Redirect to root or back when invite not found

- provide a more friendly user experience instead
  of 404'ing them.

app/controllers/invites_controller.rb

@@ -84,7 +84,7 @@ class InvitesController < ApplicationController
   def ensure_member_exists
     return if member
 
-    render_404
+    redirect_back_or_default(options: { alert: _("The invitation can not be found with the provided invite token.") })
   end
 
   def authenticate_user!

changelogs/unreleased/326734-previously-accepted-invites-should-redirect-to-the-gitlab-product.yml

+---
+title: Invalid invite tokens should redirect to the GitLab product
+merge_request: 60666
+author:
+type: other

locale/gitlab.pot

@@ -31802,6 +31802,9 @@ msgstr ""
 msgid "The interval must be one of %{intervals}."
 msgstr ""
 
+msgid "The invitation can not be found with the provided invite token."
+msgstr ""
+
 msgid "The invitation could not be accepted."
 msgstr ""
 

spec/controllers/invites_controller_spec.rb

@@ -14,10 +14,11 @@ RSpec.describe InvitesController do
     context 'when invite token is not valid' do
       let(:params) { { id: '_bogus_token_' } }
 
-      it 'renders the 404 page' do
+      it 'redirects to root' do
         request
 
-        expect(response).to have_gitlab_http_status(:not_found)
+        expect(response).to redirect_to(root_path)
+        expect(controller).to set_flash[:alert].to('The invitation can not be found with the provided invite token.')
       end
     end
   end