-#include "repository.h"
-#include "commit.h"
+#include "alloc.h"
+#include "attr.h"
 #include "blob.h"
 #include "builtin.h"
-#include "tree-walk.h"
+#include "cache-tree.h"
+#include "commit.h"
+#include "commit-reach.h"
+#include "config.h"
 #include "diff.h"
 #include "diffcore.h"
+#include "dir.h"
+#include "ll-merge.h"
+#include "lockfile.h"
+#include "object-store.h"
+#include "repository.h"
+#include "revision.h"
+#include "string-list.h"
+#include "submodule.h"
 #include "tag.h"
-#include "alloc.h"
+#include "tree-walk.h"
 #include "unpack-trees.h"
-#include "string-list.h"
 #include "xdiff-interface.h"
-#include "ll-merge.h"
-#include "attr.h"
-#include "merge-recursive.h"
-#include "dir.h"
-#include "submodule.h"
-#include "revision.h"
-#include "commit-reach.h"
 
 struct merge_options_internal {
 	int call_depth;

diff --git a/merge-recursive.c b/merge-recursive.c
index 0f689095d9..4cd6599296 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -1058,7 +1058,7 @@ static int merge_3way(struct merge_options *opt,
 		}
 	}
 
-	assert(a->path && b->path);
+	assert(a->path && b->path && o->path);
 	if (strcmp(a->path, b->path) ||
 	    (opt->ancestor != NULL && strcmp(a->path, o->path) != 0)) {
 		base_name = opt->ancestor == NULL ? NULL :

merge-recursive.c, t/t6036-recursive-corner-cases.sh, t/t6047-diff3-conflict-markers.sh

diff --git a/merge-recursive.c b/merge-recursive.c
index 4cd6599296..8ac53cacdf 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -1034,7 +1034,7 @@ static int merge_3way(struct merge_options *opt,
 {
 	mmfile_t orig, src1, src2;
 	struct ll_merge_options ll_opts = {0};
-	char *base_name, *name1, *name2;
+	char *base, *name1, *name2;
 	int merge_status;
 
 	ll_opts.renormalize = opt->renormalize;
@@ -1058,16 +1058,13 @@ static int merge_3way(struct merge_options *opt,
 		}
 	}
 
-	assert(a->path && b->path && o->path);
-	if (strcmp(a->path, b->path) ||
-	    (opt->ancestor != NULL && strcmp(a->path, o->path) != 0)) {
-		base_name = opt->ancestor == NULL ? NULL :
-			mkpathdup("%s:%s", opt->ancestor, o->path);
+	assert(a->path && b->path && o->path && opt->ancestor);
+	if (strcmp(a->path, b->path) || strcmp(a->path, o->path) != 0) {
+		base  = mkpathdup("%s:%s", opt->ancestor, o->path);
 		name1 = mkpathdup("%s:%s", branch1, a->path);
 		name2 = mkpathdup("%s:%s", branch2, b->path);
 	} else {
-		base_name = opt->ancestor == NULL ? NULL :
-			mkpathdup("%s", opt->ancestor);
+		base  = mkpathdup("%s", opt->ancestor);
 		name1 = mkpathdup("%s", branch1);
 		name2 = mkpathdup("%s", branch2);
 	}
@@ -1076,11 +1073,11 @@ static int merge_3way(struct merge_options *opt,
 	read_mmblob(&src1, &a->oid);
 	read_mmblob(&src2, &b->oid);
 
-	merge_status = ll_merge(result_buf, a->path, &orig, base_name,
+	merge_status = ll_merge(result_buf, a->path, &orig, base,
 				&src1, name1, &src2, name2,
 				opt->repo->index, &ll_opts);
 
-	free(base_name);
+	free(base);
 	free(name1);
 	free(name2);
 	free(orig.ptr);
@@ -3517,6 +3514,8 @@ static int merge_recursive_internal(struct merge_options *opt,
 	struct commit *merged_merge_bases;
 	struct tree *result_tree;
 	int clean;
+	int num_merge_bases;
+	struct strbuf commit_name = STRBUF_INIT;
 
 	if (show(opt, 4)) {
 		output(opt, 4, _("Merging:"));
@@ -3538,6 +3537,7 @@ static int merge_recursive_internal(struct merge_options *opt,
 			output_commit_title(opt, iter->item);
 	}
 
+	num_merge_bases = commit_list_count(merge_bases);
 	merged_merge_bases = pop_commit(&merge_bases);
 	if (merged_merge_bases == NULL) {
 		/* if there is no common ancestor, use an empty tree */
@@ -3579,13 +3579,26 @@ static int merge_recursive_internal(struct merge_options *opt,
 	if (!opt->priv->call_depth)
 		repo_read_index(opt->repo);
 
-	opt->ancestor = "merged common ancestors";
+	switch (num_merge_bases) {
+	case 0:
+		opt->ancestor = "<empty tree>";
+		break;
+	case 1:
+		strbuf_add_unique_abbrev(&commit_name,
+					 &merged_merge_bases->object.oid,
+					 DEFAULT_ABBREV);
+		opt->ancestor = commit_name.buf;
+		break;
+	default:
+		opt->ancestor = "merged common ancestors";
+	}
 	clean = merge_trees_internal(opt,
 				     repo_get_commit_tree(opt->repo, h1),
 				     repo_get_commit_tree(opt->repo, h2),
 				     repo_get_commit_tree(opt->repo,
 							  merged_merge_bases),
 				     &result_tree);
+	strbuf_release(&commit_name);
 	if (clean < 0) {
 		flush_output(opt);
 		return clean;
diff --git a/t/t6036-recursive-corner-cases.sh b/t/t6036-recursive-corner-cases.sh
index d23b948f27..7fddcc8c73 100755
--- a/t/t6036-recursive-corner-cases.sh
+++ b/t/t6036-recursive-corner-cases.sh
@@ -1562,6 +1562,7 @@ test_expect_success 'check nested conflicts' '
 		cd nested_conflicts &&
 
 		git clean -f &&
+		MASTER=$(git rev-parse --short master) &&
 		git checkout L2^0 &&
 
 		# Merge must fail; there is a conflict
@@ -1582,7 +1583,7 @@ test_expect_success 'check nested conflicts' '
 		git cat-file -p R1:a >theirs &&
 		test_must_fail git merge-file --diff3 \
 			-L "Temporary merge branch 1" \
-			-L "merged common ancestors"  \
+			-L "$MASTER"  \
 			-L "Temporary merge branch 2" \
 			ours  \
 			base  \
@@ -1594,7 +1595,7 @@ test_expect_success 'check nested conflicts' '
 		git cat-file -p R1:b >theirs &&
 		test_must_fail git merge-file --diff3 \
 			-L "Temporary merge branch 1" \
-			-L "merged common ancestors"  \
+			-L "$MASTER"  \
 			-L "Temporary merge branch 2" \
 			ours  \
 			base  \
@@ -1732,6 +1733,7 @@ test_expect_success 'check virtual merge base with nested conflicts' '
 	(
 		cd virtual_merge_base_has_nested_conflicts &&
 
+		MASTER=$(git rev-parse --short master) &&
 		git checkout L3^0 &&
 
 		# Merge must fail; there is a conflict
@@ -1760,7 +1762,7 @@ test_expect_success 'check virtual merge base with nested conflicts' '
 		cp left merged-once &&
 		test_must_fail git merge-file --diff3 \
 			-L "Temporary merge branch 1" \
-			-L "merged common ancestors"  \
+			-L "$MASTER"  \
 			-L "Temporary merge branch 2" \
 			merged-once \
 			base        \
diff --git a/t/t6047-diff3-conflict-markers.sh b/t/t6047-diff3-conflict-markers.sh
new file mode 100755
index 0000000000..08cb1668a5
--- /dev/null
+++ b/t/t6047-diff3-conflict-markers.sh
@@ -0,0 +1,191 @@
+#!/bin/sh
+
+test_description='recursive merge diff3 style conflict markers'
+
+. ./test-lib.sh
+
+# Setup:
+#          L1
+#            \
+#             ?
+#            /
+#          R1
+#
+# Where:
+#   L1 and R1 both have a file named 'content' but have no common history
+#
+
+test_expect_success 'setup no merge base' '
+	test_create_repo no_merge_base &&
+	(
+		cd no_merge_base &&
+
+		git checkout --orphan L &&
+		test_seq 1 9 >content &&
+		echo "A" >>content &&
+		git add content &&
+		test_tick &&
+		git commit -m "version L1 of content" &&
+
+		# Create R
+		git checkout --orphan R &&
+		test_seq 1 9 >content &&
+		echo "10" >>content &&
+		git add content &&
+		test_tick &&
+		git commit -m "version R1 of content"
+	)
+'
+
+test_expect_success 'check no merge base' '
+	(
+		cd no_merge_base &&
+
+		git checkout L^0 &&
+
+		test_must_fail git -c merge.conflictstyle=diff3 merge --allow-unrelated-histories -s recursive R^0 &&
+
+		grep "|||||| <empty tree>" content
+	)
+'
+
+# Setup:
+#          L1
+#         /  \
+#   master    ?
+#         \  /
+#          R1
+#
+# Where:
+#   L1 and R1 have modified the same file ('content') in conflicting ways
+#
+
+test_expect_success 'setup unique merge base' '
+	test_create_repo unique_merge_base &&
+	(
+		cd unique_merge_base &&
+
+		test_seq 1 9 >content &&
+		git add content &&
+		test_tick &&
+		git commit -m initial &&
+
+		git branch L &&
+		git branch R &&
+
+		# Create L1
+		git checkout L &&
+		test_seq 0 9 >content &&
+		echo "A" >>content &&
+		git add content &&
+		test_tick &&
+		git commit -m "version L1 of content" &&
+
+		# Create R1
+		git checkout R &&
+		test_seq 0 9 >content &&
+		echo "ten" >>content &&
+		git add content &&
+		git mv content renamed &&
+		test_tick &&
+		git commit -m "version R1 of content"
+	)
+'
+
+test_expect_success 'check unique merge base' '
+	(
+		cd unique_merge_base &&
+
+		git checkout L^0 &&
+		MASTER=$(git rev-parse --short master) &&
+
+		test_must_fail git -c merge.conflictstyle=diff3 merge -s recursive R^0 &&
+
+		grep "|||||| $MASTER:content" renamed
+	)
+'
+
+# Setup:
+#          L1---L2--L3
+#         /  \ /      \
+#   master    X1       ?
+#         \  / \      /
+#          R1---R2--R3
+#
+# Where:
+#   commits L1 and R1 have modified the same file in non-conflicting ways
+#   X1 is an auto-generated merge-base used when merging L1 and R1
+#   commits L2 and R2 are merges of R1 and L1 into L1 and R1, respectively
+#   commits L3 and R3 both modify 'content' in conflicting ways
+#
+
+test_expect_success 'setup multiple merge bases' '
+	test_create_repo multiple_merge_bases &&
+	(
+		cd multiple_merge_bases &&
+
+		# Create some related files now
+		test_seq 1 9 >content &&
+		git add content &&
+		test_tick &&
+		git commit -m initial &&
+
+		git branch L &&
+		git branch R &&
+
+		# Create L1
+		git checkout L &&
+		test_seq 0 9 >content &&
+		git add content &&
+		test_tick &&
+		git commit -m "version L1 of content" &&
+		git tag L1 &&
+
+		# Create R1
+		git checkout R &&
+		test_seq 1 10 >content &&
+		git add content &&
+		test_tick &&
+		git commit -m "verson R1 of content" &&
+		git tag R1 &&
+
+		# Create L2
+		git checkout L &&
+		git merge R1 &&
+
+		# Create R2
+		git checkout R &&
+		git merge L1 &&
+
+		# Create L3
+		git checkout L &&
+		test_seq 0 9 >content &&
+		echo "A" >>content &&
+		git add content &&
+		test_tick &&
+		git commit -m "version L3 of content" &&
+
+		# Create R3
+		git checkout R &&
+		test_seq 0 9 >content &&
+		echo "ten" >>content &&
+		git add content &&
+		git mv content renamed &&
+		test_tick &&
+		git commit -m "version R3 of content"
+	)
+'
+
+test_expect_success 'check multiple merge bases' '
+	(
+		cd multiple_merge_bases &&
+
+		git checkout L^0 &&
+
+		test_must_fail git -c merge.conflictstyle=diff3 merge -s recursive R^0 &&
+
+		grep "|||||| merged common ancestors:content" renamed
+	)
+'
+
+test_done

builtin/checkout.c, merge-recursive.c, merge-recursive.h

diff --git a/builtin/checkout.c b/builtin/checkout.c
index 91f8509f85..ec13116354 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -760,7 +760,7 @@ static int merge_working_tree(const struct checkout_opts *opts,
 			 */
 			init_merge_options(&o, the_repository);
 			o.verbosity = 0;
-			work = write_tree_from_memory(&o);
+			work = write_tree_from_memory(the_repository);
 
 			ret = reset_tree(new_tree,
 					 opts, 1,
diff --git a/merge-recursive.c b/merge-recursive.c
index 7f56cb0ed1..1a3c6ab7f3 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -412,10 +412,10 @@ static void unpack_trees_finish(struct merge_options *opt)
 	clear_unpack_trees_porcelain(&opt->unpack_opts);
 }
 
-struct tree *write_tree_from_memory(struct merge_options *opt)
+struct tree *write_tree_from_memory(struct repository *repo)
 {
 	struct tree *result = NULL;
-	struct index_state *istate = opt->repo->index;
+	struct index_state *istate = repo->index;
 
 	if (unmerged_index(istate)) {
 		int i;
@@ -434,11 +434,10 @@ struct tree *write_tree_from_memory(struct merge_options *opt)
 
 	if (!cache_tree_fully_valid(istate->cache_tree) &&
 	    cache_tree_update(istate, 0) < 0) {
-		err(opt, _("error building trees"));
-		return NULL;
+		BUG("error building trees");
 	}
 
-	result = lookup_tree(opt->repo, &istate->cache_tree->oid);
+	result = lookup_tree(repo, &istate->cache_tree->oid);
 
 	return result;
 }
@@ -3471,7 +3470,7 @@ static int merge_trees_internal(struct merge_options *opt,
 
 	unpack_trees_finish(opt);
 
-	if (opt->call_depth && !(*result = write_tree_from_memory(opt)))
+	if (opt->call_depth && !(*result = write_tree_from_memory(opt->repo)))
 		return -1;
 
 	return clean;
diff --git a/merge-recursive.h b/merge-recursive.h
index c2b7bb65c6..33f3d53c09 100644
--- a/merge-recursive.h
+++ b/merge-recursive.h
@@ -97,7 +97,7 @@ int merge_recursive_generic(struct merge_options *o,
 
 void init_merge_options(struct merge_options *o,
 			struct repository *repo);
-struct tree *write_tree_from_memory(struct merge_options *o);
+struct tree *write_tree_from_memory(struct repository *repo);
 
 int parse_merge_opt(struct merge_options *out, const char *s);
 

merge-recursive.c, merge-recursive.h

diff --git a/merge-recursive.c b/merge-recursive.c
index 0f8d451f2e..a5049b06a3 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -3735,21 +3735,27 @@ void init_merge_options(struct merge_options *opt,
 {
 	const char *merge_verbosity;
 	memset(opt, 0, sizeof(struct merge_options));
+
 	opt->repo = repo;
+
+	opt->detect_renames = -1;
+	opt->detect_directory_renames = 1;
+	opt->rename_limit = -1;
+
 	opt->verbosity = 2;
 	opt->buffer_output = 1;
-	opt->rename_limit = -1;
+	strbuf_init(&opt->obuf, 0);
+
 	opt->renormalize = 0;
-	opt->detect_renames = -1;
-	opt->detect_directory_renames = 1;
+
+	string_list_init(&opt->df_conflict_file_set, 1);
+
 	merge_recursive_config(opt);
 	merge_verbosity = getenv("GIT_MERGE_VERBOSITY");
 	if (merge_verbosity)
 		opt->verbosity = strtol(merge_verbosity, NULL, 10);
 	if (opt->verbosity >= 5)
 		opt->buffer_output = 0;
-	strbuf_init(&opt->obuf, 0);
-	string_list_init(&opt->df_conflict_file_set, 1);
 }
 
 int parse_merge_opt(struct merge_options *opt, const char *s)
diff --git a/merge-recursive.h b/merge-recursive.h
index e63483b8db..d57fce0daa 100644
--- a/merge-recursive.h
+++ b/merge-recursive.h
@@ -9,32 +9,44 @@ struct commit;
 struct repository;
 
 struct merge_options {
+	struct repository *repo;
+
+	/* ref names used in console messages and conflict markers */
 	const char *ancestor;
 	const char *branch1;
 	const char *branch2;
+
+	/* rename related options */
+	int detect_renames;
+	int detect_directory_renames;
+	int rename_limit;
+	int rename_score;
+	int show_rename_progress;
+
+	/* xdiff-related options (patience, ignore whitespace, ours/theirs) */
+	long xdl_opts;
 	enum {
 		MERGE_RECURSIVE_NORMAL = 0,
 		MERGE_RECURSIVE_OURS,
 		MERGE_RECURSIVE_THEIRS
 	} recursive_variant;
-	const char *subtree_shift;
+
+	/* console output related options */
+	int verbosity;
 	unsigned buffer_output; /* 1: output at end, 2: keep buffered */
+	struct strbuf obuf;     /* output buffer */
+
+	/* miscellaneous control options */
+	const char *subtree_shift;
 	unsigned renormalize : 1;
-	long xdl_opts;
-	int verbosity;
-	int detect_directory_renames;
-	int detect_renames;
-	int rename_limit;
-	int rename_score;
-	int needed_rename_limit;
-	int show_rename_progress;
+
+	/* internal fields used by the implementation (do NOT set these) */
 	int call_depth;
-	struct strbuf obuf;
+	int needed_rename_limit;
 	struct hashmap current_file_dir_set;
 	struct string_list df_conflict_file_set;
 	struct unpack_trees_options unpack_opts;
 	struct index_state orig_index;
-	struct repository *repo;
 };
 
 void init_merge_options(struct merge_options *opt, struct repository *repo);

diff --git a/merge-recursive.c b/merge-recursive.c
index 12300131fc..1163508811 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -934,9 +934,11 @@ static int update_file_flags(struct merge_options *opt,
 		}
 
 		buf = read_object_file(&contents->oid, &type, &size);
-		if (!buf)
-			return err(opt, _("cannot read object %s '%s'"),
-				   oid_to_hex(&contents->oid), path);
+		if (!buf) {
+			ret = err(opt, _("cannot read object %s '%s'"),
+				  oid_to_hex(&contents->oid), path);
+			goto free_buf;
+		}
 		if (type != OBJ_BLOB) {
 			ret = err(opt, _("blob expected for %s '%s'"),
 				  oid_to_hex(&contents->oid), path);

builtin/merge-recursive.c, builtin/stash.c, t/t3030-merge-recursive.sh

diff --git a/builtin/merge-recursive.c b/builtin/merge-recursive.c
index 5b910e351e..a4bfd8fc51 100644
--- a/builtin/merge-recursive.c
+++ b/builtin/merge-recursive.c
@@ -1,3 +1,4 @@
+#include "cache.h"
 #include "builtin.h"
 #include "commit.h"
 #include "tag.h"
@@ -63,6 +64,9 @@ int cmd_merge_recursive(int argc, const char **argv, const char *prefix)
 	if (argc - i != 3) /* "--" "<head>" "<remote>" */
 		die(_("not handling anything other than two heads merge."));
 
