rebase -r: support merge strategies other than `recursive`

We already support merge strategies in the sequencer, but only for
`pick` commands.

With this commit, we now also support them in `merge` commands. The
approach is simple: if any merge strategy option is specified, or if any
merge strategy other than `recursive` is specified, we simply spawn the
`git merge` command. Otherwise, we handle the merge in-process just as
before.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-rebase.txt

@@ -543,8 +543,6 @@ In addition, the following pairs of options are incompatible:
  * --preserve-merges and --interactive
  * --preserve-merges and --signoff
  * --preserve-merges and --rebase-merges
- * --rebase-merges and --strategy
- * --rebase-merges and --strategy-option
 
 BEHAVIORAL DIFFERENCES
 -----------------------

builtin/rebase.c

@@ -1811,15 +1811,6 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 			      "'--reschedule-failed-exec'"));
 	}
 
-	if (options.rebase_merges) {
-		if (strategy_options.nr)
-			die(_("cannot combine '--rebase-merges' with "
-			      "'--strategy-option'"));
-		if (options.strategy)
-			die(_("cannot combine '--rebase-merges' with "
-			      "'--strategy'"));
-	}
-
 	if (!options.root) {
 		if (argc < 1) {
 			struct branch *branch;

sequencer.c

@@ -3256,6 +3256,9 @@ static int do_merge(struct repository *r,
 	struct commit *head_commit, *merge_commit, *i;
 	struct commit_list *bases, *j, *reversed = NULL;
 	struct commit_list *to_merge = NULL, **tail = &to_merge;
+	const char *strategy = !opts->xopts_nr &&
+		(!opts->strategy || !strcmp(opts->strategy, "recursive")) ?
+		NULL : opts->strategy;
 	struct merge_options o;
 	int merge_arg_len, oneline_offset, can_fast_forward, ret, k;
 	static struct lock_file lock;
@@ -3404,7 +3407,7 @@ static int do_merge(struct repository *r,
 		goto leave_merge;
 	}
 
-	if (to_merge->next) {
+	if (strategy || to_merge->next) {
 		/* Octopus merge */
 		struct child_process cmd = CHILD_PROCESS_INIT;
 
@@ -3418,7 +3421,14 @@ static int do_merge(struct repository *r,
 		cmd.git_cmd = 1;
 		argv_array_push(&cmd.args, "merge");
 		argv_array_push(&cmd.args, "-s");
-		argv_array_push(&cmd.args, "octopus");
+		if (!strategy)
+			argv_array_push(&cmd.args, "octopus");
+		else {
+			argv_array_push(&cmd.args, strategy);
+			for (k = 0; k < opts->xopts_nr; k++)
+				argv_array_pushf(&cmd.args,
+						 "-X%s", opts->xopts[k]);
+		}
 		argv_array_push(&cmd.args, "--no-edit");
 		argv_array_push(&cmd.args, "--no-ff");
 		argv_array_push(&cmd.args, "--no-log");

t/t3422-rebase-incompatible-options.sh

@@ -76,14 +76,4 @@ test_expect_success REBASE_P \
 	test_must_fail git rebase --preserve-merges --rebase-merges A
 '
 
-test_expect_success '--rebase-merges incompatible with --strategy' '
-	git checkout B^0 &&
-	test_must_fail git rebase --rebase-merges -s resolve A
-'
-
-test_expect_success '--rebase-merges incompatible with --strategy-option' '
-	git checkout B^0 &&
-	test_must_fail git rebase --rebase-merges -Xignore-space-change A
-'
-
 test_done

t/t3430-rebase-merges.sh

@@ -412,4 +412,25 @@ test_expect_success '--continue after resolving conflicts after a merge' '
 	test_path_is_missing .git/MERGE_HEAD
 '
 
+test_expect_success '--rebase-merges with strategies' '
+	git checkout -b with-a-strategy F &&
+	test_tick &&
+	git merge -m "Merge conflicting-G" conflicting-G &&
+
+	: first, test with a merge strategy option &&
+	git rebase -ir -Xtheirs G &&
+	echo conflicting-G >expect &&
+	test_cmp expect G.t &&
+
+	: now, try with a merge strategy other than recursive &&
+	git reset --hard @{1} &&
+	write_script git-merge-override <<-\EOF &&
+	echo overridden$1 >>G.t
+	git add G.t
+	EOF
+	PATH="$PWD:$PATH" git rebase -ir -s override -Xxopt G &&
+	test_write_lines G overridden--xopt >expect &&
+	test_cmp expect G.t
+'
+
 test_done