[PATCH-v2 4/4] git-commit: add a prepare-commit-msg hook

[Paolo Bonzini <bonzini@gnu.org>]

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).
It can modify the commit message in-place and/or abort the commit.

It takes two parameters.  The first 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 a commit SHA1 (if a
-c, -C or --amend option was given).  The second
parameter if the name of the file that the commit log message.

The hook is not suppressed by the --no-verify option, and the
exit status is ignored by git.

While the default hook just adds a Signed-off-by line at the bottom
of the commit messsage, the hook is more intended to build a template
for the commit message following project standards, that the user
can then edit or discard altogether.
---
 Documentation/git-commit.txt        |    4 +-
 Documentation/hooks.txt             |   32 ++++++++-
 builtin-commit.c                    |   16 ++++
 t/t7505-prepare-commit-msg-hook.sh  |  130 +++++++++++++++++++++++++++++++++++
 templates/hooks--commit-msg         |    3 +
 templates/hooks--prepare-commit-msg |   14 ++++
 6 files changed, 196 insertions(+), 3 deletions(-)
 create mode 100755 t/t7505-prepare-commit-msg-hook.sh
 create mode 100644 templates/hooks--prepare-commit-msg

	I removed tests that involved a failing hook, since the
	exit status is documented to be irrelevant.

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..02c8f9d 100644
--- a/Documentation/hooks.txt
+++ b/Documentation/hooks.txt
@@ -55,7 +55,8 @@ This hook is invoked by `git-commit`, and can be bypassed
 with `\--no-verify` option.  It takes no parameter, and is
 invoked before obtaining the proposed commit log message and
 making a commit.  Exiting with non-zero status from this script
-causes the `git-commit` to abort.
+causes the `git-commit` to abort.  This hook can also modify
+the index.
 
 The default 'pre-commit' hook, when enabled, catches introduction
 of lines with trailing whitespaces and aborts the commit when
@@ -65,6 +66,35 @@ 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 two parameters.  The first 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 a commit SHA1 (if a
+`\-c`, `\-C` or `\--amend` option was given).  The second
+parameter if the name of the file that the commit log message.
+
+The hook is not suppressed by the `\--no-verify` option, and
+the exit status is ignored by `git-commit`.
+
+The hook is allowed to edit the message file in place, and
+can be used to augment the default commit message with some
+project standard information.  It can also be used for the same
+purpose as the pre-commit message, if the verification has
+to be skipped for automatic commits (e.g. during rebasing).
+
+The default 'prepare-commit-msg' hook adds a Signed-off-by line
+(doing it with a hook is not necessarily a good idea, but doing
+it in 'commit-msg' is worse because you are not reminded in
+the editor).
+
 commit-msg
 ----------
 
diff --git a/builtin-commit.c b/builtin-commit.c
index d8945ac..3f2d3a4 100644
--- a/builtin-commit.c
+++ b/builtin-commit.c
@@ -394,6 +394,7 @@ static int prepare_to_commit(const char *index_file, const char *prefix)
 	struct strbuf sb;
 	char *buffer;
 	FILE *fp;
+	const char *hook_arg = NULL;
 
 	if (!no_verify && run_hook(index_file, "pre-commit", NULL))
 		return 0;
@@ -401,32 +402,44 @@ static int prepare_to_commit(const char *index_file, const char *prefix)
 	strbuf_init(&sb, 0);
 	if (message.len) {
 		strbuf_addbuf(&sb, &message);
+		hook_arg = "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_arg = "message";
 	} else if (logfile) {
 		if (strbuf_read_file(&sb, logfile, 0) < 0)
 			die("could not read log file '%s': %s",
 			    logfile, strerror(errno));
+		hook_arg = "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_arg = 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_arg = "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_arg = "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_arg = "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_arg = "merge";
+
 	fp = fopen(git_path(commit_editmsg), "w");
 	if (fp == NULL)
 		die("could not open %s", git_path(commit_editmsg));
@@ -534,6 +547,9 @@ static int prepare_to_commit(const char *index_file, const char *prefix)
 		return 0;
 	}
 
+	run_hook(index_file, "prepare-commit-msg",
+		 git_path(commit_editmsg), hook_arg, NULL);
+
 	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..440e197
--- /dev/null
+++ b/t/t7505-prepare-commit-msg-hook.sh
@@ -0,0 +1,130 @@
+#!/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" = HEAD; then
+  set "$1" $(git-rev-parse HEAD)
+fi
+if test "$GIT_EDITOR" = :; then
+  sed -e "1s/.*/${2-default} (no editor)/" "$1" > msg.tmp
+else
+  sed -e "1s/.*/${2-default}/" "$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"
+
+'
+
+
+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..176283b
--- /dev/null
+++ b/templates/hooks--prepare-commit-msg
@@ -0,0 +1,14 @@
+#!/bin/sh
+#
+# An example hook script to prepare the commit log message.
+# Called by git-commit with one argument, the name of the file
+# that has the commit message.  The hook should exit with non-zero
+# status after issuing an appropriate message if it wants to stop the
+# commit.  The hook is allowed to edit the commit message file.
+#
+# To enable this hook, make this file executable.
+
+# This example adds a Signed-off-by line to the message, that can
+# still be edited.
+SOB=$(git var GIT_AUTHOR_IDENT | sed -n 's/^\(.*>\).*$/Signed-off-by: \1/p')
+grep -qs "^$SOB" "$1" || echo "$SOB" >> "$1"
-- 
1.5.3.4.910.gc5122-dirty