Repository: facebook/react
Pull request: [Fizz] Include a component stack in prod but only lazily generate it

When we added component stacks to Fizz in prod it severely slowed down common cases where you intentionally are throwing error for purposes of client rendering. Our parent component stack generation is very slow since call components with fake errors to generate them.

Therefore we disabled them in prod but included them in prerenders. https://github.com/facebook/react/pull/27850

However, we still kept generating data structures for them and the code still exists there for the prerenders. We could stop generating the data structures which are not completely free but also not crazy bad.

What we can do instead is just lazily generate the component stacks. This is in fact what plain stacks do anyway. This doesn't work as well in Fiber because the data structures are live but on the server they're immutable so it's fine to do it later as well.

That way you can choose to not read this getter for intentionally thrown errors - after inspecting the Error object - yet still get component stacks in prod for other errors.

Changed files:
filename: packages/react-server/src/ReactFizzServer.js
patch: @@ -908,27 +908,23 @@ type ThrownInfo = {
 export type ErrorInfo = ThrownInfo;
 export type PostponeInfo = ThrownInfo;
 
-// While we track component stacks in prod all the time we only produce a reified stack in dev and
-// during prerender in Prod. The reason for this is that the stack is useful for prerender where the timeliness
-// of the request is less critical than the observability of the execution. For renders and resumes however we
-// prioritize speed of the request.
-function getThrownInfo(
-  request: Request,
-  node: null | ComponentStackNode,
-): ThrownInfo {
-  if (
-    node &&
-    // Always produce a stack in dev
-    (__DEV__ ||
-      // Produce a stack in prod if we're in a prerender
-      request.trackedPostpones !== null)
-  ) {
-    return {
-      componentStack: getStackFromNode(node),
-    };
-  } else {
-    return {};
+function getThrownInfo(node: null | ComponentStackNode): ThrownInfo {
+  const errorInfo: ThrownInfo = {};
+  if (node) {
+    Object.defineProperty(errorInfo, 'componentStack', {
+      configurable: true,
+      enumerable: true,
+      get() {
+        // Lazyily generate the stack since it's expensive.
+        const stack = getStackFromNode(node);
+        Object.defineProperty(errorInfo, 'componentStack', {
+          value: stack,
+        });
+        return stack;
+      },
+    });
   }
+  return errorInfo;
 }
 
 function encodeErrorForBoundary(
@@ -1127,7 +1123,7 @@ function renderSuspenseBoundary(
   } catch (error: mixed) {
     contentRootSegment.status = ERRORED;
     newBoundary.status = CLIENT_RENDERED;
-    const thrownInfo = getThrownInfo(request, task.componentStack);
+    const thrownInfo = getThrownInfo(task.componentStack);
     let errorDigest;
     if (
       enablePostpone &&
@@ -1273,7 +1269,7 @@ function replaySuspenseBoundary(
     }
   } catch (error: mixed) {
     resumedBoundary.status = CLIENT_RENDERED;
-    const thrownInfo = getThrownInfo(request, task.componentStack);
+    const thrownInfo = getThrownInfo(task.componentStack);
     let errorDigest;
     if (
       enablePostpone &&
@@ -2337,7 +2333,7 @@ function replayElement(
         // in the original prerender. What's unable to complete is the child
         // replay nodes which might be Suspense boundaries which are able to
         // absorb the error and we can still continue with siblings.
-        const thrownInfo = getThrownInfo(request, task.componentStack);
+        const thrownInfo = getThrownInfo(task.componentStack);
         erroredReplay(
           request,
           task.blockedBoundary,
@@ -2868,7 +2864,7 @@ function replayFragment(
       // replay nodes which might be Suspense boundaries which are able to
       // absorb the error and we can still continue with siblings.
       // This is an error, stash the component stack if it is null.
-      const thrownInfo = getThrownInfo(request, task.componentStack);
+      const thrownInfo = getThrownInfo(task.componentStack);
       erroredReplay(
         request,
         task.blockedBoundary,
@@ -3467,7 +3463,7 @@ function renderNode(
           const trackedPostpones = request.trackedPostpones;
 
           const postponeInstance: Postpone = (x: any);
-          const thrownInfo = getThrownInfo(request, task.componentStack);
+          const thrownInfo = getThrownInfo(task.componentStack);
           const postponedSegment = injectPostponedHole(
             request,
             ((task: any): RenderTask), // We don't use ReplayTasks in prerenders.
@@ -3782,7 +3778,7 @@ function abortTask(task: Task, request: Request, error: mixed): void {
       boundary.status = CLIENT_RENDERED;
       // We construct an errorInfo from the boundary's componentStack so the error in dev will indicate which
       // boundary the message is referring to
-      const errorInfo = getThrownInfo(request, task.componentStack);
+      const errorInfo = getThrownInfo(task.componentStack);
       let errorDigest;
       if (
         enablePostpone &&
@@ -4074,15 +4070,15 @@ function retryRenderTask(
         task.abortSet.delete(task);
         const postponeInstance: Postpone = (x: any);
 
-        const postponeInfo = getThrownInfo(request, task.componentStack);
+        const postponeInfo = getThrownInfo(task.componentStack);
         logPostpone(request, postponeInstance.message, postponeInfo);
         trackPostpone(request, trackedPostpones, task, segment);
         finishedTask(request, task.blockedBoundary, segment);
         return;
       }
     }
 
-    const errorInfo = getThrownInfo(request, task.componentStack);
+    const errorInfo = getThrownInfo(task.componentStack);
     task.abortSet.delete(task);
     segment.status = ERRORED;
     erroredTask(request, task.blockedBoundary, x, errorInfo);
@@ -4156,7 +4152,7 @@ function retryReplayTask(request: Request, task: ReplayTask): void {
     }
     task.replay.pendingTasks--;
     task.abortSet.delete(task);
-    const errorInfo = getThrownInfo(request, task.componentStack);
+    const errorInfo = getThrownInfo(task.componentStack);
     erroredReplay(
       request,
       task.blockedBoundary,