Fixed incompatibility between react-debug-tools and useContext()

packages/react-debug-tools/src/__tests__/ReactHooksInspectionIntegration-test.js

@@ -427,4 +427,42 @@ describe('ReactHooksInspectionIntegration', () => {
     expect(setterCalls[0]).not.toBe(initial);
     expect(setterCalls[1]).toBe(initial);
   });
+
+  // This test case is based on an open source bug report:
+  // facebookincubator/redux-react-hook/issues/34#issuecomment-466693787
+  it('should properly advance the current hook for useContext', () => {
+    const MyContext = React.createContext(1);
+
+    let incrementCount;
+
+    function Foo(props) {
+      const context = React.useContext(MyContext);
+      const [data, setData] = React.useState({count: context});
+
+      incrementCount = () => setData(({count}) => ({count: count + 1}));
+
+      return <div>count: {data.count}</div>;
+    }
+
+    const renderer = ReactTestRenderer.create(<Foo />);
+    expect(renderer.toJSON()).toEqual({
+      type: 'div',
+      props: {},
+      children: ['count: ', '1'],
+    });
+
+    act(incrementCount);
+    expect(renderer.toJSON()).toEqual({
+      type: 'div',
+      props: {},
+      children: ['count: ', '2'],
+    });
+
+    const childFiber = renderer.root._currentFiber();
+    const tree = ReactDebugTools.inspectHooksOfFiber(childFiber);
+    expect(tree).toEqual([
+      {name: 'Context', value: 1, subHooks: []},
+      {name: 'State', value: {count: 2}, subHooks: []},
+    ]);
+  });
 });

packages/react-reconciler/src/ReactFiber.js

@@ -15,6 +15,7 @@ import type {SideEffectTag} from 'shared/ReactSideEffectTags';
 import type {ExpirationTime} from './ReactFiberExpirationTime';
 import type {UpdateQueue} from './ReactUpdateQueue';
 import type {ContextDependencyList} from './ReactFiberNewContext';
+import type {HookType} from './ReactFiberHooks';
 
 import invariant from 'shared/invariant';
 import warningWithoutStack from 'shared/warningWithoutStack';
@@ -204,6 +205,9 @@ export type Fiber = {|
   _debugSource?: Source | null,
   _debugOwner?: Fiber | null,
   _debugIsCurrentlyTiming?: boolean,
+
+  // Used to verify that the order of hooks does not change between renders.
+  _debugHookTypes?: Array<HookType> | null,
 |};
 
 let debugCounter;
@@ -285,6 +289,7 @@ function FiberNode(
     this._debugSource = null;
     this._debugOwner = null;
     this._debugIsCurrentlyTiming = false;
+    this._debugHookTypes = null;
     if (!hasBadMapPolyfill && typeof Object.preventExtensions === 'function') {
       Object.preventExtensions(this);
     }
@@ -370,6 +375,7 @@ export function createWorkInProgress(
       workInProgress._debugID = current._debugID;
       workInProgress._debugSource = current._debugSource;
       workInProgress._debugOwner = current._debugOwner;
+      workInProgress._debugHookTypes = current._debugHookTypes;
     }
 
     workInProgress.alternate = current;
@@ -723,5 +729,6 @@ export function assignFiberPropertiesInDEV(
   target._debugSource = source._debugSource;
   target._debugOwner = source._debugOwner;
   target._debugIsCurrentlyTiming = source._debugIsCurrentlyTiming;
+  target._debugHookTypes = source._debugHookTypes;
   return target;
 }