Generic type added to StackCursor. Default emptyObject replaced with null.

src/renderers/shared/fiber/ReactFiberContext.js

@@ -36,11 +36,11 @@ if (__DEV__) {
   var checkReactTypeSpec = require('checkReactTypeSpec');
 }
 
-let contextStackCursor : StackCursor = createCursor();
-let didPerformWorkStackCursor : StackCursor = createCursor();
+let contextStackCursor : StackCursor<?Object> = createCursor((null: ?Object));
+let didPerformWorkStackCursor : StackCursor<?boolean> = createCursor((null: ?boolean));
 
 function getUnmaskedContext() {
-  return contextStackCursor.current;
+  return contextStackCursor.current || emptyObject;
 }
 
 exports.getMaskedContext = function(workInProgress : Fiber) {
@@ -52,6 +52,7 @@ exports.getMaskedContext = function(workInProgress : Fiber) {
 
   const unmaskedContext = getUnmaskedContext();
   const context = {};
+
   for (let key in contextTypes) {
     context[key] = unmaskedContext[key];
   }

src/renderers/shared/fiber/ReactFiberHostContext.js

@@ -16,6 +16,8 @@ import type { Fiber } from 'ReactFiber';
 import type { HostConfig } from 'ReactFiberReconciler';
 import type { StackCursor } from 'ReactFiberStack';
 
+const emptyObject = require('emptyObject');
+
 const {
   createCursor,
   pop,
@@ -41,8 +43,8 @@ module.exports = function<T, P, I, TI, C, CX>(
     getRootHostContext,
   } = config;
 
-  let contextStackCursor : StackCursor = createCursor();
-  let rootInstanceStackCursor : StackCursor = createCursor();
+  let contextStackCursor : StackCursor<?CX> = createCursor((null: ?CX));
+  let rootInstanceStackCursor : StackCursor<?C> = createCursor((null: ?C));
 
   function getRootHostContainer() : C {
     if (rootInstanceStackCursor.current == null) {
@@ -81,7 +83,7 @@ module.exports = function<T, P, I, TI, C, CX>(
       throw new Error('Expected root host context to exist.');
     }
 
-    const context = contextStackCursor.current;
+    const context = contextStackCursor.current || emptyObject;
     const rootInstance = rootInstanceStackCursor.current;
     const nextContext = getChildHostContext(context, fiber.type, rootInstance);
 

src/renderers/shared/fiber/ReactFiberStack.js

@@ -14,14 +14,13 @@
 
 import type { Fiber } from 'ReactFiber';
 
-export type StackCursor = {|
-  current: any
+export type StackCursor<T> = {|
+  current: T
 |};
 
-const emptyObject = require('emptyObject');
 const warning = require('warning');
 
-const valueStack : Array<Object> = [];
+const valueStack : Array<any> = [];
 
 if (__DEV__) {
   var fiberStack : Array<Fiber | null> = [];
@@ -29,9 +28,9 @@ if (__DEV__) {
 
 let index = -1;
 
-exports.createCursor = function() : StackCursor {
+exports.createCursor = function<T>(defaultValue : T) : StackCursor<T> {
   return {
-    current: null,
+    current: defaultValue,
   };
 };
 
@@ -39,8 +38,8 @@ exports.isEmpty = function() : boolean {
   return index === -1;
 };
 
-exports.pop = function(
-  cursor : StackCursor,
+exports.pop = function<T>(
+  cursor : StackCursor<T>,
   fiber: Fiber | null, // TODO (bvaughn) Tighten up this type to only accept Fiber
 ) : void {
   if (index < 0) {
@@ -56,21 +55,21 @@ exports.pop = function(
     }
   }
 
-  valueStack[index] = emptyObject;
+  valueStack[index] = null;
 
   if (__DEV__) {
-    fiberStack[index] = emptyObject;
+    fiberStack[index] = null;
   }
 
   index--;
 
   cursor.current = index > -1
     ? valueStack[index]
-    : null;
+    : (null : any);
 };
 
-exports.push = function(
-  cursor : StackCursor,
+exports.push = function<T>(
+  cursor : StackCursor<T>,
   value : any,
   fiber: Fiber | null, // TODO (bvaughn) Tighten up this type to only accept Fiber
 ) : void {
@@ -85,18 +84,18 @@ exports.push = function(
   }
 };
 
-exports.reset = function(
-  cursor : StackCursor,
+exports.reset = function<T>(
+  cursor : StackCursor<T>,
 ) : void {
   while (index > -1) {
-    valueStack[index] = emptyObject;
+    valueStack[index] = null;
 
     if (__DEV__) {
-      fiberStack[index] = emptyObject;
+      fiberStack[index] = null;
     }
 
     index--;
   }
 
-  cursor.current = null;
+  cursor.current = (null : any);
 };