From 3473f3035d04957ca24d3ccc232f4263b26d6bb8 Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <bonzini@gnu.org>
Date: Tue, 5 Feb 2008 11:01:44 +0100
Subject: git-commit: support variable number of hook arguments

This is a preparatory patch to allow using run_hook for the
prepare-commit-msg hook.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin-commit.c b/builtin-commit.c
index c787bed..ec00134 100644
--- a/builtin-commit.c
+++ b/builtin-commit.c
@@ -343,6 +343,40 @@ static int run_status(FILE *fp, const char *index_file, const char *prefix, int
 	return s.commitable;
 }
 
+static int run_hook(const char *index_file, const char *name, ...)
+{
+	struct child_process hook;
+	const char *argv[10], *env[2];
+	char index[PATH_MAX];
+	va_list args;
+	int i;
+
+	va_start(args, name);
+	argv[0] = git_path("hooks/%s", name);
+	i = 0;
+	do {
+		if (++i >= ARRAY_SIZE(argv))
+			die ("run_hook(): too many arguments");
+		argv[i] = va_arg(args, const char *);
+	} while (argv[i]);
+	va_end(args);
+
+	snprintf(index, sizeof(index), "GIT_INDEX_FILE=%s", index_file);
+	env[0] = index;
+	env[1] = NULL;
+
+	if (access(argv[0], X_OK) < 0)
+		return 0;
+
+	memset(&hook, 0, sizeof(hook));
+	hook.argv = argv;
+	hook.no_stdin = 1;
+	hook.stdout_to_stderr = 1;
+	hook.env = env;
+
+	return run_command(&hook);
+}
+
 static const char sign_off_header[] = "Signed-off-by: ";
 
 static int prepare_log_message(const char *index_file, const char *prefix)
@@ -677,31 +711,6 @@ int cmd_status(int argc, const char **argv, const char *prefix)
 	return commitable ? 0 : 1;
 }
 
-static int run_hook(const char *index_file, const char *name, const char *arg)
-{
-	struct child_process hook;
-	const char *argv[3], *env[2];
-	char index[PATH_MAX];
-
-	argv[0] = git_path("hooks/%s", name);
-	argv[1] = arg;
-	argv[2] = NULL;
-	snprintf(index, sizeof(index), "GIT_INDEX_FILE=%s", index_file);
-	env[0] = index;
-	env[1] = NULL;
-
-	if (access(argv[0], X_OK) < 0)
-		return 0;
-
-	memset(&hook, 0, sizeof(hook));
-	hook.argv = argv;
-	hook.no_stdin = 1;
-	hook.stdout_to_stderr = 1;
-	hook.env = env;
-
-	return run_command(&hook);
-}
-
 static void print_summary(const char *prefix, const unsigned char *sha1)
 {
 	struct rev_info rev;
@@ -876,7 +885,7 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 		launch_editor(git_path(commit_editmsg), NULL, env);
 	}
 	if (!no_verify &&
-	    run_hook(index_file, "commit-msg", git_path(commit_editmsg))) {
+	    run_hook(index_file, "commit-msg", git_path(commit_editmsg), NULL)) {
 		rollback_index_files();
 		exit(1);
 	}
-- 
cgit v0.10.2-6-g49f6


From 406400ce4f69e79b544dd3539a71b85d99331820 Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <bonzini@gnu.org>
Date: Tue, 5 Feb 2008 11:01:45 +0100
Subject: git-commit: set GIT_EDITOR=: if editor will not be launched

This is a preparatory patch that provides a simple way for the future
prepare-commit-msg hook to discover if the editor will be launched.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/Documentation/hooks.txt b/Documentation/hooks.txt
index f110162..e8d80cf 100644
--- a/Documentation/hooks.txt
+++ b/Documentation/hooks.txt
@@ -61,6 +61,10 @@ The default 'pre-commit' hook, when enabled, catches introduction
 of lines with trailing whitespaces and aborts the commit when
 such a line is found.
 
