AO3-6359 Fix Possible to delete the pseud that corresponds with your username if the capitalization or diacritics differ

app/models/user.rb

@@ -536,25 +536,24 @@ def self.fetch_orphan_account
 
   def update_pseud_name
     return unless saved_change_to_login? && login_before_last_save.present?
-
-    old_pseud = pseuds.where(name: login_before_last_save).first
-    if login.downcase == login_before_last_save.downcase
-      old_pseud.name = login
-      old_pseud.save!
-    else
+
+    pseud_to_update = pseuds.where(name: login_before_last_save).first
+    # If the new login is (case insensitive) different from the old login
+    if login != login_before_last_save.downcase
       new_pseud = pseuds.where(name: login).first
-      # do nothing if they already have the matching pseud
+      # If the user does not have an existing pseud for the new login
       if new_pseud.blank?
-        if old_pseud.present?
-          # change the old pseud to match
-          old_pseud.name = login
-          old_pseud.save!(validate: false)
-        else
+        # If the pseud for the old login doesn't exist
+        if pseud_to_update.blank?
           # shouldn't be able to get here, but just in case
           Pseud.create!(name: login, user_id: id)
         end
+      else
+        pseud_to_update = new_pseud
       end
     end
+    pseud_to_update.name = login
+    pseud_to_update.save!(validate: justification_enabled?)
   end
 
   def reindex_user_creations_after_rename

spec/models/user_spec.rb

@@ -359,6 +359,23 @@
         expect(log_item.note).to eq("Change made by #{admin.login}")
       end
     end
+
+    context "username was changed to match an existing pseud's name except with alternate capitalization and diacritics" do
+      let(:new_pseud) { build(:pseud, name: "New_Usernamé") }
+
+      before do
+        existing_user.pseuds << new_pseud
+        existing_user.update!(login: "new_username")
+        existing_user.reload
+      end
+
+      it "pseud's capitalization and diacritics were changed to match the new username's" do 
+        expect(existing_user.pseuds.size).to eq(2)
+        expect(existing_user.pseuds.second.name).to eq(existing_user.login)
+        expect(existing_user.pseuds.second.name).to eq("new_username")
+        expect(existing_user.login).to eq("new_username")
+      end
+    end
   end
 
   describe ".search_multiple_by_email" do