Accept promise as element type (#13397)

* Accept promise as element type

On the initial render, the element will suspend as if a promise were
thrown from inside the body of the unresolved component. Siblings should
continue rendering and if the parent is a Placeholder, the promise
should be captured by that Placeholder.

When the promise resolves, rendering resumes. If the resolved value
has a `default` property, it is assumed to be the default export of
an ES module, and we use that as the component type. If it does not have
a `default` property, we use the resolved value itself.

The resolved value is stored as an expando on the promise/thenable.

* Use special types of work for lazy components

Because reconciliation is a hot path, this adds ClassComponentLazy,
FunctionalComponentLazy, and ForwardRefLazy as special types of work.
The other types are not supported, but wouldn't be placed into a
separate module regardless.

* Resolve defaultProps for lazy types

* Remove some calls to isContextProvider

isContextProvider checks the fiber tag, but it's typically called after
we've already refined the type of work. We should get rid of it. I
removed some of them in the previous commit, and deleted a few more
in this one. I left a few behind because the remaining ones would
require additional refactoring that feels outside the scope of this PR.

* Remove getLazyComponentTypeIfResolved

* Return baseProps instead of null

The caller compares the result to baseProps to see if anything changed.

* Avoid redundant checks by inlining getFiberTagFromObjectType

* Move tag resolution to ReactFiber module

* Pass next props to update* functions

We should do this with all types of work in the future.

* Refine component type before pushing/popping context

Removes unnecessary checks.

* Replace all occurrences of _reactResult with helper

* Move shared thenable logic to `shared` package

* Check type of wrapper object before resolving to `default` export

* Return resolved tag instead of reassigning

packages/react-dom/src/test-utils/ReactTestUtils.js

@@ -11,7 +11,9 @@ import {findCurrentFiberUsingSlowPath} from 'react-reconciler/reflection';
 import * as ReactInstanceMap from 'shared/ReactInstanceMap';
 import {
   ClassComponent,
+  ClassComponentLazy,
   FunctionalComponent,
+  FunctionalComponentLazy,
   HostComponent,
   HostText,
 } from 'shared/ReactTypeOfWork';
@@ -81,7 +83,9 @@ function findAllInRenderedFiberTreeInternal(fiber, test) {
       node.tag === HostComponent ||
       node.tag === HostText ||
       node.tag === ClassComponent ||
-      node.tag === FunctionalComponent
+      node.tag === ClassComponentLazy ||
+      node.tag === FunctionalComponent ||
+      node.tag === FunctionalComponentLazy
     ) {
       const publicInst = node.stateNode;
       if (test(publicInst)) {

packages/react-reconciler/src/ReactChildFiber.js

@@ -23,6 +23,7 @@ import {
 import {
   FunctionalComponent,
   ClassComponent,
+  ClassComponentLazy,
   HostText,
   HostPortal,
   Fragment,
@@ -117,7 +118,7 @@ function coerceRef(
         if (!didWarnAboutStringRefInStrictMode[componentName]) {
           warningWithoutStack(
             false,
-            'A string ref, "%s", has been found within a strict mode tree. ' +
+            'A string ref, "%s", has been found within a strict mode tree. ' +
               'String refs are a source of potential bugs and should be avoided. ' +
               'We recommend using createRef() instead.' +
               '\n%s' +
@@ -137,7 +138,8 @@ function coerceRef(
       if (owner) {
         const ownerFiber = ((owner: any): Fiber);
         invariant(
-          ownerFiber.tag === ClassComponent,
+          ownerFiber.tag === ClassComponent ||
+            ownerFiber.tag === ClassComponentLazy,
           'Stateless function components cannot have refs.',
         );
         inst = ownerFiber.stateNode;
@@ -1307,7 +1309,8 @@ function ChildReconciler(shouldTrackSideEffects) {
       // component, throw an error. If Fiber return types are disabled,
       // we already threw above.
       switch (returnFiber.tag) {
-        case ClassComponent: {
+        case ClassComponent:
+        case ClassComponentLazy: {
           if (__DEV__) {
             const instance = returnFiber.stateNode;
             if (instance.render._isMockFunction) {

packages/react-reconciler/src/ReactCurrentFiber.js

@@ -11,7 +11,9 @@ import ReactSharedInternals from 'shared/ReactSharedInternals';
 import {
   IndeterminateComponent,
   FunctionalComponent,
+  FunctionalComponentLazy,
   ClassComponent,
+  ClassComponentLazy,
   HostComponent,
   Mode,
 } from 'shared/ReactTypeOfWork';
@@ -28,7 +30,9 @@ function describeFiber(fiber: Fiber): string {
   switch (fiber.tag) {
     case IndeterminateComponent:
     case FunctionalComponent:
+    case FunctionalComponentLazy:
     case ClassComponent:
+    case ClassComponentLazy:
     case HostComponent:
     case Mode:
       const owner = fiber._debugOwner;

packages/react-reconciler/src/ReactFiber.js

@@ -33,6 +33,9 @@ import {
   ContextConsumer,
   Profiler,
   PlaceholderComponent,
+  FunctionalComponentLazy,
+  ClassComponentLazy,
+  ForwardRefLazy,
 } from 'shared/ReactTypeOfWork';
 import getComponentName from 'shared/getComponentName';
 
