Merge pull request #5346 from prometheansacrifice/warn-immutable-props

Warns when mutated props are passed.

src/renderers/shared/reconciler/ReactCompositeComponent.js

@@ -194,6 +194,18 @@ var ReactCompositeComponentMixin = {
           Component.displayName || Component.name || 'Component'
         );
       }
+
+      var propsMutated = inst.props !== publicProps;
+      var componentName =
+            Component.displayName || Component.name || 'Component';
+
+      warning(
+        typeof inst.props === 'undefined' ||
+          !propsMutated,
+        '%s(...): When calling super() in `%s`, make sure to pass ' +
+          'up the same props that your component\'s constructor was passed.',
+        componentName, componentName
+      );
     }
 
     // These should be set up in the constructor, but as a convenience for

src/renderers/shared/reconciler/__tests__/ReactCompositeComponent-test.js

@@ -1171,4 +1171,31 @@ describe('ReactCompositeComponent', function() {
 
   });
 
+  it('should warn when mutated props are passed', function() {
+
+    var container = document.createElement('div');
+
+    class Foo extends React.Component {
+      constructor(props) {
+        var _props = { idx: props.idx + '!' };
+        super(_props);
+      }
+
+      render() {
+        return <span />;
+      }
+    }
+
+    expect(console.error.calls.length).toBe(0);
+
+    ReactDOM.render(<Foo idx="qwe" />, container);
+
+    expect(console.error.calls.length).toBe(1);
+    expect(console.error.argsForCall[0][0]).toContain(
+      'Foo(...): When calling super() in `Foo`, make sure to pass ' +
+        'up the same props that your component\'s constructor was passed.'
+    );
+
+  });
+
 });