commit -v: strip diffs and submodule shortlogs from the commit message

When using the '-v' option of "git commit" the diff added to the commit
message temporarily for editing is stripped off after the user exited the
editor by searching for "\ndiff --git " and truncating the commmit message
there if it is found.

But this approach has two problems:

- when the commit message itself contains a line starting with
  "diff --git" it will be truncated there prematurely; and

- when the "diff.submodule" setting is set to "log", the diff may
  start with "Submodule <hash1>..<hash2>", which will be left in
  the commit message while it shouldn't.

Fix that by introducing a special scissor separator line starting with the
comment character ('#' or the core.commentChar config if set) followed by
two lines describing what it is for. The scissor line - which will not be
translated - is used to reliably detect the start of the diff so it can be
chopped off from the commit message, no matter what the user enters there.

Turn a known test failure fixed by this change into a successful test;
also add one for a diff starting with a submodule log and another one for
proper handling of the comment char.

Reported-by: Ari Pollak <ari@debian.org>
Signed-off-by: Jens Lehmann <Jens.Lehmann@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

4 files changed, 58 insertions, 9 deletions

diff --git a/builtin/commit.c b/builtin/commit.c
index 6ab4605cf..fedb45af8 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -1505,7 +1505,7 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 	struct strbuf sb = STRBUF_INIT;
 	struct strbuf author_ident = STRBUF_INIT;
 	const char *index_file, *reflog_msg;
-	char *nl, *p;
+	char *nl;
 	unsigned char sha1[20];
 	struct ref_lock *ref_lock;
 	struct commit_list *parents = NULL, **pptr = &parents;
@@ -1601,11 +1601,8 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 	}
 
 	/* Truncate the message just before the diff, if any. */
-	if (verbose) {
-		p = strstr(sb.buf, "\ndiff --git ");
-		if (p != NULL)
-			strbuf_setlen(&sb, p - sb.buf + 1);
-	}
+	if (verbose)
+		wt_status_truncate_message_at_cut_line(&sb);
 
 	if (cleanup_mode != CLEANUP_NONE)
 		stripspace(&sb, cleanup_mode == CLEANUP_ALL);
diff --git a/t/t7507-commit-verbose.sh b/t/t7507-commit-verbose.sh
index da5bd3b5a..2ddf28c98 100755
--- a/t/t7507-commit-verbose.sh
+++ b/t/t7507-commit-verbose.sh
@@ -65,9 +65,35 @@ test_expect_success 'diff in message is retained without -v' '
 	check_message diff
 '
 
-test_expect_failure 'diff in message is retained with -v' '
+test_expect_success 'diff in message is retained with -v' '
 	git commit --amend -F diff -v &&
 	check_message diff
 '
 
+test_expect_success 'submodule log is stripped out too with -v' '
+	git config diff.submodule log &&
+	git submodule add ./. sub &&
+	git commit -m "sub added" &&
+	(
+		cd sub &&
+		echo "more" >>file &&
+		git commit -a -m "submodule commit"
+	) &&
+	(
+		GIT_EDITOR=cat &&
+		export GIT_EDITOR &&
+		test_must_fail git commit -a -v 2>err
+	) &&
+	test_i18ngrep "Aborting commit due to empty commit message." err
+'
+
+test_expect_success 'verbose diff is stripped out with set core.commentChar' '
+	(
+		GIT_EDITOR=cat &&
+		export GIT_EDITOR &&
+		test_must_fail git -c core.commentchar=";" commit -a -v 2>err
+	) &&
+	test_i18ngrep "Aborting commit due to empty commit message." err
+'
+
 test_done
diff --git a/wt-status.c b/wt-status.c
index b4e44baa2..85390b813 100644
--- a/wt-status.c
+++ b/wt-status.c
@@ -16,6 +16,9 @@
 #include "column.h"
 #include "strbuf.h"
 
+static char cut_line[] =
+"------------------------ >8 ------------------------\n";
+
 static char default_wt_status_colors[][COLOR_MAXLEN] = {
 	GIT_COLOR_NORMAL, /* WT_STATUS_HEADER */
 	GIT_COLOR_GREEN,  /* WT_STATUS_UPDATED */
@@ -767,6 +770,18 @@ conclude:
 	status_printf_ln(s, GIT_COLOR_NORMAL, "");
 }
 
+void wt_status_truncate_message_at_cut_line(struct strbuf *buf)
+{
+	const char *p;
+	struct strbuf pattern = STRBUF_INIT;
+
+	strbuf_addf(&pattern, "%c %s", comment_line_char, cut_line);
+	p = strstr(buf->buf, pattern.buf);
+	if (p && (p == buf->buf || p[-1] == '\n'))
+		strbuf_setlen(buf, p - buf->buf);
+	strbuf_release(&pattern);
+}
+
 static void wt_status_print_verbose(struct wt_status *s)
 {
 	struct rev_info rev;
@@ -787,10 +802,20 @@ static void wt_status_print_verbose(struct wt_status *s)
 	 * If we're not going to stdout, then we definitely don't
 	 * want color, since we are going to the commit message
 	 * file (and even the "auto" setting won't work, since it
-	 * will have checked isatty on stdout).
+	 * will have checked isatty on stdout). But we then do want
+	 * to insert the scissor line here to reliably remove the
+	 * diff before committing.
 	 */
-	if (s->fp != stdout)
+	if (s->fp != stdout) {
+		const char *explanation = _("Do not touch the line above.\nEverything below will be removed.");
+		struct strbuf buf = STRBUF_INIT;
+
 		rev.diffopt.use_color = 0;
+		fprintf(s->fp, "%c %s", comment_line_char, cut_line);
+		strbuf_add_commented_lines(&buf, explanation, strlen(explanation));
+		fputs(buf.buf, s->fp);
+		strbuf_release(&buf);
+	}
 	run_diff_index(&rev, 1);
 }
 
diff --git a/wt-status.h b/wt-status.h
index 6c29e6f5e..30a481258 100644
--- a/wt-status.h
+++ b/wt-status.h
@@ -91,6 +91,7 @@ struct wt_status_state {
 	unsigned char cherry_pick_head_sha1[20];
 };
 
+void wt_status_truncate_message_at_cut_line(struct strbuf *);
 void wt_status_prepare(struct wt_status *s);
 void wt_status_print(struct wt_status *s);
 void wt_status_collect(struct wt_status *s);