Fix has_many_inversing with touch: true on a belongs_to association with inverse

`has_many_inversing` adds records to a has_many association. It does so
with destroyed records, too. So if a child was destroyed with a `touch:
true` association on the parent *and* the parent was not loaded, it
tried to load the parent to touch it. While loading the parent it added
the child record to the parent's has_many association. The logic doing
this always set the child's parent id – even if it was correct/the same
already. But since the child is destroyed, it resulted in a
`FrozenError`.

This commit prevents doing the unnecessary setting of the identical id
and therefore fixes this error.

Fixes #40943 by not doing an unneeded attribute set.

Closes #40969.

[Markus Doits + Rafael Mendonça França]

activerecord/lib/active_record/associations/belongs_to_association.rb

@@ -80,7 +80,7 @@ module ActiveRecord
             @updated = true
           end
 
-          replace_keys(record)
+          replace_keys(record, force: true)
 
           self.target = record
         end
@@ -108,8 +108,12 @@ module ActiveRecord
           reflection.counter_cache_column && owner.persisted?
         end
 
-        def replace_keys(record)
-          owner[reflection.foreign_key] = record ? record._read_attribute(primary_key(record.class)) : nil
+        def replace_keys(record, force: false)
+          target_key = record ? record._read_attribute(primary_key(record.class)) : nil
+
+          if force || owner[reflection.foreign_key] != target_key
+            owner[reflection.foreign_key] = target_key
+          end
         end
 
         def primary_key(klass)

activerecord/lib/active_record/associations/belongs_to_polymorphic_association.rb

@@ -14,9 +14,14 @@ module ActiveRecord
       end
 
       private
-        def replace_keys(record)
+        def replace_keys(record, force: false)
           super
-          owner[reflection.foreign_type] = record ? record.class.polymorphic_name : nil
+
+          target_type = record ? record.class.polymorphic_name : nil
+
+          if force || owner[reflection.foreign_type] != target_type
+            owner[reflection.foreign_type] = target_type
+          end
         end
 
         def inverse_reflection_for(record)

activerecord/test/cases/associations/belongs_to_associations_test.rb

@@ -25,6 +25,8 @@ require "models/admin/user"
 require "models/ship"
 require "models/treasure"
 require "models/parrot"
+require "models/book"
+require "models/citation"
 
 class BelongsToAssociationsTest < ActiveRecord::TestCase
   fixtures :accounts, :companies, :developers, :projects, :topics,
@@ -1177,6 +1179,17 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
     assert_equal companies(:another_firm), client.firm_with_condition
   end
 
+  def test_destroying_child_with_unloaded_parent_and_foreign_key_and_touch_is_possible_with_has_many_inversing
+    with_has_many_inversing do
+      book     = Book.create!
+      citation = book.citations.create!
+
+      assert_difference "Citation.count", -1 do
+        Citation.find(citation.id).destroy
+      end
+    end
+  end
+
   def test_polymorphic_reassignment_of_associated_id_updates_the_object
     sponsor = sponsors(:moustache_club_sponsor_for_groucho)
 
@@ -1359,6 +1372,21 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
     assert_equal toy, sponsor.reload.sponsorable
   end
 
+  class SponsorWithTouchInverse < Sponsor
+    belongs_to :sponsorable, polymorphic: true, inverse_of: :sponsors, touch: true
+  end
+
+  def test_destroying_polymorphic_child_with_unloaded_parent_and_touch_is_possible_with_has_many_inversing
+    with_has_many_inversing do
+      toy     = Toy.create!
+      sponsor = toy.sponsors.create!
+
+      assert_difference "Sponsor.count", -1 do
+        SponsorWithTouchInverse.find(sponsor.id).destroy
+      end
+    end
+  end
+
   def test_polymorphic_with_false
     assert_nothing_raised do
       Class.new(ActiveRecord::Base) do

activerecord/test/models/book.rb

@@ -3,7 +3,7 @@
 class Book < ActiveRecord::Base
   belongs_to :author
 
-  has_many :citations, foreign_key: "book1_id"
+  has_many :citations, foreign_key: "book1_id", inverse_of: :book
   has_many :references, -> { distinct }, through: :citations, source: :reference_of
 
   has_many :subscriptions

activerecord/test/models/citation.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 class Citation < ActiveRecord::Base
+  belongs_to :book, foreign_key: :book1_id, inverse_of: :citations, touch: true
   belongs_to :reference_of, class_name: "Book", foreign_key: :book2_id
   has_many :citations
 end

activerecord/test/models/toy.rb

@@ -4,5 +4,7 @@ class Toy < ActiveRecord::Base
   self.primary_key = :toy_id
   belongs_to :pet
 
+  has_many :sponsors, as: :sponsorable, inverse_of: :sponsorable
+
   scope :with_pet, -> { joins(:pet) }
 end