Repository: facebook/react
Pull request: Mark all lanes in order on every new render

This is a hack that ensures that all four lanes are visible whether you have any tracks in them or not, and that they're in the priority order within the Scheduler track group. We do want to show all even if they're not used because it shows what options you're missing out on.

<img width="1035" alt="Screenshot 2024-11-22 at 12 38 30 PM" src="https://github.com/user-attachments/assets/f30ab0b9-af5e-48ed-b042-138444352575">

In Chrome, the order of tracks within a group are determined by the earliest start time. We add fake markers at start time zero in that order eagerly. Ideally we could do this only once but because calls that aren't recorded aren't considered for ordering purposes, we need to keep adding these over and over again in case recording has just started. We can't tell when recording starts.

Currently performance.mark() are in first insertion order but performance.measure() are in the reverse order. I'm not sure that's intentional. We can always add the 0 time slot even if it's in the past. That's still considered for ordering purposes as long as the measurement is recorded at the time we call it.

Changed files:
filename: packages/react-reconciler/src/ReactFiberPerformanceTrack.js
patch: @@ -25,7 +25,6 @@ const COMPONENTS_TRACK = 'Components ⚛';
 
 // Reused to avoid thrashing the GC.
 const reusableComponentDevToolDetails = {
-  dataType: 'track-entry',
   color: 'primary',
   track: COMPONENTS_TRACK,
 };
@@ -40,7 +39,6 @@ const reusableComponentOptions = {
 const LANES_TRACK_GROUP = 'Scheduler ⚛';
 
 const reusableLaneDevToolDetails = {
-  dataType: 'track-entry',
   color: 'primary',
   track: 'Blocking', // Lane
   trackGroup: LANES_TRACK_GROUP,
@@ -57,6 +55,63 @@ export function setCurrentTrackFromLanes(lanes: number): void {
   reusableLaneDevToolDetails.track = getGroupNameOfHighestPriorityLane(lanes);
 }
 
+const blockingLaneMarker = {
+  startTime: 0,
+  detail: {
+    devtools: {
+      color: 'primary-light',
+      track: 'Blocking',
+      trackGroup: LANES_TRACK_GROUP,
+    },
+  },
+};
+
+const transitionLaneMarker = {
+  startTime: 0,
+  detail: {
+    devtools: {
+      color: 'primary-light',
+      track: 'Transition',
+      trackGroup: LANES_TRACK_GROUP,
+    },
+  },
+};
+
+const suspenseLaneMarker = {
+  startTime: 0,
+  detail: {
+    devtools: {
+      color: 'primary-light',
+      track: 'Suspense',
+      trackGroup: LANES_TRACK_GROUP,
+    },
+  },
+};
+
+const idleLaneMarker = {
+  startTime: 0,
+  detail: {
+    devtools: {
+      color: 'primary-light',
+      track: 'Idle',
+      trackGroup: LANES_TRACK_GROUP,
+    },
+  },
+};
+
+export function markAllLanesInOrder() {
+  if (supportsUserTiming) {
+    // Ensure we create all tracks in priority order. Currently performance.mark() are in
+    // first insertion order but performance.measure() are in the reverse order. We can
+    // always add the 0 time slot even if it's in the past. That's still considered for
+    // ordering.
+    performance.mark('Blocking Track', blockingLaneMarker);
+    performance.mark('Transition Track', transitionLaneMarker);
+    performance.mark('Suspense Track', suspenseLaneMarker);
+    performance.mark('Idle Track', idleLaneMarker);
+  }
+}
+
 export function logComponentRender(
   fiber: Fiber,
   startTime: number,

filename: packages/react-reconciler/src/ReactFiberWorkLoop.js
patch: @@ -82,6 +82,8 @@ import {
   logYieldTime,
   logActionYieldTime,
   logSuspendedYieldTime,
+  setCurrentTrackFromLanes,
+  markAllLanesInOrder,
 } from './ReactFiberPerformanceTrack';
 
 import {
@@ -271,7 +273,6 @@ import {
   yieldReason,
   startPingTimerByLanes,
 } from './ReactProfilerTimer';
-import {setCurrentTrackFromLanes} from './ReactFiberPerformanceTrack';
 
 // DEV stuff
 import getComponentNameFromFiber from 'react-reconciler/src/getComponentNameFromFiber';
@@ -1727,6 +1728,15 @@ function finalizeRender(lanes: Lanes, finalizationTime: number): void {
 
 function prepareFreshStack(root: FiberRoot, lanes: Lanes): Fiber {
   if (enableProfilerTimer && enableComponentPerformanceTrack) {
+    // The order of tracks within a group are determined by the earliest start time.
+    // Are tracks should show up in priority order and we should ideally always show
+    // every track. This is a hack to ensure that we're displaying all tracks in the
+    // right order. Ideally we could do this only once but because calls that aren't
+    // recorded aren't considered for ordering purposes, we need to keep adding these
+    // over and over again in case recording has just started. We can't tell when
+    // recording starts.
+    markAllLanesInOrder();
+
     const previousRenderStartTime = renderStartTime;
     // Starting a new render. Log the end of any previous renders and the
     // blocked time before the render started.