grep: add --break

With --break, an empty line is printed between matches from different
files, increasing readability.  This option is taken from ack
(http://betterthangrep.com/).
Signed-off-by: NRene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/git-grep.txt

@@ -148,6 +148,9 @@ OPTIONS
 	gives the default to color output.
 	Same as `--color=never`.
 
+--break::
+	Print an empty line between matches from different files.
+
 -[ABC] <context>::
 	Show `context` trailing (`A` -- after), or leading (`B`
 	-- before), or both (`C` -- context) lines, and place a

builtin/grep.c

@@ -822,6 +822,8 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
 		OPT_BOOLEAN('c', "count", &opt.count,
 			"show the number of matches instead of matching lines"),
 		OPT__COLOR(&opt.color, "highlight matches"),
+		OPT_BOOLEAN(0, "break", &opt.file_break,
+			"print empty line between matches from different files"),
 		OPT_GROUP(""),
 		OPT_CALLBACK('C', NULL, &opt, "n",
 			"show <n> context lines before and after matches",
@@ -976,7 +978,7 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
 		use_threads = 0;
 
 	if (use_threads) {
-		if (opt.pre_context || opt.post_context)
+		if (opt.pre_context || opt.post_context || opt.file_break)
 			skip_first_line = 1;
 		start_threads(&opt);
 	}

grep.c

@@ -721,7 +721,10 @@ static void show_line(struct grep_opt *opt, char *bol, char *eol,
 	int rest = eol - bol;
 	char *line_color = NULL;
 
-	if (opt->pre_context || opt->post_context) {
+	if (opt->file_break && opt->last_shown == 0) {
+		if (opt->show_hunk_mark)
+			opt->output(opt, "\n", 1);
+	} else if (opt->pre_context || opt->post_context) {
 		if (opt->last_shown == 0) {
 			if (opt->show_hunk_mark) {
 				output_color(opt, "--", 2, opt->color_sep);
@@ -941,7 +944,7 @@ static int grep_buffer_1(struct grep_opt *opt, const char *name,
 	if (!opt->output)
 		opt->output = std_output;
 
-	if (opt->pre_context || opt->post_context) {
+	if (opt->pre_context || opt->post_context || opt->file_break) {
 		/* Show hunk marks, except for the first file. */
 		if (opt->last_shown)
 			opt->show_hunk_mark = 1;

grep.h

@@ -110,6 +110,7 @@ struct grep_opt {
 	unsigned post_context;
 	unsigned last_shown;
 	int show_hunk_mark;
+	int file_break;
 	void *priv;
 
 	void (*output)(struct grep_opt *opt, const void *data, size_t size);

t/t7810-grep.sh

@@ -746,4 +746,32 @@ test_expect_success 'grep --color, separator' '
 	test_cmp expected actual
 '
 
+cat >expected <<EOF
+hello.c:int main(int argc, const char **argv)
+hello.c:	/* char ?? */
+
+hello_world:Hello_world
+EOF
+
+test_expect_success 'grep --break' '
+	git grep --break -e char -e lo_w hello.c hello_world >actual &&
+	test_cmp expected actual
+'
+
+cat >expected <<EOF
+hello.c:int main(int argc, const char **argv)
+hello.c-{
+--
+hello.c:	/* char ?? */
+hello.c-}
+
+hello_world:Hello_world
+hello_world-HeLLo_world
+EOF
+
+test_expect_success 'grep --break with context' '
+	git grep --break -A1 -e char -e lo_w hello.c hello_world >actual &&
+	test_cmp expected actual
+'
+
 test_done