pretty: colorize pattern matches in commit messages

The "git log" command limits its output to the commits that contain strings
matched by a pattern when the "--grep=<pattern>" option is used, but unlike
output from "git grep -e <pattern>", the matches are not highlighted,
making them harder to spot.

Teach the pretty-printer code to highlight matches from the
"--grep=<pattern>", "--author=<pattern>" and "--committer=<pattern>"
options (to view the last one, you may have to ask for --pretty=fuller).

Also, it must be noted that we are effectively greping the content twice
(because it would be a hassle to rework the existing matching code to do
a /g match and then pass it all down to the coloring code), however it only
slows down "git log --author=^H" on this repository by around 1-2%
(compared to v2.33.0), so it should be a small enough slow down to justify
the addition of the feature.

Signed-off-by: Hamza Mahfooz <someguy@effective-light.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config/color.txt

@@ -104,9 +104,12 @@ color.grep.<slot>::
 `matchContext`;;
 	matching text in context lines
 `matchSelected`;;
-	matching text in selected lines
+	matching text in selected lines. Also, used to customize the following
+	linkgit:git-log[1] subcommands: `--grep`, `--author` and `--committer`.
 `selected`;;
-	non-matching text in selected lines
+	non-matching text in selected lines. Also, used to customize the
+	following linkgit:git-log[1] subcommands: `--grep`, `--author` and
+	`--committer`.
 `separator`;;
 	separators between fields on a line (`:`, `-`, and `=`)
 	and between hunks (`--`)

pretty.c

@@ -431,6 +431,52 @@ const char *show_ident_date(const struct ident_split *ident,
 	return show_date(date, tz, mode);
 }
 
+static inline void strbuf_add_with_color(struct strbuf *sb, const char *color,
+					 const char *buf, size_t buflen)
+{
+	strbuf_addstr(sb, color);
+	strbuf_add(sb, buf, buflen);
+	if (*color)
+		strbuf_addstr(sb, GIT_COLOR_RESET);
+}
+
+static void append_line_with_color(struct strbuf *sb, struct grep_opt *opt,
+				   const char *line, size_t linelen,
+				   int color, enum grep_context ctx,
+				   enum grep_header_field field)
+{
+	const char *buf, *eol, *line_color, *match_color;
+	regmatch_t match;
+	int eflags = 0;
+
+	buf = line;
+	eol = buf + linelen;
+
+	if (!opt || !want_color(color) || opt->invert)
+		goto end;
+
+	line_color = opt->colors[GREP_COLOR_SELECTED];
+	match_color = opt->colors[GREP_COLOR_MATCH_SELECTED];
+
+	while (grep_next_match(opt, buf, eol, ctx, &match, field, eflags)) {
+		if (match.rm_so == match.rm_eo)
+			break;
+
+		strbuf_add_with_color(sb, line_color, buf, match.rm_so);
+		strbuf_add_with_color(sb, match_color, buf + match.rm_so,
+				      match.rm_eo - match.rm_so);
+		buf += match.rm_eo;
+		eflags = REG_NOTBOL;
+	}
+
+	if (eflags)
+		strbuf_add_with_color(sb, line_color, buf, eol - buf);
+	else {
+end:
+		strbuf_add(sb, buf, eol - buf);
+	}
+}
+
 void pp_user_info(struct pretty_print_context *pp,
 		  const char *what, struct strbuf *sb,
 		  const char *line, const char *encoding)
@@ -496,9 +542,26 @@ void pp_user_info(struct pretty_print_context *pp,
 			strbuf_addch(sb, '\n');
 		strbuf_addf(sb, " <%.*s>\n", (int)maillen, mailbuf);
 	} else {
-		strbuf_addf(sb, "%s: %.*s%.*s <%.*s>\n", what,
+		struct strbuf id = STRBUF_INIT;
-			    (pp->fmt == CMIT_FMT_FULLER) ? 4 : 0, "    ",
+		enum grep_header_field field = GREP_HEADER_FIELD_MAX;
-			    (int)namelen, namebuf, (int)maillen, mailbuf);
+		struct grep_opt *opt = pp->rev ? &pp->rev->grep_filter : NULL;
+
+		if (!strcmp(what, "Author"))
+			field = GREP_HEADER_AUTHOR;
+		else if (!strcmp(what, "Commit"))
+			field = GREP_HEADER_COMMITTER;
+
+		strbuf_addf(sb, "%s: ", what);
+		if (pp->fmt == CMIT_FMT_FULLER)
+			strbuf_addchars(sb, ' ', 4);
+
+		strbuf_addf(&id, "%.*s <%.*s>", (int)namelen, namebuf,
+			    (int)maillen, mailbuf);
+
+		append_line_with_color(sb, opt, id.buf, id.len, pp->color,
+				       GREP_CONTEXT_HEAD, field);
+		strbuf_addch(sb, '\n');
+		strbuf_release(&id);
 	}
 
 	switch (pp->fmt) {
@@ -1939,8 +2002,9 @@ static int pp_utf8_width(const char *start, const char *end)
 	return width;
 }
 
-static void strbuf_add_tabexpand(struct strbuf *sb, int tabwidth,
+static void strbuf_add_tabexpand(struct strbuf *sb, struct grep_opt *opt,
-				 const char *line, int linelen)
+				 int color, int tabwidth, const char *line,
+				 int linelen)
 {
 	const char *tab;
 
