--allow-unrelated-histories::
merge-tree will by default error out if the two branches specified
share no common history. This flag can be given to override that
diff --git a/builtin/merge-tree.c b/builtin/merge-tree.c
index 4aafa73c6155..273ec171e988 100644
--- a/builtin/merge-tree.c
+++ b/builtin/merge-tree.c
@@ -490,6 +490,9 @@ static int real_merge(struct merge_tree_options *o,
if (result.clean < 0)
die(_("failure to merge"));
+ if (o->merge_options.mergeability_only)
+ goto cleanup;
+
if (show_messages == -1)
show_messages = !result.clean;
@@ -522,6 +525,8 @@ static int real_merge(struct merge_tree_options *o,
}
if (o->use_stdin)
putchar(line_termination);
+
+cleanup:
merge_finalize(&opt, &result);
clear_merge_options(&opt);
return !result.clean; /* result.clean < 0 handled above */
@@ -538,6 +543,7 @@ int cmd_merge_tree(int argc,
int original_argc;
const char *merge_base = NULL;
int ret;
+ int dry_run = 0;
const char * const merge_tree_usage[] = {
N_("git merge-tree [--write-tree] [<options>] <branch1> <branch2>"),
@@ -552,6 +558,10 @@ int cmd_merge_tree(int argc,
N_("do a trivial merge only"), MODE_TRIVIAL),
OPT_BOOL(0, "messages", &o.show_messages,
N_("also show informational/conflict messages")),
+ OPT_BOOL_F(0, "dry-run",
+ &dry_run,
+ N_("suppress all output; only exit status wanted"),
+ PARSE_OPT_NONEG),
OPT_SET_INT('z', NULL, &line_termination,
N_("separate paths with the NUL character"), '\0'),
OPT_BOOL_F(0, "name-only",
@@ -583,6 +593,18 @@ int cmd_merge_tree(int argc,
argc = parse_options(argc, argv, prefix, mt_options,
merge_tree_usage, PARSE_OPT_STOP_AT_NON_OPTION);
+ if (dry_run && o.show_messages == -1)
+ o.show_messages = 0;
+ o.merge_options.mergeability_only = dry_run;
+ die_for_incompatible_opt2(dry_run, "--dry-run",
+ o.show_messages, "--messages");
+ die_for_incompatible_opt2(dry_run, "--dry-run",
+ o.name_only, "--name-only");
+ die_for_incompatible_opt2(dry_run, "--dry-run",
+ o.use_stdin, "--stdin");
+ die_for_incompatible_opt2(dry_run, "--dry-run",
+ !line_termination, "-z");
+
if (xopts.nr && o.mode == MODE_TRIVIAL)
die(_("--trivial-merge is incompatible with all other options"));
for (size_t x = 0; x < xopts.nr; x++)
diff --git a/t/t4301-merge-tree-write-tree.sh b/t/t4301-merge-tree-write-tree.sh
index f9c5883a7f7c..566a2b4ec737 100755
--- a/t/t4301-merge-tree-write-tree.sh
+++ b/t/t4301-merge-tree-write-tree.sh
@@ -54,6 +54,25 @@ test_expect_success setup '
git commit -m first-commit
'
+test_expect_success '--dry-run on clean merge' '
+ # Get rid of loose objects to start with
+ git gc &&
+ echo "0 objects, 0 kilobytes" >expect &&
+ git count-objects >actual &&
+ test_cmp expect actual &&
+
+ # Ensure merge is successful (exit code of 0)
+ git merge-tree --write-tree --dry-run side1 side3 >output &&
+
+ # Ensure there is no output
+ test_must_be_empty output &&
+
+ # Ensure no loose objects written (all new objects written would have
+ # been in "outer layer" of the merge)
+ git count-objects >actual &&
+ test_cmp expect actual
+'
+
test_expect_success 'Clean merge' '
TREE_OID=$(git merge-tree --write-tree side1 side3) &&
q_to_tab <<-EOF >expect &&
@@ -72,6 +91,25 @@ test_expect_success 'Failed merge without rename detection' '
grep "CONFLICT (modify/delete): numbers deleted" out
'
+test_expect_success '--dry-run on conflicted merge' '
+ # Get rid of loose objects to start with
+ git gc &&
+ echo "0 objects, 0 kilobytes" >expect &&
+ git count-objects >actual &&
+ test_cmp expect actual &&
+
+ # Ensure merge has conflict
+ test_expect_code 1 git merge-tree --write-tree --dry-run side1 side2 >output &&
+
+ # Ensure there is no output
+ test_must_be_empty output &&
+
+ # Ensure no loose objects written (all new objects written would have
+ # been in "outer layer" of the merge)
+ git count-objects >actual &&
+ test_cmp expect actual
+'
+
test_expect_success 'Content merge and a few conflicts' '
git checkout side1^0 &&
test_must_fail git merge side2 &&
