Allow to toggle Suspense in Components pane

shells/dev/app/index.js

@@ -32,6 +32,7 @@ function mountTestApp() {
   mountHelper(ElementTypes);
   mountHelper(EditableProps);
   mountHelper(DeeplyNestedComponents);
+  mountHelper(SuspenseTree);
 }
 
 function unmountTestApp() {

src/backend/agent.js

@@ -38,6 +38,12 @@ type SetInParams = {|
   value: any,
 |};
 
+type OverrideSuspenseParams = {|
+  id: number,
+  rendererID: number,
+  forceFallback: boolean,
+|};
+
 export default class Agent extends EventEmitter {
   _bridge: Bridge = ((null: any): Bridge);
   _isProfiling: boolean = false;
@@ -68,6 +74,7 @@ export default class Agent extends EventEmitter {
     bridge.addListener('overrideHookState', this.overrideHookState);
     bridge.addListener('overrideProps', this.overrideProps);
     bridge.addListener('overrideState', this.overrideState);
+    bridge.addListener('overrideSuspense', this.overrideSuspense);
     bridge.addListener('reloadAndProfile', this.reloadAndProfile);
     bridge.addListener('screenshotCaptured', this.screenshotCaptured);
     bridge.addListener('selectElement', this.selectElement);
@@ -302,6 +309,19 @@ export default class Agent extends EventEmitter {
     }
   };
 
+  overrideSuspense = ({
+    id,
+    rendererID,
+    forceFallback,
+  }: OverrideSuspenseParams) => {
+    const renderer = this._rendererInterfaces[rendererID];
+    if (renderer == null) {
+      console.warn(`Invalid renderer id "${rendererID}" for element "${id}"`);
+    } else {
+      renderer.overrideSuspense(id, forceFallback);
+    }
+  };
+
   setRendererInterface(
     rendererID: RendererID,
     rendererInterface: RendererInterface

src/backend/renderer.js

@@ -199,6 +199,7 @@ export function attach(
     IndeterminateComponent,
     MemoComponent,
     SimpleMemoComponent,
+    SuspenseComponent,
   } = ReactTypeOfWork;
   const {
     CONCURRENT_MODE_NUMBER,
@@ -219,7 +220,15 @@ export function attach(
     DEPRECATED_PLACEHOLDER_SYMBOL_STRING,
   } = ReactSymbols;
 
-  const { overrideHookState, overrideProps } = renderer;
+  const {
+    overrideHookState,
+    overrideProps,
+    setSuspenseHandler,
+    scheduleUpdate,
+  } = renderer;
+  const supportsEditingSuspense =
+    typeof setSuspenseHandler === 'function' &&
+    typeof scheduleUpdate === 'function';
 
   const debug = (name: string, fiber: Fiber, parentFiber: ?Fiber): void => {
     if (__DEBUG__) {
@@ -845,8 +854,7 @@ export function attach(
 
     // Suspense components only have a non-null memoizedState if they're timed-out.
     const isTimedOutSuspense =
-      nextFiber.tag === ReactTypeOfWork.SuspenseComponent &&
-      nextFiber.memoizedState !== null;
+      nextFiber.tag === SuspenseComponent && nextFiber.memoizedState !== null;
 
     if (isTimedOutSuspense) {
       // The behavior of timed-out Suspense trees is unique.
@@ -1411,6 +1419,9 @@ export function attach(
       }
     }
 
+    const isTimedOutSuspense =
+      tag === SuspenseComponent && memoizedState !== null;
+
     return {
       id,
 
@@ -1420,6 +1431,14 @@ export function attach(
       // Does the current renderer support editable function props?
       canEditFunctionProps: typeof overrideProps === 'function',
 
+      canEditSuspense:
+        supportsEditingSuspense &&
+        // If it's showing the real content, we can always flip fallback.
+        (!isTimedOutSuspense ||
+          // If it's showing fallback because we previously forced it to,
+          // allow toggling it back to remove the fallback override.
+          forceFallbackForSuspenseIDs.has(id)),
+
       // Can view component source location.
       canViewSource,
 
