Deprecate usage of `purge` and `purge_later` from the association extension.

Calling `purge` and `purge_later` from the association extension raise a
deprecation warning.
These methods will be removed in the `6.2` release.

activestorage/CHANGELOG.md

@@ -1,5 +1,9 @@
+*   Deprecate usage of `purge` and `purge_later` from the association extension.
+
+    *Jacopo Beschi*
+
 *   Allow setting a `Cache-Control` on files uploaded to GCS.
-    
+
     ```yaml
     gcs:
       service: GCS

activestorage/lib/active_storage/attached/model.rb

@@ -155,14 +155,26 @@ module ActiveStorage
 
         has_many :"#{name}_attachments", -> { where(name: name) }, as: :record, class_name: "ActiveStorage::Attachment", inverse_of: :record, dependent: :destroy, strict_loading: strict_loading do
           def purge
+            deprecate(:purge)
             each(&:purge)
             reset
           end
 
           def purge_later
+            deprecate(:purge_later)
             each(&:purge_later)
             reset
           end
+
+          private
+          def deprecate(action)
+            reflection_name = proxy_association.reflection.name
+            attached_name = reflection_name.to_s.partition("_").first
+            ActiveSupport::Deprecation.warn(<<-MSG.squish)
+              Calling `#{action}` from `#{reflection_name}` is deprecated and will be removed in Rails 7.1.
+              To migrate to Rails 7.1's behavior call `#{action}` from `#{attached_name}` instead: `#{attached_name}.#{action}`.
+            MSG
+          end
         end
         has_many :"#{name}_blobs", through: :"#{name}_attachments", class_name: "ActiveStorage::Blob", source: :blob, strict_loading: strict_loading
 

activestorage/test/models/attached/many_test.rb

@@ -456,6 +456,28 @@ class ActiveStorage::ManyAttachedTest < ActiveSupport::TestCase
     end
   end
 
+  test "purging from the attachments relation" do
+    [ create_blob(filename: "funky.jpg"), create_blob(filename: "town.jpg") ].tap do |blobs|
+      @user.highlights.attach blobs
+      assert @user.highlights.attached?
+
+      message = <<-MSG.squish
+        Calling `purge` from `highlights_attachments` is deprecated and will be removed in Rails 7.1.
+        To migrate to Rails 7.1's behavior call `purge` from `highlights` instead: `highlights.purge`.
+      MSG
+      assert_deprecated(message) do
+        assert_changes -> { @user.updated_at } do
+          @user.highlights_attachments.purge
+        end
+      end
+      assert_not @user.highlights.attached?
+      assert_not ActiveStorage::Blob.exists?(blobs.first.id)
+      assert_not ActiveStorage::Blob.exists?(blobs.second.id)
+      assert_not ActiveStorage::Blob.service.exist?(blobs.first.key)
+      assert_not ActiveStorage::Blob.service.exist?(blobs.second.key)
+    end
+  end
+
   test "purging attachment with shared blobs" do
     [
       create_blob(filename: "funky.jpg"),
@@ -529,6 +551,31 @@ class ActiveStorage::ManyAttachedTest < ActiveSupport::TestCase
     end
   end
 
+  test "purging later from the attachments relation" do
+    [ create_blob(filename: "funky.jpg"), create_blob(filename: "town.jpg") ].tap do |blobs|
+      @user.highlights.attach blobs
+      assert @user.highlights.attached?
+
+      message = <<-MSG.squish
+        Calling `purge_later` from `highlights_attachments` is deprecated and will be removed in Rails 7.1.
+        To migrate to Rails 7.1's behavior call `purge_later` from `highlights` instead: `highlights.purge_later`.
+      MSG
+      assert_deprecated(message) do
+        perform_enqueued_jobs do
+          assert_changes -> { @user.updated_at } do
+            @user.highlights_attachments.purge_later
+          end
+        end
+      end
+
+      assert_not @user.highlights.attached?
+      assert_not ActiveStorage::Blob.exists?(blobs.first.id)
+      assert_not ActiveStorage::Blob.exists?(blobs.second.id)
+      assert_not ActiveStorage::Blob.service.exist?(blobs.first.key)
+      assert_not ActiveStorage::Blob.service.exist?(blobs.second.key)
+    end
+  end
+
   test "purging attachment later with shared blobs" do
     [
       create_blob(filename: "funky.jpg"),