TZ offset minute has to be negated in the Western Hemisphere

activemodel/CHANGELOG.md

@@ -1,3 +1,8 @@
+*   Fix a bug where type casting of string to `Time` and `DateTime` doesn't
+    calculate minus minute value in TZ offset correctly.
+
+    *Akira Matsuda*
+
 *   Port the `type_for_attribute` method to Active Model. Classes that include
     `ActiveModel::Attributes` will now provide this method. This method behaves
     the same for Active Model as it does for Active Record.

activemodel/lib/active_model/type/helpers/time_value.rb

@@ -94,7 +94,13 @@ def fast_string_to_time(string)
               end
 
               if $8
-                offset = $8 == "Z" ? 0 : $8.to_i * 3600 + $9.to_i * 60
+                offset = \
+                  if $8 == "Z"
+                    0
+                  else
+                    offset_h, offset_m = $8.to_i, $9.to_i
+                    offset_h.to_i * 3600 + (offset_h.negative? ? -1 : 1) * offset_m * 60
+                  end
               end
 
               new_time($1.to_i, $2.to_i, $3.to_i, $4.to_i, $5.to_i, $6.to_i, usec, offset)

activemodel/test/cases/type/time_test.rb

@@ -18,6 +18,7 @@ def test_type_cast_time
         assert_equal ::Time.utc(2000,  1,  1, 16, 45, 54), type.cast("2015-06-13T19:45:54+03:00")
         assert_equal ::Time.utc(1999, 12, 31, 21,  7,  8), type.cast("06:07:08+09:00")
         assert_equal ::Time.utc(2000,  1,  1, 16, 45, 54), type.cast(4 => 16, 5 => 45, 6 => 54)
+        assert_equal ::Time.utc(2000,  1,  1, 3, 30, 0), type.cast("2023-01-01T00:00:00-03:30")
       end
 
       def test_user_input_in_time_zone