After callback warning

CHANGELOG.md

@@ -11,6 +11,7 @@
 * [#1252](https://github.com/ruby-grape/grape/pull/1252): Allow default to be a subset or equal to allowed values without raising IncompatibleOptionValues - [@jeradphelps](https://github.com/jeradphelps).
 * [#1255](https://github.com/ruby-grape/grape/pull/1255): Allow param type definition in `route_param` - [@namusyaka](https://github.com/namusyaka).
 * [#1257](https://github.com/ruby-grape/grape/pull/1257): Allow Proc, Symbol or String in `rescue_from with: ...` - [@namusyaka](https://github.com/namusyaka).
+* [#1285](https://github.com/ruby-grape/grape/pull/1285): Add a warning for errors appearing in `after` callbacks - [@gregormelhorn](https://github.com/gregormelhorn).
 * Your contribution here.
 
 #### Fixes

lib/grape/middleware/base.rb

@@ -29,7 +29,12 @@ def call!(env)
         begin
           @app_response = @app.call(@env)
         ensure
-          after_response = after
+          begin
+            after_response = after
+          rescue StandardError => e
+            warn "caught error of type #{e.class} in after callback inside #{self.class.name} : #{e.message}"
+            raise e
+          end
         end
 
         response = after_response || @app_response

spec/grape/middleware/base_spec.rb

@@ -48,6 +48,25 @@
     end
   end
 
+  context 'after callback with errors' do
+    it 'does not overwrite the application response' do
+      expect(subject.call({})).to eq([200, {}, 'Hi there.'])
+    end
+
+    context 'with patched warnings' do
+      before do
+        @warnings = warnings = []
+        allow_any_instance_of(Grape::Middleware::Base).to receive(:warn) { |m| warnings << m }
+        allow(subject).to receive(:after).and_raise(StandardError)
+      end
+
+      it 'does show a warning' do
+        expect { subject.call({}) }.to raise_error(StandardError)
+        expect(@warnings).not_to be_empty
+      end
+    end
+  end
+
   it 'is able to access the response' do
     subject.call({})
     expect(subject.response).to be_kind_of(Rack::Response)