@@ -278,8 +281,32 @@ const createFiber = function(
   return new FiberNode(tag, pendingProps, key, mode);
 };
 
-function shouldConstruct(Component) {
-  return !!(Component.prototype && Component.prototype.isReactComponent);
+function shouldConstruct(Component: Function) {
+  const prototype = Component.prototype;
+  return (
+    typeof prototype === 'object' &&
+    prototype !== null &&
+    typeof prototype.isReactComponent === 'object' &&
+    prototype.isReactComponent !== null
+  );
+}
+
+export function resolveLazyComponentTag(
+  fiber: Fiber,
+  Component: Function,
+): void {
+  if (typeof Component === 'function') {
+    return shouldConstruct(Component)
+      ? ClassComponentLazy
+      : FunctionalComponentLazy;
+  } else if (
+    Component !== undefined &&
+    Component !== null &&
+    Component.$$typeof
+  ) {
+    return ForwardRefLazy;
+  }
+  return IndeterminateComponent;
 }
 
 // This is used to create an alternate fiber to do work on.
@@ -390,15 +417,15 @@ export function createFiberFromElement(
   let fiber;
   const type = element.type;
   const key = element.key;
-  let pendingProps = element.props;
+  const pendingProps = element.props;
 
   let fiberTag;
   if (typeof type === 'function') {
     fiberTag = shouldConstruct(type) ? ClassComponent : IndeterminateComponent;
   } else if (typeof type === 'string') {
     fiberTag = HostComponent;
   } else {
-    switch (type) {
+    getTag: switch (type) {
       case REACT_FRAGMENT_TYPE:
         return createFiberFromFragment(
           pendingProps.children,
@@ -419,9 +446,54 @@ export function createFiberFromElement(
       case REACT_PLACEHOLDER_TYPE:
         fiberTag = PlaceholderComponent;
         break;
-      default:
-        fiberTag = getFiberTagFromObjectType(type, owner);
-        break;
+      default: {
+        if (typeof type === 'object' && type !== null) {
+          switch (type.$$typeof) {
+            case REACT_PROVIDER_TYPE:
+              fiberTag = ContextProvider;
+              break getTag;
+            case REACT_CONTEXT_TYPE:
+              // This is a consumer
+              fiberTag = ContextConsumer;
+              break getTag;
+            case REACT_FORWARD_REF_TYPE:
+              fiberTag = ForwardRef;
+              break getTag;
+            default: {
+              if (typeof type.then === 'function') {
+                fiberTag = IndeterminateComponent;
+                break getTag;
+              }
+            }
+          }
+        }
+        let info = '';
+        if (__DEV__) {
+          if (
+            type === undefined ||
+            (typeof type === 'object' &&
+              type !== null &&
+              Object.keys(type).length === 0)
+          ) {
+            info +=
+              ' You likely forgot to export your component from the file ' +
+              "it's defined in, or you might have mixed up default and " +
+              'named imports.';
+          }
+          const ownerName = owner ? getComponentName(owner.type) : null;
+          if (ownerName) {
+            info += '\n\nCheck the render method of `' + ownerName + '`.';
+          }
+        }
+        invariant(
+          false,
+          'Element type is invalid: expected a string (for built-in ' +
+            'components) or a class/function (for composite components) ' +
+            'but got: %s.%s',
+          type == null ? type : typeof type,
+          info,
+        );
+      }
     }
   }
 
@@ -437,49 +509,6 @@ export function createFiberFromElement(
   return fiber;
 }
 
-function getFiberTagFromObjectType(type, owner): TypeOfWork {
-  const $$typeof =
-    typeof type === 'object' && type !== null ? type.$$typeof : null;
-
-  switch ($$typeof) {
-    case REACT_PROVIDER_TYPE:
-      return ContextProvider;
-    case REACT_CONTEXT_TYPE:
-      // This is a consumer
-      return ContextConsumer;
-    case REACT_FORWARD_REF_TYPE:
-      return ForwardRef;
-    default: {
-      let info = '';
-      if (__DEV__) {
-        if (
-          type === undefined ||
-          (typeof type === 'object' &&
-            type !== null &&
-            Object.keys(type).length === 0)
-        ) {
-          info +=
-            ' You likely forgot to export your component from the file ' +
-            "it's defined in, or you might have mixed up default and " +
-            'named imports.';
-        }
-        const ownerName = owner ? getComponentName(owner.type) : null;
-        if (ownerName) {
-          info += '\n\nCheck the render method of `' + ownerName + '`.';
-        }
-      }
-      invariant(
-        false,
-        'Element type is invalid: expected a string (for built-in ' +
-          'components) or a class/function (for composite components) ' +
-          'but got: %s.%s',
-        type == null ? type : typeof type,
-        info,
-      );
-    }
-  }
-}
-
 export function createFiberFromFragment(
   elements: ReactFragment,
   mode: TypeOfMode,