fix(query-core): reset isPlaceholderData on select-error results

Author: hamed-bavar

.changeset/clear-stale-select-error.md

@@ -2,4 +2,4 @@
 '@tanstack/query-core': patch
 ---
 
-fix(query-core): clear a stale `select` error when the observer switches to a query without data, so the previous query's select error no longer leaks into the new pending result
+fix(query-core): clear a stale `select` error when the observer switches to a query without data, and reset `isPlaceholderData` on select-error results to match the declared result types, so a previous query's select error no longer leaks into the new result

packages/query-core/src/__tests__/queryObserver.test.tsx

@@ -643,6 +643,59 @@ describe('queryObserver', () => {
     })
   })
 
+  it('should not leak a stale select error through the memoized placeholderData path', async () => {
+    const keyA = queryKey()
+    const keyB = queryKey()
+    const keyC = queryKey()
+    const placeholder = { count: 0 }
+    const observer = new QueryObserver(queryClient, {
+      queryKey: keyA,
+      queryFn: () => sleep(10).then(() => ({ count: 1 })),
+      placeholderData: placeholder,
+      select: (data) => ({ selected: data.count }),
+    })
+    const unsubscribe = observer.subscribe(() => {})
+    await vi.advanceTimersByTimeAsync(10)
+    expect(observer.getCurrentResult()).toMatchObject({
+      status: 'success',
+      data: { selected: 1 },
+    })
+
+    observer.setOptions({
+      queryKey: keyB,
+      queryFn: () => sleep(10).then(() => ({ count: 2 })),
+      placeholderData: placeholder,
+      select: (): { selected: number } => {
+        throw new Error('selector error')
+      },
+    })
+    expect(observer.getCurrentResult()).toMatchObject({
+      status: 'error',
+    })
+
+    observer.setOptions({
+      queryKey: keyC,
+      queryFn: () => sleep(10).then(() => ({ count: 3 })),
+      placeholderData: placeholder,
+      select: (data) => ({ selected: data.count }),
+    })
+    expect(observer.getCurrentResult()).toMatchObject({
+      status: 'success',
+      data: { selected: 0 },
+      error: null,
+      isPlaceholderData: true,
+    })
+
+    await vi.advanceTimersByTimeAsync(10)
+    unsubscribe()
+
+    expect(observer.getCurrentResult()).toMatchObject({
+      status: 'success',
+      data: { selected: 3 },
+      error: null,
+    })
+  })
+
   it('should clear the select error when the query is reset', async () => {
     const key = queryKey()
     let shouldThrow = true

packages/query-core/src/queryObserver.ts

@@ -556,6 +556,7 @@ export class QueryObserver<
       data = this.#selectResult
       errorUpdatedAt = Date.now()
       status = 'error'
+      isPlaceholderData = false
     }
 
     const isFetching = newState.fetchStatus === 'fetching'