TZ offset minute has to be negated in the Western Hemisphere

When the TZ in the given string contains minus offset, both hour and minute
value has to be negated, but the current code negates hour only.
Hence, for instance in Newfoundland Time Zone (UTC−03:30), it used to return
1 hour advanced value.

Co-authored-by: Nobuyoshi Nakada <nobu@ruby-lang.org>

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*
+
 *   Raise `NoMethodError` in `ActiveModel::Type::Value#as_json` to avoid unpredictable
     results.
 

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

@@ -79,7 +79,13 @@ 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