grep: add --heading

With --heading, the filename is printed once before matches from that
file instead of at the start of each line, giving more screen space to
the actual search results.

This option is taken from ack (http://betterthangrep.com/).  And now
git grep can dress up like it:

	$ git config alias.ack "grep --break --heading --line-number"

	$ git ack -e --heading
	Documentation/git-grep.txt
	154:--heading::

	t/t7810-grep.sh
	785:test_expect_success 'grep --heading' '
	786:    git grep --heading -e char -e lo_w hello.c hello_world >actual &&
	808:    git grep --break --heading -n --color \

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/grep.c b/grep.c
index b0b860a98..04e9ba4ec 100644
--- a/grep.c
+++ b/grep.c
@@ -735,9 +735,13 @@ static void show_line(struct grep_opt *opt, char *bol, char *eol,
 			opt->output(opt, "\n", 1);
 		}
 	}
+	if (opt->heading && opt->last_shown == 0) {
+		output_color(opt, name, strlen(name), opt->color_filename);
+		opt->output(opt, "\n", 1);
+	}
 	opt->last_shown = lno;
 
-	if (opt->pathname) {
+	if (!opt->heading && opt->pathname) {
 		output_color(opt, name, strlen(name), opt->color_filename);
 		output_sep(opt, sign);
 	}