path: root/builtin
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authorJunio C Hamano <>2016-03-18 20:21:09 (GMT)
committerJunio C Hamano <>2016-03-23 19:04:48 (GMT)
commite379fdf34fee96cd205be83ff4e71699bdc32b18 (patch)
tree7e0298e9b6478958a4e153f241248217545cf23c /builtin
parent937978e0f3e750d917768c77665d5f8cfbd802b6 (diff)
merge: refuse to create too cool a merge by default
While it makes sense to allow merging unrelated histories of two projects that started independently into one, in the way "gitk" was merged to "git" itself aka "the coolest merge ever", such a merge is still an unusual event. Worse, if somebody creates an independent history by starting from a tarball of an established project and sends a pull request to the original project, "git merge" however happily creates such a merge without any sign of something unusual is happening. Teach "git merge" to refuse to create such a merge by default, unless the user passes a new "--allow-unrelated-histories" option to tell it that the user is aware that two unrelated projects are merged. Because such a "two project merge" is a rare event, a configuration option to always allow such a merge is not added. We could add the same option to "git pull" and have it passed through to underlying "git merge". I do not have a fundamental opposition against such a feature, but this commit does not do so and instead leaves it as low-hanging fruit for others, because such a "two project merge" would be done after fetching the other project into some location in the working tree of an existing project and making sure how well they fit together, it is sufficient to allow a local merge without such an option pass-through from "git pull" to "git merge". Many tests that are updated by this patch does the pass-through manually by turning: git pull something into its equivalent: git fetch something && git merge --allow-unrelated-histories FETCH_HEAD If somebody is inclined to add such an option, updated tests in this change need to be adjusted back to: git pull --allow-unrelated-histories something Signed-off-by: Junio C Hamano <>
Diffstat (limited to 'builtin')
1 files changed, 9 insertions, 3 deletions
diff --git a/builtin/merge.c b/builtin/merge.c
index 101ffef..e3db41b 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -64,6 +64,7 @@ static int option_renormalize;
static int verbosity;
static int allow_rerere_auto;
static int abort_current_merge;
+static int allow_unrelated_histories;
static int show_progress = -1;
static int default_to_upstream = 1;
static const char *sign_commit;
@@ -221,6 +222,8 @@ static struct option builtin_merge_options[] = {
OPT_BOOL(0, "abort", &abort_current_merge,
N_("abort the current in-progress merge")),
+ OPT_BOOL(0, "allow-unrelated-histories", &allow_unrelated_histories,
+ N_("allow merging unrelated histories")),
OPT_SET_INT(0, "progress", &show_progress, N_("force progress reporting"), 1),
{ OPTION_STRING, 'S', "gpg-sign", &sign_commit, N_("key-id"),
N_("GPG sign commit"), PARSE_OPT_OPTARG, NULL, (intptr_t) "" },
@@ -1397,9 +1400,12 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
update_ref("updating ORIG_HEAD", "ORIG_HEAD", head_commit->object.oid.hash,
- if (remoteheads && !common)
- ; /* No common ancestors found. We need a real merge. */
- else if (!remoteheads ||
+ if (remoteheads && !common) {
+ /* No common ancestors found. */
+ if (!allow_unrelated_histories)
+ die(_("refusing to merge unrelated histories"));
+ /* otherwise, we need a real merge. */
+ } else if (!remoteheads ||
(!remoteheads->next && !common->next &&
common->item == remoteheads->item)) {