grep: Colorize filename, line number, and separator

Colorize the filename, line number, and separator in git grep output, as
GNU grep does.  The colors are customizable through color.grep.<slot>.
The default is to only color the separator (in cyan), since this gives
the biggest legibility increase without overwhelming the user with
colors.  GNU grep also defaults cyan for the separator, but defaults to
magenta for the filename and to green for the line number, as well.

There is one difference from GNU grep: When a binary file matches
without -a, GNU grep does not color the <file> in "Binary file <file>
matches", but we do.

Like GNU grep, if --null is given, the null separators are not colored.

For config.txt, use a a sub-list to describe the slots, rather than
a single paragraph with parentheses, since this is much more readable.

Remove the cast to int for `rm_eo - rm_so` since it is not necessary.

Signed-off-by: Mark Lodato <lodatom@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

4 files changed, 78 insertions, 34 deletions

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 7103172ed..d6e4a3e0c 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -683,9 +683,23 @@ color.grep::
 	`never`), never.  When set to `true` or `auto`, use color only
 	when the output is written to the terminal.  Defaults to `false`.
 
-color.grep.match::
-	Use customized color for matches.  The value of this variable
-	may be specified as in color.branch.<slot>.
+color.grep.<slot>::
+	Use customized color for grep colorization.  `<slot>` specifies which
+	part of the line to use the specified color, and is one of
++
+--
+`filename`;;
+	filename prefix (when not using `-h`)
+`linenumber`;;
+	line number prefix (when using `-n`)
+`match`;;
+	matching text
+`separator`;;
+	separators between fields on a line (`:`, `-`, and `=`)
+	and between hunks (`--`)
+--
++
+The values of these variables may be specified as in color.branch.<slot>.
 
 color.interactive::
 	When set to `always`, always use colors for interactive prompts
diff --git a/builtin-grep.c b/builtin-grep.c
index dcc3d4841..09c2f4913 100644
--- a/builtin-grep.c
+++ b/builtin-grep.c
@@ -289,6 +289,7 @@ static int wait_all(void)
 static int grep_config(const char *var, const char *value, void *cb)
 {
 	struct grep_opt *opt = cb;
+	char *color = NULL;
 
 	switch (userdiff_config(var, value)) {
 	case 0: break;
@@ -296,17 +297,24 @@ static int grep_config(const char *var, const char *value, void *cb)
 	default: return 0;
 	}
 
-	if (!strcmp(var, "color.grep")) {
+	if (!strcmp(var, "color.grep"))
 		opt->color = git_config_colorbool(var, value, -1);
-		return 0;
-	}
-	if (!strcmp(var, "color.grep.match")) {
+	else if (!strcmp(var, "color.grep.filename"))
+		color = opt->color_filename;
+	else if (!strcmp(var, "color.grep.linenumber"))
+		color = opt->color_lineno;
+	else if (!strcmp(var, "color.grep.match"))
+		color = opt->color_match;
+	else if (!strcmp(var, "color.grep.separator"))
+		color = opt->color_sep;
+	else
+		return git_color_default_config(var, value, cb);
+	if (color) {
 		if (!value)
 			return config_error_nonbool(var);
-		color_parse(value, var, opt->color_match);
-		return 0;
+		color_parse(value, var, color);
 	}
-	return git_color_default_config(var, value, cb);
+	return 0;
 }
 
 /*
@@ -871,7 +879,10 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
 	opt.regflags = REG_NEWLINE;
 	opt.max_depth = -1;
 
+	strcpy(opt.color_filename, "");
+	strcpy(opt.color_lineno, "");
 	strcpy(opt.color_match, GIT_COLOR_BOLD_RED);
+	strcpy(opt.color_sep, GIT_COLOR_CYAN);
 	opt.color = -1;
 	git_config(grep_config, &opt);
 	if (opt.color == -1)
diff --git a/grep.c b/grep.c
index a0864f1cb..42e915d76 100644
--- a/grep.c
+++ b/grep.c
@@ -270,9 +270,28 @@ static int word_char(char ch)
 	return isalnum(ch) || ch == '_';
 }
 
