Merge pull request #19377 from sb8244/issue-19036

when a template is missing for the default render, do head no_content instead

actionpack/CHANGELOG.md

+*   For actions with no corresponding templates, render `head :no_content`
+    instead of raising an error. This allows for slimmer API controller
+    methods that simply work, without needing further instructions.
+
+    See #19036.
+
+    *Stephen Bussey*
+
 *   Provide friendlier access to request variants.
 
         request.variant = :phone

actionpack/lib/action_controller/metal/implicit_render.rb

@@ -7,7 +7,12 @@ def send_action(method, *args)
     end
 
     def default_render(*args)
-      render(*args)
+      if template_exists?(action_name.to_s, _prefixes, variants: request.variant)
+        render(*args)
+      else
+        logger.info "No template found for #{self.class.name}\##{action_name}, rendering head :no_content"
+        head :no_content
+      end
     end
 
     def method_for_action(action_name)

actionpack/test/controller/mime/respond_to_test.rb

@@ -608,19 +608,29 @@ def test_invalid_format
   end
 
   def test_invalid_variant
+    logger = ActiveSupport::LogSubscriber::TestHelper::MockLogger.new
+    old_logger, ActionController::Base.logger = ActionController::Base.logger, logger
+
     @request.variant = :invalid
-    assert_raises(ActionView::MissingTemplate) do
-      get :variant_with_implicit_rendering
-    end
+    get :variant_with_implicit_rendering
+    assert_response :no_content
+    assert_equal 1, logger.logged(:info).select{ |s| s =~ /No template found/ }.size, "Implicit head :no_content not logged"
+  ensure
+    ActionController::Base.logger = old_logger
   end
 
   def test_variant_not_set_regular_template_missing
-    assert_raises(ActionView::MissingTemplate) do
-      get :variant_with_implicit_rendering
-    end
+    get :variant_with_implicit_rendering
+    assert_response :no_content
   end
 
   def test_variant_with_implicit_rendering
+    @request.variant = :implicit
+    get :variant_with_implicit_rendering
+    assert_response :no_content
+  end
+
+  def test_variant_with_implicit_template_rendering
     @request.variant = :mobile
     get :variant_with_implicit_rendering
     assert_equal "text/html", @response.content_type

actionview/lib/action_view/lookup_context.rb

@@ -126,7 +126,7 @@ def find_all(name, prefixes = [], partial = false, keys = [], options = {})
         @view_paths.find_all(*args_for_lookup(name, prefixes, partial, keys, options))
       end
 
-      def exists?(name, prefixes = [], partial = false, keys = [], options = {})
+      def exists?(name, prefixes = [], partial = false, keys = [], **options)
         @view_paths.exists?(*args_for_lookup(name, prefixes, partial, keys, options))
       end
       alias :template_exists? :exists?