@@ -1957,7 +2021,9 @@ static void strbuf_add_tabexpand(struct strbuf *sb, int tabwidth,
 			break;
 
 		/* Output the data .. */
-		strbuf_add(sb, line, tab - line);
+		append_line_with_color(sb, opt, line, tab - line, color,
+				       GREP_CONTEXT_BODY,
+				       GREP_HEADER_FIELD_MAX);
 
 		/* .. and the de-tabified tab */
 		strbuf_addchars(sb, ' ', tabwidth - (width % tabwidth));
@@ -1972,7 +2038,8 @@ static void strbuf_add_tabexpand(struct strbuf *sb, int tabwidth,
 	 * worrying about width - there's nothing more to
 	 * align.
 	 */
-	strbuf_add(sb, line, linelen);
+	append_line_with_color(sb, opt, line, linelen, color, GREP_CONTEXT_BODY,
+			       GREP_HEADER_FIELD_MAX);
 }
 
 /*
@@ -1984,11 +2051,16 @@ static void pp_handle_indent(struct pretty_print_context *pp,
 			     struct strbuf *sb, int indent,
 			     const char *line, int linelen)
 {
+	struct grep_opt *opt = pp->rev ? &pp->rev->grep_filter : NULL;
+
 	strbuf_addchars(sb, ' ', indent);
 	if (pp->expand_tabs_in_log)
-		strbuf_add_tabexpand(sb, pp->expand_tabs_in_log, line, linelen);
+		strbuf_add_tabexpand(sb, opt, pp->color, pp->expand_tabs_in_log,
+				     line, linelen);
 	else
-		strbuf_add(sb, line, linelen);
+		append_line_with_color(sb, opt, line, linelen, pp->color,
+				       GREP_CONTEXT_BODY,
+				       GREP_HEADER_FIELD_MAX);
 }
 
 static int is_mboxrd_from(const char *line, int len)
@@ -2006,7 +2078,9 @@ void pp_remainder(struct pretty_print_context *pp,
 		  struct strbuf *sb,
 		  int indent)
 {
+	struct grep_opt *opt = pp->rev ? &pp->rev->grep_filter : NULL;
 	int first = 1;
+
 	for (;;) {
 		const char *line = *msg_p;
 		int linelen = get_one_line(line);
@@ -2027,14 +2101,17 @@ void pp_remainder(struct pretty_print_context *pp,
 		if (indent)
 			pp_handle_indent(pp, sb, indent, line, linelen);
 		else if (pp->expand_tabs_in_log)
-			strbuf_add_tabexpand(sb, pp->expand_tabs_in_log,
+			strbuf_add_tabexpand(sb, opt, pp->color,
-					     line, linelen);
+					     pp->expand_tabs_in_log, line,
+					     linelen);
 		else {
 			if (pp->fmt == CMIT_FMT_MBOXRD &&
 					is_mboxrd_from(line, linelen))
 				strbuf_addch(sb, '>');
 
-			strbuf_add(sb, line, linelen);
+			append_line_with_color(sb, opt, line, linelen,
+					       pp->color, GREP_CONTEXT_BODY,
+					       GREP_HEADER_FIELD_MAX);
 		}
 		strbuf_addch(sb, '\n');
 	}

t/t4202-log.sh

@@ -449,6 +449,57 @@ test_expect_success !FAIL_PREREQS 'log with various grep.patternType configurati
 	)
 '
 
+test_expect_success 'log --author' '
+	cat >expect <<-\EOF &&
+	Author: <BOLD;RED>A U<RESET> Thor <author@example.com>
+	EOF
+	git log -1 --color=always --author="A U" >log &&
+	grep Author log >actual.raw &&
+	test_decode_color <actual.raw >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'log --committer' '
+	cat >expect <<-\EOF &&
+	Commit:     C O Mitter <committer@<BOLD;RED>example<RESET>.com>
+	EOF
+	git log -1 --color=always --pretty=fuller --committer="example" >log &&
+	grep "Commit:" log >actual.raw &&
+	test_decode_color <actual.raw >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'log -i --grep with color' '
+	cat >expect <<-\EOF &&
+	    <BOLD;RED>Sec<RESET>ond
+	    <BOLD;RED>sec<RESET>ond
+	EOF
+	git log --color=always -i --grep=^sec >log &&
+	grep -i sec log >actual.raw &&
+	test_decode_color <actual.raw >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success '-c color.grep.selected log --grep' '
+	cat >expect <<-\EOF &&
+	    <GREEN>th<RESET><BOLD;RED>ir<RESET><GREEN>d<RESET>
+	EOF
+	git -c color.grep.selected="green" log --color=always --grep=ir >log &&
+	grep ir log >actual.raw &&
+	test_decode_color <actual.raw >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success '-c color.grep.matchSelected log --grep' '
+	cat >expect <<-\EOF &&
+	    <BLUE>i<RESET>n<BLUE>i<RESET>t<BLUE>i<RESET>al
+	EOF
+	git -c color.grep.matchSelected="blue" log --color=always --grep=i >log &&
+	grep al log >actual.raw &&
+	test_decode_color <actual.raw >actual &&
+	test_cmp expect actual
+'
+
 cat > expect <<EOF
 * Second
 * sixth