Merge pull request #8723 from bvaughn/improve-unmasked-context-caching

Improve unmasked context caching

Author: bvaughn

src/renderers/shared/fiber/ReactFiberClassComponent.js

@@ -16,8 +16,10 @@ import type { Fiber } from 'ReactFiber';
 import type { PriorityLevel } from 'ReactPriorityLevel';
 
 var {
+  cacheContext,
   getMaskedContext,
   getUnmaskedContext,
+  isContextConsumer,
 } = require('ReactFiberContext');
 var {
   addUpdate,
@@ -28,6 +30,7 @@ var {
 var { hasContextChanged } = require('ReactFiberContext');
 var { getComponentName, isMounted } = require('ReactFiberTreeReflection');
 var ReactInstanceMap = require('ReactInstanceMap');
+var emptyObject = require('emptyObject');
 var shallowEqual = require('shallowEqual');
 var warning = require('warning');
 var invariant = require('invariant');
@@ -206,15 +209,17 @@ module.exports = function(
     const ctor = workInProgress.type;
     const props = workInProgress.pendingProps;
     const unmaskedContext = getUnmaskedContext(workInProgress);
-    const context = getMaskedContext(workInProgress, unmaskedContext);
+    const needsContext = isContextConsumer(workInProgress);
+    const context = needsContext ? getMaskedContext(workInProgress, unmaskedContext) : emptyObject;
     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;
+    if (needsContext) {
+      cacheContext(workInProgress, unmaskedContext, context);
+    }
 
     return instance;
   }

src/renderers/shared/fiber/ReactFiberContext.js

@@ -57,6 +57,13 @@ function getUnmaskedContext(workInProgress : Fiber) : Object {
 }
 exports.getUnmaskedContext = getUnmaskedContext;
 
+function cacheContext(workInProgress : Fiber, unmaskedContext : Object, maskedContext : Object) {
+  const instance = workInProgress.stateNode;
+  instance.__reactInternalMemoizedUnmaskedChildContext = unmaskedContext;
+  instance.__reactInternalMemoizedMaskedChildContext = maskedContext;
+}
+exports.cacheContext = cacheContext;
+
 exports.getMaskedContext = function(workInProgress : Fiber, unmaskedContext : Object) {
   const type = workInProgress.type;
   const contextTypes = type.contextTypes;
@@ -86,9 +93,9 @@ exports.getMaskedContext = function(workInProgress : Fiber, unmaskedContext : Ob
   }
 
   // Cache unmasked context so we can avoid recreating masked context unless necessary.
+  // Context is created before the class component is instantiated so check for instance.
   if (instance) {
-    instance.__reactInternalMemoizedUnmaskedChildContext = unmaskedContext;
-    instance.__reactInternalMemoizedMaskedChildContext = context;
+    cacheContext(workInProgress, unmaskedContext, context);
   }
 
   return context;
@@ -98,6 +105,14 @@ exports.hasContextChanged = function() : boolean {
   return didPerformWorkStackCursor.current;
 };
 
+function isContextConsumer(fiber : Fiber) : boolean {
+  return (
+    fiber.tag === ClassComponent &&
+    fiber.type.contextTypes != null
+  );
+}
+exports.isContextConsumer = isContextConsumer;
+
 function isContextProvider(fiber : Fiber) : boolean {
   return (
     fiber.tag === ClassComponent &&