Fix redirects to issue sidebar JSON after sign in

request.xhr? is unreliable because the X-Requested-With header can be
missing if it is requested using `fetch`.

This changes the check to check for the HTML request format

app/controllers/projects/issues_controller.rb

@@ -323,7 +323,7 @@ class Projects::IssuesController < Projects::ApplicationController
   end
 
   def store_uri
-    if request.get? && !request.xhr?
+    if request.get? && request.format.html?
       store_location_for :user, request.fullpath
     end
   end

changelogs/unreleased/267583-fix-storing-of-issue-json-for-redirect.yml

+---
+title: Fix redirects to issue sidebar JSON when visiting the login page
+merge_request: 45194
+author:
+type: fixed

spec/controllers/projects/issues_controller_spec.rb

@@ -388,15 +388,23 @@ RSpec.describe Projects::IssuesController do
   # Rails router. A controller-style spec matches the wrong route, and
   # session['user_return_to'] becomes incorrect.
   describe 'Redirect after sign in', type: :request do
-    context 'with an AJAX request' do
+    before_all do
+      project.add_developer(user)
+    end
+
+    before do
+      login_as(user)
+    end
+
+    context 'with a JSON request' do
       it 'does not store the visited URL' do
-        get project_issue_path(project, issue), xhr: true
+        get project_issue_path(project, issue, format: :json)
 
         expect(session['user_return_to']).to be_blank
       end
     end
 
-    context 'without an AJAX request' do
+    context 'with an HTML request' do
       it 'stores the visited URL' do
         get project_issue_path(project, issue)