Skip revalidation for RSC fallback data by default

src/_internal/types.ts

@@ -116,6 +116,11 @@ export interface PublicConfiguration<
    * @link https://swr.vercel.app/docs/revalidation#disable-automatic-revalidations
    */
   revalidateIfStale: boolean
+  /**
+   * automatically revalidate when data comes from RSC fallback
+   * @defaultValue false
+   */
+  revalidateOnRSCFallback?: boolean
   /**
    * retry when fetcher has an error
    * @defaultValue true

src/_internal/utils/config.ts

@@ -60,6 +60,7 @@ export const defaultConfig: FullConfiguration = mergeObjects(
     revalidateOnReconnect: true,
     revalidateIfStale: true,
     shouldRetryOnError: true,
+    revalidateOnRSCFallback: false,
 
     // timeouts
     errorRetryInterval: slowConnection ? 10000 : 5000,

src/index/use-swr.ts

@@ -299,6 +299,9 @@ export const useSWRHandler = <Data = any, Error = any>(
     // If it's paused, we skip revalidation.
     if (getConfig().isPaused()) return false
 
+    // If RSC fallback data on initial render, use revalidateOnRSCFallback config
+    if (!isUndefined(fallback) && !isUndefined(data) && !IS_SERVER && isInitialMount) return getConfig().revalidateOnRSCFallback ?? false;
+
     // Under suspense mode, it will always fetch on render if there is no
     // stale data so no need to revalidate immediately mount it again.
     // If data exists, only revalidate if `revalidateIfStale` is true.

test/rsc-fallback.test.tsx

@@ -0,0 +1,47 @@
+import { act, fireEvent, render, screen } from '@testing-library/react'
+import React from 'react'
+import useSWR, { SWRConfig } from 'swr'
+import { sleep } from './utils'
+
+describe('RSC Fallback', () => {
+  it('should not revalidate on mount with RSC fallback data by default', async () => {
+    const fetchFn = jest.fn(() => 'updated data')
+
+    function Page() {
+      const { data } = useSWR('key', fetchFn, {
+        fallbackData: 'RSC data'
+      })
+      return <div>Data: {data}</div>
+    }
+
+    render(<Page />)
+
+    expect(screen.getByText('Data: RSC data')).toBeInTheDocument()
+    expect(fetchFn).not.toHaveBeenCalled()
+
+    await sleep(50)
+
+    expect(fetchFn).not.toHaveBeenCalled()
+  })
+
+  it('should revalidate on mount with RSC fallback data when revalidateOnRSCFallback is true', async () => {
+    const fetchFn = jest.fn(() => 'updated data')
+
+    function Page() {
+      const { data } = useSWR('key', fetchFn, {
+        fallbackData: 'RSC data',
+        revalidateOnRSCFallback: true
+      })
+      return <div>Data: {data}</div>
+    }
+
+    render(<Page />)
+
+    expect(screen.getByText('Data: RSC data')).toBeInTheDocument()    
+    expect(fetchFn).toHaveBeenCalledTimes(1)
+
+    await sleep(50)
+
+    expect(screen.getByText('Data: updated data')).toBeInTheDocument()
+  })
+})