Validate props on context providers (#12658)

* checkPropTypes in updateContextProvider

* invalid “prop”

* `type not `types` .. :l

* test

* don’t need extra check with no spelling mistake (:

* change error message to specifically address provider

* don’t need class, add extra render to make sure good props go through

* nitpicky rename

* prettier

* switch to `Context.Provider`

* add stack to warning, add extra undefined check

* separate dev check

* add stack to test

* more efficient

* remove unused function

* prettier

* const to top

packages/react-reconciler/src/ReactFiberBeginWork.js

@@ -16,6 +16,7 @@ import type {NewContext} from './ReactFiberNewContext';
 import type {HydrationContext} from './ReactFiberHydrationContext';
 import type {FiberRoot} from './ReactFiberRoot';
 import type {ExpirationTime} from './ReactFiberExpirationTime';
+import checkPropTypes from 'prop-types/checkPropTypes';
 
 import {
   IndeterminateComponent,
@@ -63,6 +64,8 @@ import {NoWork, Never} from './ReactFiberExpirationTime';
 import {AsyncMode, StrictMode} from './ReactTypeOfMode';
 import MAX_SIGNED_31_BIT_INT from './maxSigned31BitInt';
 
+const {getCurrentFiberStackAddendum} = ReactDebugCurrentFiber;
+
 let didWarnAboutBadClass;
 let didWarnAboutGetDerivedStateOnFunctionalComponent;
 let didWarnAboutStatelessRefs;
@@ -885,6 +888,20 @@ export default function<T, P, I, TI, HI, PI, C, CC, CX, PL>(
     const newValue = newProps.value;
     workInProgress.memoizedProps = newProps;
 
+    if (__DEV__) {
+      const providerPropTypes = workInProgress.type.propTypes;
+
+      if (providerPropTypes) {
+        checkPropTypes(
+          providerPropTypes,
+          newProps,
+          'prop',
+          'Context.Provider',
+          getCurrentFiberStackAddendum,
+        );
+      }
+    }
+
     let changedBits: number;
     if (oldProps === null) {
       // Initial render

packages/react/src/__tests__/ReactContextValidator-test.js

@@ -225,6 +225,28 @@ describe('ReactContextValidator', () => {
     ReactTestUtils.renderIntoDocument(<Component testContext={{foo: 'foo'}} />);
   });
 
+  it('warns of incorrect prop types on context provider', () => {
+    const TestContext = React.createContext();
+
+    TestContext.Provider.propTypes = {
+      value: PropTypes.string.isRequired,
+    };
+
+    ReactTestUtils.renderIntoDocument(<TestContext.Provider value="val" />);
+
+    class Component extends React.Component {
+      render() {
+        return <TestContext.Provider />;
+      }
+    }
+
+    expect(() => ReactTestUtils.renderIntoDocument(<Component />)).toWarnDev(
+      'Warning: Failed prop type: The prop `value` is marked as required in ' +
+        '`Context.Provider`, but its value is `undefined`.\n' +
+        '    in Component (at **)',
+    );
+  });
+
   // TODO (bvaughn) Remove this test and the associated behavior in the future.
   // It has only been added in Fiber to match the (unintentional) behavior in Stack.
   it('should warn (but not error) if getChildContext method is missing', () => {