`--showConfig` doesn't resolve `paths`

🔎 Search Terms

"showConfig", "paths", "extends", "relative"

🕗 Version & Regression Information

v5.2.2 (no regression AFAIK)

⏯ Playground Link

https://stackblitz.com/edit/stackblitz-starters-gst2kr?file=tsconfig.json

Commands:

• npm run config -> tsc --showConfig

• npm run trace -> tsc --noEmit --traceResolution
  Use this to confirm that foo does resolve to ./this-path-should-be-in-config/bar.ts

💻 Code

No response

🙁 Actual behavior

Given a tsconfig that extends another config:

./tsconfig.json

{
  "extends": "./this-path-should-be-in-config/tsconfig.json"
}

./this-path-should-be-in-config/tsconfig.json

{
  "compilerOptions": {
    "paths": {
      "foo": ["./bar"]
    }
  }
}

The resolved tsconfig (via tsc --showConfig) doesn't reflect that ./bar is actually resolved relative to ./this-path-should-be-in-config/tsconfig.json:

{
    "compilerOptions": {
        "paths": {
            "foo": [
                "./bar"
            ]
        }
    },
    "files": [
        "./file.ts"
    ]
}

🙂 Expected behavior

For the config to include the relevant information (e.g. the relative path):

{
    "compilerOptions": {
        "paths": {
            "foo": [
                "./this-path-should-be-in-config/bar"
            ]
        }
    },
    "files": [
        "./file.ts"
    ]
}

Currently, it seems to indicate that paths is resolved relative to the CWD. When it's in fact relative to this-path-should-be-in-config.

It's also impossible for a custom TypeScript paths resolver (e.g. https://github.com/privatenumber/get-tsconfig) to correctly resolve the paths aliases based on this output.

Additional information about the issue

From https://github.com/privatenumber/get-tsconfig/pull/62

Start with the linked StackBlitz reproduction and run npm run config (tsc --showConfig) and npm run trace (tsc --noEmit --traceResolution). Compare the inherited paths values in the two tsconfig.json files with the resolved module path shown by tracing. Done means --showConfig reports the path relative to the extended configuration file, while preserving the demonstrated alias resolution.