Code-server: install yarn if not already available

[DiegoBM]

Since all node installations come with npm, probably forcing users to install yarn if they are happy with npm (since they both do the same) is not desirable and will decrease reach. It would be better if yarn could be kept as a choice since it's not the default or standar.

Fallback could be implemented as mentioned in this gist by @jsynowiec's comment:
https://gist.github.com/jsynowiec/b67221be8f34ac531f17c69fdaf1efbe

[sr229]

Project is merely a standard NPM still, so you can use it without yarn. I don't get where this is coming, all yarn projects are npm-compatible (exceptions are those who use yarn workspaces).

[DiegoBM]

@sr229 try to run the scripts (for example npm install) without having yarn installed and you'll get where its coming from (hint: "yarn not found")

[kylecarbs]

We can provide a fallback to npm for sure. Might just be better to install yarn project-wide then use npx.

[DiegoBM]

That's also a good option indeed

[orzFly]

NPM cannot read yarn's yarn.lock which shall be required for consistent environment. I don't think a fallback to npm is a good idea.

+1 for install yarn project-wide.

[orzFly]

Project is merely a standard NPM still, so you can use it without yarn. I don't get where this is coming, all yarn projects are npm-compatible (exceptions are those who use yarn workspaces).

Yarn also supports alias.

[sr229]

Marking as wontfix. Already documented as a prerequisite.