fsck: report the ID of the error/warning

Some repositories written by legacy code have objects with non-fatal
fsck issues. To allow the user to ignore those issues, let's print
out the ID (e.g. when encountering "missingEmail", the user might
want to call `git config --add receive.fsck.missingEmail=warn`).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

fsck.c

@@ -189,6 +189,24 @@ void fsck_set_msg_types(struct fsck_options *options, const char *values)
 	free(to_free);
 }
 
+static void append_msg_id(struct strbuf *sb, const char *msg_id)
+{
+	for (;;) {
+		char c = *(msg_id)++;
+
+		if (!c)
+			break;
+		if (c != '_')
+			strbuf_addch(sb, tolower(c));
+		else {
+			assert(*msg_id);
+			strbuf_addch(sb, *(msg_id)++);
+		}
+	}
+
+	strbuf_addstr(sb, ": ");
+}
+
 __attribute__((format (printf, 4, 5)))
 static int report(struct fsck_options *options, struct object *object,
 	enum fsck_msg_id id, const char *fmt, ...)
@@ -197,6 +215,8 @@ static int report(struct fsck_options *options, struct object *object,
 	struct strbuf sb = STRBUF_INIT;
 	int msg_type = fsck_msg_type(id, options), result;
 
+	append_msg_id(&sb, msg_id_info[id].id_string);
+
 	va_start(ap, fmt);
 	strbuf_vaddf(&sb, fmt, ap);
 	result = options->error_func(object, msg_type, sb.buf);

t/t1450-fsck.sh

@@ -231,8 +231,8 @@ test_expect_success 'tag with incorrect tag name & missing tagger' '
 	git fsck --tags 2>out &&
 
 	cat >expect <<-EOF &&
-	warning in tag $tag: invalid '\''tag'\'' name: wrong name format
-	warning in tag $tag: invalid format - expected '\''tagger'\'' line
+	warning in tag $tag: badTagName: invalid '\''tag'\'' name: wrong name format
+	warning in tag $tag: missingTaggerEntry: invalid format - expected '\''tagger'\'' line
 	EOF
 	test_cmp expect out
 '