+All the `git-commit` hooks are invoked with the environment
+variable `GIT_EDITOR=:` if the command will not bring up an editor
+to modify the commit message.
+
 commit-msg
 ----------
 
diff --git a/builtin-commit.c b/builtin-commit.c
index ec00134..90ddbae 100644
--- a/builtin-commit.c
+++ b/builtin-commit.c
@@ -599,6 +599,8 @@ static int parse_and_validate_options(int argc, const char *argv[],
 		use_editor = 0;
 	if (edit_flag)
 		use_editor = 1;
+	if (!use_editor)
+		setenv("GIT_EDITOR", ":", 1);
 
 	if (get_sha1("HEAD", head_sha1))
 		initial_commit = 1;
-- 
cgit v0.10.2-6-g49f6


From ec84bd000a89e657b36136ec927144cd13f26079 Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <bonzini@gnu.org>
Date: Tue, 5 Feb 2008 11:01:46 +0100
Subject: git-commit: Refactor creation of log message.

This patch moves the code of run_commit, up to writing the trees, editing
the message and running the commit-msg hook to prepare_log_message.  It also
renames the latter to prepare_to_commit.

This simplifies a little the code for the next patch.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin-commit.c b/builtin-commit.c
index 90ddbae..e8cb320 100644
--- a/builtin-commit.c
+++ b/builtin-commit.c
@@ -377,9 +377,17 @@ static int run_hook(const char *index_file, const char *name, ...)
 	return run_command(&hook);
 }
 
+static int is_a_merge(const unsigned char *sha1)
+{
+	struct commit *commit = lookup_commit(sha1);
+	if (!commit || parse_commit(commit))
+		die("could not parse HEAD commit");
+	return !!(commit->parents && commit->parents->next);
+}
+
 static const char sign_off_header[] = "Signed-off-by: ";
 
-static int prepare_log_message(const char *index_file, const char *prefix)
+static int prepare_to_commit(const char *index_file, const char *prefix)
 {
 	struct stat statbuf;
 	int commitable, saved_color_setting;
@@ -387,6 +395,9 @@ static int prepare_log_message(const char *index_file, const char *prefix)
 	char *buffer;
 	FILE *fp;
 
+	if (!no_verify && run_hook(index_file, "pre-commit", NULL))
+		return 0;
+
 	strbuf_init(&sb, 0);
 	if (message.len) {
 		strbuf_addbuf(&sb, &message);
@@ -447,13 +458,38 @@ static int prepare_log_message(const char *index_file, const char *prefix)
 
 	strbuf_release(&sb);
 
-	if (!use_editor) {
+	if (use_editor) {
+		if (in_merge)
+			fprintf(fp,
+				"#\n"
+				"# It looks like you may be committing a MERGE.\n"
+				"# If this is not correct, please remove the file\n"
+				"#	%s\n"
+				"# and try again.\n"
+				"#\n",
+				git_path("MERGE_HEAD"));
+
+		fprintf(fp,
+			"\n"
+			"# Please enter the commit message for your changes.\n"
+			"# (Comment lines starting with '#' will ");
+		if (cleanup_mode == CLEANUP_ALL)
+			fprintf(fp, "not be included)\n");
+		else /* CLEANUP_SPACE, that is. */
+			fprintf(fp, "be kept.\n"
+				"# You can remove them yourself if you want to)\n");
+		if (only_include_assumed)
+			fprintf(fp, "# %s\n", only_include_assumed);
+
+		saved_color_setting = wt_status_use_color;
+		wt_status_use_color = 0;
+		commitable = run_status(fp, index_file, prefix, 1);
+		wt_status_use_color = saved_color_setting;
+	} else {
 		struct rev_info rev;
 		unsigned char sha1[20];
 		const char *parent = "HEAD";
 
-		fclose(fp);
-
 		if (!active_nr && read_cache() < 0)
 			die("Cannot read index");
 
@@ -461,48 +497,56 @@ static int prepare_log_message(const char *index_file, const char *prefix)
 			parent = "HEAD^1";
 
 		if (get_sha1(parent, sha1))
-			return !!active_nr;
+			commitable = !!active_nr;
+		else {
+			init_revisions(&rev, "");
+			rev.abbrev = 0;
+			setup_revisions(0, NULL, &rev, parent);
+			DIFF_OPT_SET(&rev.diffopt, QUIET);
+			DIFF_OPT_SET(&rev.diffopt, EXIT_WITH_STATUS);
+			run_diff_index(&rev, 1 /* cached */);
+
+			commitable = !!DIFF_OPT_TST(&rev.diffopt, HAS_CHANGES);
+		}
+	}
 
