Widen typescript peer dependency range to allow v6

[delucis]

Changes

• @astrojs/check and @astrojs/svelte use TypeScript as a peer dependency
• This PR widens the supported version range to allow TS v6

Testing

Existing tests should pass

Docs

n/a

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[ocavue]

Just FYI, @astrojs/svelte depends on svelte2tsx, which doesn't support TS6 in the peer dependency yet. So any user who uses @astrojs/svelte with TS6 will still see the peer dependency warnings.

See sveltejs/language-tools#2985

[delucis]

Just FYI, @astrojs/svelte depends on svelte2tsx, which doesn't support TS6 in the peer dependency yet. So any user who uses @astrojs/svelte with TS6 will still see the peer dependency warnings.

See sveltejs/language-tools#2985

Ah thanks for the heads up. Do you think that means we should restore the v5-only peer dependency for the Svelte integration in that case?

[ocavue]

Keeping @astrojs/svelte TS5-only peer dependency would probably be a good idea because once svelte2tsx is updated, we can bump @astrojs/svelte's version and ensure that package managers will install the latest svelte2tsx that does support TS6.

[delucis]

OK — I’ll send a PR removing the Svelte change then!

[delucis]

Done in #16472

[sebastienbarre]

I'm a bit confused. Astro itself doesn't support TS6.

[ocavue]

I'm a bit confused. Astro itself doesn't support TS6.

Astro works perfectly with TS6! Some of its dependencies haven't yet updated their peerDependencies field to indicate support for TS6, so you may encounter a few warnings during npm install. The astro repository hasn't updated its TypeScript to v6 in devDependencies yet, but this won't impact users.

[sebastienbarre]

Oh great, good to know. Do you happen to also know if work on supporting TS7 has started? Astro 7 beta maybe? Thanks

[ocavue]

I don't see any issues running my Astro project with TS7 beta (AKA tsgo).

[sebastienbarre]

But Astro will be using TS6 internally though?
If I slap "@typescript/native-preview": "7.0.0-dev.20260421.2" in my package.json, the best it can do after pnpm install is using TS6.

$ pnpm why typescript                                         
typescript@6.0.3
├─┬ @astrojs/check@0.9.9
│ ├── @sebastienbarre/astro@1.0.0 (dependencies)
│ └── @sebastienbarre/barre.me@1.0.0 (dependencies)
└─┬ tsconfck@3.1.6
  └─┬ astro@6.1.10
    ├─┬ @astrojs/mdx@5.0.4
    │ └── @sebastienbarre/astro@1.0.0 (dependencies)
    ├── @sebastienbarre/astro@1.0.0 (dependencies)
    ├── @sebastienbarre/barre.me@1.0.0 (dependencies)
    └─┬ astro-pagefind@1.8.6
      └── @sebastienbarre/astro@1.0.0 (dependencies)
      ```

[ocavue]

But Astro will be using TS6 internally though?

Yes.

You would likely need to have both TS6 and TS7 installed in your node_modules until at least TS v7.1 is released.

https://devblogs.microsoft.com/typescript/announcing-typescript-7-0-beta/

Additionally, even though 7.0 Beta is close to production-ready, we won’t have a stable programmatic API available until at least several months from now with TypeScript 7.1. Given this, we have made it a priority to ensure TypeScript can be run side-by-side with TypeScript 6.0 for the foreseeable future without any conflicts around “which tsc is which?”

As part of the 6.0/7.0 transition process, we’ve published a new compatibility package, @typescript/typescript6. This package exposes a new entry point tsc6, so that (if needed) you can run the next release of TypeScript 7.0 (which will provide a tsc binary) side-by-side without naming conflicts. It will also re-export the TypeScript 6.0 API, so that you can use tsc for TypeScript 7, while other tooling can continue to rely on 6.0.