+	if (repo_read_index_unmerged(the_repository))
+		die_resolve_conflict("merge");
+
 	o.branch1 = argv[++i];
 	o.branch2 = argv[++i];
 
diff --git a/builtin/stash.c b/builtin/stash.c
index b5a301f24d..4aa47785f9 100644
--- a/builtin/stash.c
+++ b/builtin/stash.c
@@ -427,6 +427,8 @@ static int do_apply_stash(const char *prefix, struct stash_info *info,
 				return error(_("could not save index tree"));
 
 			reset_head();
+			discard_cache();
+			read_cache();
 		}
 	}
 
diff --git a/t/t3030-merge-recursive.sh b/t/t3030-merge-recursive.sh
index ff641b348a..a37bcc58a0 100755
--- a/t/t3030-merge-recursive.sh
+++ b/t/t3030-merge-recursive.sh
@@ -667,15 +667,22 @@ test_expect_success 'merging with triple rename across D/F conflict' '
 test_expect_success 'merge-recursive remembers the names of all base trees' '
 	git reset --hard HEAD &&
 
+	# make the index match $c1 so that merge-recursive below does not
+	# fail early
+	git diff --binary HEAD $c1 -- | git apply --cached &&
+
 	# more trees than static slots used by oid_to_hex()
 	for commit in $c0 $c2 $c4 $c5 $c6 $c7
 	do
 		git rev-parse "$commit^{tree}"
 	done >trees &&
 
-	# ignore the return code -- it only fails because the input is weird
+	# ignore the return code; it only fails because the input is weird...
 	test_must_fail git -c merge.verbosity=5 merge-recursive $(cat trees) -- $c1 $c3 >out &&
 
+	# ...but make sure it fails in the expected way
+	test_i18ngrep CONFLICT.*rename/rename out &&
+
 	# merge-recursive prints in reverse order, but we do not care
 	sort <trees >expect &&
 	sed -n "s/^virtual //p" out | sort >actual &&

diff --git a/merge-recursive.c b/merge-recursive.c
index 1163508811..37bb94fb4d 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -3571,8 +3571,11 @@ int merge_recursive(struct merge_options *opt,
 		repo_read_index(opt->repo);
 
 	opt->ancestor = "merged common ancestors";
-	clean = merge_trees(opt, get_commit_tree(h1), get_commit_tree(h2),
-			    get_commit_tree(merged_common_ancestors),
+	clean = merge_trees(opt,
+			    repo_get_commit_tree(opt->repo, h1),
+			    repo_get_commit_tree(opt->repo, h2),
+			    repo_get_commit_tree(opt->repo,
+						 merged_common_ancestors),
 			    &mrtree);
 	if (clean < 0) {
 		flush_output(opt);

diff --git a/merge-recursive.c b/merge-recursive.c
index 37bb94fb4d..f5cf21e2e0 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -3381,21 +3381,14 @@ static int process_entry(struct merge_options *opt,
 	return clean_merge;
 }
 
-int merge_trees(struct merge_options *opt,
-		struct tree *head,
-		struct tree *merge,
-		struct tree *common,
-		struct tree **result)
+static int merge_trees_internal(struct merge_options *opt,
+				struct tree *head,
+				struct tree *merge,
+				struct tree *common,
+				struct tree **result)
 {
 	struct index_state *istate = opt->repo->index;
 	int code, clean;
-	struct strbuf sb = STRBUF_INIT;
-
-	if (!opt->call_depth && repo_index_has_changes(opt->repo, head, &sb)) {
-		err(opt, _("Your local changes to the following files would be overwritten by merge:\n  %s"),
-		    sb.buf);
-		return -1;
-	}
 
 	if (opt->subtree_shift) {
 		merge = shift_tree_object(opt->repo, head, merge, opt->subtree_shift);
@@ -3499,11 +3492,11 @@ static struct commit_list *reverse_commit_list(struct commit_list *list)
  * Merge the commits h1 and h2, return the resulting virtual
  * commit object and a flag indicating the cleanness of the merge.
  */
-int merge_recursive(struct merge_options *opt,
-		    struct commit *h1,
-		    struct commit *h2,
-		    struct commit_list *ca,
-		    struct commit **result)
+static int merge_recursive_internal(struct merge_options *opt,
+				    struct commit *h1,
+				    struct commit *h2,
+				    struct commit_list *ca,
+				    struct commit **result)
 {
 	struct commit_list *iter;
 	struct commit *merged_common_ancestors;
@@ -3555,7 +3548,7 @@ int merge_recursive(struct merge_options *opt,
 		saved_b2 = opt->branch2;
 		opt->branch1 = "Temporary merge branch 1";
 		opt->branch2 = "Temporary merge branch 2";
-		if (merge_recursive(opt, merged_common_ancestors, iter->item,
+		if (merge_recursive_internal(opt, merged_common_ancestors, iter->item,
 				    NULL, &merged_common_ancestors) < 0)
 			return -1;
 		opt->branch1 = saved_b1;
@@ -3571,12 +3564,12 @@ int merge_recursive(struct merge_options *opt,
 		repo_read_index(opt->repo);
 
 	opt->ancestor = "merged common ancestors";
-	clean = merge_trees(opt,
-			    repo_get_commit_tree(opt->repo, h1),
-			    repo_get_commit_tree(opt->repo, h2),
-			    repo_get_commit_tree(opt->repo,
-						 merged_common_ancestors),
-			    &mrtree);
+	clean = merge_trees_internal(opt,
+				     repo_get_commit_tree(opt->repo, h1),
+				     repo_get_commit_tree(opt->repo, h2),
+				     repo_get_commit_tree(opt->repo,
+							  merged_common_ancestors),
+				     &mrtree);
 	if (clean < 0) {
 		flush_output(opt);
 		return clean;
@@ -3596,6 +3589,59 @@ int merge_recursive(struct merge_options *opt,
 	return clean;
 }
 
+static int merge_start(struct merge_options *opt, struct tree *head)
+{
+	struct strbuf sb = STRBUF_INIT;
+
+	assert(opt->branch1 && opt->branch2);
+
+	if (repo_index_has_changes(opt->repo, head, &sb)) {
+		err(opt, _("Your local changes to the following files would be overwritten by merge:\n  %s"),
+		    sb.buf);
+		strbuf_release(&sb);
+		return -1;
+	}
+
+	return 0;
+}
+
+static void merge_finalize(struct merge_options *opt)
+{
+	/* Common code for wrapping up merges will be added here later */
+}
+
+int merge_trees(struct merge_options *opt,
+		struct tree *head,
+		struct tree *merge,
+		struct tree *common,
+		struct tree **result)
+{
+	int clean;
+
+	if (merge_start(opt, head))
+		return -1;
+	clean = merge_trees_internal(opt, head, merge, common, result);
+	merge_finalize(opt);
+
+	return clean;
+}
+
+int merge_recursive(struct merge_options *opt,
+		    struct commit *h1,
+		    struct commit *h2,
+		    struct commit_list *ca,
+		    struct commit **result)
+{
+	int clean;
+
+	if (merge_start(opt, repo_get_commit_tree(opt->repo, h1)))
+		return -1;
+	clean = merge_recursive_internal(opt, h1, h2, ca, result);
+	merge_finalize(opt);
+
+	return clean;
+}
+
 static struct commit *get_ref(struct repository *repo, const struct object_id *oid,
 			      const char *name)
 {

builtin/checkout.c, merge-recursive.c, merge-recursive.h, sequencer.c

diff --git a/builtin/checkout.c b/builtin/checkout.c
index 91f8509f85..20e38c5edc 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -708,7 +708,6 @@ static int merge_working_tree(const struct checkout_opts *opts,
 			 * give up or do a real merge, depending on
 			 * whether the merge flag was used.
 			 */
-			struct tree *result;
 			struct tree *work;
 			struct tree *old_tree;
 			struct merge_options o;
@@ -773,8 +772,7 @@ static int merge_working_tree(const struct checkout_opts *opts,
 			ret = merge_trees(&o,
 					  new_tree,
 					  work,
-					  old_tree,
-					  &result);
+					  old_tree);
 			if (ret < 0)
 				exit(128);
 			ret = reset_tree(new_tree,
diff --git a/merge-recursive.c b/merge-recursive.c
index f5cf21e2e0..4a481c3929 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -3613,14 +3613,14 @@ static void merge_finalize(struct merge_options *opt)
 int merge_trees(struct merge_options *opt,
 		struct tree *head,
 		struct tree *merge,
-		struct tree *common,
-		struct tree **result)
+		struct tree *common)
 {
 	int clean;
+	struct tree *ignored;
 
 	if (merge_start(opt, head))
 		return -1;
-	clean = merge_trees_internal(opt, head, merge, common, result);
+	clean = merge_trees_internal(opt, head, merge, common, &ignored);
 	merge_finalize(opt);
 
 	return clean;
diff --git a/merge-recursive.h b/merge-recursive.h
index c2b7bb65c6..812c456f1b 100644
--- a/merge-recursive.h
+++ b/merge-recursive.h
@@ -70,19 +70,31 @@ static inline int merge_detect_rename(struct merge_options *o)
 		o->diff_detect_rename >= 0 ? o->diff_detect_rename : 1;
 }
 
-/* merge_trees() but with recursive ancestor consolidation */
+/*
+ * merge_recursive is like merge_trees() but with recursive ancestor
+ * consolidation, and when successful, it creates an actual commit
+ * and writes its address to *result.
+ *
+ * NOTE: empirically, about a decade ago it was determined that with more
+ *       than two merge bases, optimal behavior was found when the
+ *       ancestors were passed in the order of oldest merge base to newest
+ *       one.  Also, ancestors will be consumed (emptied) so make a copy if
+ *       you need it.
+ */
 int merge_recursive(struct merge_options *o,
 		    struct commit *h1,
 		    struct commit *h2,
 		    struct commit_list *ancestors,
 		    struct commit **result);
 
-/* rename-detecting three-way merge, no recursion */
+/*
+ * rename-detecting three-way merge, no recursion; result of merge is written
+ * to opt->repo->index.
+ */
 int merge_trees(struct merge_options *o,
 		struct tree *head,
 		struct tree *merge,
-		struct tree *common,
-		struct tree **result);
+		struct tree *common);
 
 /*
  * "git-merge-recursive" can be fed trees; wrap them into
diff --git a/sequencer.c b/sequencer.c
index 34ebf8ed94..c4ed30f1b4 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -586,7 +586,7 @@ static int do_recursive_merge(struct repository *r,
 			      struct replay_opts *opts)
 {
 	struct merge_options o;
-	struct tree *result, *next_tree, *base_tree, *head_tree;
+	struct tree *next_tree, *base_tree, *head_tree;
 	int clean;
 	char **xopt;
 	struct lock_file index_lock = LOCK_INIT;
@@ -613,7 +613,7 @@ static int do_recursive_merge(struct repository *r,
 
 	clean = merge_trees(&o,
 			    head_tree,
-			    next_tree, base_tree, &result);
+			    next_tree, base_tree);
 	if (is_rebase_i(opts) && clean <= 0)
 		fputs(o.obuf.buf, stdout);
 	strbuf_release(&o.obuf);

builtin/checkout.c, cache-tree.c, cache-tree.h, merge-recursive.c, merge-recursive.h

diff --git a/builtin/checkout.c b/builtin/checkout.c
index 20e38c5edc..a7b6454061 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -709,6 +709,7 @@ static int merge_working_tree(const struct checkout_opts *opts,
 			 * whether the merge flag was used.
 			 */
 			struct tree *work;
+			struct object_id work_oid;
 			struct tree *old_tree;
 			struct merge_options o;
 			struct strbuf sb = STRBUF_INIT;
@@ -759,7 +760,10 @@ static int merge_working_tree(const struct checkout_opts *opts,
 			 */
 			init_merge_options(&o, the_repository);
 			o.verbosity = 0;
-			work = write_tree_from_memory(&o);
+			if (write_index_as_tree(&work_oid, &the_index, NULL,
+					WRITE_TREE_FROM_MEMORY, NULL) ||
+			    !(work = lookup_tree(the_repository, &work_oid)))
+				die(_("error building trees"));
 
 			ret = reset_tree(new_tree,
 					 opts, 1,
diff --git a/cache-tree.c b/cache-tree.c
index 706ffcf188..99144b1704 100644
--- a/cache-tree.c
+++ b/cache-tree.c
@@ -613,14 +613,19 @@ int write_index_as_tree(struct object_id *oid, struct index_state *index_state,
 	int entries, was_valid;
 	struct lock_file lock_file = LOCK_INIT;
 	int ret = 0;
+	int access_disk = !(flags & WRITE_TREE_FROM_MEMORY);
 
-	hold_lock_file_for_update(&lock_file, index_path, LOCK_DIE_ON_ERROR);
+	if (access_disk) {
+		hold_lock_file_for_update(&lock_file, index_path,
+					  LOCK_DIE_ON_ERROR);
 
-	entries = read_index_from(index_state, index_path, get_git_dir());
-	if (entries < 0) {
-		ret = WRITE_TREE_UNREADABLE_INDEX;
-		goto out;
+		entries = read_index_from(index_state, index_path, get_git_dir());
+		if (entries < 0) {
+			ret = WRITE_TREE_UNREADABLE_INDEX;
+			goto out;
+		}
 	}
+
 	if (flags & WRITE_TREE_IGNORE_CACHE_TREE)
 		cache_tree_free(&index_state->cache_tree);
 
@@ -633,13 +638,16 @@ int write_index_as_tree(struct object_id *oid, struct index_state *index_state,
 			ret = WRITE_TREE_UNMERGED_INDEX;
 			goto out;
 		}
-		write_locked_index(index_state, &lock_file, COMMIT_LOCK);
-		/* Not being able to write is fine -- we are only interested
-		 * in updating the cache-tree part, and if the next caller
-		 * ends up using the old index with unupdated cache-tree part
-		 * it misses the work we did here, but that is just a
-		 * performance penalty and not a big deal.
-		 */
+		if (access_disk) {
+			write_locked_index(index_state, &lock_file, COMMIT_LOCK);
+			/* Not being able to write is fine -- we are only
+			 * interested in updating the cache-tree part, and if
+			 * the next caller ends up using the old index with
+			 * unupdated cache-tree part it misses the work we
+			 * did here, but that is just a performance penalty
+			 * and not a big deal.
+			 */
+		}
 	}
 
 	if (prefix) {
@@ -655,7 +663,9 @@ int write_index_as_tree(struct object_id *oid, struct index_state *index_state,
 		oidcpy(oid, &index_state->cache_tree->oid);
 
 out:
-	rollback_lock_file(&lock_file);
+	if (access_disk)
+		rollback_lock_file(&lock_file);
+
 	return ret;
 }
 
diff --git a/cache-tree.h b/cache-tree.h
index 757bbc48bc..481ec45dfa 100644
--- a/cache-tree.h
+++ b/cache-tree.h
@@ -34,12 +34,13 @@ int cache_tree_fully_valid(struct cache_tree *);
 int cache_tree_update(struct index_state *, int);
 void cache_tree_verify(struct repository *, struct index_state *);
 
-/* bitmasks to write_cache_as_tree flags */
+/* bitmasks to write_index_as_tree flags */
 #define WRITE_TREE_MISSING_OK 1
 #define WRITE_TREE_IGNORE_CACHE_TREE 2
 #define WRITE_TREE_DRY_RUN 4
 #define WRITE_TREE_SILENT 8
 #define WRITE_TREE_REPAIR 16
+#define WRITE_TREE_FROM_MEMORY 32
 
 /* error return codes */
 #define WRITE_TREE_UNREADABLE_INDEX (-1)
diff --git a/merge-recursive.c b/merge-recursive.c
index 308e350ff1..6c38c02e3f 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -412,37 +412,6 @@ static void unpack_trees_finish(struct merge_options *opt)
 	clear_unpack_trees_porcelain(&opt->unpack_opts);
 }
 
-struct tree *write_tree_from_memory(struct merge_options *opt)
-{
-	struct tree *result = NULL;
-	struct index_state *istate = opt->repo->index;
-
-	if (unmerged_index(istate)) {
-		int i;
-		fprintf(stderr, "BUG: There are unmerged index entries:\n");
-		for (i = 0; i < istate->cache_nr; i++) {
-			const struct cache_entry *ce = istate->cache[i];
-			if (ce_stage(ce))
-				fprintf(stderr, "BUG: %d %.*s\n", ce_stage(ce),
-					(int)ce_namelen(ce), ce->name);
-		}
-		BUG("unmerged index entries in merge-recursive.c");
-	}
-
-	if (!istate->cache_tree)
-		istate->cache_tree = cache_tree();
-
-	if (!cache_tree_fully_valid(istate->cache_tree) &&
-	    cache_tree_update(istate, 0) < 0) {
-		err(opt, _("error building trees"));
-		return NULL;
-	}
-
-	result = lookup_tree(opt->repo, &istate->cache_tree->oid);
-
-	return result;
-}
-
 static int save_files_dirs(const struct object_id *oid,
 			   struct strbuf *base, const char *path,
 			   unsigned int mode, int stage, void *context)
@@ -3471,8 +3440,15 @@ static int merge_trees_internal(struct merge_options *opt,
 
 	unpack_trees_finish(opt);
 
-	if (opt->call_depth && !(*result = write_tree_from_memory(opt)))
-		return -1;
+	if (opt->call_depth) {
+		struct object_id tree_id;
+		if (write_index_as_tree(&tree_id, opt->repo->index, NULL,
+					WRITE_TREE_FROM_MEMORY, NULL) ||
+		    !(*result = lookup_tree(opt->repo, &tree_id))) {
+			err(opt, _("error building trees"));
+			return -1;
+		}
+	}
 
 	return clean;
 }
diff --git a/merge-recursive.h b/merge-recursive.h
index 812c456f1b..b3394502c7 100644
--- a/merge-recursive.h
+++ b/merge-recursive.h
@@ -109,7 +109,6 @@ int merge_recursive_generic(struct merge_options *o,
 
 void init_merge_options(struct merge_options *o,
 			struct repository *repo);
-struct tree *write_tree_from_memory(struct merge_options *o);
 
 int parse_merge_opt(struct merge_options *out, const char *s);
 

diff --git a/merge-recursive.c b/merge-recursive.c
index 6c38c02e3f..e81dec8f1f 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -681,7 +681,9 @@ static void add_flattened_path(struct strbuf *out, const char *s)
 			out->buf[i] = '_';
 }
 
-static char *unique_path(struct merge_options *opt, const char *path, const char *branch)
+static char *unique_path(struct merge_options *opt,
+			 const char *path,
+			 const char *branch)
 {
 	struct path_hashmap_entry *entry;
 	struct strbuf newpath = STRBUF_INIT;
@@ -915,7 +917,8 @@ static int update_file_flags(struct merge_options *opt,
 		}
 		if (S_ISREG(contents->mode)) {
 			struct strbuf strbuf = STRBUF_INIT;
-			if (convert_to_working_tree(opt->repo->index, path, buf, size, &strbuf)) {
+			if (convert_to_working_tree(opt->repo->index,
+						    path, buf, size, &strbuf)) {
 				free(buf);
 				size = strbuf.len;
 				buf = strbuf_detach(&strbuf, NULL);
@@ -3392,7 +3395,8 @@ static int merge_trees_internal(struct merge_options *opt,
 		 * opposed to decaring a local hashmap is for convenience
 		 * so that we don't have to pass it to around.
 		 */
-		hashmap_init(&opt->current_file_dir_set, path_hashmap_cmp, NULL, 512);
+		hashmap_init(&opt->current_file_dir_set, path_hashmap_cmp,
+			     NULL, 512);
 		get_files_dirs(opt, head);
 		get_files_dirs(opt, merge);
 
@@ -3505,7 +3509,8 @@ static int merge_recursive_internal(struct merge_options *opt,
 		struct tree *tree;
 
 		tree = lookup_tree(opt->repo, opt->repo->hash_algo->empty_tree);
-		merged_common_ancestors = make_virtual_commit(opt->repo, tree, "ancestor");
+		merged_common_ancestors = make_virtual_commit(opt->repo,
+							      tree, "ancestor");
 	}
 
 	for (iter = ca; iter; iter = iter->next) {
@@ -3617,7 +3622,8 @@ int merge_recursive(struct merge_options *opt,
 	return clean;
 }
 
