[2.0 RC] SSR hydration keys shift when memo()-wrapped prop getters are read before `children` through `<Dynamic>`, so the child never hydrates
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Assessment
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Newbie friendliness
- 58/100
- Issue type
- Bug
- Clarity
- Clearly specified
- Activity status
- Active
- Tech stack
- typescript
- Domain
- frontend
Research direction
Start by tracing server-side ssrElement prop processing and how hydration keys are allocated for children; compare those allocations with the client behavior described in the report. Use the linked StackBlitz reproduction and run its install, build, and render commands, then serve build/ and toggle the signal. Done when the child claims the matching server key and updates the in-document span.
Written by the indexing model from the issue text.
Description
Describe the bug
A component rendered through <Dynamic component="button"> can receive props whose values are ternaries over a logical expression. The compiler emits these as memo(() => …)() ? a : b getters. On the server, each read of such a getter creates a sync memo, and that memo takes a child id from the owner that is current during ssrElement's prop loop. That owner is the same one that later allocates the hydration key for the element's children. The getters are read before children, so the server's key for the child is shifted by the number of memo-wrapped props. The client doesn't make the same allocations, so it looks for the unshifted key.
As a result, the child misses hydration. The client builds a detached copy, the server-rendered node stays in the document with nothing bound to it, and later reactive updates to the child never reach the page.
We first saw this with Kobalte 2.0.0-alpha.2's Dialog.Trigger / DropdownMenu.Trigger (Button → Polymorphic → Dynamic). The repro below doesn't use Kobalte; it only copies Kobalte's prop layering.
Your Example Website or App
https://stackblitz.com/edit/solidjs-templates-gftulnlj?file=package.json
Steps to Reproduce the Bug or Issue
npm install && node build.mjs && node render.mjs- Serve
build/statically and openindex.html. - In the console, run
toggle().
Expected behavior
Expected behavior:
The server gives the child the key that follows the button's key, matching the client:
<button _hk=50 type="button"><span _hk=51 id="label">label</span></button>
The client claims <span _hk=51>, and after toggle() the in-document span gets data-on.
Actual behavior:
The server skips three ids before the child:
<main _hk=0><button _hk=50 type="button"><span _hk=54 id="label">label</span></button></main>
The client (development build) warns:
Hydration key miss for "51": no server-rendered element carries this key (template: <span id=label>label). A detached element was created instead; its subtree will not appear in the document or become interactive. …
Hydration completed with 1 unclaimed server-rendered node(s): <span _hk="54" id="label">label</span>
After toggle(), the span in the document is still _hk="54" with no data-on. The update went to the detached client copy.
Screenshots or Videos
No response
Platform
- OS: macOS
- Browser: Chrome
- Version: Version 154.0.8037.97 (Official Build) (x86_64)
Additional context
None.
- Dominant language
- TypeScript
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