lerna-typescript-demo

Sample repo illustrating an issue with TypeScript in a lerna-based monorepo.

UPDATE

I found two workarounds for the issue:

• Instead of doing lerna bootstrap, if we do lerna bootstrap --hoist, it works. This is due to --hoist making lerna unify the common rxjs dependency, and puts it in the node_modules in the root, so there is no duplication any more.
• Add rxjs as a dependency in the root package.json, and move it to the peerDependencies in the actual packages. (This results in the same ultimate setup as what lerna bootstrap --hoist produces.)
  I pushed this fix to the peer-dep branch.

Usage

Clone the repo, and install the dependencies.

npm install

Then execute

lerna bootstrap

The above command installs the dependencies for the two packages. Since the dependency from lerna-typescript-demo-ts to lerna-typescript-demo-base is an internal cross-package dependency, lerna sets that up with a symbolic link pointing to the directory of the other package. I suspect that this is what's causing the compilation error.

Then enter the directory of TypeScript package, and try to transpile.

cd packages/lerna-typescript-demo-ts
npm run transpile

The transpilation will fail with the following error:

error TS2345: Argument of type 'UnaryFunction<Observable<Bar[]>, Observable<Bar[]>>' is not assignable to parameter of type 'UnaryFunction<Observable<Bar[]>, Observable<Bar[]>>'.
  Types of parameters 'source' and 'source' are incompatible.
    Type 'Observable<Bar[]>' is not assignable to type 'Observable<Bar[]>'. Two different types with this name exist, but they are unrelated.

I suspect that this is somehow caused by the usage of the symbolic linking, because if we

1. Delete the node_modules folder inside packages/lerna-typescript-demo-ts
2. Execute npm install inside packages/lerna-typescript-demo-ts (so that it pulls down the dependency from NPM instead of linking)
3. Do the transpilation again with npm run transpile

Then it succeeds.