-static struct commit *get_ref(struct repository *repo, const struct object_id *oid,
+static struct commit *get_ref(struct repository *repo,
+			      const struct object_id *oid,
 			      const char *name)
 {
 	struct object *object;
@@ -3652,7 +3658,8 @@ int merge_recursive_generic(struct merge_options *opt,
 		int i;
 		for (i = 0; i < num_base_list; ++i) {
 			struct commit *base;
-			if (!(base = get_ref(opt->repo, base_list[i], oid_to_hex(base_list[i]))))
+			if (!(base = get_ref(opt->repo, base_list[i],
+					     oid_to_hex(base_list[i]))))
 				return err(opt, _("Could not parse object '%s'"),
 					   oid_to_hex(base_list[i]));
 			commit_list_insert(base, &ca);

merge-recursive.c, sequencer.c

diff --git a/merge-recursive.c b/merge-recursive.c
index 4a481c3929..308e350ff1 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -3583,9 +3583,6 @@ static int merge_recursive_internal(struct merge_options *opt,
 	flush_output(opt);
 	if (!opt->call_depth && opt->buffer_output < 2)
 		strbuf_release(&opt->obuf);
-	if (show(opt, 2))
-		diff_warn_rename_limit("merge.renamelimit",
-				       opt->needed_rename_limit, 0);
 	return clean;
 }
 
@@ -3607,7 +3604,9 @@ static int merge_start(struct merge_options *opt, struct tree *head)
 
 static void merge_finalize(struct merge_options *opt)
 {
-	/* Common code for wrapping up merges will be added here later */
+	if (show(opt, 2))
+		diff_warn_rename_limit("merge.renamelimit",
+				       opt->needed_rename_limit, 0);
 }
 
 int merge_trees(struct merge_options *opt,
diff --git a/sequencer.c b/sequencer.c
index c4ed30f1b4..094a4dd03d 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -617,7 +617,6 @@ static int do_recursive_merge(struct repository *r,
 	if (is_rebase_i(opts) && clean <= 0)
 		fputs(o.obuf.buf, stdout);
 	strbuf_release(&o.obuf);
-	diff_warn_rename_limit("merge.renamelimit", o.needed_rename_limit, 0);
 	if (clean < 0) {
 		rollback_lock_file(&index_lock);
 		return clean;

diff --git a/merge-recursive.c b/merge-recursive.c
index 8114e77b98..f36962b7b5 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -3482,7 +3482,7 @@ static int merge_recursive_internal(struct merge_options *opt,
 {
 	struct commit_list *iter;
 	struct commit *merged_merge_bases;
-	struct tree *mrtree;
+	struct tree *result_tree;
 	int clean;
 
 	if (show(opt, 4)) {
@@ -3552,14 +3552,15 @@ static int merge_recursive_internal(struct merge_options *opt,
 				     repo_get_commit_tree(opt->repo, h2),
 				     repo_get_commit_tree(opt->repo,
 							  merged_merge_bases),
-				     &mrtree);
+				     &result_tree);
 	if (clean < 0) {
 		flush_output(opt);
 		return clean;
 	}
 
 	if (opt->call_depth) {
-		*result = make_virtual_commit(opt->repo, mrtree, "merged tree");
+		*result = make_virtual_commit(opt->repo, result_tree,
+					      "merged tree");
 		commit_list_insert(h1, &(*result)->parents);
 		commit_list_insert(h2, &(*result)->parents->next);
 	}

diff --git a/merge-recursive.h b/merge-recursive.h
index c7ba8d0a71..c201de0fc3 100644
--- a/merge-recursive.h
+++ b/merge-recursive.h
@@ -64,10 +64,10 @@ struct collision_entry {
 	unsigned reported_already:1;
 };
 
-static inline int merge_detect_rename(struct merge_options *o)
+static inline int merge_detect_rename(struct merge_options *opt)
 {
-	return o->merge_detect_rename >= 0 ? o->merge_detect_rename :
-		o->diff_detect_rename >= 0 ? o->diff_detect_rename : 1;
+	return opt->merge_detect_rename >= 0 ? opt->merge_detect_rename :
+		opt->diff_detect_rename >= 0 ? opt->diff_detect_rename : 1;
 }
 
 /*
@@ -81,7 +81,7 @@ static inline int merge_detect_rename(struct merge_options *o)
  *       commit.  Also, merge_bases will be consumed (emptied) so make a
  *       copy if you need it.
  */
-int merge_recursive(struct merge_options *o,
+int merge_recursive(struct merge_options *opt,
 		    struct commit *h1,
 		    struct commit *h2,
 		    struct commit_list *merge_bases,
@@ -91,7 +91,7 @@ int merge_recursive(struct merge_options *o,
  * rename-detecting three-way merge, no recursion; result of merge is written
  * to opt->repo->index.
  */
-int merge_trees(struct merge_options *o,
+int merge_trees(struct merge_options *opt,
 		struct tree *head,
 		struct tree *merge,
 		struct tree *merge_base);
@@ -100,16 +100,16 @@ int merge_trees(struct merge_options *o,
  * "git-merge-recursive" can be fed trees; wrap them into
  * virtual commits and call merge_recursive() proper.
  */
-int merge_recursive_generic(struct merge_options *o,
+int merge_recursive_generic(struct merge_options *opt,
 			    const struct object_id *head,
 			    const struct object_id *merge,
 			    int num_merge_bases,
 			    const struct object_id **merge_bases,
 			    struct commit **result);
 
-void init_merge_options(struct merge_options *o,
+void init_merge_options(struct merge_options *opt,
 			struct repository *repo);
 
-int parse_merge_opt(struct merge_options *out, const char *s);
+int parse_merge_opt(struct merge_options *opt, const char *s);
 
 #endif

merge-recursive.c, merge-recursive.h

diff --git a/merge-recursive.c b/merge-recursive.c
index e81dec8f1f..8114e77b98 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -3356,24 +3356,26 @@ static int process_entry(struct merge_options *opt,
 static int merge_trees_internal(struct merge_options *opt,
 				struct tree *head,
 				struct tree *merge,
-				struct tree *common,
+				struct tree *merge_base,
 				struct tree **result)
 {
 	struct index_state *istate = opt->repo->index;
 	int code, clean;
 
 	if (opt->subtree_shift) {
-		merge = shift_tree_object(opt->repo, head, merge, opt->subtree_shift);
-		common = shift_tree_object(opt->repo, head, common, opt->subtree_shift);
+		merge = shift_tree_object(opt->repo, head, merge,
+					  opt->subtree_shift);
+		merge_base = shift_tree_object(opt->repo, head, merge_base,
+					       opt->subtree_shift);
 	}
 
-	if (oid_eq(&common->object.oid, &merge->object.oid)) {
+	if (oid_eq(&merge_base->object.oid, &merge->object.oid)) {
 		output(opt, 0, _("Already up to date!"));
 		*result = head;
 		return 1;
 	}
 
-	code = unpack_trees_start(opt, common, head, merge);
+	code = unpack_trees_start(opt, merge_base, head, merge);
 
 	if (code != 0) {
 		if (show(opt, 4) || opt->call_depth)
@@ -3401,7 +3403,7 @@ static int merge_trees_internal(struct merge_options *opt,
 		get_files_dirs(opt, merge);
 
 		entries = get_unmerged(opt->repo->index);
-		clean = detect_and_process_renames(opt, common, head, merge,
+		clean = detect_and_process_renames(opt, merge_base, head, merge,
 						   entries, &re_info);
 		record_df_conflict_files(opt, entries);
 		if (clean < 0)
@@ -3475,11 +3477,11 @@ static struct commit_list *reverse_commit_list(struct commit_list *list)
 static int merge_recursive_internal(struct merge_options *opt,
 				    struct commit *h1,
 				    struct commit *h2,
-				    struct commit_list *ca,
+				    struct commit_list *merge_bases,
 				    struct commit **result)
 {
 	struct commit_list *iter;
-	struct commit *merged_common_ancestors;
+	struct commit *merged_merge_bases;
 	struct tree *mrtree;
 	int clean;
 
@@ -3489,31 +3491,31 @@ static int merge_recursive_internal(struct merge_options *opt,
 		output_commit_title(opt, h2);
 	}
 
-	if (!ca) {
-		ca = get_merge_bases(h1, h2);
-		ca = reverse_commit_list(ca);
+	if (!merge_bases) {
+		merge_bases = get_merge_bases(h1, h2);
+		merge_bases = reverse_commit_list(merge_bases);
 	}
 
 	if (show(opt, 5)) {
-		unsigned cnt = commit_list_count(ca);
+		unsigned cnt = commit_list_count(merge_bases);
 
 		output(opt, 5, Q_("found %u common ancestor:",
 				"found %u common ancestors:", cnt), cnt);
-		for (iter = ca; iter; iter = iter->next)
+		for (iter = merge_bases; iter; iter = iter->next)
 			output_commit_title(opt, iter->item);
 	}
 
-	merged_common_ancestors = pop_commit(&ca);
-	if (merged_common_ancestors == NULL) {
+	merged_merge_bases = pop_commit(&merge_bases);
+	if (merged_merge_bases == NULL) {
 		/* if there is no common ancestor, use an empty tree */
 		struct tree *tree;
 
 		tree = lookup_tree(opt->repo, opt->repo->hash_algo->empty_tree);
-		merged_common_ancestors = make_virtual_commit(opt->repo,
-							      tree, "ancestor");
+		merged_merge_bases = make_virtual_commit(opt->repo, tree,
+							 "ancestor");
 	}
 
-	for (iter = ca; iter; iter = iter->next) {
+	for (iter = merge_bases; iter; iter = iter->next) {
 		const char *saved_b1, *saved_b2;
 		opt->call_depth++;
 		/*
@@ -3529,14 +3531,14 @@ static int merge_recursive_internal(struct merge_options *opt,
 		saved_b2 = opt->branch2;
 		opt->branch1 = "Temporary merge branch 1";
 		opt->branch2 = "Temporary merge branch 2";
-		if (merge_recursive_internal(opt, merged_common_ancestors, iter->item,
-				    NULL, &merged_common_ancestors) < 0)
+		if (merge_recursive_internal(opt, merged_merge_bases, iter->item,
+					     NULL, &merged_merge_bases) < 0)
 			return -1;
 		opt->branch1 = saved_b1;
 		opt->branch2 = saved_b2;
 		opt->call_depth--;
 
-		if (!merged_common_ancestors)
+		if (!merged_merge_bases)
 			return err(opt, _("merge returned no commit"));
 	}
 
@@ -3549,7 +3551,7 @@ static int merge_recursive_internal(struct merge_options *opt,
 				     repo_get_commit_tree(opt->repo, h1),
 				     repo_get_commit_tree(opt->repo, h2),
 				     repo_get_commit_tree(opt->repo,
-							  merged_common_ancestors),
+							  merged_merge_bases),
 				     &mrtree);
 	if (clean < 0) {
 		flush_output(opt);
@@ -3593,14 +3595,14 @@ static void merge_finalize(struct merge_options *opt)
 int merge_trees(struct merge_options *opt,
 		struct tree *head,
 		struct tree *merge,
-		struct tree *common)
+		struct tree *merge_base)
 {
 	int clean;
 	struct tree *ignored;
 
 	if (merge_start(opt, head))
 		return -1;
-	clean = merge_trees_internal(opt, head, merge, common, &ignored);
+	clean = merge_trees_internal(opt, head, merge, merge_base, &ignored);
 	merge_finalize(opt);
 
 	return clean;
@@ -3609,14 +3611,14 @@ int merge_trees(struct merge_options *opt,
 int merge_recursive(struct merge_options *opt,
 		    struct commit *h1,
 		    struct commit *h2,
-		    struct commit_list *ca,
+		    struct commit_list *merge_bases,
 		    struct commit **result)
 {
 	int clean;
 
 	if (merge_start(opt, repo_get_commit_tree(opt->repo, h1)))
 		return -1;
-	clean = merge_recursive_internal(opt, h1, h2, ca, result);
+	clean = merge_recursive_internal(opt, h1, h2, merge_bases, result);
 	merge_finalize(opt);
 
 	return clean;
@@ -3644,8 +3646,8 @@ static struct commit *get_ref(struct repository *repo,
 int merge_recursive_generic(struct merge_options *opt,
 			    const struct object_id *head,
 			    const struct object_id *merge,
-			    int num_base_list,
-			    const struct object_id **base_list,
+			    int num_merge_bases,
+			    const struct object_id **merge_bases,
 			    struct commit **result)
 {
 	int clean;
@@ -3654,14 +3656,14 @@ int merge_recursive_generic(struct merge_options *opt,
 	struct commit *next_commit = get_ref(opt->repo, merge, opt->branch2);
 	struct commit_list *ca = NULL;
 
-	if (base_list) {
+	if (merge_bases) {
 		int i;
-		for (i = 0; i < num_base_list; ++i) {
+		for (i = 0; i < num_merge_bases; ++i) {
 			struct commit *base;
-			if (!(base = get_ref(opt->repo, base_list[i],
-					     oid_to_hex(base_list[i]))))
+			if (!(base = get_ref(opt->repo, merge_bases[i],
+					     oid_to_hex(merge_bases[i]))))
 				return err(opt, _("Could not parse object '%s'"),
-					   oid_to_hex(base_list[i]));
+					   oid_to_hex(merge_bases[i]));
 			commit_list_insert(base, &ca);
 		}
 	}
diff --git a/merge-recursive.h b/merge-recursive.h
index b3394502c7..c7ba8d0a71 100644
--- a/merge-recursive.h
+++ b/merge-recursive.h
@@ -77,14 +77,14 @@ static inline int merge_detect_rename(struct merge_options *o)
  *
  * NOTE: empirically, about a decade ago it was determined that with more
  *       than two merge bases, optimal behavior was found when the
- *       ancestors were passed in the order of oldest merge base to newest
- *       one.  Also, ancestors will be consumed (emptied) so make a copy if
- *       you need it.
+ *       merge_bases were passed in the order of oldest commit to newest
+ *       commit.  Also, merge_bases will be consumed (emptied) so make a
+ *       copy if you need it.
  */
 int merge_recursive(struct merge_options *o,
 		    struct commit *h1,
 		    struct commit *h2,
-		    struct commit_list *ancestors,
+		    struct commit_list *merge_bases,
 		    struct commit **result);
 
 /*
@@ -94,7 +94,7 @@ int merge_recursive(struct merge_options *o,
 int merge_trees(struct merge_options *o,
 		struct tree *head,
 		struct tree *merge,
-		struct tree *common);
+		struct tree *merge_base);
 
 /*
  * "git-merge-recursive" can be fed trees; wrap them into
@@ -103,8 +103,8 @@ int merge_trees(struct merge_options *o,
 int merge_recursive_generic(struct merge_options *o,
 			    const struct object_id *head,
 			    const struct object_id *merge,
-			    int num_ca,
-			    const struct object_id **ca,
+			    int num_merge_bases,
+			    const struct object_id **merge_bases,
 			    struct commit **result);
 
 void init_merge_options(struct merge_options *o,

merge-recursive.c, merge-recursive.h

diff --git a/merge-recursive.c b/merge-recursive.c
index bafac63c45..a8e4a6a531 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -3743,21 +3743,27 @@ void init_merge_options(struct merge_options *opt,
 {
 	const char *merge_verbosity;
 	memset(opt, 0, sizeof(struct merge_options));
+
 	opt->repo = repo;
+
+	opt->detect_renames = -1;
+	opt->detect_directory_renames = 1;
+	opt->rename_limit = -1;
+
 	opt->verbosity = 2;
 	opt->buffer_output = 1;
-	opt->rename_limit = -1;
+	strbuf_init(&opt->obuf, 0);
+
 	opt->renormalize = 0;
-	opt->detect_renames = -1;
-	opt->detect_directory_renames = 1;
+
+	string_list_init(&opt->df_conflict_file_set, 1);
+
 	merge_recursive_config(opt);
 	merge_verbosity = getenv("GIT_MERGE_VERBOSITY");
 	if (merge_verbosity)
 		opt->verbosity = strtol(merge_verbosity, NULL, 10);
 	if (opt->verbosity >= 5)
 		opt->buffer_output = 0;
-	strbuf_init(&opt->obuf, 0);
-	string_list_init(&opt->df_conflict_file_set, 1);
 }
 
 int parse_merge_opt(struct merge_options *opt, const char *s)
diff --git a/merge-recursive.h b/merge-recursive.h
index b92a9ebce7..b6d420960b 100644
--- a/merge-recursive.h
+++ b/merge-recursive.h
@@ -9,32 +9,44 @@ struct commit;
 struct repository;
 
 struct merge_options {
+	struct repository *repo;
+
+	/* ref names used in console messages and conflict markers */
 	const char *ancestor;
 	const char *branch1;
 	const char *branch2;
+
+	/* rename related options */
+	int detect_renames;
+	int detect_directory_renames;
+	int rename_limit;
+	int rename_score;
+	int show_rename_progress;
+
+	/* xdiff-related options (patience, ignore whitespace, ours/theirs) */
+	long xdl_opts;
 	enum {
 		MERGE_RECURSIVE_NORMAL = 0,
 		MERGE_RECURSIVE_OURS,
 		MERGE_RECURSIVE_THEIRS
 	} recursive_variant;
-	const char *subtree_shift;
+
+	/* console output related options */
+	int verbosity;
 	unsigned buffer_output; /* 1: output at end, 2: keep buffered */
+	struct strbuf obuf;     /* output buffer */
+
+	/* miscellaneous control options */
+	const char *subtree_shift;
 	unsigned renormalize : 1;
-	long xdl_opts;
-	int verbosity;
-	int detect_directory_renames;
-	int detect_renames;
-	int rename_limit;
-	int rename_score;
-	int needed_rename_limit;
-	int show_rename_progress;
+
+	/* internal fields used by the implementation (do NOT set these) */
 	int call_depth;
-	struct strbuf obuf;
+	int needed_rename_limit;
 	struct hashmap current_file_dir_set;
 	struct string_list df_conflict_file_set;
 	struct unpack_trees_options unpack_opts;
 	struct index_state orig_index;
-	struct repository *repo;
 };
 
 void init_merge_options(struct merge_options *opt, struct repository *repo);

merge-recursive.c, merge-recursive.h

diff --git a/merge-recursive.c b/merge-recursive.c
index 6820578258..bafac63c45 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -385,8 +385,7 @@ static int add_cacheinfo(struct merge_options *opt,
 
 static inline int merge_detect_rename(struct merge_options *opt)
 {
-	return opt->merge_detect_rename >= 0 ? opt->merge_detect_rename :
-		opt->diff_detect_rename >= 0 ? opt->diff_detect_rename : 1;
+	return (opt->detect_renames != -1) ? opt->detect_renames : 1;
 }
 
