Steps to play

The problem being reproduced in this repository is issuing d.ts files with read-only values!

A few points to consider like the monorepo, incremental build and path alias.

Using relative imports '../../' in the bar and foo packages the build works as expected, but if you set path alias in tsconfig and use these imports by the project it breaks.

Functional build

yarn build

In this example we are building the packages individually running tsc on each synchronously along with tsc-alias -f resolving the esm imports.

If you look at the screenshot you can see that both d.ts files are correct.

Wrong build

yarn build:wrong

Now using incremental build (or even normal mode) tsc -b.

After the build if you look at packages/bar/dist/src/sample/index.d.ts and compare it to packages/foo/dist/src/sample/index.d.ts you will notice the following difference!

As can the values ​​were output correctly in the bar package, but in foo the values ​​defaulted to string.

You can even keep both files to notice changes live as you build! The

Third case

You can now try changing the @/ alias imports to the normal ../ template that is commented out in the packages/bar files and run build:wrong again and you will see that now things work too.