PostgreSQL: Ensure the database time zone matches Ruby's time zone

This restores bf6661c (reverts 7a7c608).

If `AR::Base.default_timezone = :local`, incorrect value will be saved
unless the database time zone matches Ruby's time zone.

activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb

@@ -201,9 +201,6 @@ def initialize(connection, logger, connection_parameters, config)
         super(connection, logger, config)
 
         @connection_parameters = connection_parameters
-
-        # @local_tz is initialized as nil to avoid warnings when connect tries to use it
-        @local_tz = nil
         @max_identifier_length = nil
 
         connect
@@ -219,7 +216,6 @@ def initialize(connection, logger, connection_parameters, config)
 
         @type_map = Type::HashLookupTypeMap.new
         initialize_type_map
-        @local_tz = execute("SHOW TIME ZONE", "SCHEMA").first["TimeZone"]
         @use_insert_returning = @config.key?(:insert_returning) ? self.class.type_cast_config_to_boolean(@config[:insert_returning]) : true
       end
 
@@ -695,8 +691,9 @@ def configure_connection
           unless variables["timezone"]
             if ActiveRecord::Base.default_timezone == :utc
               variables["timezone"] = "UTC"
-            elsif @local_tz
-              variables["timezone"] = @local_tz
+            else
+              offset = Time.now.utc_offset / 3600.0
+              variables["timezone"] = offset
             end
           end
 

activerecord/test/cases/adapters/postgresql/timestamp_test.rb

@@ -43,6 +43,28 @@ def test_timestamp_with_zone_values_without_rails_time_zone_support
   ensure
     @connection.reconnect!
   end
+
+  def test_timestamp_with_zone_values_with_local_timezone
+    time = Time.now.utc.change(usec: 0)
+    timestamp = nil
+
+    with_timezone_config default: :local do
+      with_env_tz "America/New_York" do
+        @connection.reconnect!
+
+        timestamp = PostgresqlTimestampWithZone.create!(id: 2, time: time)
+        timestamp.reload
+        assert_equal time, timestamp.time
+      end
+    end
+
+    @connection.reconnect!
+
+    timestamp.reload
+    assert_equal time, timestamp.time
+  ensure
+    @connection.reconnect!
+  end
 end
 
 class PostgresqlTimestampFixtureTest < ActiveRecord::PostgreSQLTestCase