Warn if first argument is not a functional component

Author: acdlite

packages/react-reconciler/src/__tests__/ReactPure-test.internal.js

@@ -170,5 +170,25 @@ describe('pure', () => {
       expect(ReactNoop.flush()).toEqual(['Old count: 0, New count: 1', 1]);
       expect(ReactNoop.getChildren()).toEqual([span(1)]);
     });
+
+    it('warns for class components', () => {
+      class SomeClass extends React.Component {
+        render() {
+          return null;
+        }
+      }
+      expect(() => pure(SomeClass)).toWarnDev(
+        'pure: The first argument must be a functional component.',
+        {withoutStack: true},
+      );
+    });
+
+    it('warns if first argument is not a function', () => {
+      expect(() => pure()).toWarnDev(
+        'pure: The first argument must be a functional component. Instead ' +
+          'received: undefined',
+        {withoutStack: true},
+      );
+    });
   }
 });

packages/react/src/pure.js

@@ -17,9 +17,19 @@ export default function pure<Props>(
     if (typeof render !== 'function') {
       warningWithoutStack(
         false,
-        'pure requires a render function but was given %s.',
+        'pure: The first argument must be a functional component. Instead ' +
+          'received: %s',
         render === null ? 'null' : typeof render,
       );
+    } else {
+      const prototype = render.prototype;
+      if (!!(prototype && prototype.isReactComponent)) {
+        warningWithoutStack(
+          false,
+          'pure: The first argument must be a functional component. Classes ' +
+            'are not supported. Use React.PureComponent instead.',
+        );
+      }
     }
   }
   return {