Fix renderDataHook mount effects when the first render suspends

.changeset/render-data-hook-suspend-effects.md

@@ -0,0 +1,7 @@
+---
+'@data-client/test': patch
+---
+
+Fix mount effects when `renderDataHook()` suspends on the first render
+
+`renderDataHook()` and `makeRenderDataHook()` now run provider mount effects when the first render suspends, including `use(useFetch())`. The hook result stays unresolved until the data arrives.

packages/test/src/makeRenderDataClient/index.tsx

@@ -8,7 +8,7 @@ import {
   GenericDispatch,
   DataClientDispatch,
 } from '@data-client/react';
-import React, { memo, Suspense } from 'react';
+import React, { memo, Suspense, useLayoutEffect, useState } from 'react';
 
 import {
   renderHook,
@@ -23,6 +23,17 @@ import { MockProps } from '../mockTypes.js';
 
 const activeCleanups = new Set<() => void>();
 
+type KickRef = { current?: React.Dispatch<React.SetStateAction<number>> };
+
+/** Sibling that commits even when the hook suspends, so we can schedule a real update. */
+function Kick({ kickRef }: { kickRef: KickRef }) {
+  const [, setKick] = useState(0);
+  useLayoutEffect(() => {
+    kickRef.current = setKick;
+  }, [kickRef]);
+  return null;
+}
+
 if (typeof afterEach === 'function') {
   afterEach(() => {
     for (const fn of activeCleanups) fn();
@@ -138,19 +149,26 @@ export default function makeRenderDataHook(
         }
       : ProviderWithResolver;
 
+    const kickRef: KickRef = {};
     const wrapper: React.ComponentType<any> = ({
       children,
       ...props
     }: React.PropsWithChildren<P>) => (
       <ProviderWithWrapper {...(props as any)}>
         <Suspense fallback={null}>{children}</Suspense>
+        <Kick kickRef={kickRef} />
       </ProviderWithWrapper>
     );
 
     const ret: any = renderHook(callback, {
       ...options,
       wrapper,
     });
+    // A suspending first render inside sync act() drops the passive-effect task.
+    // A real setState gives React a task that flushes those effects. An empty act() does not.
+    act(() => {
+      kickRef.current?.(count => count + 1);
+    });
     ret.controller = nm['controller'];
     ret.cleanup = cleanup;
     ret.allSettled = allSettled;