 static void init_tree_desc_from_tree(struct tree_desc *desc, struct tree *tree)
@@ -1885,9 +1884,7 @@ static struct diff_queue_struct *get_diffpairs(struct merge_options *opt,
 	 */
 	if (opts.detect_rename > DIFF_DETECT_RENAME)
 		opts.detect_rename = DIFF_DETECT_RENAME;
-	opts.rename_limit = opt->merge_rename_limit >= 0 ? opt->merge_rename_limit :
-			    opt->diff_rename_limit >= 0 ? opt->diff_rename_limit :
-			    1000;
+	opts.rename_limit = (opt->rename_limit != -1) ? opt->rename_limit : 1000;
 	opts.rename_score = opt->rename_score;
 	opts.show_rename_progress = opt->show_rename_progress;
 	opts.output_format = DIFF_FORMAT_NO_OUTPUT;
@@ -3719,14 +3716,14 @@ static void merge_recursive_config(struct merge_options *opt)
 {
 	char *value = NULL;
 	git_config_get_int("merge.verbosity", &opt->verbosity);
-	git_config_get_int("diff.renamelimit", &opt->diff_rename_limit);
-	git_config_get_int("merge.renamelimit", &opt->merge_rename_limit);
+	git_config_get_int("diff.renamelimit", &opt->rename_limit);
+	git_config_get_int("merge.renamelimit", &opt->rename_limit);
 	if (!git_config_get_string("diff.renames", &value)) {
-		opt->diff_detect_rename = git_config_rename("diff.renames", value);
+		opt->detect_renames = git_config_rename("diff.renames", value);
 		free(value);
 	}
 	if (!git_config_get_string("merge.renames", &value)) {
-		opt->merge_detect_rename = git_config_rename("merge.renames", value);
+		opt->detect_renames = git_config_rename("merge.renames", value);
 		free(value);
 	}
 	if (!git_config_get_string("merge.directoryrenames", &value)) {
@@ -3749,11 +3746,9 @@ void init_merge_options(struct merge_options *opt,
 	opt->repo = repo;
 	opt->verbosity = 2;
 	opt->buffer_output = 1;
-	opt->diff_rename_limit = -1;
-	opt->merge_rename_limit = -1;
+	opt->rename_limit = -1;
 	opt->renormalize = 0;
-	opt->diff_detect_rename = -1;
-	opt->merge_detect_rename = -1;
+	opt->detect_renames = -1;
 	opt->detect_directory_renames = 1;
 	merge_recursive_config(opt);
 	merge_verbosity = getenv("GIT_MERGE_VERBOSITY");
@@ -3805,16 +3800,16 @@ int parse_merge_opt(struct merge_options *opt, const char *s)
 	else if (!strcmp(s, "no-renormalize"))
 		opt->renormalize = 0;
 	else if (!strcmp(s, "no-renames"))
-		opt->merge_detect_rename = 0;
+		opt->detect_renames = 0;
 	else if (!strcmp(s, "find-renames")) {
-		opt->merge_detect_rename = 1;
+		opt->detect_renames = 1;
 		opt->rename_score = 0;
 	}
 	else if (skip_prefix(s, "find-renames=", &arg) ||
 		 skip_prefix(s, "rename-threshold=", &arg)) {
 		if ((opt->rename_score = parse_rename_score(&arg)) == -1 || *arg != 0)
 			return -1;
-		opt->merge_detect_rename = 1;
+		opt->detect_renames = 1;
 	}
 	/*
 	 * Please update $__git_merge_strategy_options in
diff --git a/merge-recursive.h b/merge-recursive.h
index ebec855a65..b92a9ebce7 100644
--- a/merge-recursive.h
+++ b/merge-recursive.h
@@ -23,10 +23,8 @@ struct merge_options {
 	long xdl_opts;
 	int verbosity;
 	int detect_directory_renames;
-	int diff_detect_rename;
-	int merge_detect_rename;
-	int diff_rename_limit;
-	int merge_rename_limit;
+	int detect_renames;
+	int rename_limit;
 	int rename_score;
 	int needed_rename_limit;
 	int show_rename_progress;

merge-recursive.c, merge-recursive.h

diff --git a/merge-recursive.c b/merge-recursive.c
index a8e4a6a531..49c7de0379 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -3592,9 +3592,6 @@ static int merge_recursive_internal(struct merge_options *opt,
 		commit_list_insert(h1, &(*result)->parents);
 		commit_list_insert(h2, &(*result)->parents->next);
 	}
-	flush_output(opt);
-	if (!opt->call_depth && opt->buffer_output < 2)
-		strbuf_release(&opt->obuf);
 	return clean;
 }
 
@@ -3616,6 +3613,9 @@ static int merge_start(struct merge_options *opt, struct tree *head)
 
 static void merge_finalize(struct merge_options *opt)
 {
+	flush_output(opt);
+	if (!opt->call_depth && opt->buffer_output < 2)
+		strbuf_release(&opt->obuf);
 	if (show(opt, 2))
 		diff_warn_rename_limit("merge.renamelimit",
 				       opt->needed_rename_limit, 0);
diff --git a/merge-recursive.h b/merge-recursive.h
index b6d420960b..12249258ef 100644
--- a/merge-recursive.h
+++ b/merge-recursive.h
@@ -34,7 +34,8 @@ struct merge_options {
 	/* console output related options */
 	int verbosity;
 	unsigned buffer_output; /* 1: output at end, 2: keep buffered */
-	struct strbuf obuf;     /* output buffer */
+	struct strbuf obuf;     /* output buffer; if buffer_output == 2, caller
+				 * must handle and call strbuf_release */
 
 	/* miscellaneous control options */
 	const char *subtree_shift;

merge-recursive.c, merge-recursive.h

diff --git a/merge-recursive.c b/merge-recursive.c
index f36962b7b5..6820578258 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -54,6 +54,24 @@ static unsigned int path_hash(const char *path)
 	return ignore_case ? strihash(path) : strhash(path);
 }
 
+/*
+ * For dir_rename_entry, directory names are stored as a full path from the
+ * toplevel of the repository and do not include a trailing '/'.  Also:
+ *
+ *   dir:                original name of directory being renamed
+ *   non_unique_new_dir: if true, could not determine new_dir
+ *   new_dir:            final name of directory being renamed
+ *   possible_new_dirs:  temporary used to help determine new_dir; see comments
+ *                       in get_directory_renames() for details
+ */
+struct dir_rename_entry {
+	struct hashmap_entry ent; /* must be the first member! */
+	char *dir;
+	unsigned non_unique_new_dir:1;
+	struct strbuf new_dir;
+	struct string_list possible_new_dirs;
+};
+
 static struct dir_rename_entry *dir_rename_find_entry(struct hashmap *hashmap,
 						      char *dir)
 {
@@ -92,6 +110,13 @@ static void dir_rename_entry_init(struct dir_rename_entry *entry,
 	string_list_init(&entry->possible_new_dirs, 0);
 }
 
+struct collision_entry {
+	struct hashmap_entry ent; /* must be the first member! */
+	char *target_file;
+	struct string_list source_files;
+	unsigned reported_already:1;
+};
+
 static struct collision_entry *collision_find_entry(struct hashmap *hashmap,
 						    char *target_file)
 {
@@ -358,6 +383,12 @@ static int add_cacheinfo(struct merge_options *opt,
 	return ret;
 }
 
+static inline int merge_detect_rename(struct merge_options *opt)
+{
+	return opt->merge_detect_rename >= 0 ? opt->merge_detect_rename :
+		opt->diff_detect_rename >= 0 ? opt->diff_detect_rename : 1;
+}
+
 static void init_tree_desc_from_tree(struct tree_desc *desc, struct tree *tree)
 {
 	parse_tree(tree);
diff --git a/merge-recursive.h b/merge-recursive.h
index c201de0fc3..ebec855a65 100644
--- a/merge-recursive.h
+++ b/merge-recursive.h
@@ -39,47 +39,50 @@ struct merge_options {
 	struct repository *repo;
 };
 
+void init_merge_options(struct merge_options *opt, struct repository *repo);
+
+/* parse the option in s and update the relevant field of opt */
+int parse_merge_opt(struct merge_options *opt, const char *s);
+
 /*
- * For dir_rename_entry, directory names are stored as a full path from the
- * toplevel of the repository and do not include a trailing '/'.  Also:
- *
- *   dir:                original name of directory being renamed
- *   non_unique_new_dir: if true, could not determine new_dir
- *   new_dir:            final name of directory being renamed
- *   possible_new_dirs:  temporary used to help determine new_dir; see comments
- *                       in get_directory_renames() for details
+ * RETURN VALUES: All the merge_* functions below return a value as follows:
+ *   > 0     Merge was clean
+ *   = 0     Merge had conflicts
+ *   < 0     Merge hit an unexpected and unrecoverable problem (e.g. disk
+ *             full) and aborted merge part-way through.
  */
-struct dir_rename_entry {
-	struct hashmap_entry ent; /* must be the first member! */
-	char *dir;
-	unsigned non_unique_new_dir:1;
-	struct strbuf new_dir;
-	struct string_list possible_new_dirs;
-};
-
-struct collision_entry {
-	struct hashmap_entry ent; /* must be the first member! */
-	char *target_file;
-	struct string_list source_files;
-	unsigned reported_already:1;
-};
 
-static inline int merge_detect_rename(struct merge_options *opt)
-{
-	return opt->merge_detect_rename >= 0 ? opt->merge_detect_rename :
-		opt->diff_detect_rename >= 0 ? opt->diff_detect_rename : 1;
-}
+/*
+ * rename-detecting three-way merge, no recursion.
+ *
+ * Outputs:
+ *   - See RETURN VALUES above
+ *   - No commit is created
+ *   - opt->repo->index has the new index
+ *   - $GIT_INDEX_FILE is not updated
+ *   - The working tree is updated with results of the merge
+ */
+int merge_trees(struct merge_options *opt,
+		struct tree *head,
+		struct tree *merge,
+		struct tree *merge_base);
 
 /*
  * merge_recursive is like merge_trees() but with recursive ancestor
- * consolidation, and when successful, it creates an actual commit
- * and writes its address to *result.
+ * consolidation and, if the commit is clean, creation of a commit.
  *
  * NOTE: empirically, about a decade ago it was determined that with more
  *       than two merge bases, optimal behavior was found when the
  *       merge_bases were passed in the order of oldest commit to newest
  *       commit.  Also, merge_bases will be consumed (emptied) so make a
  *       copy if you need it.
+ *
+ * Outputs:
+ *   - See RETURN VALUES above
+ *   - If merge is clean, a commit is created and its address written to *result
+ *   - opt->repo->index has the new index
+ *   - $GIT_INDEX_FILE is not updated
+ *   - The working tree is updated with results of the merge
  */
 int merge_recursive(struct merge_options *opt,
 		    struct commit *h1,
@@ -88,17 +91,16 @@ int merge_recursive(struct merge_options *opt,
 		    struct commit **result);
 
 /*
- * rename-detecting three-way merge, no recursion; result of merge is written
- * to opt->repo->index.
- */
-int merge_trees(struct merge_options *opt,
-		struct tree *head,
-		struct tree *merge,
-		struct tree *merge_base);
-
-/*
- * "git-merge-recursive" can be fed trees; wrap them into
- * virtual commits and call merge_recursive() proper.
+ * merge_recursive_generic can operate on trees instead of commits, by
+ * wrapping the trees into virtual commits, and calling merge_recursive().
+ * It also writes out the in-memory index to disk if the merge is successful.
+ *
+ * Outputs:
+ *   - See RETURN VALUES above
+ *   - If merge is clean, a commit is created and its address written to *result
+ *   - opt->repo->index has the new index
+ *   - $GIT_INDEX_FILE is updated
+ *   - The working tree is updated with results of the merge
  */
 int merge_recursive_generic(struct merge_options *opt,
 			    const struct object_id *head,
@@ -107,9 +109,4 @@ int merge_recursive_generic(struct merge_options *opt,
 			    const struct object_id **merge_bases,
 			    struct commit **result);
 
-void init_merge_options(struct merge_options *opt,
-			struct repository *repo);
-
-int parse_merge_opt(struct merge_options *opt, const char *s);
-
 #endif

merge-recursive.c, merge-recursive.h

diff --git a/merge-recursive.c b/merge-recursive.c
index 49c7de0379..ba635ed753 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -29,6 +29,15 @@
 #include "revision.h"
 #include "commit-reach.h"
 
+struct merge_options_internal {
+	int call_depth;
+	int needed_rename_limit;
+	struct hashmap current_file_dir_set;
+	struct string_list df_conflict_file_set;
+	struct unpack_trees_options unpack_opts;
+	struct index_state orig_index;
+};
+
 struct path_hashmap_entry {
 	struct hashmap_entry e;
 	char path[FLEX_ARRAY];
@@ -309,7 +318,8 @@ static inline void setup_rename_conflict_info(enum rename_type rename_type,
 
 static int show(struct merge_options *opt, int v)
 {
-	return (!opt->call_depth && opt->verbosity >= v) || opt->verbosity >= 5;
+	return (!opt->priv->call_depth && opt->verbosity >= v) ||
+		opt->verbosity >= 5;
 }
 
 __attribute__((format (printf, 3, 4)))
@@ -320,7 +330,7 @@ static void output(struct merge_options *opt, int v, const char *fmt, ...)
 	if (!show(opt, v))
 		return;
 
-	strbuf_addchars(&opt->obuf, ' ', opt->call_depth * 2);
+	strbuf_addchars(&opt->obuf, ' ', opt->priv->call_depth * 2);
 
 	va_start(ap, fmt);
 	strbuf_vaddf(&opt->obuf, fmt, ap);
@@ -335,7 +345,7 @@ static void output_commit_title(struct merge_options *opt, struct commit *commit
 {
 	struct merge_remote_desc *desc;
 
-	strbuf_addchars(&opt->obuf, ' ', opt->call_depth * 2);
+	strbuf_addchars(&opt->obuf, ' ', opt->priv->call_depth * 2);
 	desc = merge_remote_util(commit);
 	if (desc)
 		strbuf_addf(&opt->obuf, "virtual %s\n", desc->name);
@@ -403,43 +413,43 @@ static int unpack_trees_start(struct merge_options *opt,
 	struct tree_desc t[3];
 	struct index_state tmp_index = { NULL };
 
-	memset(&opt->unpack_opts, 0, sizeof(opt->unpack_opts));
-	if (opt->call_depth)
-		opt->unpack_opts.index_only = 1;
+	memset(&opt->priv->unpack_opts, 0, sizeof(opt->priv->unpack_opts));
+	if (opt->priv->call_depth)
+		opt->priv->unpack_opts.index_only = 1;
 	else
-		opt->unpack_opts.update = 1;
-	opt->unpack_opts.merge = 1;
-	opt->unpack_opts.head_idx = 2;
-	opt->unpack_opts.fn = threeway_merge;
-	opt->unpack_opts.src_index = opt->repo->index;
-	opt->unpack_opts.dst_index = &tmp_index;
-	opt->unpack_opts.aggressive = !merge_detect_rename(opt);
-	setup_unpack_trees_porcelain(&opt->unpack_opts, "merge");
+		opt->priv->unpack_opts.update = 1;
+	opt->priv->unpack_opts.merge = 1;
+	opt->priv->unpack_opts.head_idx = 2;
+	opt->priv->unpack_opts.fn = threeway_merge;
+	opt->priv->unpack_opts.src_index = opt->repo->index;
+	opt->priv->unpack_opts.dst_index = &tmp_index;
+	opt->priv->unpack_opts.aggressive = !merge_detect_rename(opt);
+	setup_unpack_trees_porcelain(&opt->priv->unpack_opts, "merge");
 
 	init_tree_desc_from_tree(t+0, common);
 	init_tree_desc_from_tree(t+1, head);
 	init_tree_desc_from_tree(t+2, merge);
 
-	rc = unpack_trees(3, t, &opt->unpack_opts);
+	rc = unpack_trees(3, t, &opt->priv->unpack_opts);
 	cache_tree_free(&opt->repo->index->cache_tree);
 
 	/*
-	 * Update opt->repo->index to match the new results, AFTER saving a copy
-	 * in opt->orig_index.  Update src_index to point to the saved copy.
-	 * (verify_uptodate() checks src_index, and the original index is
-	 * the one that had the necessary modification timestamps.)
+	 * Update opt->repo->index to match the new results, AFTER saving a
+	 * copy in opt->priv->orig_index.  Update src_index to point to the
+	 * saved copy.  (verify_uptodate() checks src_index, and the original
+	 * index is the one that had the necessary modification timestamps.)
 	 */
-	opt->orig_index = *opt->repo->index;
+	opt->priv->orig_index = *opt->repo->index;
 	*opt->repo->index = tmp_index;
-	opt->unpack_opts.src_index = &opt->orig_index;
+	opt->priv->unpack_opts.src_index = &opt->priv->orig_index;
 
 	return rc;
 }
 
 static void unpack_trees_finish(struct merge_options *opt)
 {
-	discard_index(&opt->orig_index);
-	clear_unpack_trees_porcelain(&opt->unpack_opts);
+	discard_index(&opt->priv->orig_index);
+	clear_unpack_trees_porcelain(&opt->priv->unpack_opts);
 }
 
 static int save_files_dirs(const struct object_id *oid,
@@ -454,7 +464,7 @@ static int save_files_dirs(const struct object_id *oid,
 
 	FLEX_ALLOC_MEM(entry, path, base->buf, base->len);
 	hashmap_entry_init(entry, path_hash(entry->path));
-	hashmap_add(&opt->current_file_dir_set, entry);
+	hashmap_add(&opt->priv->current_file_dir_set, entry);
 
 	strbuf_setlen(base, baselen);
 	return (S_ISDIR(mode) ? READ_TREE_RECURSIVE : 0);
@@ -585,7 +595,7 @@ static void record_df_conflict_files(struct merge_options *opt,
 	 * If we're merging merge-bases, we don't want to bother with
 	 * any working directory changes.
 	 */
-	if (opt->call_depth)
+	if (opt->priv->call_depth)
 		return;
 
 	/* Ensure D/F conflicts are adjacent in the entries list. */
@@ -597,7 +607,7 @@ static void record_df_conflict_files(struct merge_options *opt,
 	df_sorted_entries.cmp = string_list_df_name_compare;
 	string_list_sort(&df_sorted_entries);
 
-	string_list_clear(&opt->df_conflict_file_set, 1);
+	string_list_clear(&opt->priv->df_conflict_file_set, 1);
 	for (i = 0; i < df_sorted_entries.nr; i++) {
 		const char *path = df_sorted_entries.items[i].string;
 		int len = strlen(path);
@@ -613,7 +623,7 @@ static void record_df_conflict_files(struct merge_options *opt,
 		    len > last_len &&
 		    memcmp(path, last_file, last_len) == 0 &&
 		    path[last_len] == '/') {
-			string_list_insert(&opt->df_conflict_file_set, last_file);
+			string_list_insert(&opt->priv->df_conflict_file_set, last_file);
 		}
 
 		/*
@@ -680,8 +690,8 @@ static void update_entry(struct stage_data *entry,
 static int remove_file(struct merge_options *opt, int clean,
 		       const char *path, int no_wd)
 {
-	int update_cache = opt->call_depth || clean;
-	int update_working_directory = !opt->call_depth && !no_wd;
+	int update_cache = opt->priv->call_depth || clean;
+	int update_working_directory = !opt->priv->call_depth && !no_wd;
 
 	if (update_cache) {
 		if (remove_file_from_index(opt->repo->index, path))
@@ -724,16 +734,16 @@ static char *unique_path(struct merge_options *opt,
 	add_flattened_path(&newpath, branch);
 
 	base_len = newpath.len;
-	while (hashmap_get_from_hash(&opt->current_file_dir_set,
+	while (hashmap_get_from_hash(&opt->priv->current_file_dir_set,
 				     path_hash(newpath.buf), newpath.buf) ||
-	       (!opt->call_depth && file_exists(newpath.buf))) {
+	       (!opt->priv->call_depth && file_exists(newpath.buf))) {
 		strbuf_setlen(&newpath, base_len);
 		strbuf_addf(&newpath, "_%d", suffix++);
 	}
 
 	FLEX_ALLOC_MEM(entry, path, newpath.buf, newpath.len);
 	hashmap_entry_init(entry, path_hash(entry->path));
-	hashmap_add(&opt->current_file_dir_set, entry);
+	hashmap_add(&opt->priv->current_file_dir_set, entry);
 	return strbuf_detach(&newpath, NULL);
 }
 
