The output structures of rootDir and rootDirs are inconsistent #61883

🔎 Search Terms

rootDirs rootDir inconsistent structure

Maybe related to #44321 and #22039.

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about rootDirs (of which there are none). I tried next, 5.8.3 and 2.0.8. All exhibit this behaviour.

⏯ Playground Link

Here's a tiny repo or see below.

💻 Code

tsconfig1.json:

{"compilerOptions": {"outDir": "build", "rootDir": "src"}

tsconfig2.json:

{"compilerOptions": {"outDir": "build", "rootDirs": ["src"]}

src/foo/bar.ts is an empty file.

🙁 Actual behavior

Building with "rootDir": "src" and rootDirs: ["src"] produces different output:

$ tsc -p tsconfig1.json
$ find build/ -type f
build/foo/bar.js
$ rm -r build/
$ tsc -p tsconfig2.json
$ find build/ -type f
build/bar.js

🙂 Expected behavior

Both should do the same thing. Indeed, according to the documentation, using rootDirs ‘does not affect how TypeScript emits JavaScript’.

Additional information about the issue

For single-element arrays, of course, it doesn't really matter. But as it stands, I can't see a way to get both the non-nested structure rootDir provides and multiple root directories. #22039 perhaps suggests that setting both rootDir and rootDirs would work, but doing that makes tsc complain about whichever of rootDirs isn't in rootDir.