[PATCH] grep -P: Fix matching ^ and $

["Michał Kiedrowicz" <michal.kiedrowicz@gmail.com>]

When `git-grep` is run with -P/--perl-regexp, it doesn't match ^ and $ at
the beginning/end of the line.  This is because PCRE normally matches ^
and $ at the beginning/end of the whole text, not for each line, and git-grep
firstly passes a large chunk of text (possibly containing many lines) to
pcre_exec() before it splits the text into lines.  This makes `git-grep -P`
behave differently from `git-grep -E` and also from `grep -P` and `pcregrep`:

	$ cat file
	a
	 b
	$ git --no-pager grep --no-index -P '^ ' file
	$ git --no-pager grep --no-index -E '^ ' file
	file: b
	$ grep -c -P '^ ' file
	 b
	$ pcregrep -c '^ ' file
	 b

Reported-by: Zbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl>
Signed-off-by: Michał Kiedrowicz <michal.kiedrowicz@gmail.com>
---
 grep.c          |    2 +-
 t/t7810-grep.sh |   23 +++++++++++++++++++++++
 2 files changed, 24 insertions(+), 1 deletions(-)

diff --git a/grep.c b/grep.c
index 3821400..f492d26 100644
--- a/grep.c
+++ b/grep.c
@@ -79,7 +79,7 @@ static void compile_pcre_regexp(struct grep_pat *p, const struct grep_opt *opt)
 {
 	const char *error;
 	int erroffset;
-	int options = 0;
+	int options = PCRE_MULTILINE;
 
 	if (opt->ignore_case)
 		options |= PCRE_CASELESS;
diff --git a/t/t7810-grep.sh b/t/t7810-grep.sh
index 75f4716..dd6e6d5 100755
--- a/t/t7810-grep.sh
+++ b/t/t7810-grep.sh
@@ -47,6 +47,13 @@ test_expect_success setup '
 	echo vvv >t/v &&
 	mkdir t/a &&
 	echo vvv >t/a/v &&
+	{
+		echo "line without leading space1"
+		echo " line with leading space1"
+		echo " line with leading space2"
+		echo " line with leading space3"
+		echo "line without leading space2"
+	} >space &&
 	git add . &&
 	test_tick &&
 	git commit -m initial
@@ -893,4 +900,20 @@ test_expect_success 'mimic ack-grep --group' '
 	test_cmp expected actual
 '
 
+cat >expected <<EOF
+space: line with leading space1
+space: line with leading space2
+space: line with leading space3
+EOF
+
+test_expect_success 'grep -E "^ "' '
+	git grep -E "^ " space >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success "grep -P '^ '" '
+	git grep -P "^ " space >actual &&
+	test_cmp expected actual
+'
+
 test_done
-- 
1.7.8.4