Yarn-Linked Packages may not work in Che-Theia

[tsmaeder]

Describe the bug

I came across this problem when investigating using `yarn link' for building che-theia. Imagine this scenario:

/projects/moduleA
  package.json
  some-typescript-files.ts
/projects/moduleB
  package.json
  some-more-typescript.ts

moduleB imports stuff from moduleA. If we want to build moduleB against the master version of moduleA, we'll use the following:

cd /projects/moduleA && yarn link
cd /projects/moduleB && yarn link moduleA

now you can invoke yarn inside /projects/moduleBand you'll compile against the current state of /projects/moduleA. However, if you open an editor in moduleB on a file that imports from moduleA, you'll see an error on the import saying the module cannot be found.
What happened? I'm assuming we're using a devfile derived from our nodejs/yarn sample, the nodejs container will have home directory of /home/user. When I do the yarn link in moduleA, yarn creates a symlink in ~/.config/yarn/link. When I later do yarn link moduleA in moduleB, a symlink to ~/.config/yarn/link/moduleA is created inside /projects/moduleB/node_modules. So the compile now succeeds. However, in the che-theia container, there are two problems: first, the home folder is not shared among the different containers. So the linked module in ~/.config/yarn/link simply don't exist. And even if we declared a shared volume in the devfile for /home/user/.config/yarn/link it would not help: the link in /projects/moduleB/node_modules is to /home/user/.config/yarn/link. However, the yarn link folder in the theia container is under /home/theia/.config/yarn/link.

There is also a second problem: since the home directory is not on a persistent, volume, you'll have to run the 'yarn linkin/projects/moduleA` again each time you restart the workspace.

Che version

• latest
• nightly
• other: please specify

[ericwill]

As discussed in the standup, I think making the home folder persistent would be a good step in the right direction.

[tsmaeder]

The relevant issue is #15421

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