Allow mday in Date.iso8601 to be omitted

[Bug #12285]

ext/date/date_parse.c

@@ -2262,8 +2262,8 @@ iso8601_ext_datetime_cb(VALUE m, VALUE hash)
 	    s[i] = rb_reg_nth_match(i, m);
     }
 
-    if (!NIL_P(s[3])) {
-	set_hash("mday", str2num(s[3]));
+    if (!NIL_P(s[1])) {
+	if (!NIL_P(s[3])) set_hash("mday", str2num(s[3]));
 	if (strcmp(RSTRING_PTR(s[1]), "-") != 0) {
 	    y = str2num(s[1]);
 	    if (RSTRING_LEN(s[1]) < 4)
@@ -2320,7 +2320,7 @@ static int
 iso8601_ext_datetime(VALUE str, VALUE hash)
 {
     static const char pat_source[] =
-	"\\A\\s*(?:([-+]?\\d{2,}|-)-(\\d{2})?-(\\d{2})|"
+	"\\A\\s*(?:([-+]?\\d{2,}|-)-(\\d{2})?(?:-(\\d{2}))?|"
 		"([-+]?\\d{2,})?-(\\d{3})|"
 		"(\\d{4}|\\d{2})?-w(\\d{2})-(\\d)|"
 		"-w-(\\d))"

test/date/test_date_parse.rb

@@ -712,6 +712,9 @@ class TestDateParse < Test::Unit::TestCase
     h = Date._iso8601('2001-02-03T04:05:06.07+01:00')
     assert_equal([2001, 2, 3, 4, 5, 6, 3600],
 		 h.values_at(:year, :mon, :mday, :hour, :min, :sec, :offset))
+    h = Date._iso8601('2001-02')
+    assert_equal([2001, 2],
+		 h.values_at(:year, :mon))
 
     h = Date._iso8601('010203T040506Z')
     assert_equal([2001, 2, 3, 4, 5, 6, 0],