@@ -775,7 +785,7 @@ static int dir_in_way(struct index_state *istate, const char *path,
 static int was_tracked_and_matches(struct merge_options *opt, const char *path,
 				   const struct diff_filespec *blob)
 {
-	int pos = index_name_pos(&opt->orig_index, path, strlen(path));
+	int pos = index_name_pos(&opt->priv->orig_index, path, strlen(path));
 	struct cache_entry *ce;
 
 	if (0 > pos)
@@ -783,7 +793,7 @@ static int was_tracked_and_matches(struct merge_options *opt, const char *path,
 		return 0;
 
 	/* See if the file we were tracking before matches */
-	ce = opt->orig_index.cache[pos];
+	ce = opt->priv->orig_index.cache[pos];
 	return (oid_eq(&ce->oid, &blob->oid) && ce->ce_mode == blob->mode);
 }
 
@@ -792,7 +802,7 @@ static int was_tracked_and_matches(struct merge_options *opt, const char *path,
  */
 static int was_tracked(struct merge_options *opt, const char *path)
 {
-	int pos = index_name_pos(&opt->orig_index, path, strlen(path));
+	int pos = index_name_pos(&opt->priv->orig_index, path, strlen(path));
 
 	if (0 <= pos)
 		/* we were tracking this path before the merge */
@@ -849,12 +859,12 @@ static int was_dirty(struct merge_options *opt, const char *path)
 	struct cache_entry *ce;
 	int dirty = 1;
 
-	if (opt->call_depth || !was_tracked(opt, path))
+	if (opt->priv->call_depth || !was_tracked(opt, path))
 		return !dirty;
 
-	ce = index_file_exists(opt->unpack_opts.src_index,
+	ce = index_file_exists(opt->priv->unpack_opts.src_index,
 			       path, strlen(path), ignore_case);
-	dirty = verify_uptodate(ce, &opt->unpack_opts) != 0;
+	dirty = verify_uptodate(ce, &opt->priv->unpack_opts) != 0;
 	return dirty;
 }
 
@@ -864,8 +874,8 @@ static int make_room_for_path(struct merge_options *opt, const char *path)
 	const char *msg = _("failed to create path '%s'%s");
 
 	/* Unlink any D/F conflict files that are in the way */
-	for (i = 0; i < opt->df_conflict_file_set.nr; i++) {
-		const char *df_path = opt->df_conflict_file_set.items[i].string;
+	for (i = 0; i < opt->priv->df_conflict_file_set.nr; i++) {
+		const char *df_path = opt->priv->df_conflict_file_set.items[i].string;
 		size_t pathlen = strlen(path);
 		size_t df_pathlen = strlen(df_path);
 		if (df_pathlen < pathlen &&
@@ -875,7 +885,7 @@ static int make_room_for_path(struct merge_options *opt, const char *path)
 			       _("Removing %s to make room for subdirectory\n"),
 			       df_path);
 			unlink(df_path);
-			unsorted_string_list_delete_item(&opt->df_conflict_file_set,
+			unsorted_string_list_delete_item(&opt->priv->df_conflict_file_set,
 							 i, 0);
 			break;
 		}
@@ -916,7 +926,7 @@ static int update_file_flags(struct merge_options *opt,
 {
 	int ret = 0;
 
-	if (opt->call_depth)
+	if (opt->priv->call_depth)
 		update_wd = 0;
 
 	if (update_wd) {
@@ -1001,7 +1011,7 @@ static int update_file(struct merge_options *opt,
 		       const char *path)
 {
 	return update_file_flags(opt, contents, path,
-				 opt->call_depth || clean, !opt->call_depth);
+				 opt->priv->call_depth || clean, !opt->priv->call_depth);
 }
 
 /* Low level file merging, update and removal */
@@ -1030,7 +1040,7 @@ static int merge_3way(struct merge_options *opt,
 	ll_opts.extra_marker_size = extra_marker_size;
 	ll_opts.xdl_opts = opt->xdl_opts;
 
-	if (opt->call_depth) {
+	if (opt->priv->call_depth) {
 		ll_opts.virtual_ancestor = 1;
 		ll_opts.variant = 0;
 	} else {
@@ -1164,7 +1174,7 @@ static int merge_submodule(struct merge_options *opt,
 	struct object_array merges;
 
 	int i;
-	int search = !opt->call_depth;
+	int search = !opt->priv->call_depth;
 
 	/* store a in result in case we fail */
 	oidcpy(result, a);
@@ -1385,7 +1395,7 @@ static int handle_rename_via_dir(struct merge_options *opt,
 	int mark_conflicted = (opt->detect_directory_renames == 1);
 	assert(ren->dir_rename_original_dest);
 
-	if (!opt->call_depth && would_lose_untracked(opt, dest->path)) {
+	if (!opt->priv->call_depth && would_lose_untracked(opt, dest->path)) {
 		mark_conflicted = 1;
 		file_path = unique_path(opt, dest->path, ren->branch);
 		output(opt, 1, _("Error: Refusing to lose untracked file at %s; "
@@ -1428,12 +1438,12 @@ static int handle_change_delete(struct merge_options *opt,
 	const char *update_path = path;
 	int ret = 0;
 
-	if (dir_in_way(opt->repo->index, path, !opt->call_depth, 0) ||
-	    (!opt->call_depth && would_lose_untracked(opt, path))) {
+	if (dir_in_way(opt->repo->index, path, !opt->priv->call_depth, 0) ||
+	    (!opt->priv->call_depth && would_lose_untracked(opt, path))) {
 		update_path = alt_path = unique_path(opt, path, change_branch);
 	}
 
-	if (opt->call_depth) {
+	if (opt->priv->call_depth) {
 		/*
 		 * We cannot arbitrarily accept either a_sha or b_sha as
 		 * correct; since there is no true "middle point" between
@@ -1508,14 +1518,14 @@ static int handle_rename_delete(struct merge_options *opt,
 				     opt->branch2 : opt->branch1);
 
 	if (handle_change_delete(opt,
-				 opt->call_depth ? orig->path : dest->path,
-				 opt->call_depth ? NULL : orig->path,
+				 opt->priv->call_depth ? orig->path : dest->path,
+				 opt->priv->call_depth ? NULL : orig->path,
 				 orig, dest,
 				 rename_branch, delete_branch,
 				 _("rename"), _("renamed")))
 		return -1;
 
-	if (opt->call_depth)
+	if (opt->priv->call_depth)
 		return remove_file_from_index(opt->repo->index, dest->path);
 	else
 		return update_stages(opt, dest->path, NULL,
@@ -1552,7 +1562,7 @@ static int handle_file_collision(struct merge_options *opt,
 	/*
 	 * In the recursive case, we just opt to undo renames
 	 */
-	if (opt->call_depth && (prev_path1 || prev_path2)) {
+	if (opt->priv->call_depth && (prev_path1 || prev_path2)) {
 		/* Put first file (a->oid, a->mode) in its original spot */
 		if (prev_path1) {
 			if (update_file(opt, 1, a, prev_path1))
@@ -1581,10 +1591,10 @@ static int handle_file_collision(struct merge_options *opt,
 	/* Remove rename sources if rename/add or rename/rename(2to1) */
 	if (prev_path1)
 		remove_file(opt, 1, prev_path1,
-			    opt->call_depth || would_lose_untracked(opt, prev_path1));
+			    opt->priv->call_depth || would_lose_untracked(opt, prev_path1));
 	if (prev_path2)
 		remove_file(opt, 1, prev_path2,
-			    opt->call_depth || would_lose_untracked(opt, prev_path2));
+			    opt->priv->call_depth || would_lose_untracked(opt, prev_path2));
 
 	/*
 	 * Remove the collision path, if it wouldn't cause dirty contents
@@ -1626,12 +1636,12 @@ static int handle_file_collision(struct merge_options *opt,
 	null.mode = 0;
 
 	if (merge_mode_and_contents(opt, &null, a, b, collide_path,
-				    branch1, branch2, opt->call_depth * 2, &mfi))
+				    branch1, branch2, opt->priv->call_depth * 2, &mfi))
 		return -1;
 	mfi.clean &= !alt_path;
 	if (update_file(opt, mfi.clean, &mfi.blob, update_path))
 		return -1;
-	if (!mfi.clean && !opt->call_depth &&
+	if (!mfi.clean && !opt->priv->call_depth &&
 	    update_stages(opt, collide_path, NULL, a, b))
 		return -1;
 	free(alt_path);
@@ -1671,7 +1681,7 @@ static int handle_rename_add(struct merge_options *opt,
 				    &ci->ren1->src_entry->stages[other_stage],
 				    prev_path_desc,
 				    opt->branch1, opt->branch2,
-				    1 + opt->call_depth * 2, &mfi))
+				    1 + opt->priv->call_depth * 2, &mfi))
 		return -1;
 	free(prev_path_desc);
 
@@ -1689,7 +1699,7 @@ static char *find_path_for_conflict(struct merge_options *opt,
 				    const char *branch2)
 {
 	char *new_path = NULL;
-	if (dir_in_way(opt->repo->index, path, !opt->call_depth, 0)) {
+	if (dir_in_way(opt->repo->index, path, !opt->priv->call_depth, 0)) {
 		new_path = unique_path(opt, path, branch1);
 		output(opt, 1, _("%s is a directory in %s adding "
 			       "as %s instead"),
@@ -1720,17 +1730,17 @@ static int handle_rename_rename_1to2(struct merge_options *opt,
 	       "rename \"%s\"->\"%s\" in \"%s\"%s"),
 	       o->path, a->path, ci->ren1->branch,
 	       o->path, b->path, ci->ren2->branch,
-	       opt->call_depth ? _(" (left unresolved)") : "");
+	       opt->priv->call_depth ? _(" (left unresolved)") : "");
 
 	path_desc = xstrfmt("%s and %s, both renamed from %s",
 			    a->path, b->path, o->path);
 	if (merge_mode_and_contents(opt, o, a, b, path_desc,
 				    ci->ren1->branch, ci->ren2->branch,
-				    opt->call_depth * 2, &mfi))
+				    opt->priv->call_depth * 2, &mfi))
 		return -1;
 	free(path_desc);
 
-	if (opt->call_depth) {
+	if (opt->priv->call_depth) {
 		/*
 		 * FIXME: For rename/add-source conflicts (if we could detect
 		 * such), this is wrong.  We should instead find a unique
@@ -1845,12 +1855,12 @@ static int handle_rename_rename_2to1(struct merge_options *opt,
 				    &ci->ren1->src_entry->stages[ostage1],
 				    path_side_1_desc,
 				    opt->branch1, opt->branch2,
-				    1 + opt->call_depth * 2, &mfi_c1) ||
+				    1 + opt->priv->call_depth * 2, &mfi_c1) ||
 	    merge_mode_and_contents(opt, b,
 				    &ci->ren2->src_entry->stages[ostage2],
 				    c2, path_side_2_desc,
 				    opt->branch1, opt->branch2,
-				    1 + opt->call_depth * 2, &mfi_c2))
+				    1 + opt->priv->call_depth * 2, &mfi_c2))
 		return -1;
 	free(path_side_1_desc);
 	free(path_side_2_desc);
@@ -1891,8 +1901,8 @@ static struct diff_queue_struct *get_diffpairs(struct merge_options *opt,
 	diff_setup_done(&opts);
 	diff_tree_oid(&o_tree->object.oid, &tree->object.oid, "", &opts);
 	diffcore_std(&opts);
-	if (opts.needed_rename_limit > opt->needed_rename_limit)
-		opt->needed_rename_limit = opts.needed_rename_limit;
+	if (opts.needed_rename_limit > opt->priv->needed_rename_limit)
+		opt->priv->needed_rename_limit = opts.needed_rename_limit;
 
 	ret = xmalloc(sizeof(*ret));
 	*ret = diff_queued_diff;
@@ -3022,13 +3032,13 @@ static int handle_content_merge(struct merge_file_info *mfi,
 		reason = _("add/add");
 
 	assert(o->path && a->path && b->path);
-	if (ci && dir_in_way(opt->repo->index, path, !opt->call_depth,
+	if (ci && dir_in_way(opt->repo->index, path, !opt->priv->call_depth,
 			     S_ISGITLINK(ci->ren1->pair->two->mode)))
 		df_conflict_remains = 1;
 
 	if (merge_mode_and_contents(opt, o, a, b, path,
 				    opt->branch1, opt->branch2,
-				    opt->call_depth * 2, mfi))
+				    opt->priv->call_depth * 2, mfi))
 		return -1;
 
 	/*
@@ -3044,7 +3054,7 @@ static int handle_content_merge(struct merge_file_info *mfi,
 
 		output(opt, 3, _("Skipped %s (merged same as existing)"), path);
 		if (add_cacheinfo(opt, &mfi->blob, path,
-				  0, (!opt->call_depth && !is_dirty), 0))
+				  0, (!opt->priv->call_depth && !is_dirty), 0))
 			return -1;
 		/*
 		 * However, add_cacheinfo() will delete the old cache entry
@@ -3052,8 +3062,8 @@ static int handle_content_merge(struct merge_file_info *mfi,
 		 * flag to avoid making the file appear as if it were
 		 * deleted by the user.
 		 */
-		pos = index_name_pos(&opt->orig_index, path, strlen(path));
-		ce = opt->orig_index.cache[pos];
+		pos = index_name_pos(&opt->priv->orig_index, path, strlen(path));
+		ce = opt->priv->orig_index.cache[pos];
 		if (ce_skip_worktree(ce)) {
 			pos = index_name_pos(opt->repo->index, path, strlen(path));
 			ce = opt->repo->index->cache[pos];
@@ -3074,7 +3084,7 @@ static int handle_content_merge(struct merge_file_info *mfi,
 
 	if (df_conflict_remains || is_dirty) {
 		char *new_path;
-		if (opt->call_depth) {
+		if (opt->priv->call_depth) {
 			remove_file_from_index(opt->repo->index, path);
 		} else {
 			if (!mfi->clean) {
@@ -3332,7 +3342,7 @@ static int process_entry(struct merge_options *opt,
 			conf = _("directory/file");
 		}
 		if (dir_in_way(opt->repo->index, path,
-			       !opt->call_depth && !S_ISGITLINK(a->mode),
+			       !opt->priv->call_depth && !S_ISGITLINK(a->mode),
 			       0)) {
 			char *new_path = unique_path(opt, path, add_branch);
 			clean_merge = 0;
@@ -3341,7 +3351,7 @@ static int process_entry(struct merge_options *opt,
 			       conf, path, other_branch, path, new_path);
 			if (update_file(opt, 0, contents, new_path))
 				clean_merge = -1;
-			else if (opt->call_depth)
+			else if (opt->priv->call_depth)
 				remove_file_from_index(opt->repo->index, path);
 			free(new_path);
 		} else {
@@ -3406,7 +3416,7 @@ static int merge_trees_internal(struct merge_options *opt,
 	code = unpack_trees_start(opt, merge_base, head, merge);
 
 	if (code != 0) {
-		if (show(opt, 4) || opt->call_depth)
+		if (show(opt, 4) || opt->priv->call_depth)
 			err(opt, _("merging of trees %s and %s failed"),
 			    oid_to_hex(&head->object.oid),
 			    oid_to_hex(&merge->object.oid));
@@ -3425,7 +3435,7 @@ static int merge_trees_internal(struct merge_options *opt,
 		 * opposed to decaring a local hashmap is for convenience
 		 * so that we don't have to pass it to around.
 		 */
-		hashmap_init(&opt->current_file_dir_set, path_hashmap_cmp,
+		hashmap_init(&opt->priv->current_file_dir_set, path_hashmap_cmp,
 			     NULL, 512);
 		get_files_dirs(opt, head);
 		get_files_dirs(opt, merge);
@@ -3462,7 +3472,7 @@ static int merge_trees_internal(struct merge_options *opt,
 		string_list_clear(entries, 1);
 		free(entries);
 
-		hashmap_free(&opt->current_file_dir_set, 1);
+		hashmap_free(&opt->priv->current_file_dir_set, 1);
 
 		if (clean < 0) {
 			unpack_trees_finish(opt);
@@ -3474,7 +3484,7 @@ static int merge_trees_internal(struct merge_options *opt,
 
 	unpack_trees_finish(opt);
 
-	if (opt->call_depth) {
+	if (opt->priv->call_depth) {
 		struct object_id tree_id;
 		if (write_index_as_tree(&tree_id, opt->repo->index, NULL,
 					WRITE_TREE_FROM_MEMORY, NULL) ||
@@ -3545,7 +3555,7 @@ static int merge_recursive_internal(struct merge_options *opt,
 
 	for (iter = merge_bases; iter; iter = iter->next) {
 		const char *saved_b1, *saved_b2;
-		opt->call_depth++;
+		opt->priv->call_depth++;
 		/*
 		 * When the merge fails, the result contains files
 		 * with conflict markers. The cleanness flag is
@@ -3564,14 +3574,14 @@ static int merge_recursive_internal(struct merge_options *opt,
 			return -1;
 		opt->branch1 = saved_b1;
 		opt->branch2 = saved_b2;
-		opt->call_depth--;
+		opt->priv->call_depth--;
 
 		if (!merged_merge_bases)
 			return err(opt, _("merge returned no commit"));
 	}
 
 	discard_index(opt->repo->index);
-	if (!opt->call_depth)
+	if (!opt->priv->call_depth)
 		repo_read_index(opt->repo);
 
 	opt->ancestor = "merged common ancestors";
@@ -3586,7 +3596,7 @@ static int merge_recursive_internal(struct merge_options *opt,
 		return clean;
 	}
 
-	if (opt->call_depth) {
+	if (opt->priv->call_depth) {
 		*result = make_virtual_commit(opt->repo, result_tree,
 					      "merged tree");
 		commit_list_insert(h1, &(*result)->parents);
@@ -3608,17 +3618,21 @@ static int merge_start(struct merge_options *opt, struct tree *head)
 		return -1;
 	}
 
+	opt->priv = xcalloc(1, sizeof(*opt->priv));
+	string_list_init(&opt->priv->df_conflict_file_set, 1);
 	return 0;
 }
 
 static void merge_finalize(struct merge_options *opt)
 {
 	flush_output(opt);
-	if (!opt->call_depth && opt->buffer_output < 2)
+	if (!opt->priv->call_depth && opt->buffer_output < 2)
 		strbuf_release(&opt->obuf);
 	if (show(opt, 2))
 		diff_warn_rename_limit("merge.renamelimit",
-				       opt->needed_rename_limit, 0);
+				       opt->priv->needed_rename_limit, 0);
+	free(opt->priv);
+	opt->priv = NULL;
 }
 
 int merge_trees(struct merge_options *opt,
@@ -3756,8 +3770,6 @@ void init_merge_options(struct merge_options *opt,
 
 	opt->renormalize = 0;
 
-	string_list_init(&opt->df_conflict_file_set, 1);
-
 	merge_recursive_config(opt);
 	merge_verbosity = getenv("GIT_MERGE_VERBOSITY");
 	if (merge_verbosity)
diff --git a/merge-recursive.h b/merge-recursive.h
index 12249258ef..0d5e928832 100644
--- a/merge-recursive.h
+++ b/merge-recursive.h
@@ -1,13 +1,15 @@
 #ifndef MERGE_RECURSIVE_H
 #define MERGE_RECURSIVE_H
 
-#include "string-list.h"
-#include "unpack-trees.h"
+#include "strbuf.h"
 
 struct commit;
-
+struct commit_list;
+struct object_id;
 struct repository;
+struct tree;
 
+struct merge_options_internal;
 struct merge_options {
 	struct repository *repo;
 
@@ -41,13 +43,8 @@ struct merge_options {
 	const char *subtree_shift;
 	unsigned renormalize : 1;
 
