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, 37 insertions, 0 deletions

diff --git a/t/t7810-grep.sh b/t/t7810-grep.sh
index f55793e..1227fa6 100755
--- a/t/t7810-grep.sh
+++ b/t/t7810-grep.sh
@@ -774,4 +774,41 @@ test_expect_success 'grep --break with context' '
 	test_cmp expected actual
 '
 
+cat >expected <<EOF
+hello.c
+int main(int argc, const char **argv)
+	/* char ?? */
+hello_world
+Hello_world
+EOF
+
+test_expect_success 'grep --heading' '
+	git grep --heading -e char -e lo_w hello.c hello_world >actual &&
+	test_cmp expected actual
+'
+
+cat >expected <<EOF
+<BOLD;GREEN>hello.c<RESET>
+2:int main(int argc, const <BLACK;BYELLOW>char<RESET> **argv)
+6:	/* <BLACK;BYELLOW>char<RESET> ?? */
+
+<BOLD;GREEN>hello_world<RESET>
+3:Hel<BLACK;BYELLOW>lo_w<RESET>orld
+EOF
+
+test_expect_success 'mimic ack-grep --group' '
+	test_config color.grep.context		normal &&
+	test_config color.grep.filename		"bold green" &&
+	test_config color.grep.function		normal &&
+	test_config color.grep.linenumber	normal &&
+	test_config color.grep.match		"black yellow" &&
+	test_config color.grep.selected		normal &&
+	test_config color.grep.separator	normal &&
+
+	git grep --break --heading -n --color \
+		-e char -e lo_w hello.c hello_world |
+	test_decode_color >actual &&
+	test_cmp expected actual
+'
+
 test_done