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>

1 files changed, 155 insertions, 0 deletions

diff --git a/t/t7505-prepare-commit-msg-hook.sh b/t/t7505-prepare-commit-msg-hook.sh
new file mode 100755
index 000000000..7ddec99a6
--- /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