Module resolution fails when substituion path exists but original path directory does not

[Gozala]

TypeScript Version: 3.7.x-dev.201xxxxx

It appears that

Path substitution fails to resolve module if original path (path before substitution) directory does not exists. E.g. if module is importing module bar and corresponding package.json has "main": "src/index.js" but directory src does not exists, but substitution path like dist/src/index.d.ts exists module resolution fails.

Here is the repo with minimial reproducible example illustrating this problem https://github.com/Gozala/bug-tsc-path-substitution/tree/main-field-bug

P.S.: Appears to fail with typescript@next as well.

Search Terms:

• typeVersions
• path mapping

Code

package.json

{
  "name": "bar",
  "main": "src/index.js",
  "typesVersions": {
    "*": {
      "*": [
        "dist/*"
      ]
    }
  }
}

dist/src/index.d.ts

declare class Bar {
}

export default Bar

Expected behavior:

Module resolution should succeed

Actual behavior:

Module resolution fails

Playground Link:

This involves multiple files, please see example repo instead
https://github.com/Gozala/bug-tsc-path-substitution/tree/main-field-bug

Related Issues:

[rbuckton]

This doesn't appear to be a bug, but is the intended behavior of the feature. typesVersions is only used to override types specific to a version of TypeScript given a module that we could have resolved without typesVersions. Even though you have specified a TS version of *, typesVersions still requires a valid original path to override. As such, y\You must have a file at the main path for us to start with, even if that file is an empty index.d.ts or index.js file.