When generateMetadata performs an asynchronous action, Suspense is not being rendered until generateMetadata finish

[ebidrey]

Link to the code that reproduces this issue

https://github.com/ebidrey/suspense-generate-metadata

To Reproduce

To Reproduce

You can run this simple snippet

import { Suspense } from "react"

export async function generateMetadata() {
    const results = await fetch('https://postman-echo.com/delay/2');
    await results.json();
    return {
        title: 'Test',
        description: 'Test',
    }
}

async function PageContent() {
    const results = await fetch('https://postman-echo.com/delay/2');
    await results.json();
    return  <h1>Test</h1>
}

export default async function Page() {
    return (
        <Suspense fallback={<div>loading running 2 seconds later</div>} key={Math.random()}>
            <PageContent />
        </Suspense>
    )
}

It is also available in github repo

Current vs. Expected behavior

I expect suspense fallback to be activated immediately when the page request is made and then, the page and the metadata get streamed. Instead, page stucks for the amount of time the request to the api takes, showing nothing up to the request finished, degradating the user experience and not improving SEO in any way.

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 23.0.0: Fri Sep 15 14:41:43 PDT 2023; root:xnu-10002.1.13~1/RELEASE_ARM64_T6000
  Available memory (MB): 16384
  Available CPU cores: 10
Binaries:
  Node: 20.9.0
  npm: 10.1.0
  Yarn: 1.22.10
  pnpm: N/A
Relevant Packages:
  next: 15.0.4-canary.14 // Latest available version is detected (15.0.4-canary.14).
  eslint-config-next: 15.0.4-canary.14
  react: 19.0.0-rc-380f5d67-20241113
  react-dom: 19.0.0-rc-380f5d67-20241113
  typescript: 5.6.3
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

Metadata, Performance

Which stage(s) are affected? (Select all that apply)

next dev (local), next build (local), next start (local), Vercel (Deployed), Other (Deployed)

Additional context

Tested in latest canary and stable.

[markcarroll]

I've hit this same issue too. It has forced me to change all my page titles to generic static strings so that suspense fallback gets rendered.