@@ -1667,6 +1686,45 @@ export function attach(
     startProfiling();
   }
 
+  // React will switch between these implementations depending on whether
+  // we have any manually suspended Fibers or not.
+
+  function shouldSuspendFiberAlwaysFalse() {
+    return false;
+  }
+
+  let forceFallbackForSuspenseIDs = new Set();
+  function shouldSuspendFiberAccordingToSet(fiber) {
+    const id = getFiberID(getPrimaryFiber(((fiber: any): Fiber)));
+    return forceFallbackForSuspenseIDs.has(id);
+  }
+
+  function overrideSuspense(id, forceFallback) {
+    if (
+      typeof setSuspenseHandler !== 'function' ||
+      typeof scheduleUpdate !== 'function'
+    ) {
+      throw new Error(
+        'Expected overrideSuspense() to not get called for earlier React versions.'
+      );
+    }
+    if (forceFallback) {
+      forceFallbackForSuspenseIDs.add(id);
+      if (forceFallbackForSuspenseIDs.size === 1) {
+        // First override is added. Switch React to slower path.
+        setSuspenseHandler(shouldSuspendFiberAccordingToSet);
+      }
+    } else {
+      forceFallbackForSuspenseIDs.delete(id);
+      if (forceFallbackForSuspenseIDs.size === 0) {
+        // Last override is gone. Switch React back to fast path.
+        setSuspenseHandler(shouldSuspendFiberAlwaysFalse);
+      }
+    }
+    const fiber = idToFiberMap.get(id);
+    scheduleUpdate(fiber);
+  }
+
   return {
     cleanup,
     flushInitialOperations,
@@ -1680,6 +1738,7 @@ export function attach(
     handleCommitFiberUnmount,
     inspectElement,
     prepareViewElementSource,
+    overrideSuspense,
     renderer,
     selectElement,
     setInContext,

src/backend/types.js

@@ -45,6 +45,10 @@ export type ReactRenderer = {
     value: any
   ) => void,
 
+  // 16.9+
+  scheduleUpdate?: ?(fiber: Object) => void,
+  setSuspenseHandler?: ?(shouldSuspend: (fiber: Object) => boolean) => void,
+
   // Only injected by React v16.8+ in order to support hooks inspection.
   currentDispatcherRef?: {| current: null | Dispatcher |},
 };
@@ -95,6 +99,7 @@ export type RendererInterface = {
   handleCommitFiberRoot: (fiber: Object) => void,
   handleCommitFiberUnmount: (fiber: Object) => void,
   inspectElement: (id: number) => InspectedElement | null,
+  overrideSuspense: (id: number, forceFallback: boolean) => void,
   prepareViewElementSource: (id: number) => void,
   renderer: ReactRenderer | null,
   selectElement: (id: number) => void,

src/devtools/views/Components/SelectedElement.js

@@ -20,6 +20,7 @@ import {
   ElementTypeForwardRef,
   ElementTypeFunction,
   ElementTypeMemo,
+  ElementTypeSuspense,
 } from '../../types';
 
 import type { InspectedElement } from './types';
@@ -115,6 +116,8 @@ type InspectedElementViewProps = {|
   inspectedElement: InspectedElement,
 |};
 
+const IS_SUSPENDED = 'Suspended';
+
 function InspectedElementView({
   element,
   inspectedElement,
@@ -123,6 +126,7 @@ function InspectedElementView({
   const {
     canEditFunctionProps,
     canEditHooks,
+    canEditSuspense,
     context,
     hooks,
     owners,
@@ -137,6 +141,7 @@ function InspectedElementView({
   let overrideContextFn = null;
   let overridePropsFn = null;
   let overrideStateFn = null;
+  let overrideSuspenseFn = null;
   if (type === ElementTypeClass) {
     overrideContextFn = (path: Array<string | number>, value: any) => {
       const rendererID = store.getRendererIDForElement(id);
@@ -160,6 +165,14 @@ function InspectedElementView({
       const rendererID = store.getRendererIDForElement(id);
       bridge.send('overrideProps', { id, path, rendererID, value });
     };
+  } else if (type === ElementTypeSuspense && canEditSuspense) {
+    overrideSuspenseFn = (path: Array<string | number>, value: boolean) => {
+      if (path.length !== 1 && path !== IS_SUSPENDED) {
+        throw new Error('Unexpected path.');
+      }
+      const rendererID = store.getRendererIDForElement(id);
+      bridge.send('overrideSuspense', { id, rendererID, forceFallback: value });
+    };
   }
 
   return (
@@ -170,11 +183,21 @@ function InspectedElementView({
         overrideValueFn={overridePropsFn}
         showWhenEmpty
       />
-      <InspectedElementTree
-        label="state"
-        data={state}
-        overrideValueFn={overrideStateFn}
-      />
+      {type === ElementTypeSuspense ? (
+        <InspectedElementTree
+          label="suspense"
+          data={{
+            [IS_SUSPENDED]: state !== null,
+          }}
+          overrideValueFn={overrideSuspenseFn}
+        />
+      ) : (
+        <InspectedElementTree
+          label="state"
+          data={state}
+          overrideValueFn={overrideStateFn}
+        />
+      )}
       <HooksTree canEditHooks={canEditHooks} hooks={hooks} id={id} />
       <InspectedElementTree
         label="context"

src/devtools/views/Components/types.js

@@ -41,6 +41,9 @@ export type InspectedElement = {|
   // Does the current renderer support editable function props?
   canEditFunctionProps: boolean,
 
+  // Is this Suspense, and can its value be overriden now?
+  canEditSuspense: boolean,
+
   // Can view component source location.
   canViewSource: boolean,