Revert "Remove deprecated support for the pre-Ruby 2.4 behavior of to_time"

This reverts commit b1b2c6d.

Author: matthewd

activesupport/lib/active_support.rb

@@ -111,15 +111,17 @@ def self.cache_format_version=(value)
   end
 
   def self.to_time_preserves_timezone
-    ActiveSupport.deprecator.warn(
-      "`config.active_support.to_time_preserves_timezone` has been deprecated and will be removed in Rails 7.3."
-    )
+    DateAndTime::Compatibility.preserve_timezone
   end
 
   def self.to_time_preserves_timezone=(value)
-    ActiveSupport.deprecator.warn(
-      "`config.active_support.to_time_preserves_timezone` has been deprecated and will be removed in Rails 7.3."
-    )
+    unless value
+      ActiveSupport.deprecator.warn(
+        "Support for the pre-Ruby 2.4 behavior of to_time has been deprecated and will be removed in Rails 7.2."
+      )
+    end
+
+    DateAndTime::Compatibility.preserve_timezone = value
   end
 
   def self.utc_to_local_returns_utc_offset_times

activesupport/lib/active_support/core_ext/date_and_time/compatibility.rb

@@ -4,6 +4,15 @@
 
 module DateAndTime
   module Compatibility
+    # If true, +to_time+ preserves the timezone offset of receiver.
+    #
+    # NOTE: With Ruby 2.4+ the default for +to_time+ changed from
+    # converting to the local system time, to preserving the offset
+    # of the receiver. For backwards compatibility we're overriding
+    # this behavior, but new apps will have an initializer that sets
+    # this to true, because the new behavior is preferred.
+    mattr_accessor :preserve_timezone, instance_writer: false, default: false
+
     # Change the output of <tt>ActiveSupport::TimeZone.utc_to_local</tt>.
     #
     # When +true+, it returns local times with a UTC offset, with +false+ local
@@ -18,17 +27,5 @@ module Compatibility
     #   # With `utc_to_local_returns_utc_offset_times = true`, local time is returned with UTC offset:
     #   zone.utc_to_local(Time.utc(2000, 1)) # => 1999-12-31 19:00:00 -0500
     mattr_accessor :utc_to_local_returns_utc_offset_times, instance_writer: false, default: false
-
-    def self.preserve_timezone
-      ActiveSupport.deprecator.warn(
-        "`DateAndTime::Compatibility.preserve_timezone` has been deprecated and will be removed in Rails 7.3."
-      )
-    end
-
-    def self.preserve_timezone=(value)
-      ActiveSupport.deprecator.warn(
-        "`DateAndTime::Compatibility.preserve_timezone=` has been deprecated and will be removed in Rails 7.3."
-      )
-    end
   end
 end

activesupport/lib/active_support/core_ext/date_time/compatibility.rb

@@ -8,9 +8,11 @@ class DateTime
 
   silence_redefinition_of_method :to_time
 
-  # Return an instance of +Time+ with the same UTC offset
-  # as +self+.
+  # Either return an instance of +Time+ with the same UTC offset
+  # as +self+ or an instance of +Time+ representing the same time
+  # in the local system timezone depending on the setting of
+  # on the setting of +ActiveSupport.to_time_preserves_timezone+.
   def to_time
-    getlocal(utc_offset)
+    preserve_timezone ? getlocal(utc_offset) : getlocal
   end
 end

activesupport/lib/active_support/core_ext/time/compatibility.rb

@@ -8,8 +8,9 @@ class Time
 
   silence_redefinition_of_method :to_time
 
-  # Returns +self+.
+  # Either return +self+ or the time in the local system timezone depending
+  # on the setting of +ActiveSupport.to_time_preserves_timezone+.
   def to_time
-    self
+    preserve_timezone ? self : getlocal
   end
 end

activesupport/lib/active_support/time_with_zone.rb

@@ -479,10 +479,15 @@ def to_datetime
       @to_datetime ||= utc.to_datetime.new_offset(Rational(utc_offset, 86_400))
     end
 
-    # Returns an instance of +Time+ with the same UTC offset
-    # as +self+.
+    # Returns an instance of +Time+, either with the same UTC offset
+    # as +self+ or in the local system timezone depending on the setting
+    # of +ActiveSupport.to_time_preserves_timezone+.
     def to_time
-      @to_time_with_instance_offset ||= getlocal(utc_offset)
+      if preserve_timezone
+        @to_time_with_instance_offset ||= getlocal(utc_offset)
+      else
+        @to_time_with_system_offset ||= getlocal
+      end
     end
 
     # So that +self+ <tt>acts_like?(:time)</tt>.

activesupport/test/abstract_unit.rb

@@ -24,6 +24,11 @@
 # Show backtraces for deprecated behavior for quicker cleanup.
 ActiveSupport.deprecator.debug = true
 
+# Default to Ruby 2.4+ to_time behavior but allow running tests with old behavior
+ActiveSupport.deprecator.silence do
+  ActiveSupport.to_time_preserves_timezone = ENV.fetch("PRESERVE_TIMEZONES", "1") == "1"
+end
+
 ActiveSupport::Cache.format_version = 7.1
 
 # Disable available locale checks to avoid warnings running the test suite.