-		init_revisions(&rev, "");
-		rev.abbrev = 0;
-		setup_revisions(0, NULL, &rev, parent);
-		DIFF_OPT_SET(&rev.diffopt, QUIET);
-		DIFF_OPT_SET(&rev.diffopt, EXIT_WITH_STATUS);
-		run_diff_index(&rev, 1 /* cached */);
+	fclose(fp);
+
+	if (!commitable && !in_merge && !allow_empty &&
+	    !(amend && is_a_merge(head_sha1))) {
+		run_status(stdout, index_file, prefix, 0);
+		unlink(commit_editmsg);
+		return 0;
+	}
 
-		return !!DIFF_OPT_TST(&rev.diffopt, HAS_CHANGES);
+	/*
+	 * Re-read the index as pre-commit hook could have updated it,
+	 * and write it out as a tree.  We must do this before we invoke
+	 * the editor and after we invoke run_status above.
+	 */
+	discard_cache();
+	read_cache_from(index_file);
+	if (!active_cache_tree)
+		active_cache_tree = cache_tree();
+	if (cache_tree_update(active_cache_tree,
+			      active_cache, active_nr, 0, 0) < 0) {
+		error("Error building trees");
+		return 0;
 	}
 
-	if (in_merge)
-		fprintf(fp,
-			"#\n"
-			"# It looks like you may be committing a MERGE.\n"
-			"# If this is not correct, please remove the file\n"
-			"#	%s\n"
-			"# and try again.\n"
-			"#\n",
-			git_path("MERGE_HEAD"));
-
-	fprintf(fp,
-		"\n"
-		"# Please enter the commit message for your changes.\n"
-		"# (Comment lines starting with '#' will ");
-	if (cleanup_mode == CLEANUP_ALL)
-		fprintf(fp, "not be included)\n");
-	else /* CLEANUP_SPACE, that is. */
-		fprintf(fp, "be kept.\n"
-			"# You can remove them yourself if you want to)\n");
-	if (only_include_assumed)
-		fprintf(fp, "# %s\n", only_include_assumed);
-
-	saved_color_setting = wt_status_use_color;
-	wt_status_use_color = 0;
-	commitable = run_status(fp, index_file, prefix, 1);
-	wt_status_use_color = saved_color_setting;
+	if (use_editor) {
+		char index[PATH_MAX];
+		const char *env[2] = { index, NULL };
+		snprintf(index, sizeof(index), "GIT_INDEX_FILE=%s", index_file);
+		launch_editor(git_path(commit_editmsg), NULL, env);
+	}
 
-	fclose(fp);
+	if (!no_verify &&
+	    run_hook(index_file, "commit-msg", git_path(commit_editmsg), NULL)) {
+		return 0;
+	}
 
-	return commitable;
+	return 1;
 }
 
 /*
@@ -761,14 +805,6 @@ int git_commit_config(const char *k, const char *v)
 	return git_status_config(k, v);
 }
 
-static int is_a_merge(const unsigned char *sha1)
-{
-	struct commit *commit = lookup_commit(sha1);
-	if (!commit || parse_commit(commit))
-		die("could not parse HEAD commit");
-	return !!(commit->parents && commit->parents->next);
-}
-
 static const char commit_utf8_warn[] =
 "Warning: commit message does not conform to UTF-8.\n"
 "You may want to amend it after fixing the message, or set the config\n"
@@ -800,34 +836,14 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 
 	index_file = prepare_index(argc, argv, prefix);
 
-	if (!no_verify && run_hook(index_file, "pre-commit", NULL)) {
-		rollback_index_files();
-		return 1;
-	}
-
-	if (!prepare_log_message(index_file, prefix) && !in_merge &&
-	    !allow_empty && !(amend && is_a_merge(head_sha1))) {
-		run_status(stdout, index_file, prefix, 0);
+	/* Set up everything for writing the commit object.  This includes
+	   running hooks, writing the trees, and interacting with the user.  */
+	if (!prepare_to_commit(index_file, prefix)) {
 		rollback_index_files();
-		unlink(commit_editmsg);
 		return 1;
 	}
 
