[PATCH v2] merge: Run commit-msg hook

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From: Orgad Shaneh <orgads@gmail.com>

commit-msg is needed to either validate the commit message or edit it.

Gerrit for instance uses this hook to append its Change-Id footer. The
hook is installed on the user's machine, and it is expected to append
the footer for each commit that the user creates.

This is relevant to merge commit just like any other commit. Currently
this hook is only called for simple commits, so Gerrit user that tries
to push a merge commit has to amend it first in order to execute the
hook that appends the footer.

prepare-commit-msg hook is already called on merge, but commit-msg isn't.
It looks like unlike pre-commit not being executed, which was a conscious
decision[1], commit-msg was never considered.

[1] http://thread.gmane.org/gmane.comp.version-control.git/151297/focus=151435

Signed-off-by: Orgad Shaneh <orgads@gmail.com>
---
 Documentation/git-merge.txt | 6 +++++-
 builtin/merge.c             | 7 ++++++-
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/Documentation/git-merge.txt b/Documentation/git-merge.txt
index b758d55..59508aa 100644
--- a/Documentation/git-merge.txt
+++ b/Documentation/git-merge.txt
@@ -11,7 +11,7 @@ SYNOPSIS
 [verse]
 'git merge' [-n] [--stat] [--no-commit] [--squash] [--[no-]edit]
 	[-s <strategy>] [-X <strategy-option>] [-S[<keyid>]]
-	[--[no-]allow-unrelated-histories]
+	[--[no-]allow-unrelated-histories] [--no-verify]
 	[--[no-]rerere-autoupdate] [-m <msg>] [<commit>...]
 'git merge' <msg> HEAD <commit>...
 'git merge' --abort
@@ -87,6 +87,10 @@ invocations. The automated message can include the branch description.
 	Allow the rerere mechanism to update the index with the
 	result of auto-conflict resolution if possible.
 
+--no-verify::
+	This option bypasses the commit-msg hook.
+	See also linkgit:githooks[5].
+
 --abort::
 	Abort the current conflict resolution process, and
 	try to reconstruct the pre-merge state.
diff --git a/builtin/merge.c b/builtin/merge.c
index b555a1b..30c03c8 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -51,7 +51,7 @@ static const char * const builtin_merge_usage[] = {
 static int show_diffstat = 1, shortlog_len = -1, squash;
 static int option_commit = 1;
 static int option_edit = -1;
-static int allow_trivial = 1, have_message, verify_signatures;
+static int allow_trivial = 1, have_message, verify_signatures, no_verify;
 static int overwrite_ignore = 1;
 static struct strbuf merge_msg = STRBUF_INIT;
 static struct strategy **use_strategies;
@@ -228,6 +228,7 @@ static struct option builtin_merge_options[] = {
 	{ OPTION_STRING, 'S', "gpg-sign", &sign_commit, N_("key-id"),
 	  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, "no-verify", &no_verify, N_("bypass commit-msg hook")),
 	OPT_END()
 };
 
@@ -809,6 +810,10 @@ static void prepare_to_commit(struct commit_list *remoteheads)
 		if (launch_editor(git_path_merge_msg(), NULL, NULL))
 			abort_commit(remoteheads, NULL);
 	}
+	if (!no_verify &&
+	    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)
-- 
2.8.1