Typescript 7 crashes svelte2tsx and svelte-check

[Suya1671]

Describe the bug

Using the new typescript 7 preview RC (https://devblogs.microsoft.com/typescript/announcing-typescript-7-0-rc/#using-typescript-7.0-rc), it seems that svelte2tsx and svelte-check both immediately crash when trying to load the typescript compiler

using svelte-package (which uses svelte2tsx)

extension:dev | > No "exports" main defined in /home/suya/Projects/leseliwazi/node_modules/.pnpm/svelte2tsx@0.7.56_svelte@5.56.3_@typescript-eslint+types@8.61.1__typescript@7.0.1-rc/node_modules/typescript/package.json
extension:dev |     at exportsNotFound (node:internal/modules/esm/resolve:310:10)
extension:dev |     at packageExportsResolve (node:internal/modules/esm/resolve:658:9)
extension:dev |     at resolveExports (node:internal/modules/cjs/loader:685:36)
extension:dev |     at Module._findPath (node:internal/modules/cjs/loader:752:31)
extension:dev |     at Module._resolveFilename (node:internal/modules/cjs/loader:1461:27)
extension:dev |     at wrapResolveFilename (node:internal/modules/cjs/loader:1049:27)
extension:dev |     at defaultResolveImplForCJSLoading (node:internal/modules/cjs/loader:1073:10)
extension:dev |     at resolveForCJSWithHooks (node:internal/modules/cjs/loader:1094:12)
extension:dev |     at Module._load (node:internal/modules/cjs/loader:1262:25)
extension:dev |     at wrapModuleLoad (node:internal/modules/cjs/loader:255:19)

using svelte-check

leseliwazi/extensions/core on  HEAD (fd5881a) [!] via  v24.15.0 via ❄️  impure (nix-shell-env)
❯ pnpm exec svelte-check
node:internal/modules/cjs/loader:692
      throw e;
      ^

Error [ERR_PACKAGE_PATH_NOT_EXPORTED]: No "exports" main defined in /home/suya/Projects/leseliwazi/node_modules/.pnpm/svelte-check@4.6.0_picomatch@4.0.4_svelte@5.56.3_@typescript-eslint+types@8.61.1__typescript@7.0.1-rc/node_modules/typescript/package.json
    at exportsNotFound (node:internal/modules/esm/resolve:310:10)
    at packageExportsResolve (node:internal/modules/esm/resolve:658:9)
    at resolveExports (node:internal/modules/cjs/loader:685:36)
    at Module._findPath (node:internal/modules/cjs/loader:752:31)
    at Module._resolveFilename (node:internal/modules/cjs/loader:1461:27)
    at wrapResolveFilename (node:internal/modules/cjs/loader:1049:27)
    at defaultResolveImplForCJSLoading (node:internal/modules/cjs/loader:1073:10)
    at resolveForCJSWithHooks (node:internal/modules/cjs/loader:1094:12)
    at Module._load (node:internal/modules/cjs/loader:1262:25)
    at wrapModuleLoad (node:internal/modules/cjs/loader:255:19) {
  code: 'ERR_PACKAGE_PATH_NOT_EXPORTED'
}

Node.js v24.15.0
```
Passing `--tsgo` does not help

### Reproduction

1. create a new sveltekit repo setup with typescript
2. install `typescript@rc`
3. try run svelte-check
4. observe error

### Expected behaviour

`svelte-check` & co to Just Work OOTB

### System Info

- OS: NixOS
- IDE: Zed

### Which package is the issue about?

svelte2tsx

### Additional Information, eg. Screenshots

_No response_

[jasonlyu123]

Yeah. This is expected. You can't use TypeScript 7 just yet. It's fundamentally incompatible with svelte-check and svelte-package. For now, only @typescript/native-preview is supported. And you still need TypeScript 6.

For it to work, we need to replace static import with typescript with dynamic imports. This is because we need both TypeScript 6 and 7 even in --tsgo mode.

[serhalp]

👋🏼 Would you accept a PR documenting this? It took quite a few detours for me to get here from that error 😅.

[jasonlyu123]

I am not sure if a documentation file on GitHub helps much. Package managers like npm should already warn about incompatibility. The TypeScript 7 RC announcement also stated that a stable API isn't yet available for other tools.

That being said, a runtime check that throws an error explaining is probably better. My plan is to add the check and explain how to work around it in the error message.

Regarding the solution, I thought more about it and think it might be better to allow --tsgo and --tsgo-experimental-api to use an npm alias, as mentioned in the TypeScript 7 RC announcement. Replacing static imports to "typescript" does work. But it might be a breaking change to downstream libraries. And users will still run into issues in svelte-kit sync or typescript-eslint.

[Suya1671]

https://devblogs.microsoft.com/typescript/announcing-typescript-7-0/ typescript 7 is now out of RC, although

It’s worth calling out that workflows that use Vue, MDX, Astro, Svelte, and others will likely not yet be able to leverage TypeScript 7. Similarly, specialized type-checking within templates like Angular will also likely not use TypeScript 7. This is mainly because TypeScript 7 does not yet expose a stable programmatic API, and so tools (such as Volar) which embed TypeScript into their own compilers and language services can only currently rely on TypeScript 6.0. We expect this to be a point-in-time issue, as we are committed to providing a solution here. We will be actively working with the maintainers of these projects to ensure TypeScript 7 supports these workflows.

[hyunbinseo]

It seems a bit late since TS7 is now stable, but the peer deps versioning should be narrowed:

{
  "peerDependencies": {
    "svelte": "^4.0.0 || ^5.0.0-next.0",
    "typescript": ">=5.0.0"
  }
}

I had no issue bumping to typescript@7 to be faced with this error when checking:

TypeError: Cannot read properties of undefined (reading 'useCaseSensitiveFileNames')