 	/*
-	 * Re-read the index as pre-commit hook could have updated it,
-	 * and write it out as a tree.
-	 */
-	discard_cache();
-	read_cache_from(index_file);
-	if (!active_cache_tree)
-		active_cache_tree = cache_tree();
-	if (cache_tree_update(active_cache_tree,
-			      active_cache, active_nr, 0, 0) < 0) {
-		rollback_index_files();
-		die("Error building trees");
-	}
-
-	/*
 	 * The commit object
 	 */
 	strbuf_init(&sb, 0);
@@ -878,19 +894,8 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 		strbuf_addf(&sb, "encoding %s\n", git_commit_encoding);
 	strbuf_addch(&sb, '\n');
 
-	/* Get the commit message and validate it */
+	/* Finally, get the commit message */
 	header_len = sb.len;
-	if (use_editor) {
-		char index[PATH_MAX];
-		const char *env[2] = { index, NULL };
-		snprintf(index, sizeof(index), "GIT_INDEX_FILE=%s", index_file);
-		launch_editor(git_path(commit_editmsg), NULL, env);
-	}
-	if (!no_verify &&
-	    run_hook(index_file, "commit-msg", git_path(commit_editmsg), NULL)) {
-		rollback_index_files();
-		exit(1);
-	}
 	if (strbuf_read_file(&sb, git_path(commit_editmsg), 0) < 0) {
 		rollback_index_files();
 		die("could not read commit message");
diff --git a/t/t7502-commit.sh b/t/t7502-commit.sh
index aaf497e..b780fdd 100755
--- a/t/t7502-commit.sh
+++ b/t/t7502-commit.sh
@@ -154,4 +154,33 @@ test_expect_success 'cleanup commit messages (strip,-F,-e)' '
 
 '
 
+pwd=`pwd`
+cat >> .git/FAKE_EDITOR << EOF
+#! /bin/sh
+echo editor started > "$pwd/.git/result"
+exit 0
+EOF
+chmod +x .git/FAKE_EDITOR
+
+test_expect_success 'do not fire editor in the presence of conflicts' '
+
+	git clean
+	echo f>g
+	git add g
+	git commit -myes
+	git branch second
+	echo master>g
+	echo g>h
+	git add g h
+	git commit -mmaster
+	git checkout second
+	echo second>g
+	git add g
+	git commit -msecond
+	git cherry-pick -n master
+	echo "editor not started" > .git/result
+	GIT_EDITOR=`pwd`/.git/FAKE_EDITOR git commit && exit 1  # should fail
+	test "`cat .git/result`" = "editor not started"
+'
+
 test_done
-- 
cgit v0.10.2-6-g49f6


From 8089c85bcba89464b9b2a32fa948ed85eb367e70 Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <bonzini@gnu.org>
Date: Tue, 5 Feb 2008 08:04:18 +0100
Subject: git-commit: add a prepare-commit-msg hook

The prepare-commit-msg hook is run whenever a "fresh" commit message
is prepared, just before it is shown in the editor (if it is).
Its purpose is to modify the commit message in-place.

It takes one to three parameters.  The first is the name of the file that
the commit log message.  The second is the source of the commit message,
and can be: "message" (if a -m or -F option was given); "template" (if a
-t option was given or the configuration option commit.template is set);
"merge" (if the commit is a merge or a .git/MERGE_MSG file exists);
"squash" (if a .git/SQUASH_MSG file exists); or "commit", followed by
a commit SHA1 as the third parameter (if a -c, -C or --amend option
was given).

If its exit status is non-zero, git-commit will abort.  The hook is
not suppressed by the --no-verify option, so it should not be used
as a replacement for the pre-commit hook.

The sample prepare-commit-msg comments out the `Conflicts:` part of
a merge's commit message; other examples are commented out, including
adding a Signed-off-by line at the bottom of the commit messsage,
that the user can then edit or discard altogether.

