`format: true` does not override existing format constraints.

Closes #9466.

Passing `format: true` used to override the constraints: { format: /json/ }
with `/.+/`. This patch only sets the format if there is no constraint present.

1 files changed, 24 insertions, 0 deletions

diff --git a/actionpack/test/dispatch/routing_test.rb b/actionpack/test/dispatch/routing_test.rb
index 4775324b43..89f406a3d0 100644
--- a/actionpack/test/dispatch/routing_test.rb
+++ b/actionpack/test/dispatch/routing_test.rb
@@ -3407,6 +3407,8 @@ class TestFormatConstraints < ActionDispatch::IntegrationTest
 
       get '/string', to: ok, constraints: { format: 'json'  }
       get '/regexp',  to: ok, constraints: { format: /json/ }
+      get '/json_only', to: ok, format: true, constraints: { format: /json/ }
+      get '/xml_only', to: ok, format: 'xml'
     end
   end
 
@@ -3434,6 +3436,28 @@ class TestFormatConstraints < ActionDispatch::IntegrationTest
     get 'http://www.example.com/regexp.html'
     assert_response :not_found
   end
+
+  def test_enforce_with_format_true_with_constraint
+    get 'http://www.example.com/json_only.json'
+    assert_response :success
+
+    get 'http://www.example.com/json_only.html'
+    assert_response :not_found
+
+    get 'http://www.example.com/json_only'
+    assert_response :not_found
+  end
+
+  def test_enforce_with_string
+    get 'http://www.example.com/xml_only.xml'
+    assert_response :success
+
+    get 'http://www.example.com/xml_only'
+    assert_response :success
+
+    get 'http://www.example.com/xml_only.json'
+    assert_response :not_found
+  end
 end
 
 class TestRouteDefaults < ActionDispatch::IntegrationTest