[PATCH 2/2] rebase: add a config option for --rebase-merges

[Alex Henrie <alexhenrie24@gmail.com>]

At the same time, stop accepting --rebase-merges="" as a synonym of
--rebase-merges=no-rebase-cousins.

Signed-off-by: Alex Henrie <alexhenrie24@gmail.com>
---
 Documentation/config/rebase.txt |  3 ++
 builtin/rebase.c                | 50 ++++++++++++++-----
 t/t3430-rebase-merges.sh        | 87 +++++++++++++++++++++++++++++++++
 3 files changed, 127 insertions(+), 13 deletions(-)

diff --git a/Documentation/config/rebase.txt b/Documentation/config/rebase.txt
index f19bd0e040..d956ec4441 100644
--- a/Documentation/config/rebase.txt
+++ b/Documentation/config/rebase.txt
@@ -67,3 +67,6 @@ rebase.rescheduleFailedExec::
 
 rebase.forkPoint::
 	If set to false set `--no-fork-point` option by default.
+
+rebase.merges::
+	Default value of `--rebase-merges` option.
diff --git a/builtin/rebase.c b/builtin/rebase.c
index 96c0474379..ab4c3b2870 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -771,6 +771,25 @@ static int run_specific_rebase(struct rebase_options *opts)
 	return status ? -1 : 0;
 }
 
+static void parse_merges_value(struct rebase_options *options, const char *value)
+{
+	if (value) {
+		if (!strcmp("drop", value)) {
+			options->rebase_merges = 0;
+			return;
+		}
+
+		if (!strcmp("no-rebase-cousins", value))
+			options->rebase_cousins = 0;
+		else if (!strcmp("rebase-cousins", value))
+			options->rebase_cousins = 1;
+		else
+			die(_("Unknown mode: %s"), value);
+	}
+
+	options->rebase_merges = 1;
+}
+
 static int rebase_config(const char *var, const char *value, void *data)
 {
 	struct rebase_options *opts = data;
@@ -815,6 +834,14 @@ static int rebase_config(const char *var, const char *value, void *data)
 		return 0;
 	}
 
+	if (!strcmp(var, "rebase.merges")) {
+		const char *rebase_merges;
+		if (!git_config_string(&rebase_merges, var, value) &&
+		    rebase_merges && *rebase_merges)
+			parse_merges_value(opts, rebase_merges);
+		return 0;
+	}
+
 	if (!strcmp(var, "rebase.backend")) {
 		return git_config_string(&opts->default_backend, var, value);
 	}
@@ -980,6 +1007,13 @@ static int parse_opt_empty(const struct option *opt, const char *arg, int unset)
 	return 0;
 }
 
+static int parse_opt_merges(const struct option *opt, const char *arg, int unset)
+{
+	BUG_ON_OPT_NEG(unset);
+	parse_merges_value(opt->value, arg);
+	return 0;
+}
+
 static void NORETURN error_on_missing_default_upstream(void)
 {
 	struct branch *current_branch = branch_get(NULL);
@@ -1035,7 +1069,6 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	struct object_id branch_base;
 	int ignore_whitespace = 0;
 	const char *gpg_sign = NULL;
-	const char *rebase_merges = NULL;
 	struct string_list strategy_options = STRING_LIST_INIT_NODUP;
 	struct object_id squash_onto;
 	char *squash_onto_name = NULL;
@@ -1137,10 +1170,9 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 			   &options.allow_empty_message,
 			   N_("allow rebasing commits with empty messages"),
 			   PARSE_OPT_HIDDEN),
-		{OPTION_STRING, 'r', "rebase-merges", &rebase_merges,
-			N_("mode"),
+		OPT_CALLBACK_F('r', "rebase-merges", &options, N_("mode"),
 			N_("try to rebase merges instead of skipping them"),
-			PARSE_OPT_OPTARG, NULL, (intptr_t)""},
+			PARSE_OPT_OPTARG, parse_opt_merges),
 		OPT_BOOL(0, "fork-point", &options.fork_point,
 			 N_("use 'merge-base --fork-point' to refine upstream")),
 		OPT_STRING('s', "strategy", &options.strategy,
@@ -1436,16 +1468,8 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	if (options.exec.nr)
 		imply_merge(&options, "--exec");
 
