Use correct timezone when parsing date in json

Fixes https://github.com/rails/rails/issues/22171

Time specified in ISO 8601 format without `Z` should be considered as local
time, yet until now it was treated as UTC.

This commit fixes problem by parsing time using timezone specified in
application config.

The downside of this solution is performance hit (`Time.zone.parse` is ~ 1.6x
slower than `Time.parse`), so maybe there's a better solution.

activesupport/CHANGELOG.md

+*   Fix parsing JSON time in `YYYY-MM-DD hh:mm:ss` (without `Z`).
+    Before such time was considered in UTC timezone, now, to comply with standard, it uses local timezone.
+
+    *Grzegorz Witek*
+
 *   Match `HashWithIndifferentAccess#default`'s behaviour with `Hash#default`.
 
     *David Cornu*

activesupport/lib/active_support/json/decoding.rb

@@ -8,7 +8,8 @@ module ActiveSupport
 
   module JSON
     # matches YAML-formatted dates
-    DATE_REGEX = /^(?:\d{4}-\d{2}-\d{2}|\d{4}-\d{1,2}-\d{1,2}[T \t]+\d{1,2}:\d{2}:\d{2}(\.[0-9]*)?(([ \t]*)Z|[-+]\d{2}?(:\d{2})?))$/
+    DATE_REGEX = /^\d{4}-\d{2}-\d{2}$/
+    DATETIME_REGEX = /^(?:\d{4}-\d{2}-\d{2}|\d{4}-\d{1,2}-\d{1,2}[T \t]+\d{1,2}:\d{2}:\d{2}(\.[0-9]*)?(([ \t]*)Z|[-+]\d{2}?(:\d{2})?)?)$/
 
     class << self
       # Parses a JSON string (JavaScript Object Notation) into a hash.
@@ -48,7 +49,13 @@ def convert_dates_from(data)
           nil
         when DATE_REGEX
           begin
-            DateTime.parse(data)
+            Date.parse(data)
+          rescue ArgumentError
+            data
+          end
+        when DATETIME_REGEX
+          begin
+            Time.zone.parse(data)
           rescue ArgumentError
             data
           end

activesupport/test/json/decoding_test.rb

 require 'abstract_unit'
 require 'active_support/json'
 require 'active_support/time'
+require 'time_zone_test_helpers'
 
 class TestJSONDecoding < ActiveSupport::TestCase
+  include TimeZoneTestHelpers
+
   class Foo
     def self.json_create(object)
       "Foo"
@@ -24,10 +27,11 @@ def self.json_create(object)
     %(["2007-01-01 01:12:34 Z"])                 => [Time.utc(2007, 1, 1, 1, 12, 34)],
     %(["2007-01-01 01:12:34 Z", "2007-01-01 01:12:35 Z"]) => [Time.utc(2007, 1, 1, 1, 12, 34), Time.utc(2007, 1, 1, 1, 12, 35)],
     # no time zone
-    %({"a": "2007-01-01 01:12:34"})              => {'a' => "2007-01-01 01:12:34"},
+    %({"a": "2007-01-01 01:12:34"})              => {'a' => Time.new(2007, 1, 1, 1, 12, 34, "-05:00")},
     # invalid date
     %({"a": "1089-10-40"})                       => {'a' => "1089-10-40"},
     # xmlschema date notation
+    %({"a": "2009-08-10T19:01:02"})              => {'a' => Time.new(2009, 8, 10, 19, 1, 2, "-04:00")},
     %({"a": "2009-08-10T19:01:02Z"})             => {'a' => Time.utc(2009, 8, 10, 19, 1, 2)},
     %({"a": "2009-08-10T19:01:02+02:00"})        => {'a' => Time.utc(2009, 8, 10, 17, 1, 2)},
     %({"a": "2009-08-10T19:01:02-05:00"})        => {'a' => Time.utc(2009, 8, 11, 00, 1, 2)},
@@ -72,10 +76,12 @@ def self.json_create(object)
 
   TESTS.each_with_index do |(json, expected), index|
     test "json decodes #{index}" do
-      with_parse_json_times(true) do
-        silence_warnings do
-          assert_equal expected, ActiveSupport::JSON.decode(json), "JSON decoding \
-          failed for #{json}"
+      with_tz_default 'Eastern Time (US & Canada)' do
+        with_parse_json_times(true) do
+          silence_warnings do
+            assert_equal expected, ActiveSupport::JSON.decode(json), "JSON decoding \
+            failed for #{json}"
+          end
         end
       end
     end