Dont recreate maked context unless unmasked context changes

scripts/fiber/tests-passing.txt

@@ -1165,6 +1165,7 @@ src/renderers/shared/fiber/__tests__/ReactIncremental-test.js
 * reads context when setState is above the provider
 * maintains the correct context when providers bail out due to low priority
 * maintains the correct context when unwinding due to an error in render
+* should not recreate masked context unless inputs have changed
 
 src/renderers/shared/fiber/__tests__/ReactIncrementalErrorHandling-test.js
 * catches render error in a boundary during full deferred mounting

src/renderers/shared/fiber/ReactFiberBeginWork.js

@@ -31,6 +31,7 @@ var {
 var ReactTypeOfWork = require('ReactTypeOfWork');
 var {
   getMaskedContext,
+  getUnmaskedContext,
   hasContextChanged,
   pushContextProvider,
   pushTopLevelContextObject,
@@ -210,7 +211,8 @@ module.exports = function<T, P, I, TI, C, CX, CI>(
       return bailoutOnAlreadyFinishedWork(current, workInProgress);
     }
 
-    var context = getMaskedContext(workInProgress);
+    var unmaskedContext = getUnmaskedContext(workInProgress);
+    var context = getMaskedContext(workInProgress, unmaskedContext);
 
     var nextChildren;
 
@@ -427,7 +429,8 @@ module.exports = function<T, P, I, TI, C, CX, CI>(
     }
     var fn = workInProgress.type;
     var props = workInProgress.pendingProps;
-    var context = getMaskedContext(workInProgress);
+    var unmaskedContext = getUnmaskedContext(workInProgress);
+    var context = getMaskedContext(workInProgress, unmaskedContext);
 
     var value;
 

src/renderers/shared/fiber/ReactFiberClassComponent.js

@@ -17,6 +17,7 @@ import type { PriorityLevel } from 'ReactPriorityLevel';
 
 var {
   getMaskedContext,
+  getUnmaskedContext,
 } = require('ReactFiberContext');
 var {
   addUpdate,
@@ -204,10 +205,17 @@ module.exports = function(
   function constructClassInstance(workInProgress : Fiber) : any {
     const ctor = workInProgress.type;
     const props = workInProgress.pendingProps;
-    const context = getMaskedContext(workInProgress);
+    const unmaskedContext = getUnmaskedContext(workInProgress);
+    const context = getMaskedContext(workInProgress, unmaskedContext);
     const instance = new ctor(props, context);
     adoptClassInstance(workInProgress, instance);
     checkClassInstance(workInProgress);
+
+    // Cache unmasked context so we can avoid recreating masked context unless necessary.
+    // ReactFiberContext usually updates this cache but can't for newly-created instances.
+    instance.__reactInternalMemoizedUnmaskedChildContext = unmaskedContext;
+    instance.__reactInternalMemoizedMaskedChildContext = context;
+
     return instance;
   }
 
@@ -221,9 +229,11 @@ module.exports = function(
       throw new Error('There must be pending props for an initial mount.');
     }
 
+    const unmaskedContext = getUnmaskedContext(workInProgress);
+
     instance.props = props;
     instance.state = state;
-    instance.context = getMaskedContext(workInProgress);
+    instance.context = getMaskedContext(workInProgress, unmaskedContext);
 
     if (typeof instance.componentWillMount === 'function') {
       instance.componentWillMount();
@@ -256,7 +266,8 @@ module.exports = function(
         throw new Error('There should always be pending or memoized props.');
       }
     }
-    const newContext = getMaskedContext(workInProgress);
+    const newUnmaskedContext = getUnmaskedContext(workInProgress);
+    const newContext = getMaskedContext(workInProgress, newUnmaskedContext);
 
