patchgit-grep: add --color to highlight matches

Documentation/git-grep.txt, builtin-grep.c, grep.c, grep.h

diff --git a/Documentation/git-grep.txt b/Documentation/git-grep.txt
index a97f055..20ef098 100644
--- a/Documentation/git-grep.txt
+++ b/Documentation/git-grep.txt
@@ -16,6 +16,7 @@ SYNOPSIS
 	   [-F | --fixed-strings] [-n]
 	   [-l | --files-with-matches] [-L | --files-without-match]
 	   [-c | --count] [--all-match]
+	   [--color]
 	   [-A <post-context>] [-B <pre-context>] [-C <context>]
 	   [-f <file>] [-e] <pattern>
 	   [--and|--or|--not|(|)|-e <pattern>...] [<tree>...]
@@ -85,6 +86,9 @@ OPTIONS
 	Instead of showing every matched line, show the number of
 	lines that match.
 
+--color::
+	Show colored matches.
+
 -[ABC] <context>::
 	Show `context` trailing (`A` -- after), or leading (`B`
 	-- before), or both (`C` -- context) lines, and place a
diff --git a/builtin-grep.c b/builtin-grep.c
index ef29910..118ec32 100644
--- a/builtin-grep.c
+++ b/builtin-grep.c
@@ -386,7 +386,7 @@ static int grep_cache(struct grep_opt *opt, const char **paths, int cached)
 	 * we grep through the checked-out files. It tends to
 	 * be a lot more optimized
 	 */
-	if (!cached) {
+	if (!cached && !opt->color) {
 		hit = external_grep(opt, paths, cached);
 		if (hit >= 0)
 			return hit;
@@ -708,6 +708,10 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
 			opt.relative = 0;
 			continue;
 		}
+		if (!strcmp("--color", arg)) {
+			opt.color = 1;
+			continue;
+		}
 		if (!strcmp("--", arg)) {
 			/* later processing wants to have this at argv[1] */
 			argv--;
diff --git a/grep.c b/grep.c
index f67d671..7cc05b0 100644
--- a/grep.c
+++ b/grep.c
@@ -247,7 +247,10 @@ static int fixmatch(const char *pattern, char *line, regmatch_t *match)
 	}
 }
 
-static int match_one_pattern(struct grep_opt *opt, struct grep_pat *p, char *bol, char *eol, enum grep_context ctx)
+static int match_one_pattern_1(struct grep_opt *opt, struct grep_pat *p,
+			       char *bol, char *eol,
+			       enum grep_context ctx, int eflags,
+			       int *rm_so, int *rm_eo)
 {
 	int hit = 0;
 	int at_true_bol = 1;
@@ -261,7 +264,7 @@ static int match_one_pattern(struct grep_opt *opt, struct grep_pat *p, char *bol
 	if (!opt->fixed) {
 		regex_t *exp = &p->regexp;
 		hit = !regexec(exp, bol, ARRAY_SIZE(pmatch),
-			       pmatch, 0);
+			       pmatch, eflags);
 	}
 	else {
 		hit = !fixmatch(p->pattern, bol, pmatch);
@@ -298,9 +301,20 @@ static int match_one_pattern(struct grep_opt *opt, struct grep_pat *p, char *bol
 			goto again;
 		}
 	}
+	if (hit) {
+		if (rm_so)
+			*rm_so = pmatch[0].rm_so;
+		if (rm_eo)
+			*rm_eo = pmatch[0].rm_eo;
+	}
 	return hit;
 }
 
+static int match_one_pattern(struct grep_opt *opt, struct grep_pat *p, char *bol, char *eol, enum grep_context ctx)
+{
+	return match_one_pattern_1(opt, p, bol, eol, ctx, 0, NULL, NULL);
+}
+
 static int match_expr_eval(struct grep_opt *o,
 			   struct grep_expr *x,
 			   char *bol, char *eol,
@@ -365,6 +379,42 @@ static int match_line(struct grep_opt *opt, char *bol, char *eol,
 	return 0;
 }
 
+static void show_line_colored(struct grep_opt *opt, char *bol, char *eol,
+			      const char *name, unsigned lno, char sign)
+{
+	struct grep_pat *p;
+	int rm_so, rm_eo, eflags = 0;
+	int ch;
+
+	if (opt->pathname)
+		printf("%s%c", name, sign);
+	if (opt->linenum)
+		printf("%d%c", lno, sign);
+
+	ch = *eol;
+	*eol = 0;
+	while (bol < eol) {
+		for (p = opt->pattern_list; p; p = p->next) {
+			if (match_one_pattern_1(opt, p, bol, eol, GREP_CONTEXT_BODY, eflags, &rm_so, &rm_eo))
+				break;
+		}
+
+		/* No match, break the loop */
+		if (!p ||
+		    (rm_so < 0) || (eol - bol) <= rm_so ||
+		    (rm_eo < 0) || (eol - bol) < rm_eo)
+			break;
+
+		printf("%.*s\033[31m\033[1m%.*s\033[m",
+		       rm_so, bol,
+		       rm_eo-rm_so, bol+rm_so);
+		bol += rm_eo;
+		eflags = REG_NOTBOL;
+	}
+	printf("%s\n", bol);
+	*eol = ch;
+}
+
 static int grep_buffer_1(struct grep_opt *opt, const char *name,
 			 char *buf, unsigned long size, int collect_hits)
 {
@@ -466,8 +516,12 @@ static int grep_buffer_1(struct grep_opt *opt, const char *name,
 			}
 			if (last_shown && lno != last_shown + 1)
 				printf(hunk_mark);
-			if (!opt->count)
-				show_line(opt, bol, eol, name, lno, ':');
+			if (!opt->count) {
+				if (opt->color)
+					show_line_colored(opt, bol, eol, name, lno, ':');
+				else
+					show_line(opt, bol, eol, name, lno, ':');
+			}
 			last_shown = last_hit = lno;
 		}
 		else if (last_hit &&
diff --git a/grep.h b/grep.h
index d252dd2..979f7d0 100644
--- a/grep.h
+++ b/grep.h
@@ -68,6 +68,7 @@ struct grep_opt {
 	unsigned extended:1;
 	unsigned relative:1;
 	unsigned pathname:1;
+	unsigned color:1;
 	int regflags;
 	unsigned pre_context;
 	unsigned post_context;