-	if (rebase_merges && strcmp("drop", rebase_merges)) {
-		if (!*rebase_merges)
-			; /* default mode; do nothing */
-		else if (!strcmp("rebase-cousins", rebase_merges))
-			options.rebase_cousins = 1;
-		else if (strcmp("no-rebase-cousins", rebase_merges))
-			die(_("Unknown mode: %s"), rebase_merges);
-		options.rebase_merges = 1;
+	if (options.rebase_merges)
 		imply_merge(&options, "--rebase-merges");
-	}
 
 	if (options.type == REBASE_APPLY) {
 		if (ignore_whitespace)
diff --git a/t/t3430-rebase-merges.sh b/t/t3430-rebase-merges.sh
index 861c8405f2..9be07249cc 100755
--- a/t/t3430-rebase-merges.sh
+++ b/t/t3430-rebase-merges.sh
@@ -298,6 +298,92 @@ test_expect_success 'do not rebase cousins unless asked for' '
 	EOF
 '
 
+test_expect_success '--rebase-merges="" is invalid syntax' '
+	echo "fatal: Unknown mode: " >expect &&
+	! git rebase --rebase-merges="" HEAD^ 2>actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rebase.merges="" is equivalent to not passing --rebase-merges' '
+	git config rebase.merges "" &&
+	git checkout -b config-merges-blank E &&
+	git rebase C &&
+	test_cmp_graph C.. <<-\EOF
+	* B
+	* D
+	o C
+	EOF
+'
+
+test_expect_success 'rebase.merges=rebase-cousins is equivalent to --rebase-merges=rebase-cousins' '
+	git config rebase.merges rebase-cousins &&
+	git checkout -b config-rebase-cousins main &&
+	git rebase HEAD^ &&
+	test_cmp_graph HEAD^.. <<-\EOF
+	*   Merge the topic branch '\''onebranch'\''
+	|\
+	| * D
+	| * G
+	|/
+	o H
+	EOF
+'
+
+test_expect_success '--rebase-merges=drop overrides rebase.merges=no-rebase-cousins' '
+	git config rebase.merges no-rebase-cousins &&
+	git checkout -b override-config-no-rebase-cousins E &&
+	git rebase --rebase-merges=drop C &&
+	test_cmp_graph C.. <<-\EOF
+	* B
+	* D
+	o C
+	EOF
+'
+
+test_expect_success '--rebase-merges=no-rebase-cousins overrides rebase.merges=rebase-cousins' '
+	git config rebase.merges rebase-cousins &&
+	git checkout -b override-config-rebase-cousins main &&
+	git rebase --rebase-merges=no-rebase-cousins HEAD^ &&
+	test_cmp_graph HEAD^.. <<-\EOF
+	*   Merge the topic branch '\''onebranch'\''
+	|\
+	| * D
+	| * G
+	o | H
+	|/
+	o A
+	EOF
+'
+
+test_expect_success '--rebase-merges overrides rebase.merges=drop' '
+	git config rebase.merges drop &&
+	git checkout -b override-config-merges-drop main &&
+	git rebase --rebase-merges HEAD^ &&
+	test_cmp_graph HEAD^.. <<-\EOF
+	*   Merge the topic branch '\''onebranch'\''
+	|\
+	| * D
+	| * G
+	o | H
+	|/
+	o A
+	EOF
+'
+
+test_expect_success '--rebase-merges does not override rebase.merges=rebase-cousins' '
+	git config rebase.merges rebase-cousins &&
+	git checkout -b no-override-config-rebase-cousins main &&
+	git rebase --rebase-merges HEAD^ &&
+	test_cmp_graph HEAD^.. <<-\EOF
+	*   Merge the topic branch '\''onebranch'\''
+	|\
+	| * D
+	| * G
+	|/
+	o H
+	EOF
+'
+
 test_expect_success 'refs/rewritten/* is worktree-local' '
 	git worktree add wt &&
 	cat >wt/script-from-scratch <<-\EOF &&
@@ -408,6 +494,7 @@ test_expect_success 'a "merge" into a root commit is a fast-forward' '
 '
 
 test_expect_success 'A root commit can be a cousin, treat it that way' '
+	git config --unset rebase.merges &&
 	git checkout --orphan khnum &&
 	test_commit yama &&
 	git checkout -b asherah main &&
-- 
2.39.2