Building new records with enum scopes now works as expected

Previously, this would give an `ArgumentError`:

   class Issue < ActiveRecord::Base
     enum :status, [:open, :finished]
   end

   Issue.open.build # => ArgumentError: '0' is not a valid status
   Issue.open.create # => ArgumentError: '0' is not a valid status

PR #13542 muted the error, but the issue remains. This commit fixes
the issue by allowing the enum value to be written directly via the
setter:

   Issue.new.status = 0 # This now sets status to :open

Assigning a value directly via the setter like this is not part of the
documented public API, so users should not rely on this behavior.

Closes #13530.

1 files changed, 8 insertions, 2 deletions

diff --git a/activerecord/lib/active_record/enum.rb b/activerecord/lib/active_record/enum.rb
index c042a2f232..3dd093b8a2 100644
--- a/activerecord/lib/active_record/enum.rb
+++ b/activerecord/lib/active_record/enum.rb
@@ -72,10 +72,16 @@ module ActiveRecord
         _enum_methods_module.module_eval do
           # def status=(value) self[:status] = STATUS[value] end
           define_method("#{name}=") { |value|
-            unless enum_values.has_key?(value) || enum_values.has_value?(value) || value.blank?
+            if enum_values.has_key?(value)|| value.blank?
+              self[name] = enum_values[value]
+            elsif enum_values.has_value?(value)
+              # Assigning a value directly is not a end-user fetaure, hence it's not documented.
+              # This is used internally to make building objects from the generated scopes work
+              # as expected, i.e. +Conversation.archived.build.archived?+ should be true.
+              self[name] = value
+            else
               raise ArgumentError, "'#{value}' is not a valid #{name}"
             end
-            self[name] = enum_values[value]
           }
 
           # def status() STATUS.key self[:status] end