builtin/merge: honor commit-msg hook for merges

Similar to 65969d4 (merge: honor prepare-commit-msg hook, 2011-02-14)
merge should also honor the commit-msg hook: When a merge is stopped due
to conflicts or --no-commit, the subsequent commit calls the commit-msg
hook.  However, it is not called after a clean merge. Fix this
inconsistency by invoking the hook after clean merges as well.

This change is motivated by Gerrit's commit-msg hook to install a ChangeId
trailer into the commit message. Without such a ChangeId, Gerrit refuses
to accept any commit by default, such that the inconsistency of (not)
running the commit-msg hook between commit and merge leads to confusion
and might block people from getting their work done.

As the githooks man page is very vocal about the possibility of skipping
the commit-msg hook via the --no-verify option, implement the option
in merge, too.

'git merge --continue' is currently implemented as calling cmd_commit
with no further arguments. This works for most other merge related options,
such as demonstrated via the --allow-unrelated-histories flag in the
test. The --no-verify option however is not remembered across invocations
of git-merge. Originally the author assumed an alternative in which the
'git merge --continue' command accepts the --no-verify flag, but that
opens up the discussion which flags are allows to the continued merge
command and which must be given in the first invocation.

Signed-off-by: Stefan Beller <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: stefanbeller

builtin/merge.c

@@ -73,6 +73,7 @@ static int show_progress = -1;
 static int default_to_upstream = 1;
 static int signoff;
 static const char *sign_commit;
+static int verify_msg = 1;
 
 static struct strategy all_strategy[] = {
 	{ "recursive",  DEFAULT_TWOHEAD | NO_TRIVIAL },
@@ -236,6 +237,7 @@ static struct option builtin_merge_options[] = {
 	  N_("GPG sign commit"), PARSE_OPT_OPTARG, NULL, (intptr_t) "" },
 	OPT_BOOL(0, "overwrite-ignore", &overwrite_ignore, N_("update ignored files (default)")),
 	OPT_BOOL(0, "signoff", &signoff, N_("add Signed-off-by:")),
+	OPT_BOOL(0, "verify", &verify_msg, N_("verify commit-msg hook")),
 	OPT_END()
 };
 
@@ -780,6 +782,12 @@ static void prepare_to_commit(struct commit_list *remoteheads)
 		if (launch_editor(git_path_merge_msg(), NULL, NULL))
 			abort_commit(remoteheads, NULL);
 	}
+
+	if (verify_msg && run_commit_hook(0 < option_edit, get_index_file(),
+					  "commit-msg",
+					  git_path_merge_msg(), NULL))
+		abort_commit(remoteheads, NULL);
+
 	read_merge_msg(&msg);
 	strbuf_stripspace(&msg, 0 < option_edit);
 	if (!msg.len)

t/t7504-commit-msg-hook.sh

@@ -101,6 +101,10 @@ cat > "$HOOK" <<EOF
 exit 1
 EOF
 
+commit_msg_is () {
+	test "$(git log --pretty=format:%s%b -1)" = "$1"
+}
+
 test_expect_success 'with failing hook' '
 
 	echo "another" >> file &&
@@ -135,6 +139,32 @@ test_expect_success '--no-verify with failing hook (editor)' '
 
 '
 
+test_expect_success 'merge fails with failing hook' '
+
+	test_when_finished "git branch -D newbranch" &&
+	test_when_finished "git checkout -f master" &&
+	git checkout --orphan newbranch &&
+	: >file2 &&
+	git add file2 &&
+	git commit --no-verify file2 -m in-side-branch &&
+	test_must_fail git merge --allow-unrelated-histories master &&
+	commit_msg_is "in-side-branch" # HEAD before merge
+
+'
+
+test_expect_success 'merge bypasses failing hook with --no-verify' '
+
+	test_when_finished "git branch -D newbranch" &&
+	test_when_finished "git checkout -f master" &&
+	git checkout --orphan newbranch &&
+	: >file2 &&
+	git add file2 &&
+	git commit --no-verify file2 -m in-side-branch &&
+	git merge --no-verify --allow-unrelated-histories master &&
+	commit_msg_is "Merge branch '\''master'\'' into newbranch"
+'
+
+
 chmod -x "$HOOK"
 test_expect_success POSIXPERM 'with non-executable hook' '
 
@@ -178,10 +208,6 @@ exit 0
 EOF
 chmod +x "$HOOK"
 
-commit_msg_is () {
-	test "$(git log --pretty=format:%s%b -1)" = "$1"
-}
-
 test_expect_success 'hook edits commit message' '
 
 	echo "additional" >> file &&
@@ -217,7 +243,36 @@ test_expect_success "hook doesn't edit commit message (editor)" '
 	echo "more plus" > FAKE_MSG &&
 	GIT_EDITOR="\"\$FAKE_EDITOR\"" git commit --no-verify &&
 	commit_msg_is "more plus"
+'
 
+test_expect_success 'hook called in git-merge picks up commit message' '
+	test_when_finished "git branch -D newbranch" &&
+	test_when_finished "git checkout -f master" &&
+	git checkout --orphan newbranch &&
+	: >file2 &&
+	git add file2 &&
+	git commit --no-verify file2 -m in-side-branch &&
+	git merge --allow-unrelated-histories master &&
+	commit_msg_is "new message"
+'
+
+test_expect_failure 'merge --continue remembers --no-verify' '
+	test_when_finished "git branch -D newbranch" &&
+	test_when_finished "git checkout -f master" &&
+	git checkout master &&
+	echo a >file2 &&
+	git add file2 &&
+	git commit --no-verify -m "add file2 to master" &&
+	git checkout -b newbranch master^ &&
+	echo b >file2 &&
+	git add file2 &&
+	git commit --no-verify file2 -m in-side-branch &&
+	git merge --no-verify -m not-rewritten-by-hook master &&
+	# resolve conflict:
+	echo c >file2 &&
+	git add file2 &&
+	git merge --continue &&
+	commit_msg_is not-rewritten-by-hook
 '
 
 # set up fake editor to replace `pick` by `reword`
@@ -237,4 +292,5 @@ test_expect_success 'hook is called for reword during `rebase -i`' '
 
 '
 
+
 test_done