revision: add --grep-reflog to filter commits by reflog messages

Similar to --author/--committer which filters commits by author and
committer header fields. --grep-reflog adds a fake "reflog" header to
commit and a grep filter to search on that line.

All rules to --author/--committer apply except no timestamp stripping.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/rev-list-options.txt

@@ -51,6 +51,14 @@ endif::git-rev-list[]
 	commits whose author matches any of the given patterns are
 	chosen (similarly for multiple `--committer=<pattern>`).
 
+--grep-reflog=<pattern>::
+
+	Limit the commits output to ones with reflog entries that
+	match the specified pattern (regular expression). With
+	more than one `--grep-reflog`, commits whose reflog message
+	matches any of the given patterns are chosen. Ignored unless
+	`--walk-reflogs` is given.
+
 --grep=<pattern>::
 
 	Limit the commits output to ones with log message that

grep.c

@@ -697,6 +697,7 @@ static struct {
 } header_field[] = {
 	{ "author ", 7 },
 	{ "committer ", 10 },
+	{ "reflog ", 7 },
 };
 
 static int match_one_pattern(struct grep_pat *p, char *bol, char *eol,

grep.h

@@ -30,6 +30,7 @@ enum grep_context {
 enum grep_header_field {
 	GREP_HEADER_AUTHOR = 0,
 	GREP_HEADER_COMMITTER,
+	GREP_HEADER_REFLOG,
 
 	/* Must be at the end of the enum */
 	GREP_HEADER_FIELD_MAX

revision.c

@@ -1595,6 +1595,9 @@ static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg
 	} else if ((argcount = parse_long_opt("committer", argv, &optarg))) {
 		add_header_grep(revs, GREP_HEADER_COMMITTER, optarg);
 		return argcount;
+	} else if ((argcount = parse_long_opt("grep-reflog", argv, &optarg))) {
+		add_header_grep(revs, GREP_HEADER_REFLOG, optarg);
+		return argcount;
 	} else if ((argcount = parse_long_opt("grep", argv, &optarg))) {
 		add_message_grep(revs, optarg);
 		return argcount;
@@ -2210,10 +2213,23 @@ static int rewrite_parents(struct rev_info *revs, struct commit *commit)
 
 static int commit_match(struct commit *commit, struct rev_info *opt)
 {
+	int retval;
+	struct strbuf buf = STRBUF_INIT;
 	if (!opt->grep_filter.pattern_list && !opt->grep_filter.header_list)
 		return 1;
-	return grep_buffer(&opt->grep_filter,
+	if (opt->reflog_info) {
-			   commit->buffer, strlen(commit->buffer));
+		strbuf_addstr(&buf, "reflog ");
+		get_reflog_message(&buf, opt->reflog_info);
+		strbuf_addch(&buf, '\n');
+		strbuf_addstr(&buf, commit->buffer);
+	}
+	if (buf.len)
+		retval = grep_buffer(&opt->grep_filter, buf.buf, buf.len);
+	else
+		retval = grep_buffer(&opt->grep_filter,
+				     commit->buffer, strlen(commit->buffer));
+	strbuf_release(&buf);
+	return retval;
 }
 
 static inline int want_ancestry(struct rev_info *revs)

t/t7810-grep.sh

@@ -546,6 +546,32 @@ test_expect_success 'log grep (6)' '
 	test_cmp expect actual
 '
 
+test_expect_success 'log grep (7)' '
+	git log -g --grep-reflog="commit: third" --pretty=tformat:%s >actual &&
+	echo third >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'log grep (8)' '
+	git log -g --grep-reflog="commit: third" --grep-reflog="commit: second" --pretty=tformat:%s >actual &&
+	{
+		echo third && echo second
+	} >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'log grep (9)' '
+	git log -g --grep-reflog="commit: third" --author="Thor" --pretty=tformat:%s >actual &&
+	echo third >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'log grep (9)' '
+	git log -g --grep-reflog="commit: third" --author="non-existant" --pretty=tformat:%s >actual &&
+	: >expect &&
+	test_cmp expect actual
+'
+
 test_expect_success 'log with multiple --grep uses union' '
 	git log --grep=i --grep=r --format=%s >actual &&
 	{