Merge branch 'jc/merge-detached-head-name'

The default merge message prepared by "git merge" records the name
of the current branch; the name can be overridden with a new option
to allow users to pretend a merge is made on a different branch.

* jc/merge-detached-head-name:
  merge: allow to pretend a merge is made into a different branch

Documentation/git-fmt-merge-msg.txt

@@ -9,7 +9,7 @@ git-fmt-merge-msg - Produce a merge commit message
 SYNOPSIS
 --------
 [verse]
-'git fmt-merge-msg' [-m <message>] [--log[=<n>] | --no-log]
+'git fmt-merge-msg' [-m <message>] [--into-name <branch>] [--log[=<n>] | --no-log]
 'git fmt-merge-msg' [-m <message>] [--log[=<n>] | --no-log] -F <file>
 
 DESCRIPTION
@@ -44,6 +44,10 @@ OPTIONS
 	Use <message> instead of the branch names for the first line
 	of the log message.  For use with `--log`.
 
+--into-name <branch>::
+	Prepare the merge message as if merging to the branch `<branch>`,
+	instead of the name of the real branch to which the merge is made.
+
 -F <file>::
 --file <file>::
 	Take the list of merged objects from <file> instead of

Documentation/git-merge.txt

@@ -12,7 +12,8 @@ SYNOPSIS
 'git merge' [-n] [--stat] [--no-commit] [--squash] [--[no-]edit]
 	[--no-verify] [-s <strategy>] [-X <strategy-option>] [-S[<keyid>]]
 	[--[no-]allow-unrelated-histories]
-	[--[no-]rerere-autoupdate] [-m <msg>] [-F <file>] [<commit>...]
+	[--[no-]rerere-autoupdate] [-m <msg>] [-F <file>]
+	[--into-name <branch>] [<commit>...]
 'git merge' (--continue | --abort | --quit)
 
 DESCRIPTION
@@ -76,6 +77,11 @@ The 'git fmt-merge-msg' command can be
 used to give a good default for automated 'git merge'
 invocations. The automated message can include the branch description.
 
+--into-name <branch>::
+	Prepare the default merge message as if merging to the branch
+	`<branch>`, instead of the name of the real branch to which
+	the merge is made.
+
 -F <file>::
 --file=<file>::
 	Read the commit message to be used for the merge commit (in

builtin/fmt-merge-msg.c

@@ -12,6 +12,7 @@ int cmd_fmt_merge_msg(int argc, const char **argv, const char *prefix)
 {
 	const char *inpath = NULL;
 	const char *message = NULL;
+	char *into_name = NULL;
 	int shortlog_len = -1;
 	struct option options[] = {
 		{ OPTION_INTEGER, 0, "log", &shortlog_len, N_("n"),
@@ -23,6 +24,8 @@ int cmd_fmt_merge_msg(int argc, const char **argv, const char *prefix)
 		  DEFAULT_MERGE_LOG_LEN },
 		OPT_STRING('m', "message", &message, N_("text"),
 			N_("use <text> as start of message")),
+		OPT_STRING(0, "into-name", &into_name, N_("name"),
+			   N_("use <name> instead of the real target branch")),
 		OPT_FILENAME('F', "file", &inpath, N_("file to read from")),
 		OPT_END()
 	};
@@ -56,6 +59,7 @@ int cmd_fmt_merge_msg(int argc, const char **argv, const char *prefix)
 	opts.add_title = !message;
 	opts.credit_people = 1;
 	opts.shortlog_len = shortlog_len;
+	opts.into_name = into_name;
 
 	ret = fmt_merge_msg(&input, &output, &opts);
 	if (ret)

builtin/merge.c

@@ -87,6 +87,7 @@ static int signoff;
 static const char *sign_commit;
 static int autostash;
 static int no_verify;
+static char *into_name;
 
