Enabling server actions breaks hydration of custom elements

[stephenwf]

Link to the code that reproduces this issue

https://codesandbox.io/p/sandbox/nextjs-server-actions-hydration-rv6jjs

To Reproduce

1. Enable experimental.serverActions
2. Add a JSX element that is not in the HTML tags (e.g. <some-element>)
3. Add children to that element (e.g. <some-element><div>hi</div></some-element>)
4. Run next dev

Current vs. Expected behavior

Current hydration error:

app-index.js:31 Warning: Expected server HTML to contain a matching <div> in <some-element>.
    at div
    at some-element
    at div
    at main

Expected: well.. Expected server HTML to contain a matching <div> in <some-element>.

Verify canary release

• I verified that the issue exists in the latest Next.js canary release

Provide environment information

Operating System:
  Platform: linux
  Arch: x64
  Version: #1 SMP PREEMPT_DYNAMIC Sun Aug  6 20:05:33 UTC 2023
Binaries:
  Node: 20.7.0
  npm: 10.1.0
  Yarn: 1.22.19
  pnpm: N/A
Relevant Packages:
  next: 13.5.4
  eslint-config-next: 13.5.4
  react: 18.2.0
  react-dom: 18.2.0
  typescript: 5.2.2
Next.js Config:
  output: N/A

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

App Router

Additional context

Non-working example with latest:
https://codesandbox.io/p/sandbox/nextjs-with-server-actions-fgjnsl?file=%2Fapp%2Fpage.tsx%3A8%2C9-10%2C24

Non-working example with canary:
https://codesandbox.io/p/sandbox/nextjs-with-server-actions-canary-2tj2j4?file=%2Fapp%2Fpage.tsx%3A8%2C1-10%2C24

Working example without server actions enabled:
https://codesandbox.io/p/sandbox/nextjs-without-server-actions-mn9xgz?file=%2Fapp%2Fpage.tsx%3A1%2C1

[kelihansen]

Is this the same as #51141? I was having what I believe is a related issue, where the style prop of a custom element was null on the server. I just confirmed that it's fixed when I use next@13.5.6-canary.1 (which includes this React canary fix)

[stephenwf]

ah yes, that looks like the same issue! Sorry - I did try to search for "custom elements" without any luck.

[github-actions]

This closed issue has been automatically locked because it had no new activity for 2 weeks. If you are running into a similar issue, please create a new issue with the steps to reproduce. Thank you.