merge: --no-verify to bypass pre-merge-commit hook

Analogous to commit, introduce a '--no-verify' option which bypasses the
pre-merge-commit hook. The shorthand '-n' is taken by '--no-stat'
already.

[js: * reworded commit message to reflect current state of --no-stat flag
       and new hook name
     * fixed flag documentation to reflect new hook name
     * cleaned up trailing whitespace
     * squashed test changes from the original series' patch 4/4
     * modified tests to follow pattern from this series' patch 1/4
     * added a test case for --no-verify with non-executable hook
     * when testing that the merge hook did not run, make sure we
       actually have a merge to perform (by resetting the "side" branch
       to its original state).

]

Improved-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Michael J Gruber <git@grubix.eu>
Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Josh Steadmon <steadmon@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/githooks.txt

@@ -106,7 +106,8 @@ the use of non-ASCII filenames.
 pre-merge-commit
 ~~~~~~~~~~~~~~~~
 
-This hook is invoked by linkgit:git-merge[1]. It takes no parameters, and is
+This hook is invoked by linkgit:git-merge[1], and can be bypassed
+with the `--no-verify` option.  It takes no parameters, and is
 invoked after the merge has been carried out successfully and before
 obtaining the proposed commit log message to
 make a commit.  Exiting with a non-zero status from this script

builtin/merge.c

@@ -287,7 +287,7 @@ 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, "no-verify", &no_verify, N_("bypass commit-msg hook")),
+	OPT_BOOL(0, "no-verify", &no_verify, N_("bypass pre-merge-commit and commit-msg hooks")),
 	OPT_END()
 };
 
@@ -818,7 +818,7 @@ static void prepare_to_commit(struct commit_list *remoteheads)
 	struct strbuf msg = STRBUF_INIT;
 	const char *index_file = get_index_file();
 
-	if (run_commit_hook(0 < option_edit, index_file, "pre-merge-commit", NULL))
+	if (!no_verify && run_commit_hook(0 < option_edit, index_file, "pre-merge-commit", NULL))
 		abort_commit(remoteheads, NULL);
 	/*
 	 * Re-read the index as pre-merge-commit hook could have updated it,

t/t7503-pre-commit-and-pre-merge-commit-hooks.sh

@@ -84,6 +84,15 @@ test_expect_success '--no-verify with no hook' '
 	test_path_is_missing actual_hooks
 '
 
+test_expect_success '--no-verify with no hook (merge)' '
+	test_when_finished "rm -f actual_hooks" &&
+	git branch -f side side-orig &&
+	git checkout side &&
+	git merge --no-verify -m "merge master" master &&
+	git checkout master &&
+	test_path_is_missing actual_hooks
+'
+
 test_expect_success 'with succeeding hook' '
 	test_when_finished "rm -f \"$PRECOMMIT\" expected_hooks actual_hooks" &&
 	cp "$HOOKDIR/success.sample" "$PRECOMMIT" &&
@@ -131,6 +140,16 @@ test_expect_success '--no-verify with succeeding hook' '
 	test_path_is_missing actual_hooks
 '
 
+test_expect_success '--no-verify with succeeding hook (merge)' '
+	test_when_finished "rm -f \"$PREMERGE\" actual_hooks" &&
+	cp "$HOOKDIR/success.sample" "$PREMERGE" &&
+	git branch -f side side-orig &&
+	git checkout side &&
+	git merge --no-verify -m "merge master" master &&
+	git checkout master &&
+	test_path_is_missing actual_hooks
+'
+
 test_expect_success 'with failing hook' '
 	test_when_finished "rm -f \"$PRECOMMIT\" expected_hooks actual_hooks" &&
 	cp "$HOOKDIR/fail.sample" "$PRECOMMIT" &&
@@ -160,6 +179,16 @@ test_expect_success 'with failing hook (merge)' '
 	test_cmp expected_hooks actual_hooks
 '
 
+test_expect_success '--no-verify with failing hook (merge)' '
+	test_when_finished "rm -f \"$PREMERGE\" actual_hooks" &&
+	cp "$HOOKDIR/fail.sample" "$PREMERGE" &&
+	git branch -f side side-orig &&
+	git checkout side &&
+	git merge --no-verify -m "merge master" master &&
+	git checkout master &&
+	test_path_is_missing actual_hooks
+'
+
 test_expect_success POSIXPERM 'with non-executable hook' '
 	test_when_finished "rm -f \"$PRECOMMIT\" actual_hooks" &&
 	cp "$HOOKDIR/non-exec.sample" "$PRECOMMIT" &&
@@ -188,6 +217,16 @@ test_expect_success POSIXPERM 'with non-executable hook (merge)' '
 	test_path_is_missing actual_hooks
 '
 
+test_expect_success POSIXPERM '--no-verify with non-executable hook (merge)' '
+	test_when_finished "rm -f \"$PREMERGE\" actual_hooks" &&
+	cp "$HOOKDIR/non-exec.sample" "$PREMERGE" &&
+	git branch -f side side-orig &&
+	git checkout side &&
+	git merge --no-verify -m "merge master" master &&
+	git checkout master &&
+	test_path_is_missing actual_hooks
+'
+
 test_expect_success 'with hook requiring GIT_PREFIX' '
 	test_when_finished "rm -rf \"$PRECOMMIT\" expected_hooks actual_hooks success" &&
 	cp "$HOOKDIR/require-prefix.sample" "$PRECOMMIT" &&