Avoid purging attached blob when replacing it with itself

activestorage/lib/active_storage/attached/one.rb

@@ -64,12 +64,16 @@ def purge_later
 
     private
       def replace(attachable)
-        blob.tap do
+        unless attachable == blob
+          previous_blob = blob
+
           transaction do
             detach
             write_attachment build_attachment_from(attachable)
           end
-        end.purge_later
+
+          previous_blob.purge_later
+        end
       end
 
       def build_attachment_from(attachable)

activestorage/test/models/attachments_test.rb

@@ -56,6 +56,18 @@ class ActiveStorage::AttachmentsTest < ActiveSupport::TestCase
     assert ActiveStorage::Blob.service.exist?(@user.avatar.key)
   end
 
+  test "replace attached blob with itself" do
+    @user.avatar.attach create_blob(filename: "funky.jpg")
+
+    assert_no_changes -> { @user.reload.avatar.blob } do
+      assert_no_changes -> { @user.reload.avatar.attachment } do
+        assert_no_enqueued_jobs do
+          @user.avatar.attach @user.avatar.blob
+        end
+      end
+    end
+  end
+
   test "attach blob to new record" do
     user = User.new(name: "Jason")