patchgrep -P: Fix matching ^ and $

> 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

> Michał Kiedrowicz<michal.kiedrowicz@gmail.com>  wrote:
>
>> 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`:

> @@ -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
> +'

> From: Michał Kiedrowicz <michal.kiedrowicz@gmail.com>
>
> When a fix for matching ^ and $ with -P was commited to master in
> fba4f1 (grep -P: Fix matching ^ and $), the tests were missing the
> LIBPCRE prerequisite check and were dropped from the patch. Here are
> the tests guarded with LIBPCRE.