[PATCH v5 0/2] merge-tree: allow specifying a base commit when --write-tree is passed

Thanks for Elijah's work. I'm very excited that merge-ort is integrated into the git merge-tree, which means that we can use merge-ort in bare repositories to optimize merge performance.

In this patch, I introduce a new --merge-base=<commit> option to allow callers to specify a merge-base for the merge. This may allow users to implement git cherry-pick and git rebase in bare repositories with git merge-tree cmd.

Changes since v1:

 * Changed merge_incore_recursive() to merge_incore_nonrecursive() when
   merge-base is specified.
 * Fixed c style problem.
 * Moved commit lookup/die logic out to the parsing logic in
   cmd_merge_tree().
 * use test_commit for test

Changes since v2:

 * commit message
 * Rebased on top of en/merge-tree-sequence.
 * Set opt.ancestor to o->merge_base. Because opt.ancestor is a *char. To
   make it easier to pass parameters, I moved
   lookup_commit_reference_by_name() to real_ merge() again.
 * Added test comment.

Changes since v3:

 * support --merge-base in conjunction with --stdin

Kyle Zhao (2):
  merge-tree.c: add --merge-base=<commit> option
  merge-tree.c: allow specifying the merge-base when --stdin is passed

 Documentation/git-merge-tree.txt | 16 ++++++++
 builtin/merge-tree.c             | 65 ++++++++++++++++++++++++++------
 t/t4301-merge-tree-write-tree.sh | 55 +++++++++++++++++++++++++++
 3 files changed, 124 insertions(+), 12 deletions(-)

base-commit: ec1edbcb56ac05e9980299b05924c5c1b51d68b4
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1397%2Fkeyu98%2Fkz%2Fmerge-tree-option-merge-base-v5
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1397/keyu98/kz/merge-tree-option-merge-base-v5
Pull-Request: https://github.com/gitgitgadget/git/pull/1397

Range-diff vs v4:

 1:  bba854fc8fa ! 1:  01df0d1a6a7 merge-tree.c: add --merge-base=<commit> option
     @@ builtin/merge-tree.c: int cmd_merge_tree(int argc, const char **argv, const char
       		OPT_END()
       	};
       
     +@@ builtin/merge-tree.c: int cmd_merge_tree(int argc, const char **argv, const char *prefix)
     + 
     + 		if (o.mode == MODE_TRIVIAL)
     + 			die(_("--trivial-merge is incompatible with all other options"));
     ++		if (merge_base)
     ++			die(_("--merge-base is incompatible with --stdin"));
     + 		line_termination = '\0';
     + 		while (strbuf_getline_lf(&buf, stdin) != EOF) {
     + 			struct strbuf **split;
      @@ builtin/merge-tree.c: int cmd_merge_tree(int argc, const char **argv, const char *prefix)
       			if (!split[0] || !split[1] || split[2])
       				die(_("malformed input line: '%s'."), buf.buf);
 2:  db47fbc663e ! 2:  3bdfad03cca merge-tree.c: support --merge-base in conjunction with --stdin
     @@ Metadata
      Author: Kyle Zhao <kylezhao@tencent.com>
      
       ## Commit message ##
     -    merge-tree.c: support --merge-base in conjunction with --stdin
     +    merge-tree.c: allow specifying the merge-base when --stdin is passed
      
     -    The previous change add "--merge-base" option in order to allow users to
     -    specify merge-base for the merge. But it doesn't compatible well with
     -    --stdin, because multiple batched merges can only have the same specified
     -    base.
     +    The previous commit added a `--merge-base` option in order to allow
     +    using a specified merge-base for the merge.  Extend the input accepted
     +    by `--stdin` to also allow a specified merge-base with each merge
     +    requested.  For example:
      
     -    This patch allows users to pass --merge-base option into the input line,
     -    such as:
     +        printf "<b3> -- <b1> <b2>" | git merge-tree --stdin
      
     -        printf "--merge-base=<b3> <b1> <b2>" | git merge-tree --stdin
     -
     -    This does a merge of b1 and b2, and uses b3 as the merge-base.
     +    does a merge of b1 and b2, and uses b3 as the merge-base.
      
