[Reconciler] Set ProfileMode for Host Root Fiber by default in dev (facebook#34432)

hoxyq · web-flow · commit 0e10ee906e3e · 2025-09-12T12:20:39.000+01:00
Requiring DevTools to be present for dev builds seems like an overkill,
let's enable the instrumentation by default.

Nothing changes for profiling or production artifacts.
diff --git a/packages/react-reconciler/src/ReactFiber.js b/packages/react-reconciler/src/ReactFiber.js
@@ -532,10 +532,10 @@ export function createHostRootFiber(
     mode = NoMode;
   }
 
-  if (enableProfilerTimer && isDevToolsPresent) {
-    // Always collect profile timings when DevTools are present.
-    // This enables DevTools to start capturing timing at any point–
-    // Without some nodes in the tree having empty base times.
+  if (__DEV__ || (enableProfilerTimer && isDevToolsPresent)) {
+    // dev: Enable profiling instrumentation by default.
+    // profile: enabled if DevTools is present or subtree is wrapped in <Profiler>.
+    // production: disabled.
     mode |= ProfileMode;
   }
 
diff --git a/packages/react/src/__tests__/ReactProfiler-test.internal.js b/packages/react/src/__tests__/ReactProfiler-test.internal.js
@@ -125,6 +125,7 @@ describe(`onRender`, () => {
     expect(callback).toHaveBeenCalledTimes(1);
   });
 
+  // @gate !__DEV__
   it('does not record times for components outside of Profiler tree', async () => {
     // Mock the Scheduler module so we can track how many times the current
     // time is read
