add legacy context API warning in strict mode

packages/react-reconciler/src/ReactFiberClassComponent.js

@@ -668,6 +668,11 @@ function mountClassInstance(
         workInProgress,
         instance,
       );
+
+      ReactStrictModeWarnings.recordLegacyContextWarning(
+        workInProgress,
+        instance,
+      );
     }
 
     if (warnAboutDeprecatedLifecycles) {

packages/react-reconciler/src/ReactFiberScheduler.js

@@ -42,6 +42,7 @@ import {
   enableUserTimingAPI,
   replayFailedUnitOfWorkWithInvokeGuardedCallback,
   warnAboutDeprecatedLifecycles,
+  warnAboutLegacyContextAPI,
 } from 'shared/ReactFeatureFlags';
 import getComponentName from 'shared/getComponentName';
 import invariant from 'fbjs/lib/invariant';
@@ -439,6 +440,10 @@ function commitAllLifeCycles(
     if (warnAboutDeprecatedLifecycles) {
       ReactStrictModeWarnings.flushPendingDeprecationWarnings();
     }
+
+    if (warnAboutLegacyContextAPI) {
+      ReactStrictModeWarnings.flushLegacyContextWarning();
+    }
   }
   while (nextEffect !== null) {
     const effectTag = nextEffect.effectTag;

packages/react-reconciler/src/ReactStrictModeWarnings.js

@@ -21,13 +21,17 @@ type LIFECYCLE =
   | 'UNSAFE_componentWillUpdate';
 type LifecycleToComponentsMap = {[lifecycle: LIFECYCLE]: Array<Fiber>};
 type FiberToLifecycleMap = Map<Fiber, LifecycleToComponentsMap>;
+type FiberArray = Array<Fiber>;
+type FiberToFiberComponentsMap = Map<Fiber, FiberArray>;
 
 const ReactStrictModeWarnings = {
   discardPendingWarnings(): void {},
   flushPendingDeprecationWarnings(): void {},
   flushPendingUnsafeLifecycleWarnings(): void {},
   recordDeprecationWarnings(fiber: Fiber, instance: any): void {},
   recordUnsafeLifecycleWarnings(fiber: Fiber, instance: any): void {},
+  recordLegacyContextWarning(fiber: Fiber, instance: any): void {},
+  flushLegacyContextWarning(): void {},
 };
 
 if (__DEV__) {
@@ -41,10 +45,12 @@ if (__DEV__) {
   let pendingComponentWillReceivePropsWarnings: Array<Fiber> = [];
   let pendingComponentWillUpdateWarnings: Array<Fiber> = [];
   let pendingUnsafeLifecycleWarnings: FiberToLifecycleMap = new Map();
+  let pendingLegacyContextWarning: FiberToFiberComponentsMap = new Map();
 
   // Tracks components we have already warned about.
   const didWarnAboutDeprecatedLifecycles = new Set();
   const didWarnAboutUnsafeLifecycles = new Set();
+  const didWarnAboutLegacyContext = new Set();
 
   const setToSortedString = set => {
     const array = [];
@@ -59,6 +65,7 @@ if (__DEV__) {
     pendingComponentWillReceivePropsWarnings = [];
     pendingComponentWillUpdateWarnings = [];
     pendingUnsafeLifecycleWarnings = new Map();
+    pendingLegacyContextWarning = new Map();
   };
 
