Clear unnecessary legacy URLs

When renaming a page back to a URL it used to have, we get a legacy URL
that is the same as the current URL of the page, which can lead to
infinite redirects. This deletes any legacy URLs that are the same as
the current URL name in a callback.

app/models/alchemy/page/page_naming.rb

@@ -25,6 +25,8 @@ module PageNaming
         after_update :update_descendants_urlnames,
           if: :saved_change_to_urlname?
 
+        before_save :destroy_obsolete_legacy_urls, if: :renamed?
+
         after_move :update_urlname!
       end
 
@@ -55,6 +57,11 @@ def update_descendants_urlnames
         descendants.each(&:update_urlname!)
       end
 
+      def destroy_obsolete_legacy_urls
+        obsolete_legacy_urls = legacy_urls.select { |legacy_url| legacy_url.urlname == urlname }
+        legacy_urls.destroy(obsolete_legacy_urls)
+      end
+
       # Sets the urlname to a url friendly slug.
       # Either from name, or if present, from urlname.
       # The urlname contains the whole path including parent urlnames.

spec/models/alchemy/page_spec.rb

@@ -1689,6 +1689,18 @@ def copy_children_to(new_parent)
           expect(page.legacy_urls.pluck(:urlname)).to include("parentparent/parent/page")
         end
       end
+
+      context "if new urlname exists as a legacy url" do
+        it "will delete obsolete legacy_urls" do
+          expect(page.urlname).to eq("parentparent/parent/page")
+          page.update!(urlname: "other-name")
+          expect(page.legacy_urls.pluck(:urlname)).to include("parentparent/parent/page")
+          page.update!(urlname: "page")
+          expect(page.legacy_urls.pluck(:urlname)).to include("parentparent/parent/other-name")
+          expect(page.urlname).to eq("parentparent/parent/page")
+          expect(page.legacy_urls.pluck(:urlname)).not_to include("parentparent/parent/page")
+        end
+      end
     end
 
     describe "#update_node!" do