Extraneous errors in "internal" folders in `node_modules`

[DavidArchibald]

Describe the bug

tsc ignores errors in folders named internal in dependencies at a minimum. There may be more situations in which it ignores errors and it seems that svelte-check does not faithfully reproduce these conditions.

Reproduction

You can download this zip svelte-check-reproduction.zip and then:

1. Unextract the zip.
2. Inside of it, run npm install.
3. Move the dependency folder into node_modules (if you do this too early it will be deleted).
4. Run ./node_modules/typescript/bin/tsc --noEmit and you won't get an error in noIssue.ts
5. Run ./node_modules/svelte-check/bin/svelte-check and get an error because of reproduction.svelte.

Alternatively if you want to create this situation from scratch:

1. Create an empty folder.
2. Initialize a project with npm init or whatever your preferred package manager is.
3. Run npm install svelte-check.
4. Create a tsconfig.json with these contents:

{
    "compilerOptions": {
        "strictNullChecks": true,
        "noUncheckedIndexedAccess": true
    }
}

9. To simulate having an erroring dependency create a node_modules/dependency/internal/index.js file with the contents:

const array = [1, 2, 3];

const item: number = array[4]; // Only an error when noUncheckedIndexedAccess is set to true.

10. Create a node_modules/dependency/index.js file with the contents import "./internal/index.js";
11. Create a reproduction.svelte file with the contents:

<script lang="ts">
    import "dependency";
</script>

12. Run ./node_modules/svelte-check/bin/svelte-check

You should get this error:

====================================
Loading svelte-check in workspace: svelte-check-reproduction
Getting Svelte diagnostics...

svelte-check-reproduction/node_modules/dependency/index.ts:3:7
Error: Type 'number | undefined' is not assignable to type 'number'.
  Type 'undefined' is not assignable to type 'number'. 

const item: number = array[4]; // Only an error when noUncheckedIndexedAccess and strictNullChecks is set to true.


====================================
svelte-check found 1 error and 0 warnings in 1 file

Expected behaviour

I expected no error.

For example in my zip I have a noIssue.ts file with the contents:

import "dependency";

You will not see the issue when you run ./node_modules/typescript/bin/tsc --noEmit nor ./node_modules/svelte-check/bin/svelte-check.

You won't even get an error if you run svelte-check or tsc on the results of svelte2tsx on the contents of reproduction.svelte like so:

import { svelte2tsx } from "svelte2tsx"

const result = svelte2tsx(`<script lang="ts">
    import "dependency";
</script>`);

console.log(result.code);

(you will need to set the package.json type to "type": "module").

This results in:

///<reference types="svelte" />
;
import "dependency";
function render() {

    
;
async () => {};
return { props: /** @type {Record<string, never>} */ ({}), slots: {}, events: {} }}

export default class extends __sveltets_2_createSvelte2TsxComponent(__sveltets_2_partial(__sveltets_2_with_any_event(render()))) {
}

Which does not error (after you resolve the missing dependencies).

System Info

• OS: Windows/WSL2
• IDE: VSCode

Which package is the issue about?

svelte-check

Additional Information, eg. Screenshots

No response

[jasonlyu123]

I can't reproduce this I get the error in both tsc and svelte-check. I think you might make some mistake while preparing the reproduction. The dependency/index.ts in your zip is actually import 'internal/index.ts' instead of import './internal/index.ts'.