Merge pull request rails#52443 from Shopify/optimize-fast_string_to_time

Optimize `fast_string_to_time`

Author: byroot

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

@@ -70,18 +70,33 @@ def new_time(year, mon, mday, hour, min, sec, microsec, offset = nil)
           /x
 
           if RUBY_VERSION >= "3.2"
-            def fast_string_to_time(string)
-              return unless ISO_DATETIME.match?(string)
-
-              if is_utc?
-                # XXX: Wrapping the Time object with Time.at because Time.new with `in:` in Ruby 3.2.0 used to return an invalid Time object
-                # see: https://bugs.ruby-lang.org/issues/19292
-                ::Time.at(::Time.new(string, in: "UTC"))
-              else
-                ::Time.new(string)
+            if Time.new(2000, 1, 1, 0, 0, 0, "-00:00").yday != 1 # Early 3.2.x had a bug
+              # BUG: Wrapping the Time object with Time.at because Time.new with `in:` in Ruby 3.2.0
+              # used to return an invalid Time object
+              # see: https://bugs.ruby-lang.org/issues/19292
+              def fast_string_to_time(string)
+                return unless string.include?("-") #  Time.new("1234") # => 1234-01-01 00:00:00
+
+                if is_utc?
+                  ::Time.at(::Time.new(string, in: "UTC"))
+                else
+                  ::Time.new(string)
+                end
+              rescue ArgumentError
+                nil
+              end
+            else
+              def fast_string_to_time(string)
+                return unless string.include?("-") #  Time.new("1234") # => 1234-01-01 00:00:00
+
+                if is_utc?
+                  ::Time.new(string, in: "UTC")
+                else
+                  ::Time.new(string)
+                end
+              rescue ArgumentError
+                nil
               end
-            rescue ArgumentError
-              nil
             end
           else
             def fast_string_to_time(string)

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

@@ -7,7 +7,11 @@ module Type
     module Helpers # :nodoc: all
       module Timezone
         def is_utc?
-          ::Time.zone_default.nil? || ::Time.zone_default.match?("UTC")
+          if default = ::Time.zone_default
+            default.name == "UTC"
+          else
+            true
+          end
         end
 
         def default_timezone