 static struct strategy all_strategy[] = {
 	{ "recursive",  NO_TRIVIAL },
@@ -286,6 +287,8 @@ static struct option builtin_merge_options[] = {
 	{ OPTION_LOWLEVEL_CALLBACK, 'F', "file", &merge_msg, N_("path"),
 		N_("read message from file"), PARSE_OPT_NONEG,
 		NULL, 0, option_read_message },
+	OPT_STRING(0, "into-name", &into_name, N_("name"),
+		   N_("use <name> instead of the real target")),
 	OPT__VERBOSITY(&verbosity),
 	OPT_BOOL(0, "abort", &abort_current_merge,
 		N_("abort the current in-progress merge")),
@@ -1121,6 +1124,7 @@ static void prepare_merge_message(struct strbuf *merge_names, struct strbuf *mer
 	opts.add_title = !have_message;
 	opts.shortlog_len = shortlog_len;
 	opts.credit_people = (0 < option_edit);
+	opts.into_name = into_name;
 
 	fmt_merge_msg(merge_names, merge_msg, &opts);
 	if (merge_msg->len)

fmt-merge-msg.c

@@ -650,12 +650,15 @@ int fmt_merge_msg(struct strbuf *in, struct strbuf *out,
 
 	memset(&merge_parents, 0, sizeof(merge_parents));
 
-	/* get current branch */
+	/* learn the commit that we merge into and the current branch name */
 	current_branch = current_branch_to_free =
 		resolve_refdup("HEAD", RESOLVE_REF_READING, &head_oid, NULL);
 	if (!current_branch)
 		die("No current branch");
-	if (starts_with(current_branch, "refs/heads/"))
+
+	if (opts->into_name)
+		current_branch = opts->into_name;
+	else if (starts_with(current_branch, "refs/heads/"))
 		current_branch += 11;
 
 	find_merge_parents(&merge_parents, in, &head_oid);

fmt-merge-msg.h

@@ -9,6 +9,7 @@ struct fmt_merge_msg_opts {
 	unsigned add_title:1,
 		credit_people:1;
 	int shortlog_len;
+	const char *into_name;
 };
 
 extern int merge_log_config;

t/t6200-fmt-merge-msg.sh

@@ -633,7 +633,35 @@ test_expect_success 'merge-msg with "merging" an annotated tag' '
 	test_cmp expected .git/MERGE_MSG
 '
 
+test_expect_success 'merge --into-name=<name>' '
+	test_when_finished "git checkout main" &&
+	git checkout -B side main &&
+	git commit --allow-empty -m "One step ahead" &&
+
+	git checkout --detach main &&
+	git merge --no-ff side &&
+	git show -s --format="%s" >full.0 &&
+	head -n1 full.0 >actual &&
+	# expect that HEAD is shown as-is
+	grep -e "Merge branch .side. into HEAD$" actual &&
+
+	git reset --hard main &&
+	git merge --no-ff --into-name=main side &&
+	git show -s --format="%s" >full.1 &&
+	head -n1 full.1 >actual &&
+	# expect that we pretend to be merging to main, that is suppressed
+	grep -e "Merge branch .side.$" actual &&
+
+	git checkout -b throwaway main &&
+	git merge --no-ff --into-name=main side &&
+	git show -s --format="%s" >full.2 &&
+	head -n1 full.2 >actual &&
+	# expect that we pretend to be merging to main, that is suppressed
+	grep -e "Merge branch .side.$" actual
+'
+
 test_expect_success 'merge.suppressDest configuration' '
+	test_when_finished "git checkout main" &&
 	git checkout -B side main &&
 	git commit --allow-empty -m "One step ahead" &&
 	git checkout main &&
@@ -650,7 +678,19 @@ test_expect_success 'merge.suppressDest configuration' '
 	git -c merge.suppressDest="ma?*[rn]" fmt-merge-msg <.git/FETCH_HEAD >full.3 &&
 	head -n1 full.3 >actual &&
 	grep -e "Merge branch .side." actual &&
-	! grep -e " into main$" actual
+	! grep -e " into main$" actual &&
+
+	git checkout --detach HEAD &&
+	git -c merge.suppressDest="main" fmt-merge-msg <.git/FETCH_HEAD >full.4 &&
+	head -n1 full.4 >actual &&
+	grep -e "Merge branch .side. into HEAD$" actual &&
+
+	git -c merge.suppressDest="main" fmt-merge-msg \
+		--into-name=main <.git/FETCH_HEAD >full.5 &&
+	head -n1 full.5 >actual &&
+	grep -e "Merge branch .side." actual &&
+	! grep -e " into main$" actual &&
+	! grep -e " into HEAD$" actual
 '
 
 test_done