fix: handle error in numberToPos and formatError

[milahu]

old behavior

1. formatError is trying to handle error1
2. formatError calls numberToPos
3. numberToPos throws error2
4. only error2 is printed
5. error1 is not printed

for example

Error: offset is longer than source length!
    at numberToPos (node_modules/vite/dist/node/chunks/dep-972722fa.js:4247:15)
    at formatError (node_modules/vite/dist/node/chunks/dep-972722fa.js:51169:24)
    at TransformContext.error (node_modules/vite/dist/node/chunks/dep-972722fa.js:51149:19)
    at Object.transform (node_modules/vite/dist/node/chunks/dep-972722fa.js:51357:25)
    at async transformRequest (node_modules/vite/dist/node/chunks/dep-972722fa.js:67098:29)
    at async instantiateModule (node_modules/vite/dist/node/chunks/dep-972722fa.js:73732:10)

new behavior

formatError: error in numberToPos (Error: offset is longer than source length! offset 126 > length 48) while handling the error:
Expected valid tag name
4: </script>
5: 
6: <p>Lorem ipsum < dolor sit</p>
                   ^
ParseError: Expected valid tag name
    at error (node_modules/svelte/compiler.mjs:17698:19)
    at Parser$1.error (node_modules/svelte/compiler.mjs:17774:9)
    [...]

---

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Before submitting the PR, please make sure you do the following

• Read the Contributing Guidelines.
• Read the Pull Request Guidelines and follow the Commit Convention.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.

[milahu]

TODO verify that err is visible

[milahu]

how to add a unit test for this?
vite.createServer -> createPluginContainer -> formatError

broken code is passed to the plugin -> plugin throws error1
plugin returns a broken sourcemap -> numberToPos throws error2 "offset is longer than source length"

scripts/jestPerTestSetup.ts calls server = await (await createServer(options)).listen()

[Shinigami92]

@patak-js Do we even test logged errors?
I'm not sure if we need to test this 🤔

[Shinigami92]

Converted to draft until TODO verify that err is visible is resolved

[milahu]

TODO verify that err is visible

done manually, this is non-trivial to test

note: this is NOT visible in npm run build

$ npm run dev 

> @ dev svelte/mdsvex/sveltekit-bugs
> svelte-kit dev

Pre-bundling dependencies:
  svelte/store
  svelte
  svelte/animate
  svelte/easing
  svelte/internal
  (...and 2 more)
(this will be run only when your dependencies or config have changed)

  SvelteKit v1.0.0-next.159

  local:   http://localhost:3000
  network: not exposed

  Use --host to expose server to other devices on this network


Error in error handler:
Error: offset is longer than source length! offset 126 > length 48
    at numberToPos (vite/dist/node/chunks/dep-7017d082.js:4256:15)
    at formatError (vite/dist/node/chunks/dep-7017d082.js:50004:35)
    at TransformContext.error (vite/dist/node/chunks/dep-7017d082.js:49984:19)
    at Object.transform (vite/dist/node/chunks/dep-7017d082.js:50200:25)
    at async transformRequest (vite/dist/node/chunks/dep-7017d082.js:64964:29)
    at async instantiateModule (vite/dist/node/chunks/dep-7017d082.js:74748:10)

Expected valid tag name
4: </script>
5: 
6: <p>Lorem ipsum < dolor sit</p>
                   ^
ParseError: Expected valid tag name
    at error (svelte/compiler.mjs:17697:19)
    at Parser$1.error (svelte/compiler.mjs:17773:9)
    at read_tag_name (svelte/compiler.mjs:16918:16)
    at tag (svelte/compiler.mjs:16768:18)
    at new Parser$1 (svelte/compiler.mjs:17732:21)
    at parse$3 (svelte/compiler.mjs:17864:20)
    at compile (svelte/compiler.mjs:31303:17)
    at compileSvelte (vite-plugin-svelte/dist/index.js:301:20)
    at async TransformContext.transform (vite-plugin-svelte/dist/index.js:1325:27)
    at async Object.transform (vite/dist/node/chunks/dep-7017d082.js:50197:30)

[milahu]

note: currently, the browser runtime shows only the second error

500
Expected valid tag name
4: </script>
5: 
6: <p>Lorem ipsum < dolor sit</p>
                   ^
ParseError: Expected valid tag name
    at error (svelte/compiler.mjs:17697:19)
    at Parser$1.error (svelte/compiler.mjs:17773:9)
    [...]