Add readContext to ReactPartialRendererHooks

packages/react-dom/src/__tests__/ReactDOMServerIntegrationHooks-test.internal.js

@@ -646,5 +646,21 @@ describe('ReactDOMServerHooks', () => {
         expect(domNode.lastChild.textContent).toEqual('Baz: 5');
       },
     );
+
+    itThrowsWhenRendering(
+      'if used inside a class component',
+      async render => {
+        const Context = React.createContext({}, () => {});
+        class Counter extends React.Component {
+          render() {
+            let [count] = useContext(Context);
+            return <Text text={count} />;
+          }
+        }
+
+        return render(<Counter />);
+      },
+      'Hooks can only be called inside the body of a function component.',
+    );
   });
 });

packages/react-dom/src/server/ReactPartialRendererHooks.js

@@ -138,10 +138,18 @@ export function finishHooks(
   return children;
 }
 
+function readContext<T>(
+  context: ReactContext<T>,
+  observedBits: void | number | boolean,
+): T {
+  return context._currentValue;
+}
+
 function useContext<T>(
   context: ReactContext<T>,
   observedBits: void | number | boolean,
 ): T {
+  resolveCurrentlyRenderingComponent();
   return context._currentValue;
 }
 
@@ -349,7 +357,7 @@ function inputsAreEqual(arr1, arr2) {
 function noop(): void {}
 
 export const Dispatcher = {
-  readContext: useContext,
+  readContext,
   useContext,
   useMemo,
   useReducer,