-	/* internal fields used by the implementation (do NOT set these) */
-	int call_depth;
-	int needed_rename_limit;
-	struct hashmap current_file_dir_set;
-	struct string_list df_conflict_file_set;
-	struct unpack_trees_options unpack_opts;
-	struct index_state orig_index;
+	/* internal fields used by the implementation */
+	struct merge_options_internal *priv;
 };
 
 void init_merge_options(struct merge_options *opt, struct repository *repo);

diff --git a/merge-recursive.c b/merge-recursive.c
index ba635ed753..27e0bdf48c 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -4,30 +4,31 @@
  * The thieves were Alex Riesen and Johannes Schindelin, in June/July 2006
  */
 #include "cache.h"
-#include "config.h"
+#include "merge-recursive.h"
+
 #include "advice.h"
-#include "lockfile.h"
-#include "cache-tree.h"
-#include "object-store.h"
-#include "repository.h"
-#include "commit.h"
+#include "alloc.h"
+#include "attr.h"
 #include "blob.h"
 #include "builtin.h"
-#include "tree-walk.h"
+#include "cache-tree.h"
+#include "commit.h"
+#include "commit-reach.h"
+#include "config.h"
 #include "diff.h"
 #include "diffcore.h"
+#include "dir.h"
+#include "ll-merge.h"
+#include "lockfile.h"
+#include "object-store.h"
+#include "repository.h"
+#include "revision.h"
+#include "string-list.h"
+#include "submodule.h"
 #include "tag.h"
-#include "alloc.h"
+#include "tree-walk.h"
 #include "unpack-trees.h"
-#include "string-list.h"
 #include "xdiff-interface.h"
-#include "ll-merge.h"
-#include "attr.h"
-#include "merge-recursive.h"
-#include "dir.h"
-#include "submodule.h"
-#include "revision.h"
-#include "commit-reach.h"
 
 struct merge_options_internal {
 	int call_depth;

merge-recursive.c, merge-recursive.h

diff --git a/merge-recursive.c b/merge-recursive.c
index 27e0bdf48c..49eb50c17b 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -1046,10 +1046,10 @@ static int merge_3way(struct merge_options *opt,
 		ll_opts.variant = 0;
 	} else {
 		switch (opt->recursive_variant) {
-		case MERGE_RECURSIVE_OURS:
+		case MERGE_VARIANT_OURS:
 			ll_opts.variant = XDL_MERGE_FAVOR_OURS;
 			break;
-		case MERGE_RECURSIVE_THEIRS:
+		case MERGE_VARIANT_THEIRS:
 			ll_opts.variant = XDL_MERGE_FAVOR_THEIRS;
 			break;
 		default:
@@ -1359,15 +1359,15 @@ static int merge_mode_and_contents(struct merge_options *opt,
 							&b->oid);
 		} else if (S_ISLNK(a->mode)) {
 			switch (opt->recursive_variant) {
-			case MERGE_RECURSIVE_NORMAL:
+			case MERGE_VARIANT_NORMAL:
 				oidcpy(&result->blob.oid, &a->oid);
 				if (!oid_eq(&a->oid, &b->oid))
 					result->clean = 0;
 				break;
-			case MERGE_RECURSIVE_OURS:
+			case MERGE_VARIANT_OURS:
 				oidcpy(&result->blob.oid, &a->oid);
 				break;
-			case MERGE_RECURSIVE_THEIRS:
+			case MERGE_VARIANT_THEIRS:
 				oidcpy(&result->blob.oid, &b->oid);
 				break;
 			}
@@ -3786,9 +3786,9 @@ int parse_merge_opt(struct merge_options *opt, const char *s)
 	if (!s || !*s)
 		return -1;
 	if (!strcmp(s, "ours"))
-		opt->recursive_variant = MERGE_RECURSIVE_OURS;
+		opt->recursive_variant = MERGE_VARIANT_OURS;
 	else if (!strcmp(s, "theirs"))
-		opt->recursive_variant = MERGE_RECURSIVE_THEIRS;
+		opt->recursive_variant = MERGE_VARIANT_THEIRS;
 	else if (!strcmp(s, "subtree"))
 		opt->subtree_shift = "";
 	else if (skip_prefix(s, "subtree=", &arg))
diff --git a/merge-recursive.h b/merge-recursive.h
index 0d5e928832..350fb43a01 100644
--- a/merge-recursive.h
+++ b/merge-recursive.h
@@ -28,9 +28,9 @@ struct merge_options {
 	/* xdiff-related options (patience, ignore whitespace, ours/theirs) */
 	long xdl_opts;
 	enum {
-		MERGE_RECURSIVE_NORMAL = 0,
-		MERGE_RECURSIVE_OURS,
-		MERGE_RECURSIVE_THEIRS
+		MERGE_VARIANT_NORMAL = 0,
+		MERGE_VARIANT_OURS,
+		MERGE_VARIANT_THEIRS
 	} recursive_variant;
 
 	/* console output related options */

merge-recursive.c, t/t6036-recursive-corner-cases.sh, t/t6047-diff3-conflict-markers.sh

diff --git a/merge-recursive.c b/merge-recursive.c
index f1e2658457..6d5dce17fc 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -1034,7 +1034,7 @@ static int merge_3way(struct merge_options *opt,
 {
 	mmfile_t orig, src1, src2;
 	struct ll_merge_options ll_opts = {0};
-	char *base_name, *name1, *name2;
+	char *base, *name1, *name2;
 	int merge_status;
 
 	ll_opts.renormalize = opt->renormalize;
@@ -1058,16 +1058,13 @@ static int merge_3way(struct merge_options *opt,
 		}
 	}
 
-	assert(a->path && b->path && o->path);
-	if (strcmp(a->path, b->path) ||
-	    (opt->ancestor != NULL && strcmp(a->path, o->path) != 0)) {
-		base_name = opt->ancestor == NULL ? NULL :
-			mkpathdup("%s:%s", opt->ancestor, o->path);
+	assert(a->path && b->path && o->path && opt->ancestor);
+	if (strcmp(a->path, b->path) || strcmp(a->path, o->path) != 0) {
+		base  = mkpathdup("%s:%s", opt->ancestor, o->path);
 		name1 = mkpathdup("%s:%s", branch1, a->path);
 		name2 = mkpathdup("%s:%s", branch2, b->path);
 	} else {
-		base_name = opt->ancestor == NULL ? NULL :
-			mkpathdup("%s", opt->ancestor);
+		base  = mkpathdup("%s", opt->ancestor);
 		name1 = mkpathdup("%s", branch1);
 		name2 = mkpathdup("%s", branch2);
 	}
@@ -1076,11 +1073,11 @@ static int merge_3way(struct merge_options *opt,
 	read_mmblob(&src1, &a->oid);
 	read_mmblob(&src2, &b->oid);
 
-	merge_status = ll_merge(result_buf, a->path, &orig, base_name,
+	merge_status = ll_merge(result_buf, a->path, &orig, base,
 				&src1, name1, &src2, name2,
 				opt->repo->index, &ll_opts);
 
-	free(base_name);
+	free(base);
 	free(name1);
 	free(name2);
 	free(orig.ptr);
@@ -3523,6 +3520,8 @@ static int merge_recursive_internal(struct merge_options *opt,
 	struct commit *merged_merge_bases;
 	struct tree *result_tree;
 	int clean;
+	int num_merge_bases;
+	struct strbuf merge_base_abbrev = STRBUF_INIT;
 
 	if (show(opt, 4)) {
 		output(opt, 4, _("Merging:"));
@@ -3544,6 +3543,7 @@ static int merge_recursive_internal(struct merge_options *opt,
 			output_commit_title(opt, iter->item);
 	}
 
+	num_merge_bases = commit_list_count(merge_bases);
 	merged_merge_bases = pop_commit(&merge_bases);
 	if (merged_merge_bases == NULL) {
 		/* if there is no common ancestor, use an empty tree */
@@ -3585,13 +3585,26 @@ static int merge_recursive_internal(struct merge_options *opt,
 	if (!opt->priv->call_depth)
 		repo_read_index(opt->repo);
 
-	opt->ancestor = "merged common ancestors";
+	switch (num_merge_bases) {
+	case 0:
+		opt->ancestor = "<empty tree>";
+		break;
+	case 1:
+		strbuf_add_unique_abbrev(&merge_base_abbrev,
+					 &merged_merge_bases->object.oid,
+					 DEFAULT_ABBREV);
+		opt->ancestor = merge_base_abbrev.buf;
+		break;
+	default:
+		opt->ancestor = "merged common ancestors";
+	}
 	clean = merge_trees_internal(opt,
 				     repo_get_commit_tree(opt->repo, h1),
 				     repo_get_commit_tree(opt->repo, h2),
 				     repo_get_commit_tree(opt->repo,
 							  merged_merge_bases),
 				     &result_tree);
+	strbuf_release(&merge_base_abbrev);
 	if (clean < 0) {
 		flush_output(opt);
 		return clean;
@@ -3644,6 +3657,8 @@ int merge_trees(struct merge_options *opt,
 	int clean;
 	struct tree *ignored;
 
+	assert(opt->ancestor != NULL);
+
 	if (merge_start(opt, head))
 		return -1;
 	clean = merge_trees_internal(opt, head, merge, merge_base, &ignored);
@@ -3660,6 +3675,8 @@ int merge_recursive(struct merge_options *opt,
 {
 	int clean;
 
+	assert(opt->ancestor == NULL);
+
 	if (merge_start(opt, repo_get_commit_tree(opt->repo, h1)))
 		return -1;
 	clean = merge_recursive_internal(opt, h1, h2, merge_bases, result);
diff --git a/t/t6036-recursive-corner-cases.sh b/t/t6036-recursive-corner-cases.sh
index d23b948f27..7fddcc8c73 100755
--- a/t/t6036-recursive-corner-cases.sh
+++ b/t/t6036-recursive-corner-cases.sh
@@ -1562,6 +1562,7 @@ test_expect_success 'check nested conflicts' '
 		cd nested_conflicts &&
 
 		git clean -f &&
+		MASTER=$(git rev-parse --short master) &&
 		git checkout L2^0 &&
 
 		# Merge must fail; there is a conflict
@@ -1582,7 +1583,7 @@ test_expect_success 'check nested conflicts' '
 		git cat-file -p R1:a >theirs &&
 		test_must_fail git merge-file --diff3 \
 			-L "Temporary merge branch 1" \
-			-L "merged common ancestors"  \
+			-L "$MASTER"  \
 			-L "Temporary merge branch 2" \
 			ours  \
 			base  \
@@ -1594,7 +1595,7 @@ test_expect_success 'check nested conflicts' '
 		git cat-file -p R1:b >theirs &&
 		test_must_fail git merge-file --diff3 \
 			-L "Temporary merge branch 1" \
-			-L "merged common ancestors"  \
+			-L "$MASTER"  \
 			-L "Temporary merge branch 2" \
 			ours  \
 			base  \
@@ -1732,6 +1733,7 @@ test_expect_success 'check virtual merge base with nested conflicts' '
 	(
 		cd virtual_merge_base_has_nested_conflicts &&
 
+		MASTER=$(git rev-parse --short master) &&
 		git checkout L3^0 &&
 
 		# Merge must fail; there is a conflict
@@ -1760,7 +1762,7 @@ test_expect_success 'check virtual merge base with nested conflicts' '
 		cp left merged-once &&
 		test_must_fail git merge-file --diff3 \
 			-L "Temporary merge branch 1" \
-			-L "merged common ancestors"  \
+			-L "$MASTER"  \
 			-L "Temporary merge branch 2" \
 			merged-once \
 			base        \
diff --git a/t/t6047-diff3-conflict-markers.sh b/t/t6047-diff3-conflict-markers.sh
new file mode 100755
index 0000000000..f69c8256bc
--- /dev/null
+++ b/t/t6047-diff3-conflict-markers.sh
@@ -0,0 +1,189 @@
+#!/bin/sh
+
+test_description='recursive merge diff3 style conflict markers'
+
+. ./test-lib.sh
+
+# Setup:
+#          L1
+#            \
+#             ?
+#            /
+#          R1
+#
+# Where:
+#   L1 and R1 both have a file named 'content' but have no common history
+#
+
+test_expect_success 'setup no merge base' '
+	test_create_repo no_merge_base &&
+	(
+		cd no_merge_base &&
+
+		git checkout -b L &&
+		test_commit A content A &&
+
+		git checkout --orphan R &&
+		test_commit B content B
+	)
+'
+
+test_expect_success 'check no merge base' '
+	(
+		cd no_merge_base &&
+
+		git checkout L^0 &&
+
+		test_must_fail git -c merge.conflictstyle=diff3 merge --allow-unrelated-histories -s recursive R^0 &&
+
+		grep "|||||| <empty tree>" content
+	)
+'
+
+# Setup:
+#          L1
+#         /  \
+#   master    ?
+#         \  /
+#          R1
+#
+# Where:
+#   L1 and R1 have modified the same file ('content') in conflicting ways
+#
+
+test_expect_success 'setup unique merge base' '
+	test_create_repo unique_merge_base &&
+	(
+		cd unique_merge_base &&
+
+		test_commit base content "1
+2
+3
+4
+5
+" &&
+
+		git branch L &&
+		git branch R &&
+
+		git checkout L &&
+		test_commit L content "1
+2
+3
+4
+5
+7" &&
+
+		git checkout R &&
+		git rm content &&
+		test_commit R renamed "1
+2
+3
+4
+5
+six"
+	)
+'
+
+test_expect_success 'check unique merge base' '
+	(
+		cd unique_merge_base &&
+
+		git checkout L^0 &&
+		MASTER=$(git rev-parse --short master) &&
+
+		test_must_fail git -c merge.conflictstyle=diff3 merge -s recursive R^0 &&
+
+		grep "|||||| $MASTER:content" renamed
+	)
+'
+
+# Setup:
+#          L1---L2--L3
+#         /  \ /      \
+#   master    X1       ?
+#         \  / \      /
+#          R1---R2--R3
+#
+# Where:
+#   commits L1 and R1 have modified the same file in non-conflicting ways
+#   X1 is an auto-generated merge-base used when merging L1 and R1
+#   commits L2 and R2 are merges of R1 and L1 into L1 and R1, respectively
+#   commits L3 and R3 both modify 'content' in conflicting ways
+#
+
+test_expect_success 'setup multiple merge bases' '
+	test_create_repo multiple_merge_bases &&
+	(
+		cd multiple_merge_bases &&
+
+		test_commit initial content "1
+2
+3
+4
+5" &&
+
+		git branch L &&
+		git branch R &&
+
+		# Create L1
+		git checkout L &&
+		test_commit L1 content "0
+1
+2
+3
+4
+5" &&
+
+		# Create R1
+		git checkout R &&
+		test_commit R1 content "1
+2
+3
+4
+5
+6" &&
+
+		# Create L2
+		git checkout L &&
+		git merge R1 &&
+
+		# Create R2
+		git checkout R &&
+		git merge L1 &&
+
+		# Create L3
+		git checkout L &&
+		test_commit L3 content "0
+1
+2
+3
+4
+5
+A" &&
+
+		# Create R3
+		git checkout R &&
+		git rm content &&
+		test_commit R3 renamed "0
+2
+3
+4
+5
+six"
+	)
+'
+
+test_expect_success 'check multiple merge bases' '
+	(
+		cd multiple_merge_bases &&
+
+		git checkout L^0 &&
+
+		test_must_fail git -c merge.conflictstyle=diff3 merge -s recursive R^0 &&
+
+		grep "|||||| merged common ancestors:content" renamed
+	)
+'
+
+test_done

diff --git a/merge-recursive.c b/merge-recursive.c
index 49eb50c17b..f1e2658457 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -1058,7 +1058,7 @@ static int merge_3way(struct merge_options *opt,
 		}
 	}
 
-	assert(a->path && b->path);
+	assert(a->path && b->path && o->path);
 	if (strcmp(a->path, b->path) ||
 	    (opt->ancestor != NULL && strcmp(a->path, o->path) != 0)) {
 		base_name = opt->ancestor == NULL ? NULL :

diff --git a/merge-recursive.c b/merge-recursive.c
index 6b812d67e3..1d960fa64b 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -1043,7 +1043,7 @@ static int merge_3way(struct merge_options *opt,
 		}
 	}
 
-	assert(a->path && b->path);
+	assert(a->path && b->path && o->path);
 	if (strcmp(a->path, b->path) ||
 	    (opt->ancestor != NULL && strcmp(a->path, o->path) != 0)) {
 		base_name = opt->ancestor == NULL ? NULL :

diff --git a/merge-recursive.c b/merge-recursive.c
index 1d960fa64b..a67ea4957a 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -1019,7 +1019,7 @@ static int merge_3way(struct merge_options *opt,
 {
 	mmfile_t orig, src1, src2;
 	struct ll_merge_options ll_opts = {0};
-	char *base_name, *name1, *name2;
+	char *base, *name1, *name2;
 	int merge_status;
 
 	ll_opts.renormalize = opt->renormalize;
@@ -1043,16 +1043,13 @@ static int merge_3way(struct merge_options *opt,
 		}
 	}
 
-	assert(a->path && b->path && o->path);
-	if (strcmp(a->path, b->path) ||
-	    (opt->ancestor != NULL && strcmp(a->path, o->path) != 0)) {
-		base_name = opt->ancestor == NULL ? NULL :
-			mkpathdup("%s:%s", opt->ancestor, o->path);
+	assert(a->path && b->path && o->path && opt->ancestor);
+	if (strcmp(a->path, b->path) || strcmp(a->path, o->path) != 0) {
+		base  = mkpathdup("%s:%s", opt->ancestor, o->path);
 		name1 = mkpathdup("%s:%s", branch1, a->path);
 		name2 = mkpathdup("%s:%s", branch2, b->path);
 	} else {
-		base_name = opt->ancestor == NULL ? NULL :
-			mkpathdup("%s", opt->ancestor);
+		base  = mkpathdup("%s", opt->ancestor);
 		name1 = mkpathdup("%s", branch1);
 		name2 = mkpathdup("%s", branch2);
 	}
@@ -1061,11 +1058,11 @@ static int merge_3way(struct merge_options *opt,
 	read_mmblob(&src1, &a->oid);
 	read_mmblob(&src2, &b->oid);
 
-	merge_status = ll_merge(result_buf, a->path, &orig, base_name,
+	merge_status = ll_merge(result_buf, a->path, &orig, base,
 				&src1, name1, &src2, name2,
 				opt->repo->index, &ll_opts);
 
-	free(base_name);
+	free(base);
 	free(name1);
 	free(name2);
 	free(orig.ptr);
@@ -3390,6 +3387,8 @@ int merge_trees(struct merge_options *opt,
 	int code, clean;
 	struct strbuf sb = STRBUF_INIT;
 
+	assert(opt->ancestor != NULL);
+
 	if (!opt->call_depth && repo_index_has_changes(opt->repo, head, &sb)) {
 		err(opt, _("Your local changes to the following files would be overwritten by merge:\n  %s"),
 		    sb.buf);

diff --git a/builtin/checkout.c b/builtin/checkout.c
index 6123f732a2..d5b946dc3a 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -713,6 +713,7 @@ static int merge_working_tree(const struct checkout_opts *opts,
 			struct tree *old_tree;
 			struct merge_options o;
 			struct strbuf sb = STRBUF_INIT;
+			struct strbuf old_commit_shortname = STRBUF_INIT;
 
 			if (!opts->merge)
 				return 1;
@@ -768,6 +769,12 @@ static int merge_working_tree(const struct checkout_opts *opts,
 			if (ret)
 				return ret;
 			o.ancestor = old_branch_info->name;
+			if (old_branch_info->name == NULL) {
+				strbuf_add_unique_abbrev(&old_commit_shortname,
+							 &old_branch_info->commit->object.oid,
+							 DEFAULT_ABBREV);
+				o.ancestor = old_commit_shortname.buf;
+			}
 			o.branch1 = new_branch_info->name;
 			o.branch2 = "local";
 			ret = merge_trees(&o,
@@ -781,6 +788,7 @@ static int merge_working_tree(const struct checkout_opts *opts,
 					 opts, 0,
 					 writeout_error);
 			strbuf_release(&o.obuf);
+			strbuf_release(&old_commit_shortname);
 			if (ret)
 				return ret;
 		}

merge-recursive.c, t/t6036-recursive-corner-cases.sh, t/t6047-diff3-conflict-markers.sh

diff --git a/merge-recursive.c b/merge-recursive.c
index a67ea4957a..3a7a9514b9 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -3507,6 +3507,11 @@ int merge_recursive(struct merge_options *opt,
 	struct commit *merged_common_ancestors;
 	struct tree *mrtree;
 	int clean;
+	int num_merge_bases;
+	struct strbuf merge_base_abbrev = STRBUF_INIT;
+
+	if (!opt->call_depth)
+		assert(opt->ancestor == NULL);
 
 	if (show(opt, 4)) {
 		output(opt, 4, _("Merging:"));
@@ -3528,6 +3533,7 @@ int merge_recursive(struct merge_options *opt,
 			output_commit_title(opt, iter->item);
 	}
 
