[PATCH] merge: --ff-one-only to apply FF if commit is one

From: Ruslan Yakauleu via GitGitGadget <gitgitgadget@gmail.com>
Date: Oct 25, 2023, 08:58 UTC
Message-ID: <pull.1599.git.git.1698224280816.gitgitgadget@gmail.com>

From: Ruslan Yakauleu <ruslan.yakauleu@gmail.com>

A new option --ff-one-only to control the merging strategy. For one commit option works like -ff to avoid extra merge commit. In other cases the option works like --no-ff to create merge commit for complex features.

Signed-off-by: Ruslan Yakauleu <ruslan.yakauleu@gmail.com>
---
    merge: --ff-one-only to apply FF if commit is one
    
    A new option --ff-one-only to control the merging strategy. For one
    commit option works like -ff to avoid extra merge commit. In other cases
    the option works like --no-ff to create merge commit for complex
    features.
    
    Plenty of developers want to simplify merge history. We have two main
    merging strategies:
    
     * Fast-forward (--ff) - There we can lose merge commits for complex
       features and if we need to roll back some feature we can't revert
       just one commit.
     * Merge (--no-ff) - There we have extra merges for extra simple
       changes.
    
    Before, the user had to choose between --ff/--no-ff every time to have
    history without extra merges for simple changes and to use merges for
    complex features.
    
    Ways to use the new option: git merge --ff-one-only git config merge.ff
    one-only git config branch.master.mergeoptions --ff-one-only

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1599%2FQuAzI%2Fmerge%2Fff-one-only-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1599/QuAzI/merge/ff-one-only-v1
Pull-Request: https://github.com/git/git/pull/1599

 Documentation/config/merge.txt |  3 +++
 builtin/merge.c                | 18 +++++++++++++++++-
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/Documentation/config/merge.txt b/Documentation/config/merge.txt
index 8851b6cedef..6cd5daa4d64 100644
--- a/Documentation/config/merge.txt
+++ b/Documentation/config/merge.txt
@@ -31,6 +31,9 @@ merge.ff::
 	a case (equivalent to giving the `--no-ff` option from the command
 	line). When set to `only`, only such fast-forward merges are
 	allowed (equivalent to giving the `--ff-only` option from the
+	command line). When set to `one-only`, fast-forward merge allowed
+	only for one commit, in other way extra merge commit should be
+	created (equivalent to giving the `--ff-one-only` option from the
 	command line).
 
 merge.verifySignatures::
diff --git a/builtin/merge.c b/builtin/merge.c
index d748d46e135..100f0021e56 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -110,7 +110,8 @@ static const char *pull_twohead, *pull_octopus;
 enum ff_type {
 	FF_NO,
 	FF_ALLOW,
-	FF_ONLY
+	FF_ONLY,
+	FF_ONE_ONLY
 };
 
 static enum ff_type fast_forward = FF_ALLOW;
@@ -258,6 +259,7 @@ static struct option builtin_merge_options[] = {
 		N_("edit message before committing")),
 	OPT_CLEANUP(&cleanup_arg),
 	OPT_SET_INT(0, "ff", &fast_forward, N_("allow fast-forward (default)"), FF_ALLOW),
+	OPT_SET_INT(0, "ff-one-only", &fast_forward, N_("allow fast-forward if only one commit"), FF_ONE_ONLY),
 	OPT_SET_INT_F(0, "ff-only", &fast_forward,
 		      N_("abort if fast-forward is not possible"),
 		      FF_ONLY, PARSE_OPT_NONEG),
@@ -631,6 +633,8 @@ static int git_merge_config(const char *k, const char *v,
 			fast_forward = boolval ? FF_ALLOW : FF_NO;
 		} else if (v && !strcmp(v, "only")) {
 			fast_forward = FF_ONLY;
+		} else if (v && !strcmp(v, "one-only")) {
+			fast_forward = FF_ONE_ONLY;
 		} /* do not barf on values from future versions of git */
 		return 0;
 	} else if (!strcmp(k, "merge.defaulttoupstream")) {
@@ -1527,6 +1531,18 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 		free(list);
 	}
 
+	if (fast_forward == FF_ONE_ONLY) {
+		fast_forward = FF_NO;
+
+		/* check that we have one and only one commit to merge */
+		if (squash || ((!remoteheads->next &&
+				!common->next &&
+				oideq(&common->item->object.oid, &head_commit->object.oid)) &&
+				oideq(&remoteheads->item->parents->item->object.oid, &head_commit->object.oid))) {
+			fast_forward = FF_ALLOW;
+		}
+	}
+
 	update_ref("updating ORIG_HEAD", "ORIG_HEAD",
 		   &head_commit->object.oid, NULL, 0, UPDATE_REFS_DIE_ON_ERR);
 

base-commit: 2e8e77cbac8ac17f94eee2087187fa1718e38b14

-- 
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