write generated types to __types directories

[Rich-Harris]

• fixes Circular reference when using generated endpoint types #4701
• fixes generated types should be removed each time svelte-kit sync happens #4973

Changes where generated types are written to:

-import type { RequestHandler } from './foo';
+import type { RequestHandler } from './__types/foo';

though the fix seems a bit... unidiomatic? would love a gut check from typescript-heads. little surprised this didn't come up sooner

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[Rich-Harris]

If we do end up doing this, i wonder if we should make the same change to the JSDoc comments, and the examples in the docs:

-/** @type {import('./index').RequestHandler} */
+/** @type {import('./index.d').RequestHandler} */

It works either way, but there might be some value in consistency

[coryvirok]

I'm not a Typescript expert, but Microsoft seems to think having files with the same name, (e.g. foo.d.ts and foo.ts) is a bad idea - microsoft/TypeScript#7624

Maybe one solution would be to put the generated types file in types/foo.d.ts?

Tangentially related, I'd like to have my *.d.ts files in src/types/ and I see that the generated subtree of types follows this convention. Meaning, the generated type declarations are put in .svelte-kit/types/. So maybe it's an opportunity to move app.d.ts into src/types/app.d.ts? That could clean up the conventions on where Svelte is storing types and also solve this issue because generated types would no longer be in src/routes/foo.d.ts and would instead be in src/types/routes/foo.d.ts.

[dummdidumm]

I'm not a Typescript expert, but Microsoft seems to think having files with the same name, (e.g. foo.d.ts and foo.ts) is a bad idea - microsoft/TypeScript#7624

I second this. The TS resolution algorithm has a certain order to resolve files (ts>dts>js, this is why the solution in this PR works because it first appends the ts ending) and I think it wasn't intended to support two files which only differ by file ending. The more robust fix would therefore probably be to create a type file name that is distinct, for example taking advantage of our "double underscore is reserved": import("./__types.index"), or as a folder import("./__types/index"). If we don't want that, the given solution works, (ab)using the TS file ending resolution order.

[ignatiusmb]

I third it.

[benmccann]

I suppose I'd lean towards:

/** @type {import('./__types/index').RequestHandler} */

[Rich-Harris]

Updated to use __types, this is now ready for review

[orta]

Yeah, this fits

[dummdidumm]

Looks good to me apart from the seemingly unrelated packaging changes

[dummdidumm]

These also seem unrelated, but possibly ok to keep because else prettier complains (?)