Absolute paths are not resolved in tsconfig.json paths

[iamakulov]

Hey Evan, I believe I found a bug. When tsconfig.json has absolute paths in its compilerOptions.paths, ESBuild doesn’t resolve these paths properly.

Details

Consider the following tsconfig.json (with an absolute path in its alias):

{
  "compilerOptions": {
    "baseUrl": ".",
    "paths": {
      "alias/*": ["/tmp/esbuild-tsconfig/subdir/*"]
    }
  }
}

With this tsconfig.json and files like

// /tmp/esbuild-tsconfig/index.js
import subdep from "alias/subfile";
console.log(subdep);

// /tmp/esbuild-tsconfig/subdir/subfile.ts
export default 5;

ESBuild won’t find alias/subfile:

$ esbuild --bundle index.ts --outdir=dist
 > index.ts: error: Could not resolve "alias/subfile" (mark it as external to exclude it from the bundle)
    1 │ import subdep from "alias/subfile";
      ╵                    ~~~~~~~~~~~~~~~

1 error

The error would go away if we replace the absolute path with the relative one:

{
  "compilerOptions": {
    "baseUrl": ".",
    "paths": {
      "alias/*": ["./subdir/*"]
    }
  }
}

From my experiments, this issue affects at least:

• the extends field
• the compilerOptions.paths field

Repro

Repository: https://github.com/iamakulov/esbuild-tsconfig-repro

Steps to reproduce:

# Clone the repository into `/tmp/esbuild-tsconfig`
git clone https://github.com/iamakulov/esbuild-tsconfig-repro.git /tmp/esbuild-tsconfig

# Install dependencies
yarn

# Run ESBuild
yarn esbuild --bundle index.ts --outdir=dist

When this matters

This doesn’t matter in general, since pretty much every tsconfig.json uses relative paths. However, this matters for autogenerated tsconfigs – where relative paths are more complicated to compute (as they are relative to baseUrl which may be inherited). In that case, absolute paths are more convenient. (Semi-related to #783.)

[susiwen8]

I think your path is wrong, according to path-mapping,

Please notice that "paths" are resolved relative to "baseUrl". When setting "baseUrl" to another value than ".", i.e. the directory of tsconfig.json, the mappings must be changed accordingly.

So you should do

{
  "compilerOptions": {
    "baseUrl": ".",
    "outDir": "./dist",
    "paths": {
      "alias/*": ["subdir/*"]
    }
  }
}

[evanw]

Thanks for the heads up. This is currently missing test coverage, and is a bug in esbuild. Will fix.

Please notice that "paths" are resolved relative to "baseUrl".

TypeScript's notion of "resolving relative to" involves not doing resolution for absolute directories. Here is the documentation from the actual code in the compiler that ends up doing this:

Combines paths. If a path is absolute, it replaces any previous path. Relative paths are not simplified.

// Non-rooted
combinePaths("path", "to", "file.ext") === "path/to/file.ext"
combinePaths("path", "dir", "..", "to", "file.ext") === "path/dir/../to/file.ext"
// POSIX
combinePaths("/path", "to", "file.ext") === "/path/to/file.ext"
combinePaths("/path", "/to", "file.ext") === "/to/file.ext"
// DOS
combinePaths("c:/path", "to", "file.ext") === "c:/path/to/file.ext"
combinePaths("c:/path", "c:/to", "file.ext") === "c:/to/file.ext"
// URL
combinePaths("file:///path", "to", "file.ext") === "file:///path/to/file.ext"
combinePaths("file:///path", "file:///to", "file.ext") === "file:///to/file.ext"