fix(svelte): async warning

[florian-lefebvre]

Changes

• Closes Experimental.async error when using Svelte v5.39 #14508
• Svelte logs a warning when awaiting render when compilerOptions.experimental.async is not enabled
• I first tried checking if the result of render was a promise to await it conditionnally, but that doesn't work because of how it's implemented in svelte: https://github.com/sveltejs/svelte/blob/main/packages/svelte/src/internal/server/renderer.js#L352-L384. then is always present
• So I took inspiration from the react integration and created an internal virtual module id that allows retrieving compilerOptions.experimental.async. I don't see a better fix without a change in svelte itself

Testing

Manual and tests added

Docs

Changeset

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[ascorbic]

I think this is fine as a workaround, but I think this should really be fixed in Svelte.

[florian-lefebvre]

I'll open an issue upstream

[ascorbic]

I wonder if @elliott-with-the-longest-name-on-github has any ideas for how to do this more cleanly

[elliott-with-the-longest-name-on-github]

Hmm, let me forward this to the team -- maybe we can expose it somehow...

[florian-lefebvre]

@elliott-with-the-longest-name-on-github see sveltejs/svelte#16934

[elliott-with-the-longest-name-on-github]

Thank you!