+	num_merge_bases = commit_list_count(ca);
 	merged_common_ancestors = pop_commit(&ca);
 	if (merged_common_ancestors == NULL) {
 		/* if there is no common ancestor, use an empty tree */
@@ -3568,10 +3574,23 @@ int merge_recursive(struct merge_options *opt,
 	if (!opt->call_depth)
 		repo_read_index(opt->repo);
 
-	opt->ancestor = "merged common ancestors";
+	switch (num_merge_bases) {
+	case 0:
+		opt->ancestor = "<empty tree>";
+		break;
+	case 1:
+		strbuf_add_unique_abbrev(&merge_base_abbrev,
+					 &merged_common_ancestors->object.oid,
+					 DEFAULT_ABBREV);
+		opt->ancestor = merge_base_abbrev.buf;
+		break;
+	default:
+		opt->ancestor = "merged common ancestors";
+	}
 	clean = merge_trees(opt, get_commit_tree(h1), get_commit_tree(h2),
 			    get_commit_tree(merged_common_ancestors),
 			    &mrtree);
+	strbuf_release(&merge_base_abbrev);
 	if (clean < 0) {
 		flush_output(opt);
 		return clean;
diff --git a/t/t6036-recursive-corner-cases.sh b/t/t6036-recursive-corner-cases.sh
index d23b948f27..7fddcc8c73 100755
--- a/t/t6036-recursive-corner-cases.sh
+++ b/t/t6036-recursive-corner-cases.sh
@@ -1562,6 +1562,7 @@ test_expect_success 'check nested conflicts' '
 		cd nested_conflicts &&
 
 		git clean -f &&
+		MASTER=$(git rev-parse --short master) &&
 		git checkout L2^0 &&
 
 		# Merge must fail; there is a conflict
@@ -1582,7 +1583,7 @@ test_expect_success 'check nested conflicts' '
 		git cat-file -p R1:a >theirs &&
 		test_must_fail git merge-file --diff3 \
 			-L "Temporary merge branch 1" \
-			-L "merged common ancestors"  \
+			-L "$MASTER"  \
 			-L "Temporary merge branch 2" \
 			ours  \
 			base  \
@@ -1594,7 +1595,7 @@ test_expect_success 'check nested conflicts' '
 		git cat-file -p R1:b >theirs &&
 		test_must_fail git merge-file --diff3 \
 			-L "Temporary merge branch 1" \
-			-L "merged common ancestors"  \
+			-L "$MASTER"  \
 			-L "Temporary merge branch 2" \
 			ours  \
 			base  \
@@ -1732,6 +1733,7 @@ test_expect_success 'check virtual merge base with nested conflicts' '
 	(
 		cd virtual_merge_base_has_nested_conflicts &&
 
+		MASTER=$(git rev-parse --short master) &&
 		git checkout L3^0 &&
 
 		# Merge must fail; there is a conflict
@@ -1760,7 +1762,7 @@ test_expect_success 'check virtual merge base with nested conflicts' '
 		cp left merged-once &&
 		test_must_fail git merge-file --diff3 \
 			-L "Temporary merge branch 1" \
-			-L "merged common ancestors"  \
+			-L "$MASTER"  \
 			-L "Temporary merge branch 2" \
 			merged-once \
 			base        \
diff --git a/t/t6047-diff3-conflict-markers.sh b/t/t6047-diff3-conflict-markers.sh
new file mode 100755
index 0000000000..f69c8256bc
--- /dev/null
+++ b/t/t6047-diff3-conflict-markers.sh
@@ -0,0 +1,189 @@
+#!/bin/sh
+
+test_description='recursive merge diff3 style conflict markers'
+
+. ./test-lib.sh
+
+# Setup:
+#          L1
+#            \
+#             ?
+#            /
+#          R1
+#
+# Where:
+#   L1 and R1 both have a file named 'content' but have no common history
+#
+
+test_expect_success 'setup no merge base' '
+	test_create_repo no_merge_base &&
+	(
+		cd no_merge_base &&
+
+		git checkout -b L &&
+		test_commit A content A &&
+
+		git checkout --orphan R &&
+		test_commit B content B
+	)
+'
+
+test_expect_success 'check no merge base' '
+	(
+		cd no_merge_base &&
+
+		git checkout L^0 &&
+
+		test_must_fail git -c merge.conflictstyle=diff3 merge --allow-unrelated-histories -s recursive R^0 &&
+
+		grep "|||||| <empty tree>" content
+	)
+'
+
+# Setup:
+#          L1
+#         /  \
+#   master    ?
+#         \  /
+#          R1
+#
+# Where:
+#   L1 and R1 have modified the same file ('content') in conflicting ways
+#
+
+test_expect_success 'setup unique merge base' '
+	test_create_repo unique_merge_base &&
+	(
+		cd unique_merge_base &&
+
+		test_commit base content "1
+2
+3
+4
+5
+" &&
+
+		git branch L &&
+		git branch R &&
+
+		git checkout L &&
+		test_commit L content "1
+2
+3
+4
+5
+7" &&
+
+		git checkout R &&
+		git rm content &&
+		test_commit R renamed "1
+2
+3
+4
+5
+six"
+	)
+'
+
+test_expect_success 'check unique merge base' '
+	(
+		cd unique_merge_base &&
+
+		git checkout L^0 &&
+		MASTER=$(git rev-parse --short master) &&
+
+		test_must_fail git -c merge.conflictstyle=diff3 merge -s recursive R^0 &&
+
+		grep "|||||| $MASTER:content" renamed
+	)
+'
+
+# Setup:
+#          L1---L2--L3
+#         /  \ /      \
+#   master    X1       ?
+#         \  / \      /
+#          R1---R2--R3
+#
+# Where:
+#   commits L1 and R1 have modified the same file in non-conflicting ways
+#   X1 is an auto-generated merge-base used when merging L1 and R1
+#   commits L2 and R2 are merges of R1 and L1 into L1 and R1, respectively
+#   commits L3 and R3 both modify 'content' in conflicting ways
+#
+
+test_expect_success 'setup multiple merge bases' '
+	test_create_repo multiple_merge_bases &&
+	(
+		cd multiple_merge_bases &&
+
+		test_commit initial content "1
+2
+3
+4
+5" &&
+
+		git branch L &&
+		git branch R &&
+
+		# Create L1
+		git checkout L &&
+		test_commit L1 content "0
+1
+2
+3
+4
+5" &&
+
+		# Create R1
+		git checkout R &&
+		test_commit R1 content "1
+2
+3
+4
+5
+6" &&
+
+		# Create L2
+		git checkout L &&
+		git merge R1 &&
+
+		# Create R2
+		git checkout R &&
+		git merge L1 &&
+
+		# Create L3
+		git checkout L &&
+		test_commit L3 content "0
+1
+2
+3
+4
+5
+A" &&
+
+		# Create R3
+		git checkout R &&
+		git rm content &&
+		test_commit R3 renamed "0
+2
+3
+4
+5
+six"
+	)
+'
+
+test_expect_success 'check multiple merge bases' '
+	(
+		cd multiple_merge_bases &&
+
+		git checkout L^0 &&
+
+		test_must_fail git -c merge.conflictstyle=diff3 merge -s recursive R^0 &&
+
+		grep "|||||| merged common ancestors:content" renamed
+	)
+'
+
+test_done

builtin/am.c, merge-recursive.c, merge-recursive.h

diff --git a/builtin/am.c b/builtin/am.c
index 1aea657a7f..037e828efe 100644
--- a/builtin/am.c
+++ b/builtin/am.c
@@ -1538,7 +1538,7 @@ static int fall_back_threeway(const struct am_state *state, const char *index_pa
 	o.branch1 = "HEAD";
 	their_tree_name = xstrfmt("%.*s", linelen(state->msg), state->msg);
 	o.branch2 = their_tree_name;
-	o.detect_directory_renames = 0;
+	o.detect_directory_renames = MERGE_DIRECTORY_RENAMES_NONE;
 
 	if (state->quiet)
 		o.verbosity = 0;
diff --git a/merge-recursive.c b/merge-recursive.c
index 3a7a9514b9..dd2ee5edee 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -1375,7 +1375,8 @@ static int handle_rename_via_dir(struct merge_options *opt,
 	const struct rename *ren = ci->ren1;
 	const struct diff_filespec *dest = ren->pair->two;
 	char *file_path = dest->path;
-	int mark_conflicted = (opt->detect_directory_renames == 1);
+	int mark_conflicted = (opt->detect_directory_renames ==
+			       MERGE_DIRECTORY_RENAMES_CONFLICT);
 	assert(ren->dir_rename_original_dest);
 
 	if (!opt->call_depth && would_lose_untracked(opt, dest->path)) {
@@ -2860,8 +2861,9 @@ static int detect_and_process_renames(struct merge_options *opt,
 	head_pairs = get_diffpairs(opt, common, head);
 	merge_pairs = get_diffpairs(opt, common, merge);
 
-	if ((opt->detect_directory_renames == 2) ||
-	    (opt->detect_directory_renames == 1 && !opt->call_depth)) {
+	if ((opt->detect_directory_renames == MERGE_DIRECTORY_RENAMES_TRUE) ||
+	    (opt->detect_directory_renames == MERGE_DIRECTORY_RENAMES_CONFLICT &&
+	     !opt->call_depth)) {
 		dir_re_head = get_directory_renames(head_pairs);
 		dir_re_merge = get_directory_renames(merge_pairs);
 
@@ -3119,7 +3121,8 @@ static int handle_rename_normal(struct merge_options *opt,
 	clean = handle_content_merge(&mfi, opt, path, was_dirty(opt, path),
 				     o, a, b, ci);
 
-	if (clean && opt->detect_directory_renames == 1 &&
+	if (clean &&
+	    opt->detect_directory_renames == MERGE_DIRECTORY_RENAMES_CONFLICT &&
 	    ren->dir_rename_original_dest) {
 		if (update_stages(opt, path,
 				  NULL,
@@ -3164,12 +3167,12 @@ static int warn_about_dir_renamed_entries(struct merge_options *opt,
 		return clean;
 
 	/* Sanity checks */
-	assert(opt->detect_directory_renames > 0);
+	assert(opt->detect_directory_renames > MERGE_DIRECTORY_RENAMES_NONE);
 	assert(ren->dir_rename_original_type == 'A' ||
 	       ren->dir_rename_original_type == 'R');
 
 	/* Check whether to treat directory renames as a conflict */
-	clean = (opt->detect_directory_renames == 2);
+	clean = (opt->detect_directory_renames == MERGE_DIRECTORY_RENAMES_TRUE);
 
 	is_add = (ren->dir_rename_original_type == 'A');
 	if (ren->dir_rename_original_type == 'A' && clean) {
@@ -3684,9 +3687,12 @@ static void merge_recursive_config(struct merge_options *opt)
 	if (!git_config_get_string("merge.directoryrenames", &value)) {
 		int boolval = git_parse_maybe_bool(value);
 		if (0 <= boolval) {
-			opt->detect_directory_renames = boolval ? 2 : 0;
+			opt->detect_directory_renames = boolval ?
+				MERGE_DIRECTORY_RENAMES_TRUE :
+				MERGE_DIRECTORY_RENAMES_NONE;
 		} else if (!strcasecmp(value, "conflict")) {
-			opt->detect_directory_renames = 1;
+			opt->detect_directory_renames =
+				MERGE_DIRECTORY_RENAMES_CONFLICT;
 		} /* avoid erroring on values from future versions of git */
 		free(value);
 	}
@@ -3706,7 +3712,7 @@ void init_merge_options(struct merge_options *opt,
 	opt->renormalize = 0;
 	opt->diff_detect_rename = -1;
 	opt->merge_detect_rename = -1;
-	opt->detect_directory_renames = 1;
+	opt->detect_directory_renames = MERGE_DIRECTORY_RENAMES_CONFLICT;
 	merge_recursive_config(opt);
 	merge_verbosity = getenv("GIT_MERGE_VERBOSITY");
 	if (merge_verbosity)
diff --git a/merge-recursive.h b/merge-recursive.h
index c2b7bb65c6..f1b6ef38ae 100644
--- a/merge-recursive.h
+++ b/merge-recursive.h
@@ -22,7 +22,11 @@ struct merge_options {
 	unsigned renormalize : 1;
 	long xdl_opts;
 	int verbosity;
-	int detect_directory_renames;
+	enum {
+		MERGE_DIRECTORY_RENAMES_NONE = 0,
+		MERGE_DIRECTORY_RENAMES_CONFLICT = 1,
+		MERGE_DIRECTORY_RENAMES_TRUE = 2
+	} detect_directory_renames;
 	int diff_detect_rename;
 	int merge_detect_rename;
 	int diff_rename_limit;

diff --git a/merge-recursive.c b/merge-recursive.c
index dd2ee5edee..eae3e4fbcc 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -934,9 +934,11 @@ static int update_file_flags(struct merge_options *opt,
 		}
 
 		buf = read_object_file(&contents->oid, &type, &size);
-		if (!buf)
-			return err(opt, _("cannot read object %s '%s'"),
-				   oid_to_hex(&contents->oid), path);
+		if (!buf) {
+			ret = err(opt, _("cannot read object %s '%s'"),
+				  oid_to_hex(&contents->oid), path);
+			goto free_buf;
+		}
 		if (type != OBJ_BLOB) {
 			ret = err(opt, _("blob expected for %s '%s'"),
 				  oid_to_hex(&contents->oid), path);

diff --git a/merge-recursive.c b/merge-recursive.c
index eae3e4fbcc..fb668fc84c 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -3592,8 +3592,11 @@ int merge_recursive(struct merge_options *opt,
 	default:
 		opt->ancestor = "merged common ancestors";
 	}
-	clean = merge_trees(opt, get_commit_tree(h1), get_commit_tree(h2),
-			    get_commit_tree(merged_common_ancestors),
+	clean = merge_trees(opt,
+			    repo_get_commit_tree(opt->repo, h1),
+			    repo_get_commit_tree(opt->repo, h2),
+			    repo_get_commit_tree(opt->repo,
+						 merged_common_ancestors),
 			    &mrtree);
 	strbuf_release(&merge_base_abbrev);
 	if (clean < 0) {

builtin/merge-recursive.c, builtin/stash.c, t/t3030-merge-recursive.sh

diff --git a/builtin/merge-recursive.c b/builtin/merge-recursive.c
index 5b910e351e..a4bfd8fc51 100644
--- a/builtin/merge-recursive.c
+++ b/builtin/merge-recursive.c
@@ -1,3 +1,4 @@
+#include "cache.h"
 #include "builtin.h"
 #include "commit.h"
 #include "tag.h"
@@ -63,6 +64,9 @@ int cmd_merge_recursive(int argc, const char **argv, const char *prefix)
 	if (argc - i != 3) /* "--" "<head>" "<remote>" */
 		die(_("not handling anything other than two heads merge."));
 
+	if (repo_read_index_unmerged(the_repository))
+		die_resolve_conflict("merge");
+
 	o.branch1 = argv[++i];
 	o.branch2 = argv[++i];
 
diff --git a/builtin/stash.c b/builtin/stash.c
index b5a301f24d..4aa47785f9 100644
--- a/builtin/stash.c
+++ b/builtin/stash.c
@@ -427,6 +427,8 @@ static int do_apply_stash(const char *prefix, struct stash_info *info,
 				return error(_("could not save index tree"));
 
 			reset_head();
+			discard_cache();
+			read_cache();
 		}
 	}
 
diff --git a/t/t3030-merge-recursive.sh b/t/t3030-merge-recursive.sh
index ff641b348a..a37bcc58a0 100755
--- a/t/t3030-merge-recursive.sh
+++ b/t/t3030-merge-recursive.sh
@@ -667,15 +667,22 @@ test_expect_success 'merging with triple rename across D/F conflict' '
 test_expect_success 'merge-recursive remembers the names of all base trees' '
 	git reset --hard HEAD &&
 
+	# make the index match $c1 so that merge-recursive below does not
+	# fail early
+	git diff --binary HEAD $c1 -- | git apply --cached &&
+
 	# more trees than static slots used by oid_to_hex()
 	for commit in $c0 $c2 $c4 $c5 $c6 $c7
 	do
 		git rev-parse "$commit^{tree}"
 	done >trees &&
 
-	# ignore the return code -- it only fails because the input is weird
+	# ignore the return code; it only fails because the input is weird...
 	test_must_fail git -c merge.verbosity=5 merge-recursive $(cat trees) -- $c1 $c3 >out &&
 
+	# ...but make sure it fails in the expected way
+	test_i18ngrep CONFLICT.*rename/rename out &&
+
 	# merge-recursive prints in reverse order, but we do not care
 	sort <trees >expect &&
 	sed -n "s/^virtual //p" out | sort >actual &&

diff --git a/merge-recursive.c b/merge-recursive.c
index fb668fc84c..ded2e1bcfb 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -3382,23 +3382,14 @@ static int process_entry(struct merge_options *opt,
 	return clean_merge;
 }
 
-int merge_trees(struct merge_options *opt,
-		struct tree *head,
-		struct tree *merge,
-		struct tree *common,
-		struct tree **result)
+static int merge_trees_internal(struct merge_options *opt,
+				struct tree *head,
+				struct tree *merge,
+				struct tree *common,
+				struct tree **result)
 {
 	struct index_state *istate = opt->repo->index;
 	int code, clean;
-	struct strbuf sb = STRBUF_INIT;
-
-	assert(opt->ancestor != NULL);
-
-	if (!opt->call_depth && repo_index_has_changes(opt->repo, head, &sb)) {
-		err(opt, _("Your local changes to the following files would be overwritten by merge:\n  %s"),
-		    sb.buf);
-		return -1;
-	}
 
 	if (opt->subtree_shift) {
 		merge = shift_tree_object(opt->repo, head, merge, opt->subtree_shift);
@@ -3502,11 +3493,11 @@ static struct commit_list *reverse_commit_list(struct commit_list *list)
  * Merge the commits h1 and h2, return the resulting virtual
  * commit object and a flag indicating the cleanness of the merge.
  */
-int merge_recursive(struct merge_options *opt,
-		    struct commit *h1,
-		    struct commit *h2,
-		    struct commit_list *ca,
-		    struct commit **result)
+static int merge_recursive_internal(struct merge_options *opt,
+				    struct commit *h1,
+				    struct commit *h2,
+				    struct commit_list *ca,
+				    struct commit **result)
 {
 	struct commit_list *iter;
 	struct commit *merged_common_ancestors;
@@ -3515,9 +3506,6 @@ int merge_recursive(struct merge_options *opt,
 	int num_merge_bases;
 	struct strbuf merge_base_abbrev = STRBUF_INIT;
 
