About this repo

This is to demonstrate a bug in the JupyterLab bundler. It consists of 3 packages in a monorepo setup:

• @testtest/foo-package: A top-level JupyterLab extension
• @testtest/bar-package: A dependency of foo
• @testtest/batman-leaf: A grandchild dependency of foo

None of these packages are on NPM.

Setup

Link each package:

jupyter labextension link ./packages/batman --no-build
jupyter labextension link ./packages/bar --no-build
jupyter labextension install ./package/foo  --no-build # can also use link

Now attempt a build:

jupyter lab build

It will fail when attempting to build bar-package:

Couldn't find package "@testtest/[email protected]" required by "@testtest/bar-package@file:linked_packages/testtest-bar-package-0.0.1-26a01b6e57a23185b090ca63cdbb71fc934dec47.tgz" on the "npm" registry.

Cause

What's happening is that when foo-package is loaded, the dependency on bar-package is correctly transformed to point to the link. However, this process is not recursive: bar-package has a dependency on batman-leaf, but that dependency is not transformed by the build toolchain.

The practical effect of this is nil IFF batman-leaf is already published on NPM: Yarn will either see that the linked version is newer (by versioning) or it will flatten the tree to point to the linked version. However, if batman-leaf is not on a registry, the build fails.

You can prove this by setting up a private repository. In another console:

yarn global add verdaccio
verdaccio

This will print a URL to your console, typically on localhost. You can verify the registry is up by navigating to it in a browser window.

Publish the dependent packages to this private repo:

# enter literally anything for the username and password at the prompts, the
# credentials aren't checked
npm login

# publish the leaf packages
npm publish ./packages/batman --registry http://url-for-your-private-repo
npm publish ./packages/bar --registry http://url-for-your-private-repo

Then, add the following to your .yarnrc:

"@testtest:registry" "http://url-for-your-private-repo"

Run the build again with jupyter lab build, and this time it will succeed.

You can verify it loaded by opening JupyterLab and looking for the following console output in Dev Tools:

Loaded the @testtest/foo-package package!
NaNNaNNaNNaNNaNNaNNaN Batman

You can verify that the local packages are being used by running jupyter lab --watch and making some trivial change.