revision: make --grep search in notes too if shown

Notes are shown after commit body. From user perspective it looks
pretty much like commit body and they may assume --grep would search
in that part too.

Make it so.

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

Documentation/rev-list-options.txt

@@ -66,6 +66,9 @@ endif::git-rev-list[]
 	more than one `--grep=<pattern>`, commits whose message
 	matches any of the given patterns are chosen (but see
 	`--all-match`).
++
+When `--show-notes` is in effect, the message from the notes as
+if it is part of the log message.
 
 --all-match::
 	Limit the commits output to ones that match all given --grep,

revision.c

@@ -2231,6 +2231,14 @@ static int commit_match(struct commit *commit, struct rev_info *opt)
 	if (buf.len)
 		strbuf_addstr(&buf, commit->buffer);
 
+	/* Append "fake" message parts as needed */
+	if (opt->show_notes) {
+		if (!buf.len)
+			strbuf_addstr(&buf, commit->buffer);
+		format_display_notes(commit->object.sha1, &buf,
+				     get_log_output_encoding(), 0);
+	}
+
 	/* Find either in the commit object, or in the temporary */
 	if (buf.len)
 		retval = grep_buffer(&opt->grep_filter, buf.buf, buf.len);