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fix(i18n): allow getLocaleDir fallback to compile under TypeScript 6#3824

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SAY-5:fix/i18n-locale-language-ts6
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fix(i18n): allow getLocaleDir fallback to compile under TypeScript 6#3824
SAY-5 wants to merge 1 commit intowithastro:mainfrom
SAY-5:fix/i18n-locale-language-ts6

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@SAY-5 SAY-5 commented Apr 15, 2026

Per #3822, after upgrading to TypeScript v6 (which ships a newer DOM lib that knows about both Intl.Locale.textInfo and Intl.Locale.getTextInfo), tsc --noEmit fails with:

Property 'language' does not exist on type 'never'.

The two if branches in getLocaleDir narrow locale to never because TypeScript now sees both branches as exhaustive, which leaves the fallback unreachable from a type-narrowing standpoint.

Cast locale back to Intl.Locale in the fallback so the runtime path (Firefox before either property is supported) still compiles. Runtime behaviour is unchanged. The longer-term cleanup tracked in #3572 is still the right path; this is the small forward fix users need today.

Closes #3822

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@github-actions github-actions Bot added the 🌟 core Changes to Starlight’s main package label Apr 15, 2026
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@delucis delucis mentioned this pull request Apr 20, 2026
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Thanks for the PR @SAY-5! Looks like there’s a lint error due to the “unnecessary” as (from TypeScript v5’s perspective). Could you take a look?

To ensure compatibility across users with both TS 5 and TS 6, it might be better to use a // @ts-ignore comment instead of type casting in this case. We do that in a few other places in the code base where there’s TS code that can error is some projects but not in others (so we can’t use // @ts-expect-error).

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SAY-5 commented Apr 21, 2026

Thanks @delucis! Switched to @ts-ignore on the property access and dropped the cast. That keeps TS 5 happy (no unnecessary-cast lint) and TS 6 happy (narrowed type no longer carries language, directive silences it). The runtime property is always present because the in guards above only narrow statically.

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delucis commented Apr 22, 2026

@SAY-5 Looks like the lint job is still failing. You can see how we ignore this lint rule for @ts-ignore elsewhere in the codebase — I’d suggest doing the same here.

You can run pnpm lint locally to double check these kinds of things.

@SAY-5
fix(i18n): use @ts-ignore instead of cast for getLocaleDir fallback
c78f12d 
Switch from `(locale as Intl.Locale).language` to a plain property
access with a `@ts-ignore` directive. Per @delucis' review, the cast
lints as "unnecessary" under TypeScript v5, while the property is
reachable at runtime and only missing from the TypeScript v6 narrowed
type. `@ts-ignore` keeps both compilers happy without lint noise.

Signed-off-by: SAY-5 <[email protected]>
@SAY-5 SAY-5 closed this Apr 23, 2026
@SAY-5 SAY-5 force-pushed the fix/i18n-locale-language-ts6 branch from 8ddf6aa to c78f12d Compare April 23, 2026 04:16
@delucis delucis mentioned this pull request Apr 23, 2026
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TypeScript v6: Property 'language' does not exist on type 'never'

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