Signed-off-by: Paolo Bonzini <bonzini@gnu.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/Documentation/git-commit.txt b/Documentation/git-commit.txt
index c3725b2..b4ae61f 100644
--- a/Documentation/git-commit.txt
+++ b/Documentation/git-commit.txt
@@ -280,8 +280,8 @@ order).
 
 HOOKS
 -----
-This command can run `commit-msg`, `pre-commit`, and
-`post-commit` hooks.  See link:hooks.html[hooks] for more
+This command can run `commit-msg`, `prepare-commit-msg`, `pre-commit`,
+and `post-commit` hooks.  See link:hooks.html[hooks] for more
 information.
 
 
diff --git a/Documentation/hooks.txt b/Documentation/hooks.txt
index e8d80cf..76b8d77 100644
--- a/Documentation/hooks.txt
+++ b/Documentation/hooks.txt
@@ -65,6 +65,31 @@ All the `git-commit` hooks are invoked with the environment
 variable `GIT_EDITOR=:` if the command will not bring up an editor
 to modify the commit message.
 
+prepare-commit-msg
+------------------
+
+This hook is invoked by `git-commit` right after preparing the
+default log message, and before the editor is started.
+
+It takes one to three parameters.  The first is the name of the file
+that the commit log message.  The second is the source of the commit
+message, and can be: `message` (if a `\-m` or `\-F` option was
+given); `template` (if a `\-t` option was given or the
+configuration option `commit.template` is set); `merge` (if the
+commit is a merge or a `.git/MERGE_MSG` file exists); `squash`
+(if a `.git/SQUASH_MSG` file exists); or `commit`, followed by
+a commit SHA1 (if a `\-c`, `\-C` or `\--amend` option was given).
+
+If the exit status is non-zero, `git-commit` will abort.
+
+The purpose of the hook is to edit the message file in place, and
+it is not suppressed by the `\--no-verify` option.  A non-zero exit
+means a failure of the hook and aborts the commit.  It should not
+be used as replacement for pre-commit hook.
+
+The sample `prepare-commit-msg` hook that comes with git comments
+out the `Conflicts:` part of a merge's commit message.
+
 commit-msg
 ----------
 
diff --git a/builtin-commit.c b/builtin-commit.c
index e8cb320..03caa30 100644
--- a/builtin-commit.c
+++ b/builtin-commit.c
@@ -394,6 +394,8 @@ static int prepare_to_commit(const char *index_file, const char *prefix)
 	struct strbuf sb;
 	char *buffer;
 	FILE *fp;
+	const char *hook_arg1 = NULL;
+	const char *hook_arg2 = NULL;
 
 	if (!no_verify && run_hook(index_file, "pre-commit", NULL))
 		return 0;
@@ -401,32 +403,47 @@ static int prepare_to_commit(const char *index_file, const char *prefix)
 	strbuf_init(&sb, 0);
 	if (message.len) {
 		strbuf_addbuf(&sb, &message);
+		hook_arg1 = "message";
 	} else if (logfile && !strcmp(logfile, "-")) {
 		if (isatty(0))
 			fprintf(stderr, "(reading log message from standard input)\n");
 		if (strbuf_read(&sb, 0, 0) < 0)
 			die("could not read log from standard input");
+		hook_arg1 = "message";
 	} else if (logfile) {
 		if (strbuf_read_file(&sb, logfile, 0) < 0)
 			die("could not read log file '%s': %s",
 			    logfile, strerror(errno));
+		hook_arg1 = "message";
 	} else if (use_message) {
 		buffer = strstr(use_message_buffer, "\n\n");
 		if (!buffer || buffer[2] == '\0')
 			die("commit has empty message");
 		strbuf_add(&sb, buffer + 2, strlen(buffer + 2));
+		hook_arg1 = "commit";
+		hook_arg2 = use_message;
 	} else if (!stat(git_path("MERGE_MSG"), &statbuf)) {
 		if (strbuf_read_file(&sb, git_path("MERGE_MSG"), 0) < 0)
 			die("could not read MERGE_MSG: %s", strerror(errno));
+		hook_arg1 = "merge";
 	} else if (!stat(git_path("SQUASH_MSG"), &statbuf)) {
 		if (strbuf_read_file(&sb, git_path("SQUASH_MSG"), 0) < 0)
 			die("could not read SQUASH_MSG: %s", strerror(errno));
+		hook_arg1 = "squash";
 	} else if (template_file && !stat(template_file, &statbuf)) {
 		if (strbuf_read_file(&sb, template_file, 0) < 0)
 			die("could not read %s: %s",
 			    template_file, strerror(errno));
+		hook_arg1 = "template";
 	}
 