          Signed-off-by: Kyle Zhao <kylezhao@tencent.com>
      
     @@ Documentation/git-merge-tree.txt: OPTIONS
       --merge-base=<commit>::
       	Instead of finding the merge-bases for <branch1> and <branch2>,
      -	specify a merge-base for the merge.
     -+	specify a merge-base for the merge. When --stdin is passed, this
     -+	option should be passed into the input line.
     ++	specify a merge-base for the merge. This option is incompatible
     ++	with `--stdin`.
       
       [[OUTPUT]]
       OUTPUT
     +@@ Documentation/git-merge-tree.txt: with linkgit:git-merge[1]:
     +   * any messages that would have been printed to stdout (the
     +     <<IM,Informational messages>>)
     + 
     ++INPUT FORMAT
     ++------------
     ++'git merge-tree --stdin' input format is fully text based. Each line
     ++has this format:
     ++
     ++	[<base-commit> -- ]<branch1> <branch2>
     ++
     ++If one line is separated by `--`, the string before the separator is
     ++used for specifying a merge-base for the merge and the string after
     ++the separator describes the branches to be merged.
     ++
     + MISTAKES TO AVOID
     + -----------------
     + 
      
       ## builtin/merge-tree.c ##
      @@ builtin/merge-tree.c: int cmd_merge_tree(int argc, const char **argv, const char *prefix)
     - 
     - 		if (o.mode == MODE_TRIVIAL)
     - 			die(_("--trivial-merge is incompatible with all other options"));
     -+		if (merge_base)
     -+			die(_("--merge-base should be passed into the input line"));
     - 		line_termination = '\0';
       		while (strbuf_getline_lf(&buf, stdin) != EOF) {
       			struct strbuf **split;
       			int result;
      +			const char *input_merge_base = NULL;
     -+			const char *arg;
       
       			split = strbuf_split(&buf, ' ');
      -			if (!split[0] || !split[1] || split[2])
     @@ builtin/merge-tree.c: int cmd_merge_tree(int argc, const char **argv, const char
       				die(_("malformed input line: '%s'."), buf.buf);
       			strbuf_rtrim(split[0]);
      -			result = real_merge(&o, merge_base, split[0]->buf, split[1]->buf, prefix);
     ++			strbuf_rtrim(split[1]);
      +
     -+			/* parse --merge-base=<commit> option */
     -+			arg = split[0]->buf;
     -+			if (skip_prefix(arg, "--merge-base=", &arg))
     -+				input_merge_base = arg;
     ++			/* parse the merge-base */
     ++			if (!strcmp(split[1]->buf, "--")) {
     ++				input_merge_base = split[0]->buf;
     ++			}
      +
     -+			if (input_merge_base && split[2] && !split[3]) {
     -+				strbuf_rtrim(split[1]);
     -+				result = real_merge(&o, input_merge_base, split[1]->buf, split[2]->buf, prefix);
     ++			if (input_merge_base && split[2] && split[3] && !split[4]) {
     ++				strbuf_rtrim(split[2]);
     ++				strbuf_rtrim(split[3]);
     ++				result = real_merge(&o, input_merge_base, split[2]->buf, split[3]->buf, prefix);
      +			} else if (!input_merge_base && !split[2]) {
      +				result = real_merge(&o, NULL, split[0]->buf, split[1]->buf, prefix);
      +			} else {
     @@ t/t4301-merge-tree-write-tree.sh: test_expect_success '--stdin with both a succe
      +test_expect_success '--merge-base is incompatible with --stdin' '
      +	test_must_fail git merge-tree --merge-base=side1 --stdin 2>expect &&
      +
     -+	grep "^fatal: --merge-base should be passed into the input line" expect
     ++	grep "^fatal: --merge-base is incompatible with --stdin" expect
      +'
      +
       # specify merge-base as parent of branch2
     @@ t/t4301-merge-tree-write-tree.sh: test_expect_success 'specify merge-base as par
       	)
       '
       
     ++# Since the earlier tests have verified that individual merge-tree calls
     ++# are doing the right thing, this test case is only used to test whether
     ++# the input format is available.
     ++
      +test_expect_success '--stdin with both a normal merge and a merge-base specified merge' '
      +	cd base-b2-p &&
     -+	printf "c1 c3\n--merge-base=c2 c1 c3" | git merge-tree --stdin >actual &&
     ++	printf "c1 c3\nc2 -- c1 c3" | git merge-tree --stdin >actual &&
      +
      +	printf "1\0" >expect &&
      +	git merge-tree --write-tree -z c1 c3 >>expect &&