+static void output_color(struct grep_opt *opt, const void *data, size_t size,
+			 const char *color)
+{
+	if (opt->color && color && color[0]) {
+		opt->output(opt, color, strlen(color));
+		opt->output(opt, data, size);
+		opt->output(opt, GIT_COLOR_RESET, strlen(GIT_COLOR_RESET));
+	} else
+		opt->output(opt, data, size);
+}
+
+static void output_sep(struct grep_opt *opt, char sign)
+{
+	if (opt->null_following_name)
+		opt->output(opt, "\0", 1);
+	else
+		output_color(opt, &sign, 1, opt->color_sep);
+}
+
 static void show_name(struct grep_opt *opt, const char *name)
 {
-	opt->output(opt, name, strlen(name));
+	output_color(opt, name, strlen(name), opt->color_filename);
 	opt->output(opt, opt->null_following_name ? "\0" : "\n", 1);
 }
 
@@ -510,31 +529,30 @@ static void show_line(struct grep_opt *opt, char *bol, char *eol,
 		      const char *name, unsigned lno, char sign)
 {
 	int rest = eol - bol;
-	char sign_str[1];
 
-	sign_str[0] = sign;
 	if (opt->pre_context || opt->post_context) {
 		if (opt->last_shown == 0) {
-			if (opt->show_hunk_mark)
-				opt->output(opt, "--\n", 3);
-			else
+			if (opt->show_hunk_mark) {
+				output_color(opt, "--", 2, opt->color_sep);
+				opt->output(opt, "\n", 1);
+			} else
 				opt->show_hunk_mark = 1;
-		} else if (lno > opt->last_shown + 1)
-			opt->output(opt, "--\n", 3);
+		} else if (lno > opt->last_shown + 1) {
+			output_color(opt, "--", 2, opt->color_sep);
+			opt->output(opt, "\n", 1);
+		}
 	}
 	opt->last_shown = lno;
 
-	if (opt->null_following_name)
-		sign_str[0] = '\0';
 	if (opt->pathname) {
-		opt->output(opt, name, strlen(name));
-		opt->output(opt, sign_str, 1);
+		output_color(opt, name, strlen(name), opt->color_filename);
+		output_sep(opt, sign);
 	}
 	if (opt->linenum) {
 		char buf[32];
 		snprintf(buf, sizeof(buf), "%d", lno);
-		opt->output(opt, buf, strlen(buf));
-		opt->output(opt, sign_str, 1);
+		output_color(opt, buf, strlen(buf), opt->color_lineno);
+		output_sep(opt, sign);
 	}
 	if (opt->color) {
 		regmatch_t match;
@@ -548,12 +566,9 @@ static void show_line(struct grep_opt *opt, char *bol, char *eol,
 				break;
 
 			opt->output(opt, bol, match.rm_so);
-			opt->output(opt, opt->color_match,
-				    strlen(opt->color_match));
-			opt->output(opt, bol + match.rm_so,
-				    (int)(match.rm_eo - match.rm_so));
-			opt->output(opt, GIT_COLOR_RESET,
-				    strlen(GIT_COLOR_RESET));
+			output_color(opt, bol + match.rm_so,
+				     match.rm_eo - match.rm_so,
+				     opt->color_match);
 			bol += match.rm_eo;
 			rest -= match.rm_eo;
 			eflags = REG_NOTBOL;
@@ -823,7 +838,8 @@ static int grep_buffer_1(struct grep_opt *opt, const char *name,
 				return 1;
 			if (binary_match_only) {
 				opt->output(opt, "Binary file ", 12);
-				opt->output(opt, name, strlen(name));
+				output_color(opt, name, strlen(name),
+					     opt->color_filename);
 				opt->output(opt, " matches\n", 9);
 				return 1;
 			}
@@ -882,9 +898,9 @@ static int grep_buffer_1(struct grep_opt *opt, const char *name,
 	 */
 	if (opt->count && count) {
 		char buf[32];
-		opt->output(opt, name, strlen(name));
-		snprintf(buf, sizeof(buf), "%c%u\n",
-			 opt->null_following_name ? '\0' : ':', count);
+		output_color(opt, name, strlen(name), opt->color_filename);
+		output_sep(opt, ':');
+		snprintf(buf, sizeof(buf), "%u\n", count);
 		opt->output(opt, buf, strlen(buf));
 	}
 	return !!last_hit;
diff --git a/grep.h b/grep.h
index 970308799..36919ee21 100644
--- a/grep.h
+++ b/grep.h
@@ -84,7 +84,10 @@ struct grep_opt {
 	int color;
 	int max_depth;
 	int funcname;
+	char color_filename[COLOR_MAXLEN];
+	char color_lineno[COLOR_MAXLEN];
 	char color_match[COLOR_MAXLEN];
+	char color_sep[COLOR_MAXLEN];
 	int regflags;
 	unsigned pre_context;
 	unsigned post_context;