adds childContextTypes warnings for functional components

ReactStatelessComponent-test.js fails due to warnings not showing up when functional components mount or update. This PR ports the existing warnings from stack and re-applies them to fiber functional components and attempts to re-use some logic in ReactFiberContext that currently exists for showing warnings when dealing with class components.

Author: trueadm

scripts/fiber/tests-passing-except-dev.txt

@@ -139,9 +139,6 @@ src/renderers/__tests__/ReactHostOperationHistoryHook-test.js
 * gets reported when a child is inserted
 * gets reported when a child is removed
 
-src/renderers/__tests__/ReactStatelessComponent-test.js
-* should warn for childContextTypes on a functional component
-
 src/renderers/dom/shared/__tests__/ReactDOMComponent-test.js
 * should not warn when server-side rendering `onScroll`
 * should warn about incorrect casing on properties (ssr)

scripts/fiber/tests-passing.txt

@@ -777,6 +777,7 @@ src/renderers/__tests__/ReactStatelessComponent-test.js
 * should update stateless component
 * should unmount stateless component
 * should pass context thru stateless component
+* should warn for childContextTypes on a functional component
 * should throw when stateless component returns undefined
 * should throw on string refs in pure functions
 * should warn when given a string ref

src/renderers/shared/fiber/ReactFiberBeginWork.js

@@ -67,6 +67,9 @@ var invariant = require('invariant');
 if (__DEV__) {
   var ReactDebugCurrentFiber = require('ReactDebugCurrentFiber');
   var warning = require('warning');
+  var {
+    warnAboutMissingGetChildContext,
+  } = require('ReactFiberContext');
 
   var warnedAboutStatelessRefs = {};
 }
@@ -479,6 +482,18 @@ module.exports = function<T, P, I, TI, PI, C, CX, PL>(
       // Proceed under the assumption that this is a functional component
       workInProgress.tag = FunctionalComponent;
       if (__DEV__) {
+        const Component = workInProgress.type;
+
+        if (Component) {
+          warning(
+            !Component.childContextTypes,
+            '%s(...): childContextTypes cannot be defined on a functional component.',
+            Component.displayName || Component.name || 'Component'
+          );
+          if (Component.childContextTypes) {
+            warnAboutMissingGetChildContext(workInProgress);
+          }
+        }
         if (workInProgress.ref !== null) {
           let info = '';
           const ownerName = ReactDebugCurrentFiber.getCurrentFiberOwnerName();

src/renderers/shared/fiber/ReactFiberContext.js

@@ -32,9 +32,30 @@ const {
   push,
 } = require('ReactFiberStack');
 
+var warnAboutMissingGetChildContext;
+
 if (__DEV__) {
   var checkReactTypeSpec = require('checkReactTypeSpec');
   var warnedAboutMissingGetChildContext = {};
+
+  // TODO (bvaughn) Replace this behavior with an invariant() in the future.
+  // It has only been added in Fiber to match the (unintentional) behavior in Stack.
+  warnAboutMissingGetChildContext = (fiber: Fiber) => {
+    const componentName = getComponentName(fiber);
+
+    if (!warnedAboutMissingGetChildContext[componentName]) {
+      warnedAboutMissingGetChildContext[componentName] = true;
+      warning(
+        false,
+        '%s.childContextTypes is specified but there is no getChildContext() method ' +
+        'on the instance. You can either define getChildContext() on %s or remove ' +
+        'childContextTypes from it.',
+        componentName,
+        componentName,
+      );
+    }
+  };
+  module.exports.warnAboutMissingGetChildContext = warnAboutMissingGetChildContext;
 }
 
 // A cursor to the current merged context object on the stack.
@@ -144,23 +165,9 @@ function processChildContext(fiber : Fiber, parentContext : Object, isReconcilin
   const instance = fiber.stateNode;
   const childContextTypes = fiber.type.childContextTypes;
 
-  // TODO (bvaughn) Replace this behavior with an invariant() in the future.
-  // It has only been added in Fiber to match the (unintentional) behavior in Stack.
   if (typeof instance.getChildContext !== 'function') {
     if (__DEV__) {
-      const componentName = getComponentName(fiber);
-
-      if (!warnedAboutMissingGetChildContext[componentName]) {
-        warnedAboutMissingGetChildContext[componentName] = true;
-        warning(
-          false,
-          '%s.childContextTypes is specified but there is no getChildContext() method ' +
-          'on the instance. You can either define getChildContext() on %s or remove ' +
-          'childContextTypes from it.',
-          componentName,
-          componentName,
-        );
-      }
+      warnAboutMissingGetChildContext(fiber);
     }
     return parentContext;
   }