+	/*
+	 * This final case does not modify the template message,
+	 * it just sets the argument to the prepare-commit-msg hook.
+	 */
+	else if (in_merge)
+		hook_arg1 = "merge";
+
 	fp = fopen(git_path(commit_editmsg), "w");
 	if (fp == NULL)
 		die("could not open %s", git_path(commit_editmsg));
@@ -534,6 +551,10 @@ static int prepare_to_commit(const char *index_file, const char *prefix)
 		return 0;
 	}
 
+	if (run_hook(index_file, "prepare-commit-msg",
+		     git_path(commit_editmsg), hook_arg1, hook_arg2, NULL))
+		return 0;
+
 	if (use_editor) {
 		char index[PATH_MAX];
 		const char *env[2] = { index, NULL };
diff --git a/t/t7505-prepare-commit-msg-hook.sh b/t/t7505-prepare-commit-msg-hook.sh
new file mode 100755
index 0000000..7ddec99
--- /dev/null
+++ b/t/t7505-prepare-commit-msg-hook.sh
@@ -0,0 +1,155 @@
+#!/bin/sh
+
+test_description='prepare-commit-msg hook'
+
+. ./test-lib.sh
+
+test_expect_success 'with no hook' '
+
+	echo "foo" > file &&
+	git add file &&
+	git commit -m "first"
+
+'
+
+# set up fake editor for interactive editing
+cat > fake-editor <<'EOF'
+#!/bin/sh
+exit 0
+EOF
+chmod +x fake-editor
+FAKE_EDITOR="$(pwd)/fake-editor"
+export FAKE_EDITOR
+
+# now install hook that always succeeds and adds a message
+HOOKDIR="$(git rev-parse --git-dir)/hooks"
+HOOK="$HOOKDIR/prepare-commit-msg"
+mkdir -p "$HOOKDIR"
+cat > "$HOOK" <<'EOF'
+#!/bin/sh
+if test "$2" = commit; then
+  source=$(git-rev-parse "$3")
+else
+  source=${2-default}
+fi
+if test "$GIT_EDITOR" = :; then
+  sed -e "1s/.*/$source (no editor)/" "$1" > msg.tmp
+else
+  sed -e "1s/.*/$source/" "$1" > msg.tmp
+fi
+mv msg.tmp "$1"
+exit 0
+EOF
+chmod +x "$HOOK"
+
+echo dummy template > "$(git rev-parse --git-dir)/template"
+
+test_expect_success 'with hook (-m)' '
+
+	echo "more" >> file &&
+	git add file &&
+	git commit -m "more" &&
+	test "`git log -1 --pretty=format:%s`" = "message (no editor)"
+
+'
+
+test_expect_success 'with hook (-m editor)' '
+
+	echo "more" >> file &&
+	git add file &&
+	GIT_EDITOR="$FAKE_EDITOR" git commit -e -m "more more" &&
+	test "`git log -1 --pretty=format:%s`" = message
+
+'
+
+test_expect_success 'with hook (-t)' '
+
+	echo "more" >> file &&
+	git add file &&
+	git commit -t "$(git rev-parse --git-dir)/template" &&
+	test "`git log -1 --pretty=format:%s`" = template
+
+'
+
+test_expect_success 'with hook (-F)' '
+
+	echo "more" >> file &&
+	git add file &&
+	(echo more | git commit -F -) &&
+	test "`git log -1 --pretty=format:%s`" = "message (no editor)"
+
+'
+
+test_expect_success 'with hook (-F editor)' '
+
+	echo "more" >> file &&
+	git add file &&
+	(echo more more | GIT_EDITOR="$FAKE_EDITOR" git commit -e -F -) &&
+	test "`git log -1 --pretty=format:%s`" = message
+
+'
+
+test_expect_success 'with hook (-C)' '
+
+	head=`git rev-parse HEAD` &&
+	echo "more" >> file &&
+	git add file &&
+	git commit -C $head &&
+	test "`git log -1 --pretty=format:%s`" = "$head (no editor)"
+
+'
+
+test_expect_success 'with hook (editor)' '
+
+	echo "more more" >> file &&
+	git add file &&
+	GIT_EDITOR="$FAKE_EDITOR" git commit &&
+	test "`git log -1 --pretty=format:%s`" = default
+
+'
+
+test_expect_success 'with hook (--amend)' '
+
+	head=`git rev-parse HEAD` &&
+	echo "more" >> file &&
+	git add file &&
+	GIT_EDITOR="$FAKE_EDITOR" git commit --amend &&
+	test "`git log -1 --pretty=format:%s`" = "$head"
+
+'
+
+test_expect_success 'with hook (-c)' '
+
+	head=`git rev-parse HEAD` &&
+	echo "more" >> file &&
+	git add file &&
+	GIT_EDITOR="$FAKE_EDITOR" git commit -c $head &&
+	test "`git log -1 --pretty=format:%s`" = "$head"
+
+'
+
+cat > "$HOOK" <<'EOF'
+#!/bin/sh
+exit 1
+EOF
+
+test_expect_success 'with failing hook' '
+
+	head=`git rev-parse HEAD` &&
+	echo "more" >> file &&
+	git add file &&
+	! GIT_EDITOR="$FAKE_EDITOR" git commit -c $head
+
+'
+
+test_expect_success 'with failing hook (--no-verify)' '
+
+	head=`git rev-parse HEAD` &&
+	echo "more" >> file &&
+	git add file &&
+	! GIT_EDITOR="$FAKE_EDITOR" git commit --no-verify -c $head
+
+'
+
+
+test_done
diff --git a/templates/hooks--commit-msg b/templates/hooks--commit-msg
index c5cdb9d..4ef86eb 100644
--- a/templates/hooks--commit-msg
+++ b/templates/hooks--commit-msg
@@ -9,6 +9,9 @@
 # To enable this hook, make this file executable.
 
