[regression 4.2.4-4.3.2] TS 4.3 builds .d.ts using import statements referencing absolute project paths instead of relative paths

[ronjouch]

🔎 Search Terms

regression declaration file .d.ts imports relative absolute projects project-based build 4.3 4.3.x

🕗 Version & Regression Information

• This changed between versions 4.2.4 and 4.3.2
• Issue remains reproducible in the latest next build, currently 4.4.0-dev.20210602

⏯ Playground Link

Here is a repo with a minimal scenario (5 TS files + tsconfig.json):
https://github.com/ronjouch/ts43-import-regression

Just clone it and run npm run repro (after verifying what the script does)

💻 Code

This bug seems to be about projects, imports/exports through multiple files, so it gets confusing when having to list the multiple files here in a linear issue. Please check the repo.

Or see https://github.com/ronjouch/ts43-import-regression/commit/f55df20fc7cacd946cd3cd2ad5f99a08d7606290

🙁 Actual behavior

TS 4.3 writes .d.ts files that contain import statements referencing the local absolute project folder name (src-types in my example), which is meaningless and will cause dependents of the library to break.
See the second & third section of npm run repro (a helper script that builds under 4.2 & 4.3, and greps the culprit output):

===== Now with TS 4.3: the relative import will no longer be relative but absolute using the
===== project folder name, causing the library to break when used in another context

+ typescript@4.3.2
updated 1 package in 0.688s

> ts43-import-regression@1.0.0 compile /home/ronanj/ts43-import-regression
> tsc --build src-types src-dogs

    protected static getDogConfig: () => import("src-types").DogConfig;
                     HERE: bad, absolute import ^^^^^^^^^^^

===== And lets see if it is fixed in the last nightly...
+ typescript@4.4.0-dev.20210602
updated 1 package in 0.662s

> ts43-import-regression@1.0.0 compile /home/ronanj/ts43-import-regression
> tsc --build src-types src-dogs

    protected static getDogConfig: () => import("src-types").DogConfig;

🙂 Expected behavior

TS should resolve types in .d.ts using relative imports.
This is what happens with TS 4.2.4, see the first section of npm run repro:

+ typescript@4.2.4
updated 1 package in 0.687s

> ts43-import-regression@1.0.0 compile /home/ronanj/ts43-import-regression
> tsc --build src-types src-dogs

    protected static getDogConfig: () => import("..").DogConfig;
                  HERE: good, a relative import ^^^^
===== Notice above how the type of getDogConfig type was compiled to a proper *relative* import,
===== through index.ts itself referencing something relative. Good.

[weswigham]

OK, I spent way, way too long getting this into a testable baseline format before going "doh" and realizing that this is actually just working as expected ("regression" or no) - we prefer nonrelative paths where possible, and the baseUrl compiler option indicates that nonrelative references from that given path are a-OK (seriously: you're allowed to write these paths in your code and we won't issue an error). If you remove the baseUrl option form your base config, we'll no longer generate paths like this.