TS5011 errors with TypeScript 6.0: transpileModule called with rootDir: undefined

[julioz]

Bug Report

Problem

When using ts-loader with TypeScript 6.0, builds fail with TS5011 errors:

TS5011: The common source directory of 'tsconfig.json' is './src/connect'.
The 'rootDir' setting must be explicitly set to this or another path to adjust
your output's file layout.

This happens even when rootDir is correctly configured in tsconfig.json.

Root Cause

In dist/index.js line 419, the getTranspilationEmit function explicitly strips rootDir when calling transpileModule():

const { outputText, sourceMapText, diagnostics } = instance.compiler.transpileModule(contents, {
    compilerOptions: { ...instance.compilerOptions, rootDir: undefined },
    // ...
});

In TypeScript 5.x this was harmless — the compiler silently inferred rootDir from the common source directory. In TypeScript 6.0, this inference was removed and rootDir must be explicitly set. Setting it to undefined now triggers TS5011.

Suggested Fix

Remove the rootDir: undefined override so the tsconfig's rootDir flows through:

compilerOptions: { ...instance.compilerOptions },

Or, if there was a reason rootDir was originally stripped (to avoid output path computation in transpile-only mode), consider omitting it only when rootDir isn't explicitly configured.

Workaround

Patch ts-loader to remove the rootDir: undefined override. With yarn:

yarn patch ts-loader
# Edit dist/index.js line 419: remove `rootDir: undefined`
yarn patch-commit -s <patch-dir>

Environment

• ts-loader: 9.5.2 and 9.5.4 (both affected)
• TypeScript: 6.0.2
• webpack: 5.x

Related

• ts-loader forces 'isolatedModules' enabled when transpileOnly: true #1645 (similar pattern — ts-loader overriding compilerOptions in transpileOnly mode)

[errorx666]

In dist/index.js line 419, the getTranspilationEmit function explicitly strips rootDir when calling transpileModule():

Why is this being done? Are there any potential drawbacks to not stripping rootDir?

I can open a PR to fix this but I'd like to know the rationale behind it.

[danielweck]

Why is this being done? Are there any potential drawbacks to not stripping rootDir?

I'd like to learn more about that too.
Thank you :)

[johnnyreilly]

I'm afraid I haven't had chance to look at this yet. I'm dealing with some personal issues. If someone would like to take a look and open a prospective PR that would be helpful

[johnnyreilly]

@julioz the idea you suggest seems sensible. To be honest I can't remember the original rationale for this. I invite you to dig through git for when it was introduced, but I suspect it has been in place for a long time and maybe for reasons that no longer apply.

I'd be open to seeing if making the suggested change resolves things, and how it impacts the execution tests suite that run against multiple TypeScript versions

[johnnyreilly]

The original source of this behaviour is: #598

This was to resolve issue: #597

That problem occurred in 2017 and with these versions:

"typescript": "~2.4.0",
"ts-loader": "^2.2.1",

If the tests pass then we can likely assume that the changes in TypeScript since 2017 mean this is no longer an issue.

[johnnyreilly]

The related pull request looks promising. If the tests pass we'll look to merge. Unfortunately we can't publish immediately as I need to migrate ts-loader to trusted publishing: #1680

[johnnyreilly]

This should have fixed with v9.5.7 - gosh trusted publishing is hostile https://github.com/TypeStrong/ts-loader/actions/runs/23890002966/job/69660956084

[danielweck]

I'm afraid I haven't had chance to look at this yet. I'm dealing with some personal issues.

Classic open-source maintainer tale :)
Thank you for fixing this so promptly, and Trusted Publishing is definitely a positive evolution!! :D

[tchoi-rs]

Unfortunately I'm still getting the same error on 9.5.7.

[danielweck]

Unfortunately I'm still getting the same error on 9.5.7

The update fixed the problem at my end.