 # Uncomment the below to add a Signed-off-by line to the message.
+# Doing this in a hook is a bad idea in general, but the prepare-commit-msg
+# hook is more suited to it.
+#
 # SOB=$(git var GIT_AUTHOR_IDENT | sed -n 's/^\(.*>\).*$/Signed-off-by: \1/p')
 # grep -qs "^$SOB" "$1" || echo "$SOB" >> "$1"
 
diff --git a/templates/hooks--prepare-commit-msg b/templates/hooks--prepare-commit-msg
new file mode 100644
index 0000000..ff0f42a
--- /dev/null
+++ b/templates/hooks--prepare-commit-msg
@@ -0,0 +1,36 @@
+#!/bin/sh
+#
+# An example hook script to prepare the commit log message.
+# Called by git-commit with the name of the file that has the
+# commit message, followed by the description of the commit
+# message's source.  The hook's purpose is to edit the commit
+# message file.  If the hook fails with a non-zero status,
+# the commit is aborted.
+#
+# To enable this hook, make this file executable.
+
+# This hook includes three examples.  The first comments out the
+# "Conflicts:" part of a merge commit.
+#
+# The second includes the output of "git diff --name-status -r"
+# into the message, just before the "git status" output.  It is
+# commented because it doesn't cope with --amend or with squashed
+# commits.
+#
+# The third example adds a Signed-off-by line to the message, that can
+# still be edited.  This is rarely a good idea.
+
+case "$2 $3" in
+  merge)
+    sed -i '/^Conflicts:/,/#/!b;s/^/# &/;s/^# #/#/' "$1" ;;
+
+# ""|template)
+#   perl -i -pe '
+#      print "\n" . `git diff --cached --name-status -r`
+#	 if /^#/ && $first++ == 0' "$1" ;;
+
+  *) ;;
+esac
+
+# SOB=$(git var GIT_AUTHOR_IDENT | sed -n 's/^\(.*>\).*$/Signed-off-by: \1/p')
+# grep -qs "^$SOB" "$1" || echo "$SOB" >> "$1"
-- 
cgit v0.10.2-6-g49f6