     // TODO: Should we deal with a setState that happened after the last
     // componentWillMount and before this componentWillMount? Probably
@@ -277,7 +288,7 @@ module.exports = function(
     const newInstance = constructClassInstance(workInProgress);
     newInstance.props = newProps;
     newInstance.state = newState = newInstance.state || null;
-    newInstance.context = getMaskedContext(workInProgress);
+    newInstance.context = newContext;
 
     if (typeof newInstance.componentWillMount === 'function') {
       newInstance.componentWillMount();
@@ -314,7 +325,8 @@ module.exports = function(
       }
     }
     const oldContext = instance.context;
-    const newContext = getMaskedContext(workInProgress);
+    const newUnmaskedContext = getUnmaskedContext(workInProgress);
+    const newContext = getMaskedContext(workInProgress, newUnmaskedContext);
 
     // Note: During these life-cycles, instance.props/instance.state are what
     // ever the previously attempted to render - not the "current". However,

src/renderers/shared/fiber/ReactFiberContext.js

@@ -55,15 +55,26 @@ function getUnmaskedContext(workInProgress : Fiber) : Object {
   }
   return contextStackCursor.current;
 }
+exports.getUnmaskedContext = getUnmaskedContext;
 
-exports.getMaskedContext = function(workInProgress : Fiber) {
+exports.getMaskedContext = function(workInProgress : Fiber, unmaskedContext : Object) {
   const type = workInProgress.type;
   const contextTypes = type.contextTypes;
   if (!contextTypes) {
     return emptyObject;
   }
 
-  const unmaskedContext = getUnmaskedContext(workInProgress);
+  // Avoid recreating masked context unless unmasked context has changed.
+  // Failing to do this will result in unnecessary calls to componentWillReceiveProps.
+  // This may trigger infinite loops if componentWillReceiveProps calls setState.
+  const instance = workInProgress.stateNode;
+  if (
+    instance &&
+    instance.__reactInternalMemoizedUnmaskedChildContext === unmaskedContext
+  ) {
+    return instance.__reactInternalMemoizedMaskedChildContext;
+  }
+
   const context = {};
   for (let key in contextTypes) {
     context[key] = unmaskedContext[key];
@@ -74,6 +85,12 @@ exports.getMaskedContext = function(workInProgress : Fiber) {
     checkReactTypeSpec(contextTypes, context, 'context', name, null, workInProgress);
   }
 
+  // Cache unmasked context so we can avoid recreating masked context unless necessary.
+  if (instance) {
+    instance.__reactInternalMemoizedUnmaskedChildContext = unmaskedContext;
+    instance.__reactInternalMemoizedMaskedChildContext = context;
+  }
+
   return context;
 };
 

src/renderers/shared/fiber/__tests__/ReactIncremental-test.js

@@ -2021,4 +2021,50 @@ describe('ReactIncremental', () => {
     });
     ReactNoop.flush();
   });
+
+  it('should not recreate masked context unless inputs have changed', () => {
+    const ops = [];
+
+    let scuCounter = 0;
+
+    class MyComponent extends React.Component {
+      static contextTypes = {};
+      componentDidMount(prevProps, prevState) {
+        ops.push('componentDidMount');
+        this.setState({ setStateInCDU: true });
+      }
+      componentDidUpdate(prevProps, prevState) {
+        ops.push('componentDidUpdate');
+        if (this.state.setStateInCDU) {
+          this.setState({ setStateInCDU: false });
+        }
+      }
+      componentWillReceiveProps(nextProps) {
+        ops.push('componentWillReceiveProps');
+        this.setState({ setStateInCDU: true });
+      }
+      render() {
+        ops.push('render');
+        return null;
+      }
+      shouldComponentUpdate(nextProps, nextState) {
+        ops.push('shouldComponentUpdate');
+        return scuCounter++ < 5; // Don't let test hang
+      }
+    }
+
+    ReactNoop.render(<MyComponent />);
+    ReactNoop.flush();
+
+    expect(ops).toEqual([
+      'render',
+      'componentDidMount',
+      'shouldComponentUpdate',
+      'render',
+      'componentDidUpdate',
+      'shouldComponentUpdate',
+      'render',
+      'componentDidUpdate',
+    ]);
+  });
 });