[DevTools] Fix commit index reset when switching profiler roots (#35672)

Fixes #31463,
#30114.

When switching between roots in the profiler flamegraph, the commit
index was preserved from the previous root. This caused an error
"Invalid commit X. There are only Y commits." when the new root had
fewer commits than the selected index.

This fix resets the commit index to 0 (or null if no commits) when the
commitData changes, which happens when switching roots.

Author: hoxyq

packages/react-devtools-shared/src/__tests__/profilerContext-test.js

@@ -776,6 +776,84 @@ describe('ProfilerContext', () => {
     document.body.removeChild(profilerContainer);
   });
 
+  it('should reset commit index when switching to a different root', async () => {
+    const Parent = () => <Child />;
+    const Child = () => null;
+
+    const containerA = document.createElement('div');
+    const containerB = document.createElement('div');
+
+    const rootA = ReactDOMClient.createRoot(containerA);
+    const rootB = ReactDOMClient.createRoot(containerB);
+
+    utils.act(() => rootA.render(<Parent />));
+    utils.act(() => rootB.render(<Parent />));
+
+    // Profile and record different numbers of commits for each root
+    // Root A: 5 commits, Root B: 2 commits
+    await utils.actAsync(() => store.profilerStore.startProfiling());
+    await utils.actAsync(() => rootA.render(<Parent />)); // Root A commit 1
+    await utils.actAsync(() => rootA.render(<Parent />)); // Root A commit 2
+    await utils.actAsync(() => rootA.render(<Parent />)); // Root A commit 3
+    await utils.actAsync(() => rootA.render(<Parent />)); // Root A commit 4
+    await utils.actAsync(() => rootA.render(<Parent />)); // Root A commit 5
+    await utils.actAsync(() => rootB.render(<Parent />)); // Root B commit 1
+    await utils.actAsync(() => rootB.render(<Parent />)); // Root B commit 2
+    await utils.actAsync(() => store.profilerStore.stopProfiling());
+
+    let context: Context = ((null: any): Context);
+    function ContextReader() {
+      context = React.useContext(ProfilerContext);
+      return null;
+    }
+
+    await utils.actAsync(() =>
+      TestRenderer.create(
+        <Contexts>
+          <ContextReader />
+        </Contexts>,
+      ),
+    );
+
+    // Verify we have profiling data for both roots
+    expect(context.didRecordCommits).toBe(true);
+    expect(context.profilingData).not.toBeNull();
+
+    const rootIDs = Array.from(context.profilingData.dataForRoots.keys());
+    expect(rootIDs.length).toBe(2);
+
+    const [rootAID, rootBID] = rootIDs;
+    const rootAData = context.profilingData.dataForRoots.get(rootAID);
+    const rootBData = context.profilingData.dataForRoots.get(rootBID);
+
+    expect(rootAData.commitData.length).toBe(5);
+    expect(rootBData.commitData.length).toBe(2);
+
+    // Select root A and navigate to commit 4 (index 3)
+    await utils.actAsync(() => context.setRootID(rootAID));
+    expect(context.rootID).toBe(rootAID);
+    expect(context.selectedCommitIndex).toBe(0);
+
+    await utils.actAsync(() => context.selectCommitIndex(3));
+    expect(context.selectedCommitIndex).toBe(3);
+
+    // Switch to root B which only has 2 commits
+    // The commit index should be reset to 0, not stay at 3 (which would be invalid)
+    await utils.actAsync(() => context.setRootID(rootBID));
+    expect(context.rootID).toBe(rootBID);
+    // Should be reset to 0 since commit 3 doesn't exist in root B
+    expect(context.selectedCommitIndex).toBe(0);
+
+    // Verify we can still navigate in root B
+    await utils.actAsync(() => context.selectCommitIndex(1));
+    expect(context.selectedCommitIndex).toBe(1);
+
+    // Switch back to root A - should reset to 0
+    await utils.actAsync(() => context.setRootID(rootAID));
+    expect(context.rootID).toBe(rootAID);
+    expect(context.selectedCommitIndex).toBe(0);
+  });
+
   it('should handle commit selection edge cases when filtering commits', async () => {
     const Scheduler = require('scheduler');
 

packages/react-devtools-shared/src/devtools/views/Profiler/useCommitFilteringAndNavigation.js

@@ -45,6 +45,14 @@ export function useCommitFilteringAndNavigation(
     null,
   );
 
+  // Reset commit index when commitData changes (e.g., when switching roots).
+  const [previousCommitData, setPreviousCommitData] =
+    useState<Array<CommitDataFrontend>>(commitData);
+  if (previousCommitData !== commitData) {
+    setPreviousCommitData(commitData);
+    selectCommitIndex(commitData.length > 0 ? 0 : null);
+  }
+
   const calculateFilteredIndices = useCallback(
     (enabled: boolean, minDuration: number): Array<number> => {
       return commitData.reduce((reduced: Array<number>, commitDatum, index) => {