fix: export private legacy ComponentType (#14256)

[Theo-Steiner]

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The transitionary interface ComponentType not being exported from the *.svelte module declaration causes issues when running tsc with "declaration": true: error TS4082: Default export of the module has or is using private name 'ComponentType'.

Exporting the interface from the solves this problem in my reproduction (see: #14256)

Fixed Reproduction

pnpm add https://pkg.pr.new/svelte@14257

holy smokes, pkg.pr.new is cool:
Broken reproduction with svelte@5.1.9
↓
Fixed reproduction with svelte@https://pkg.pr.new/svelte@14257

Question:

since packages/svelte/src/ambient.d.ts is included in packages/svelte/types/index.d.ts when building I wasn't sure if I should commit both files into this branch?
the ci lint job told me what to do

[changeset-bot]

🦋 Changeset detected

Latest commit: c4c544b

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[Rich-Harris]

preview: https://svelte-dev-git-preview-svelte-14257-svelte.vercel.app/

this is an automated message

[github-actions]

Playground

pnpm add https://pkg.pr.new/svelte@14257

[dummdidumm]

This feels like the wrong fix to me, because it means people can now import ComponentType from every .svelte import, if they're not using the TS plugin. There has to be some other way to make it work without exporting it from the *.svelte module.

[Theo-Steiner]

I've updated the PR to use a different approach, basically we declare a module svelte/transitionary in this case, that exports the TransitionaryComponentType instead. That way typescript is happy and users can't accidentally import the transitionary type

[Rich-Harris]

Can we use 'legacy' rather than 'transitionary'?

[Rich-Harris]

(my spellchecker doesn't even recognize the latter as a real word)

[Theo-Steiner]

Can we use 'legacy' rather than 'transitionary'?

I agree that transitionary is a bit weird 😅
svelte/legacy already exists though and I wasn't sure if redeclaring it would cause any problems since they end up in the same svelte/types/index.d.ts module in the end

[dummdidumm]

It will definetely cause problems. But I suggest instead to not create a new module for it, rather export a type from svelte/legacy which does what you want and use that within the svelte module declaration

[Theo-Steiner]

rather export a type from svelte/legacy which does what you want and use that within the svelte module declaration

I moved the type to packages/svelte/src/legacy/legacy-client.js so that is exported as part of 'svelte/legacy' & renamed it to LegacyComponentType, is this along the lines of what you envisioned?

[dummdidumm]

looks good - add a changeset and we're good to merge 👍

[Theo-Steiner]

Added a changeset 🎉

[dummdidumm]

thank you!