   ReactStrictModeWarnings.flushPendingUnsafeLifecycleWarnings = () => {
@@ -289,6 +296,67 @@ if (__DEV__) {
       });
     }
   };
+
+  ReactStrictModeWarnings.recordLegacyContextWarning = (
+    fiber: Fiber,
+    instance: any,
+  ) => {
+    const strictRoot = findStrictRoot(fiber);
+    if (strictRoot === null) {
+      warning(
+        false,
+        'Expected to find a StrictMode component in a strict mode tree. ' +
+          'This error is likely caused by a bug in React. Please file an issue.',
+      );
+      return;
+    }
+
+    // Dedup strategy: Warn once per component.
+    if (didWarnAboutLegacyContext.has(fiber.type)) {
+      return;
+    }
+
+    let warningsForRoot = pendingLegacyContextWarning.get(strictRoot);
+
+    if (
+      typeof instance.getChildContext === 'function' ||
+      fiber.type.contextTypes != null ||
+      fiber.type.childContextTypes != null
+    ) {
+      if (warningsForRoot === undefined) {
+        warningsForRoot = [];
+        pendingLegacyContextWarning.set(strictRoot, warningsForRoot);
+      }
+      warningsForRoot.push(fiber);
+    }
+  };
+
+  ReactStrictModeWarnings.flushLegacyContextWarning = () => {
+    ((pendingLegacyContextWarning: any): FiberToFiberComponentsMap).forEach(
+      (fiberArray: FiberArray, strictRoot) => {
+        const uniqueNames = new Set();
+        fiberArray.forEach(fiber => {
+          uniqueNames.add(getComponentName(fiber) || 'Component');
+          didWarnAboutLegacyContext.add(fiber.type);
+        });
+
+        const sortedNames = setToSortedString(uniqueNames);
+        const strictRootComponentStack = getStackAddendumByWorkInProgressFiber(
+          strictRoot,
+        );
+
+        warning(
+          false,
+          'Legacy context API has been detected within a strict-mode tree: %s' +
+            '\n\nPlease update the following components: %s' +
+            '\n\nLearn more about this warning here:' +
+            '\nhttps://fb.me/react-strict-mode-warnings',
+          strictRootComponentStack,
+          sortedNames,
+        );
+      },
+    );
+  };
 }
 
 export default ReactStrictModeWarnings;

packages/react/src/__tests__/ReactStrictMode-test.internal.js

@@ -12,6 +12,7 @@
 let React;
 let ReactFeatureFlags;
 let ReactTestRenderer;
+let PropTypes;
 
 describe('ReactStrictMode', () => {
   describe('debugRenderPhaseSideEffects', () => {
@@ -805,4 +806,72 @@ describe('ReactStrictMode', () => {
       renderer.update(<OuterComponent />);
     });
   });
+
+  describe('context legacy', () => {
+    beforeEach(() => {
+      jest.resetModules();
+      React = require('react');
+      ReactTestRenderer = require('react-test-renderer');
+      PropTypes = require('prop-types');
+      ReactFeatureFlags = require('shared/ReactFeatureFlags');
+      ReactFeatureFlags.warnAboutLegacyContextAPI = true;
+    });
+
+    it('should warn if the legacy context API have been used in strict mode', () => {
+      class LegacyContextProvider extends React.Component {
+        getChildContext() {
+          return {color: 'purple'};
+        }
+
+        render() {
+          return <LegacyContextConsumer />;
+        }
+      }
+
+      LegacyContextProvider.childContextTypes = {
+        color: PropTypes.string,
+      };
+
+      class LegacyContextConsumer extends React.Component {
+        render() {
+          return null;
+        }
+      }
+
+      const {StrictMode} = React;
+
+      class Root extends React.Component {
+        render() {
+          return (
+            <div>
+              <StrictMode>
+                <LegacyContextProvider />
+              </StrictMode>
+            </div>
+          );
+        }
+      }
+
+      LegacyContextConsumer.contextTypes = {
+        color: PropTypes.string,
+      };
+
+      let rendered;
+
+      expect(() => {
+        rendered = ReactTestRenderer.create(<Root />);
+      }).toWarnDev(
+        'Warning: Legacy context API has been detected within a strict-mode tree: ' +
+          '\n    in div (at **)' +
+          '\n    in Root (at **)' +
+          '\n\nPlease update the following components: LegacyContextConsumer, LegacyContextProvider' +
+          '\n\nLearn more about this warning here:' +
+          '\nhttps://fb.me/react-strict-mode-warnings',
+      );
+
+      // Dedupe
+      rendered = ReactTestRenderer.create(<Root />);
+      rendered.update(<Root />);
+    });
+  });
 });

packages/shared/ReactFeatureFlags.js

@@ -33,6 +33,9 @@ export const replayFailedUnitOfWorkWithInvokeGuardedCallback = __DEV__;
 // Warn about deprecated, async-unsafe lifecycles; relates to RFC #6:
 export const warnAboutDeprecatedLifecycles = false;
 
