[Experimental] API for reading context from within any render phase function

packages/react-noop-renderer/src/createReactNoop.js

@@ -662,7 +662,10 @@ function createReactNoop(reconciler: Function, useMutation: boolean) {
             '- ' +
             // need to explicitly coerce Symbol to a string
             (fiber.type ? fiber.type.name || fiber.type.toString() : '[root]'),
-          '[' + fiber.expirationTime + (fiber.pendingProps ? '*' : '') + ']',
+          '[' +
+            fiber.childExpirationTime +
+            (fiber.pendingProps ? '*' : '') +
+            ']',
         );
         if (fiber.updateQueue) {
           logUpdateQueue(fiber.updateQueue, depth);

packages/react-reconciler/src/ReactFiber.js

@@ -14,6 +14,7 @@ import type {TypeOfMode} from './ReactTypeOfMode';
 import type {TypeOfSideEffect} from 'shared/ReactTypeOfSideEffect';
 import type {ExpirationTime} from './ReactFiberExpirationTime';
 import type {UpdateQueue} from './ReactUpdateQueue';
+import type {ContextDependency} from './ReactFiberNewContext';
 
 import invariant from 'shared/invariant';
 import {enableProfilerTimer} from 'shared/ReactFeatureFlags';
@@ -124,6 +125,9 @@ export type Fiber = {|
   // The state used to create the output
   memoizedState: any,
 
+  // A linked-list of contexts that this fiber depends on
+  firstContextDependency: ContextDependency<mixed> | null,
+
   // Bitfield that describes properties about the fiber and its subtree. E.g.
   // the AsyncMode flag indicates whether the subtree should be async-by-
   // default. When a fiber is created, it inherits the mode of its
@@ -145,9 +149,12 @@ export type Fiber = {|
   lastEffect: Fiber | null,
 
   // Represents a time in the future by which this work should be completed.
-  // This is also used to quickly determine if a subtree has no pending changes.
+  // Does not include work found in its subtree.
   expirationTime: ExpirationTime,
 
+  // This is used to quickly determine if a subtree has no pending changes.
+  childExpirationTime: ExpirationTime,
+
   // This is a pooled version of a Fiber. Every fiber that gets updated will
   // eventually have a pair. There are cases when we can clean up pairs to save
   // memory if we need to.
@@ -213,6 +220,7 @@ function FiberNode(
   this.memoizedProps = null;
   this.updateQueue = null;
   this.memoizedState = null;
+  this.firstContextDependency = null;
 
   this.mode = mode;
 
@@ -224,6 +232,7 @@ function FiberNode(
   this.lastEffect = null;
 
   this.expirationTime = NoWork;
+  this.childExpirationTime = NoWork;
 
   this.alternate = null;
 
@@ -325,12 +334,21 @@ export function createWorkInProgress(
     }
   }
 
-  workInProgress.expirationTime = expirationTime;
+  // Don't touching the subtree's expiration time, which has not changed.
+  workInProgress.childExpirationTime = current.childExpirationTime;
+  if (pendingProps !== current.pendingProps) {
+    // This fiber has new props.
+    workInProgress.expirationTime = expirationTime;
+  } else {
+    // This fiber's props have not changed.
+    workInProgress.expirationTime = current.expirationTime;
+  }
 
   workInProgress.child = current.child;
   workInProgress.memoizedProps = current.memoizedProps;
   workInProgress.memoizedState = current.memoizedState;
   workInProgress.updateQueue = current.updateQueue;
+  workInProgress.firstContextDependency = current.firstContextDependency;
 
   // These will be overridden during the parent's reconciliation
   workInProgress.sibling = current.sibling;
@@ -559,12 +577,14 @@ export function assignFiberPropertiesInDEV(
   target.memoizedProps = source.memoizedProps;
   target.updateQueue = source.updateQueue;
   target.memoizedState = source.memoizedState;
+  target.firstContextDependency = source.firstContextDependency;
   target.mode = source.mode;
   target.effectTag = source.effectTag;
   target.nextEffect = source.nextEffect;
   target.firstEffect = source.firstEffect;
   target.lastEffect = source.lastEffect;
   target.expirationTime = source.expirationTime;
+  target.childExpirationTime = source.childExpirationTime;
   target.alternate = source.alternate;
   if (enableProfilerTimer) {
     target.actualDuration = source.actualDuration;