[PATCH] grep: fix match highlighting for combined patterns with context lines

[Zoltan Klinger <zoltan.klinger@gmail.com>]

When git grep is run with combined patterns such as '-e p1 --and -e p2'
and surrounding context lines are requested, the output contains
incorrectly highlighted matches.

Consider the following output (highlighted matches are surrounded by '*'
characters):
    $ cat testfile
    foo a
    foo b
    foo bar
    baz bar foo
    bar x
    bar y
    $ git grep -n -C2 -e foo --and -e bar testfile
    testfile-1-*foo* a
    testfile-2-*foo* b
    testfile:3:*foo* *bar*
    testfile:4:baz *bar* *foo*
    testfile-5-*bar* x
    testfile-6-*bar* y

Lines 1, 2, 5 and 6 do not match the combined patterns, they only
contain incorrectly highlighted 'false positives'.

Modify the show_line() function in grep.c to highlight matches only on
lines that match the combined pattern. Do not highlight matches on lines
that provide only context or contain only the function name of the match.

The output of the same command after the change:
    $ git grep -n -C2 -e foo --and -e bar testfile
    testfile-1-foo a
    testfile-2-foo b
    testfile:3:*foo* *bar*
    testfile:4:baz *bar* *foo*
    testfile-5-bar x
    testfile-6-bar y

Signed-off-by: Zoltan Klinger <zoltan.klinger@gmail.com>
---
 grep.c          |  7 +++--
 t/t7810-grep.sh | 90 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 95 insertions(+), 2 deletions(-)

diff --git a/grep.c b/grep.c
index 4dc31ea..3c4d68e 100644
--- a/grep.c
+++ b/grep.c
@@ -1121,9 +1121,12 @@ static void show_line(struct grep_opt *opt, char *bol, char *eol,
 		enum grep_context ctx = GREP_CONTEXT_BODY;
 		int ch = *eol;
 		int eflags = 0;
+		char *match_color = NULL;
 
-		if (sign == ':')
+		if (sign == ':') {
 			line_color = opt->color_selected;
+			match_color = opt->color_match;
+		}
 		else if (sign == '-')
 			line_color = opt->color_context;
 		else if (sign == '=')
@@ -1136,7 +1139,7 @@ static void show_line(struct grep_opt *opt, char *bol, char *eol,
 			output_color(opt, bol, match.rm_so, line_color);
 			output_color(opt, bol + match.rm_so,
 				     match.rm_eo - match.rm_so,
-				     opt->color_match);
+				     match_color);
 			bol += match.rm_eo;
 			rest -= match.rm_eo;
 			eflags = REG_NOTBOL;
diff --git a/t/t7810-grep.sh b/t/t7810-grep.sh
index 40615de..b0d6b6f 100755
--- a/t/t7810-grep.sh
+++ b/t/t7810-grep.sh
@@ -1202,4 +1202,94 @@ test_expect_success LIBPCRE 'grep -P "^ "' '
 	test_cmp expected actual
 '
 
+cat >expected <<EOF
+space-line without leading space1
+space: line <RED>with <RESET>leading space1
+space: line <RED>with <RESET>leading <RED>space2<RESET>
+space: line <RED>with <RESET>leading space3
+space:line without leading <RED>space2<RESET>
+EOF
+
+test_expect_success 'grep --color -e A -e B with context' '
+	test_config color.grep.context		normal &&
+	test_config color.grep.filename		normal &&
+	test_config color.grep.function		normal &&
+	test_config color.grep.linenumber	normal &&
+	test_config color.grep.match		red &&
+	test_config color.grep.selected		normal &&
+	test_config color.grep.separator	normal &&
+
+	git grep --color=always -C2 -e "with " -e space2  space |
+	test_decode_color >actual &&
+	test_cmp expected actual
+'
+
+cat >expected <<EOF
+space-line without leading space1
+space- line with leading space1
+space: line <RED>with <RESET>leading <RED>space2<RESET>
+space- line with leading space3
+space-line without leading space2
+EOF
+
+test_expect_success 'grep --color -e A --and -e B with context' '
+	test_config color.grep.context		normal &&
+	test_config color.grep.filename		normal &&
+	test_config color.grep.function		normal &&
+	test_config color.grep.linenumber	normal &&
+	test_config color.grep.match		red &&
+	test_config color.grep.selected		normal &&
+	test_config color.grep.separator	normal &&
+
+	git grep --color=always -C2 -e "with " --and -e space2  space |
+	test_decode_color >actual &&
+	test_cmp expected actual
+'
+
+cat >expected <<EOF
+space-line without leading space1
+space: line <RED>with <RESET>leading space1
+space- line with leading space2
+space: line <RED>with <RESET>leading space3
+space-line without leading space2
+EOF
+
+test_expect_success 'grep --color -e A --and --not -e B with context' '
+	test_config color.grep.context		normal &&
+	test_config color.grep.filename		normal &&
+	test_config color.grep.function		normal &&
+	test_config color.grep.linenumber	normal &&
+	test_config color.grep.match		red &&
+	test_config color.grep.selected		normal &&
+	test_config color.grep.separator	normal &&
+
+	git grep --color=always -C2 -e "with " --and --not -e space2  space |
+	test_decode_color >actual &&
+	test_cmp expected actual
+'
+
+cat >expected <<EOF
+hello.c-#include <stdio.h>
+hello.c=int main(int argc, const char **argv)
+hello.c-{
+hello.c:	pr<RED>int<RESET>f("<RED>Hello<RESET> world.\n");
+hello.c-	return 0;
+hello.c-	/* char ?? */
+hello.c-}
+EOF
+
+test_expect_success 'grep --color -e A --and -e B -p with context' '
+	test_config color.grep.context		normal &&
+	test_config color.grep.filename		normal &&
+	test_config color.grep.function		normal &&
+	test_config color.grep.linenumber	normal &&
+	test_config color.grep.match		red &&
+	test_config color.grep.selected		normal &&
+	test_config color.grep.separator	normal &&
+
+	git grep --color=always -p -C3 -e int --and -e Hello --no-index hello.c |
+	test_decode_color >actual &&
+	test_cmp expected actual
+'
+
 test_done
-- 
2.1.1