Fix "null" instead of the component stack in a warning

src/renderers/__tests__/ReactStatelessComponent-test.js

@@ -295,6 +295,43 @@ describe('ReactStatelessComponent', () => {
     console.error.calls.reset();
   });
 
+  // This guards against a regression caused by clearing the current debug fiber.
+  // https://github.com/facebook/react/issues/10831
+  it('should warn when giving a function ref with context', () => {
+    spyOn(console, 'error');
+
+    function Child() {
+      return null;
+    }
+    Child.contextTypes = {
+      foo: PropTypes.string,
+    };
+
+    class Parent extends React.Component {
+      static childContextTypes = {
+        foo: PropTypes.string,
+      };
+      getChildContext() {
+        return {
+          foo: 'bar',
+        };
+      }
+      render() {
+        return <Child ref={function() {}} />;
+      }
+    }
+
+    ReactTestUtils.renderIntoDocument(<Parent />);
+    expectDev(console.error.calls.count()).toBe(1);
+    expectDev(normalizeCodeLocInfo(console.error.calls.argsFor(0)[0])).toBe(
+      'Warning: Stateless function components cannot be given refs. ' +
+        'Attempts to access this ref will fail.\n\nCheck the render method ' +
+        'of `Parent`.\n' +
+        '    in Child (at **)\n' +
+        '    in Parent (at **)',
+    );
+  });
+
   it('should provide a null ref', () => {
     function Child() {
       return <div />;

src/renderers/shared/fiber/ReactFiberContext.js

@@ -89,15 +89,20 @@ exports.getMaskedContext = function(
 
   if (__DEV__) {
     const name = getComponentName(workInProgress) || 'Unknown';
-    ReactDebugCurrentFiber.setCurrentFiber(workInProgress, null);
+    if (workInProgress !== ReactDebugCurrentFiber.current) {
+      warning(
+        false,
+        'Expected the work in progress to match the currently processed fiber. ' +
+          'This error is likely caused by a bug in React. Please file an issue.',
+      );
+    }
     checkPropTypes(
       contextTypes,
       context,
       'context',
       name,
       ReactDebugCurrentFiber.getCurrentFiberStackAddendum,
     );
-    ReactDebugCurrentFiber.resetCurrentFiber();
   }
 
   // Cache unmasked context so we can avoid recreating masked context unless necessary.
@@ -184,11 +189,19 @@ function processChildContext(
 
   let childContext;
   if (__DEV__) {
+    // TODO: we only have to store the "previous" fiber and phase and restore them
+    // because this method can be called outside of reconciliation. We can remove this
+    // when we stop supporting unstable_renderSubtreeIntoContainer.
+    const previousCurrentFiber = ReactDebugCurrentFiber.current;
+    const previousCurrentPhase = ReactDebugCurrentFiber.phase;
     ReactDebugCurrentFiber.setCurrentFiber(fiber, 'getChildContext');
     startPhaseTimer(fiber, 'getChildContext');
     childContext = instance.getChildContext();
     stopPhaseTimer();
-    ReactDebugCurrentFiber.resetCurrentFiber();
+    ReactDebugCurrentFiber.setCurrentFiber(
+      previousCurrentFiber,
+      previousCurrentPhase,
+    );
   } else {
     childContext = instance.getChildContext();
   }
@@ -208,6 +221,11 @@ function processChildContext(
     // assume anything about the given fiber. We won't pass it down if we aren't sure.
     // TODO: remove this hack when we delete unstable_renderSubtree in Fiber.
     const workInProgress = isReconciling ? fiber : null;
+    // TODO: we only have to store the "previous" fiber and phase and restore them
+    // because this method can be called outside of reconciliation. We can remove this
+    // when we stop supporting unstable_renderSubtreeIntoContainer.
+    const previousCurrentFiber = ReactDebugCurrentFiber.current;
+    const previousCurrentPhase = ReactDebugCurrentFiber.phase;
     ReactDebugCurrentFiber.setCurrentFiber(workInProgress, null);
     checkPropTypes(
       childContextTypes,
@@ -216,7 +234,10 @@ function processChildContext(
       name,
       ReactDebugCurrentFiber.getCurrentFiberStackAddendum,
     );
-    ReactDebugCurrentFiber.resetCurrentFiber();
+    ReactDebugCurrentFiber.setCurrentFiber(
+      previousCurrentFiber,
+      previousCurrentPhase,
+    );
   }
 
   return {...parentContext, ...childContext};