+// Warn about legacy context API
+export const warnAboutLegacyContextAPI = false;
+
 // Gather advanced timing metrics for Profiler subtrees.
 export const enableProfilerTimer = __DEV__;
 

packages/shared/forks/ReactFeatureFlags.native-fabric-fb.js

@@ -18,6 +18,7 @@ export const enableUserTimingAPI = __DEV__;
 export const enableGetDerivedStateFromCatch = false;
 export const enableSuspense = false;
 export const warnAboutDeprecatedLifecycles = false;
+export const warnAboutLegacyContextAPI = __DEV__;
 export const replayFailedUnitOfWorkWithInvokeGuardedCallback = __DEV__;
 export const enableProfilerTimer = __DEV__;
 export const fireGetDerivedStateFromPropsOnStateUpdates = true;

packages/shared/forks/ReactFeatureFlags.native-fabric-oss.js

@@ -18,6 +18,7 @@ export const enableUserTimingAPI = __DEV__;
 export const enableGetDerivedStateFromCatch = false;
 export const enableSuspense = false;
 export const warnAboutDeprecatedLifecycles = false;
+export const warnAboutLegacyContextAPI = false;
 export const replayFailedUnitOfWorkWithInvokeGuardedCallback = __DEV__;
 export const enableProfilerTimer = false;
 export const fireGetDerivedStateFromPropsOnStateUpdates = true;

packages/shared/forks/ReactFeatureFlags.native-fb.js

@@ -26,6 +26,7 @@ export const {
 
 // The rest of the flags are static for better dead code elimination.
 export const enableUserTimingAPI = __DEV__;
+export const warnAboutLegacyContextAPI = __DEV__;
 
 // Only used in www builds.
 export function addUserTimingListener() {

packages/shared/forks/ReactFeatureFlags.native-oss.js

@@ -19,6 +19,7 @@ export const enableSuspense = false;
 export const enableUserTimingAPI = __DEV__;
 export const replayFailedUnitOfWorkWithInvokeGuardedCallback = __DEV__;
 export const warnAboutDeprecatedLifecycles = false;
+export const warnAboutLegacyContextAPI = false;
 export const enableProfilerTimer = __DEV__;
 export const fireGetDerivedStateFromPropsOnStateUpdates = true;
 

packages/shared/forks/ReactFeatureFlags.persistent.js

@@ -18,6 +18,7 @@ export const enableUserTimingAPI = __DEV__;
 export const enableGetDerivedStateFromCatch = false;
 export const enableSuspense = false;
 export const warnAboutDeprecatedLifecycles = false;
+export const warnAboutLegacyContextAPI = false;
 export const replayFailedUnitOfWorkWithInvokeGuardedCallback = __DEV__;
 export const enableProfilerTimer = false;
 export const fireGetDerivedStateFromPropsOnStateUpdates = true;

packages/shared/forks/ReactFeatureFlags.test-renderer.js

@@ -18,6 +18,7 @@ export const enableUserTimingAPI = __DEV__;
 export const enableGetDerivedStateFromCatch = false;
 export const enableSuspense = false;
 export const warnAboutDeprecatedLifecycles = false;
+export const warnAboutLegacyContextAPI = false;
 export const replayFailedUnitOfWorkWithInvokeGuardedCallback = false;
 export const enableProfilerTimer = false;
 export const fireGetDerivedStateFromPropsOnStateUpdates = true;

packages/shared/forks/ReactFeatureFlags.www.js

@@ -23,6 +23,7 @@ export const {
 } = require('ReactFeatureFlags');
 
 // The rest of the flags are static for better dead code elimination.
+export const warnAboutLegacyContextAPI = __DEV__;
 
 // In www, we have experimental support for gathering data
 // from User Timing API calls in production. By default, we

scripts/rollup/shims/react-native-fb/ReactFeatureFlags.js

@@ -14,6 +14,7 @@ const ReactFeatureFlags = {
   debugRenderPhaseSideEffects: false,
   debugRenderPhaseSideEffectsForStrictMode: false,
   warnAboutDeprecatedLifecycles: true,
+  warnAboutLegacyContextAPI: true,
 };
 
 module.exports = ReactFeatureFlags;