packageId is not set when calling resolveModuleName on a directory with an index.d.ts file in a dependency

[TheLazySquid]

🔎 Search Terms

packageId, resolveModuleName, index.d.ts

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about this issue

⏯ Playground Link

https://github.com/user-attachments/files/28815038/repro.zip

💻 Code

import ts from "typescript";
import { resolve } from "path";

const importer = resolve("node_modules/@dimforge/rapier2d-compat/pipeline/world.d.ts");

const resolved1 = ts.resolveModuleName("../control", importer, {}, ts.sys);
const resolved2 = ts.resolveModuleName("../control/index", importer, {}, ts.sys);

console.log(resolved1.resolvedModule.packageId); // undefined
console.log(resolved2.resolvedModule.packageId); // defined properly
console.log(resolved1.resolvedModule.resolvedFileName === resolved2.resolvedModule.resolvedFileName); // true

🙁 Actual behavior

If a dependency contains a directory with a file called index.d.ts, say dir/index.d.ts, resolving the file with typescript.resolveModuleName only sets resolvedModule.packageId when resolving dir/index, and not when resolving dir. In both cases resolvedModule.resolvedFileName is the same.

I tested this with moduleResolution: "bundler" and ran into the same issue.

🙂 Expected behavior

packageId should be set regardless of if the index file was resolved indirectly

Additional information about the issue

I noticed this issue with @dimforge/rapier2d-compat, but I imagine it happens elsewhere. This is an issue for me because rollup-plugin-dts doesn't know that it should inline the types because it doesn't know the name of the module they are from.