[Feature #18033] Parse more strictly conformant with ISO-8601

* 4-digits or more is required as year
* Minutes and seconds parts are not ommittable

test/ruby/test_time.rb

@@ -67,8 +67,12 @@ class TestTime < Test::Unit::TestCase
     assert_equal(t, Time.new("2020-12-25 00:56:17 +0900"))
     assert_equal(t, Time.new("2020-12-25 00:57:47 +090130"))
     assert_equal(t, Time.new("2020-12-25T00:56:17+09:00"))
-    assert_equal(Time.utc(2020, 12, 24, 15, 56, 0), Time.new("2020-12-25 00:56 +09:00"))
-    assert_equal(Time.utc(2020, 12, 24, 15, 0, 0), Time.new("2020-12-25 00 +09:00"))
+    assert_raise_with_message(ArgumentError, /missing sec part/) {
+      Time.new("2020-12-25 00:56 +09:00")
+    }
+    assert_raise_with_message(ArgumentError, /missing min part/) {
+      Time.new("2020-12-25 00 +09:00")
+    }
 
     assert_equal(Time.new(2021, 12, 25, in: "+09:00"), Time.new("2021-12-25+09:00"))
 
@@ -79,7 +83,7 @@ class TestTime < Test::Unit::TestCase
     assert_raise_with_message(ArgumentError, "subsecond expected after dot: 00:56:17. ") {
       Time.new("2020-12-25 00:56:17. +0900")
     }
-    assert_raise_with_message(ArgumentError, /year must be 2 or 4\+/) {
+    assert_raise_with_message(ArgumentError, /year must be 4 or more/) {
       Time.new("021-12-25 00:00:00.123456 +09:00")
     }
     assert_raise_with_message(ArgumentError, /fraction min is.*56\./) {

time.c

@@ -2519,8 +2519,8 @@ time_init_parse(rb_execution_context_t *ec, VALUE klass, VALUE str, VALUE zone,
     if (NIL_P(year)) {
         rb_raise(rb_eArgError, "can't parse: %+"PRIsVALUE, str);
     }
-    else if (ndigits != 2 && ndigits < 4) {
-        rb_raise(rb_eArgError, "year must be 2 or 4+ digits: %.*s", (int)ndigits, ptr - ndigits);
+    else if (ndigits < 4) {
+        rb_raise(rb_eArgError, "year must be 4 or more digits: %.*s", (int)ndigits, ptr - ndigits);
     }
     do {
 #define peekable_p(n) ((ptrdiff_t)(n) < (end - ptr))
@@ -2538,15 +2538,20 @@ time_init_parse(rb_execution_context_t *ec, VALUE klass, VALUE str, VALUE zone,
         if (!ISDIGIT(peekc_n(1))) break;
 #define nofraction(x) \
         if (peek('.')) { \
-            rb_raise(rb_eArgError, "fraction %s is not supported: %.*s", #x, \
+            rb_raise(rb_eArgError, "fraction " #x " is not supported: %.*s", \
+                     (int)(ptr + 1 - time_part), time_part); \
+        }
+#define need_colon(x) \
+        if (!peek(':')) { \
+            rb_raise(rb_eArgError, "missing " #x " part: %.*s", \
                      (int)(ptr + 1 - time_part), time_part); \
         }
         expect_two_digits(hour);
         nofraction(hour);
-        if (!peek(':')) break;
+        need_colon(min);
         expect_two_digits(min);
         nofraction(min);
-        if (!peek(':')) break;
+        need_colon(sec);
         expect_two_digits(sec);
         if (peek('.')) {
             ptr++;