-	if (!opt->call_depth)
-		assert(opt->ancestor == NULL);
-
 	if (show(opt, 4)) {
 		output(opt, 4, _("Merging:"));
 		output_commit_title(opt, h1);
@@ -3564,7 +3552,7 @@ int merge_recursive(struct merge_options *opt,
 		saved_b2 = opt->branch2;
 		opt->branch1 = "Temporary merge branch 1";
 		opt->branch2 = "Temporary merge branch 2";
-		if (merge_recursive(opt, merged_common_ancestors, iter->item,
+		if (merge_recursive_internal(opt, merged_common_ancestors, iter->item,
 				    NULL, &merged_common_ancestors) < 0)
 			return -1;
 		opt->branch1 = saved_b1;
@@ -3592,12 +3580,12 @@ int merge_recursive(struct merge_options *opt,
 	default:
 		opt->ancestor = "merged common ancestors";
 	}
-	clean = merge_trees(opt,
-			    repo_get_commit_tree(opt->repo, h1),
-			    repo_get_commit_tree(opt->repo, h2),
-			    repo_get_commit_tree(opt->repo,
-						 merged_common_ancestors),
-			    &mrtree);
+	clean = merge_trees_internal(opt,
+				     repo_get_commit_tree(opt->repo, h1),
+				     repo_get_commit_tree(opt->repo, h2),
+				     repo_get_commit_tree(opt->repo,
+							  merged_common_ancestors),
+				     &mrtree);
 	strbuf_release(&merge_base_abbrev);
 	if (clean < 0) {
 		flush_output(opt);
@@ -3618,6 +3606,61 @@ int merge_recursive(struct merge_options *opt,
 	return clean;
 }
 
+static int merge_start(struct merge_options *opt, struct tree *head)
+{
+	struct strbuf sb = STRBUF_INIT;
+
+	if (repo_index_has_changes(opt->repo, head, &sb)) {
+		err(opt, _("Your local changes to the following files would be overwritten by merge:\n  %s"),
+		    sb.buf);
+		strbuf_release(&sb);
+		return -1;
+	}
+
+	return 0;
+}
+
+static void merge_finalize(struct merge_options *opt)
+{
+	/* Common code for wrapping up merges will be added here later */
+}
+
+int merge_trees(struct merge_options *opt,
+		struct tree *head,
+		struct tree *merge,
+		struct tree *common,
+		struct tree **result)
+{
+	int clean;
+
+	assert(opt->ancestor != NULL);
+
+	if (merge_start(opt, head))
+		return -1;
+	clean = merge_trees_internal(opt, head, merge, common, result);
+	merge_finalize(opt);
+
+	return clean;
+}
+
+int merge_recursive(struct merge_options *opt,
+		    struct commit *h1,
+		    struct commit *h2,
+		    struct commit_list *ca,
+		    struct commit **result)
+{
+	int clean;
+
+	assert(opt->ancestor == NULL);
+
+	if (merge_start(opt, repo_get_commit_tree(opt->repo, h1)))
+		return -1;
+	clean = merge_recursive_internal(opt, h1, h2, ca, result);
+	merge_finalize(opt);
+
+	return clean;
+}
+
 static struct commit *get_ref(struct repository *repo, const struct object_id *oid,
 			      const char *name)
 {

builtin/checkout.c, merge-recursive.c, merge-recursive.h, sequencer.c

diff --git a/builtin/checkout.c b/builtin/checkout.c
index d5b946dc3a..90e0eaf25e 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -708,7 +708,6 @@ static int merge_working_tree(const struct checkout_opts *opts,
 			 * give up or do a real merge, depending on
 			 * whether the merge flag was used.
 			 */
-			struct tree *result;
 			struct tree *work;
 			struct tree *old_tree;
 			struct merge_options o;
@@ -780,8 +779,7 @@ static int merge_working_tree(const struct checkout_opts *opts,
 			ret = merge_trees(&o,
 					  new_tree,
 					  work,
-					  old_tree,
-					  &result);
+					  old_tree);
 			if (ret < 0)
 				exit(128);
 			ret = reset_tree(new_tree,
diff --git a/merge-recursive.c b/merge-recursive.c
index ded2e1bcfb..89e9a7518c 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -3628,16 +3628,16 @@ static void merge_finalize(struct merge_options *opt)
 int merge_trees(struct merge_options *opt,
 		struct tree *head,
 		struct tree *merge,
-		struct tree *common,
-		struct tree **result)
+		struct tree *common)
 {
 	int clean;
+	struct tree *ignored;
 
 	assert(opt->ancestor != NULL);
 
 	if (merge_start(opt, head))
 		return -1;
-	clean = merge_trees_internal(opt, head, merge, common, result);
+	clean = merge_trees_internal(opt, head, merge, common, &ignored);
 	merge_finalize(opt);
 
 	return clean;
diff --git a/merge-recursive.h b/merge-recursive.h
index f1b6ef38ae..18012fff9d 100644
--- a/merge-recursive.h
+++ b/merge-recursive.h
@@ -74,19 +74,31 @@ static inline int merge_detect_rename(struct merge_options *o)
 		o->diff_detect_rename >= 0 ? o->diff_detect_rename : 1;
 }
 
-/* merge_trees() but with recursive ancestor consolidation */
+/*
+ * merge_recursive is like merge_trees() but with recursive ancestor
+ * consolidation, and when successful, it creates an actual commit
+ * and writes its address to *result.
+ *
+ * NOTE: empirically, about a decade ago it was determined that with more
+ *       than two merge bases, optimal behavior was found when the
+ *       ancestors were passed in the order of oldest merge base to newest
+ *       one.  Also, ancestors will be consumed (emptied) so make a copy if
+ *       you need it.
+ */
 int merge_recursive(struct merge_options *o,
 		    struct commit *h1,
 		    struct commit *h2,
 		    struct commit_list *ancestors,
 		    struct commit **result);
 
-/* rename-detecting three-way merge, no recursion */
+/*
+ * rename-detecting three-way merge, no recursion; result of merge is written
+ * to opt->repo->index.
+ */
 int merge_trees(struct merge_options *o,
 		struct tree *head,
 		struct tree *merge,
-		struct tree *common,
-		struct tree **result);
+		struct tree *common);
 
 /*
  * "git-merge-recursive" can be fed trees; wrap them into
diff --git a/sequencer.c b/sequencer.c
index 34ebf8ed94..c4ed30f1b4 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -586,7 +586,7 @@ static int do_recursive_merge(struct repository *r,
 			      struct replay_opts *opts)
 {
 	struct merge_options o;
-	struct tree *result, *next_tree, *base_tree, *head_tree;
+	struct tree *next_tree, *base_tree, *head_tree;
 	int clean;
 	char **xopt;
 	struct lock_file index_lock = LOCK_INIT;
@@ -613,7 +613,7 @@ static int do_recursive_merge(struct repository *r,
 
 	clean = merge_trees(&o,
 			    head_tree,
-			    next_tree, base_tree, &result);
+			    next_tree, base_tree);
 	if (is_rebase_i(opts) && clean <= 0)
 		fputs(o.obuf.buf, stdout);
 	strbuf_release(&o.obuf);

merge-recursive.c, sequencer.c

diff --git a/merge-recursive.c b/merge-recursive.c
index 89e9a7518c..6cee867d37 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -3600,9 +3600,6 @@ static int merge_recursive_internal(struct merge_options *opt,
 	flush_output(opt);
 	if (!opt->call_depth && opt->buffer_output < 2)
 		strbuf_release(&opt->obuf);
-	if (show(opt, 2))
-		diff_warn_rename_limit("merge.renamelimit",
-				       opt->needed_rename_limit, 0);
 	return clean;
 }
 
@@ -3622,7 +3619,9 @@ static int merge_start(struct merge_options *opt, struct tree *head)
 
 static void merge_finalize(struct merge_options *opt)
 {
-	/* Common code for wrapping up merges will be added here later */
+	if (show(opt, 2))
+		diff_warn_rename_limit("merge.renamelimit",
+				       opt->needed_rename_limit, 0);
 }
 
 int merge_trees(struct merge_options *opt,
diff --git a/sequencer.c b/sequencer.c
index c4ed30f1b4..094a4dd03d 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -617,7 +617,6 @@ static int do_recursive_merge(struct repository *r,
 	if (is_rebase_i(opts) && clean <= 0)
 		fputs(o.obuf.buf, stdout);
 	strbuf_release(&o.obuf);
-	diff_warn_rename_limit("merge.renamelimit", o.needed_rename_limit, 0);
 	if (clean < 0) {
 		rollback_lock_file(&index_lock);
 		return clean;

diff --git a/merge-recursive.c b/merge-recursive.c
index d0153ba971..bffb5eac7d 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -3477,7 +3477,7 @@ static int merge_recursive_internal(struct merge_options *opt,
 {
 	struct commit_list *iter;
 	struct commit *merged_merge_bases;
-	struct tree *mrtree;
+	struct tree *result_tree;
 	int clean;
 	int num_merge_bases;
 	struct strbuf merge_base_abbrev = STRBUF_INIT;
@@ -3562,7 +3562,7 @@ static int merge_recursive_internal(struct merge_options *opt,
 				     repo_get_commit_tree(opt->repo, h2),
 				     repo_get_commit_tree(opt->repo,
 							  merged_merge_bases),
-				     &mrtree);
+				     &result_tree);
 	strbuf_release(&merge_base_abbrev);
 	if (clean < 0) {
 		flush_output(opt);
@@ -3570,7 +3570,8 @@ static int merge_recursive_internal(struct merge_options *opt,
 	}
 
 	if (opt->call_depth) {
-		*result = make_virtual_commit(opt->repo, mrtree, "merged tree");
+		*result = make_virtual_commit(opt->repo, result_tree,
+					      "merged tree");
 		commit_list_insert(h1, &(*result)->parents);
 		commit_list_insert(h2, &(*result)->parents->next);
 	}

merge-recursive.c, merge-recursive.h

diff --git a/merge-recursive.c b/merge-recursive.c
index 40f2c6ad55..d0153ba971 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -3357,24 +3357,26 @@ static int process_entry(struct merge_options *opt,
 static int merge_trees_internal(struct merge_options *opt,
 				struct tree *head,
 				struct tree *merge,
-				struct tree *common,
+				struct tree *merge_base,
 				struct tree **result)
 {
 	struct index_state *istate = opt->repo->index;
 	int code, clean;
 
 	if (opt->subtree_shift) {
-		merge = shift_tree_object(opt->repo, head, merge, opt->subtree_shift);
-		common = shift_tree_object(opt->repo, head, common, opt->subtree_shift);
+		merge = shift_tree_object(opt->repo, head, merge,
+					  opt->subtree_shift);
+		merge_base = shift_tree_object(opt->repo, head, merge_base,
+					       opt->subtree_shift);
 	}
 
-	if (oid_eq(&common->object.oid, &merge->object.oid)) {
+	if (oid_eq(&merge_base->object.oid, &merge->object.oid)) {
 		output(opt, 0, _("Already up to date!"));
 		*result = head;
 		return 1;
 	}
 
-	code = unpack_trees_start(opt, common, head, merge);
+	code = unpack_trees_start(opt, merge_base, head, merge);
 
 	if (code != 0) {
 		if (show(opt, 4) || opt->call_depth)
@@ -3402,7 +3404,7 @@ static int merge_trees_internal(struct merge_options *opt,
 		get_files_dirs(opt, merge);
 
 		entries = get_unmerged(opt->repo->index);
-		clean = detect_and_process_renames(opt, common, head, merge,
+		clean = detect_and_process_renames(opt, merge_base, head, merge,
 						   entries, &re_info);
 		record_df_conflict_files(opt, entries);
 		if (clean < 0)
@@ -3470,11 +3472,11 @@ static struct commit_list *reverse_commit_list(struct commit_list *list)
 static int merge_recursive_internal(struct merge_options *opt,
 				    struct commit *h1,
 				    struct commit *h2,
-				    struct commit_list *ca,
+				    struct commit_list *merge_bases,
 				    struct commit **result)
 {
 	struct commit_list *iter;
-	struct commit *merged_common_ancestors;
+	struct commit *merged_merge_bases;
 	struct tree *mrtree;
 	int clean;
 	int num_merge_bases;
@@ -3486,32 +3488,32 @@ static int merge_recursive_internal(struct merge_options *opt,
 		output_commit_title(opt, h2);
 	}
 
-	if (!ca) {
-		ca = get_merge_bases(h1, h2);
-		ca = reverse_commit_list(ca);
+	if (!merge_bases) {
+		merge_bases = get_merge_bases(h1, h2);
+		merge_bases = reverse_commit_list(merge_bases);
 	}
 
 	if (show(opt, 5)) {
-		unsigned cnt = commit_list_count(ca);
+		unsigned cnt = commit_list_count(merge_bases);
 
 		output(opt, 5, Q_("found %u common ancestor:",
 				"found %u common ancestors:", cnt), cnt);
-		for (iter = ca; iter; iter = iter->next)
+		for (iter = merge_bases; iter; iter = iter->next)
 			output_commit_title(opt, iter->item);
 	}
 
-	num_merge_bases = commit_list_count(ca);
-	merged_common_ancestors = pop_commit(&ca);
-	if (merged_common_ancestors == NULL) {
+	num_merge_bases = commit_list_count(merge_bases);
+	merged_merge_bases = pop_commit(&merge_bases);
+	if (merged_merge_bases == NULL) {
 		/* if there is no common ancestor, use an empty tree */
 		struct tree *tree;
 
 		tree = lookup_tree(opt->repo, opt->repo->hash_algo->empty_tree);
-		merged_common_ancestors = make_virtual_commit(opt->repo,
-							      tree, "ancestor");
+		merged_merge_bases = make_virtual_commit(opt->repo, tree,
+							 "ancestor");
 	}
 
-	for (iter = ca; iter; iter = iter->next) {
+	for (iter = merge_bases; iter; iter = iter->next) {
 		const char *saved_b1, *saved_b2;
 		opt->call_depth++;
 		/*
@@ -3527,14 +3529,14 @@ static int merge_recursive_internal(struct merge_options *opt,
 		saved_b2 = opt->branch2;
 		opt->branch1 = "Temporary merge branch 1";
 		opt->branch2 = "Temporary merge branch 2";
-		if (merge_recursive_internal(opt, merged_common_ancestors, iter->item,
-				    NULL, &merged_common_ancestors) < 0)
+		if (merge_recursive_internal(opt, merged_merge_bases, iter->item,
+					     NULL, &merged_merge_bases) < 0)
 			return -1;
 		opt->branch1 = saved_b1;
 		opt->branch2 = saved_b2;
 		opt->call_depth--;
 
-		if (!merged_common_ancestors)
+		if (!merged_merge_bases)
 			return err(opt, _("merge returned no commit"));
 	}
 
@@ -3548,7 +3550,7 @@ static int merge_recursive_internal(struct merge_options *opt,
 		break;
 	case 1:
 		strbuf_add_unique_abbrev(&merge_base_abbrev,
-					 &merged_common_ancestors->object.oid,
+					 &merged_merge_bases->object.oid,
 					 DEFAULT_ABBREV);
 		opt->ancestor = merge_base_abbrev.buf;
 		break;
@@ -3559,7 +3561,7 @@ static int merge_recursive_internal(struct merge_options *opt,
 				     repo_get_commit_tree(opt->repo, h1),
 				     repo_get_commit_tree(opt->repo, h2),
 				     repo_get_commit_tree(opt->repo,
-							  merged_common_ancestors),
+							  merged_merge_bases),
 				     &mrtree);
 	strbuf_release(&merge_base_abbrev);
 	if (clean < 0) {
@@ -3602,7 +3604,7 @@ static void merge_finalize(struct merge_options *opt)
 int merge_trees(struct merge_options *opt,
 		struct tree *head,
 		struct tree *merge,
-		struct tree *common)
+		struct tree *merge_base)
 {
 	int clean;
 	struct tree *ignored;
@@ -3611,7 +3613,7 @@ int merge_trees(struct merge_options *opt,
 
 	if (merge_start(opt, head))
 		return -1;
-	clean = merge_trees_internal(opt, head, merge, common, &ignored);
+	clean = merge_trees_internal(opt, head, merge, merge_base, &ignored);
 	merge_finalize(opt);
 
 	return clean;
@@ -3620,7 +3622,7 @@ int merge_trees(struct merge_options *opt,
 int merge_recursive(struct merge_options *opt,
 		    struct commit *h1,
 		    struct commit *h2,
-		    struct commit_list *ca,
+		    struct commit_list *merge_bases,
 		    struct commit **result)
 {
 	int clean;
@@ -3629,7 +3631,7 @@ int merge_recursive(struct merge_options *opt,
 
 	if (merge_start(opt, repo_get_commit_tree(opt->repo, h1)))
 		return -1;
-	clean = merge_recursive_internal(opt, h1, h2, ca, result);
+	clean = merge_recursive_internal(opt, h1, h2, merge_bases, result);
 	merge_finalize(opt);
 
 	return clean;
@@ -3657,8 +3659,8 @@ static struct commit *get_ref(struct repository *repo,
 int merge_recursive_generic(struct merge_options *opt,
 			    const struct object_id *head,
 			    const struct object_id *merge,
-			    int num_base_list,
-			    const struct object_id **base_list,
+			    int num_merge_bases,
+			    const struct object_id **merge_bases,
 			    struct commit **result)
 {
 	int clean;
@@ -3667,14 +3669,14 @@ int merge_recursive_generic(struct merge_options *opt,
 	struct commit *next_commit = get_ref(opt->repo, merge, opt->branch2);
 	struct commit_list *ca = NULL;
 
-	if (base_list) {
+	if (merge_bases) {
 		int i;
-		for (i = 0; i < num_base_list; ++i) {
+		for (i = 0; i < num_merge_bases; ++i) {
 			struct commit *base;
-			if (!(base = get_ref(opt->repo, base_list[i],
-					     oid_to_hex(base_list[i]))))
+			if (!(base = get_ref(opt->repo, merge_bases[i],
+					     oid_to_hex(merge_bases[i]))))
 				return err(opt, _("Could not parse object '%s'"),
-					   oid_to_hex(base_list[i]));
+					   oid_to_hex(merge_bases[i]));
 			commit_list_insert(base, &ca);
 		}
 	}
diff --git a/merge-recursive.h b/merge-recursive.h
index 0a3033bdb0..6f351098a5 100644
--- a/merge-recursive.h
+++ b/merge-recursive.h
@@ -81,14 +81,14 @@ static inline int merge_detect_rename(struct merge_options *o)
  *
  * NOTE: empirically, about a decade ago it was determined that with more
  *       than two merge bases, optimal behavior was found when the
- *       ancestors were passed in the order of oldest merge base to newest
- *       one.  Also, ancestors will be consumed (emptied) so make a copy if
- *       you need it.
+ *       merge_bases were passed in the order of oldest commit to newest
+ *       commit.  Also, merge_bases will be consumed (emptied) so make a
+ *       copy if you need it.
  */
 int merge_recursive(struct merge_options *o,
 		    struct commit *h1,
 		    struct commit *h2,
-		    struct commit_list *ancestors,
+		    struct commit_list *merge_bases,
 		    struct commit **result);
 
 /*
@@ -98,7 +98,7 @@ int merge_recursive(struct merge_options *o,
 int merge_trees(struct merge_options *o,
 		struct tree *head,
 		struct tree *merge,
-		struct tree *common);
+		struct tree *merge_base);
 
 /*
  * "git-merge-recursive" can be fed trees; wrap them into
@@ -107,8 +107,8 @@ int merge_trees(struct merge_options *o,
 int merge_recursive_generic(struct merge_options *o,
 			    const struct object_id *head,
 			    const struct object_id *merge,
-			    int num_ca,
-			    const struct object_id **ca,
+			    int num_merge_bases,
+			    const struct object_id **merge_bases,
 			    struct commit **result);
 
 void init_merge_options(struct merge_options *o,