touch parent model when an attachment is purged

Currently `delete` is used on the `purge` and `purge_later` methods,
that prevent any callbacks to be triggered which causes the parent
model to not be updated when an attachment is purged. This behaviour
cause issues on some caching strategies as reported here: https://github.com/rails/rails/issues/39858

Changes:

* Add `record&.touch` on `attachment#purge`
* Add `record&.touch` on `attachment#purge_later`
* Remove extra blank line on attachment.rb
* Add tests which are failing before this change and pass after the change

activestorage/CHANGELOG.md

+*   Touch parent model when an attachment is purged.
+
+    *Víctor Pérez Rodríguez*
+
 *   Files can now be served by proxying them from the underlying storage service
     instead of redirecting to a signed service URL. Use the
     `rails_storage_proxy_path` and `_url` helpers to proxy an attached file:

activestorage/app/models/active_storage/attachment.rb

@@ -21,13 +21,19 @@ class ActiveStorage::Attachment < ActiveRecord::Base
 
   # Synchronously deletes the attachment and {purges the blob}[rdoc-ref:ActiveStorage::Blob#purge].
   def purge
-    delete
+    transaction do
+      delete
+      record&.touch
+    end
     blob&.purge
   end
 
   # Deletes the attachment and {enqueues a background job}[rdoc-ref:ActiveStorage::Blob#purge_later] to purge the blob.
   def purge_later
-    delete
+    transaction do
+      delete
+      record&.touch
+    end
     blob&.purge_later
   end
 
@@ -48,7 +54,6 @@ def purge_dependent_blob_later
       blob&.purge_later if dependent == :purge_later
     end
 
-
     def dependent
       record.attachment_reflections[name]&.options[:dependent]
     end

activestorage/test/database/create_users_migration.rb

@@ -5,6 +5,7 @@ def change
     create_table :users do |t|
       t.string :name
       t.integer :group_id
+      t.timestamps
     end
   end
 end

activestorage/test/models/attached/many_test.rb

@@ -445,7 +445,9 @@ class ActiveStorage::ManyAttachedTest < ActiveSupport::TestCase
       @user.highlights.attach blobs
       assert @user.highlights.attached?
 
-      @user.highlights.purge
+      assert_changes -> { @user.updated_at } do
+        @user.highlights.purge
+      end
       assert_not @user.highlights.attached?
       assert_not ActiveStorage::Blob.exists?(blobs.first.id)
       assert_not ActiveStorage::Blob.exists?(blobs.second.id)
@@ -487,7 +489,9 @@ class ActiveStorage::ManyAttachedTest < ActiveSupport::TestCase
       assert @user.highlights.attached?
 
       perform_enqueued_jobs do
-        @user.highlights.purge_later
+        assert_changes -> { @user.updated_at } do
+          @user.highlights.purge_later
+        end
       end
 
       assert_not @user.highlights.attached?

activestorage/test/models/attached/one_test.rb

@@ -449,7 +449,9 @@ def upload.open
       @user.avatar.attach blob
       assert @user.avatar.attached?
 
-      @user.avatar.purge
+      assert_changes -> { @user.updated_at } do
+        @user.avatar.purge
+      end
       assert_not @user.avatar.attached?
       assert_not ActiveStorage::Blob.exists?(blob.id)
       assert_not ActiveStorage::Blob.service.exist?(blob.key)
@@ -478,7 +480,9 @@ def upload.open
       assert @user.avatar.attached?
 
       perform_enqueued_jobs do
-        @user.avatar.purge_later
+        assert_changes -> { @user.updated_at } do
+          @user.avatar.purge_later
+        end
       end
 
       assert_not @user.avatar.attached?