Add example for nodejs toolchain with npm_install repository rule

[kczulko]

While applying latest rules_nodejs(5.8.0) to one of the projects I'm working on, I saw there's no longer an option to pass vendored_node to npm_install rule.

Following this "migration guide" it was found out (thx @avdv @aherrmann ) that using proper npm_install::node_reporitory value does the job.

However there's an issue of suffixing toolchain names which rules_nodejs does - see nixpkgs-nodejs_linux_amd64 as one of the names. E.g. now macos build fails with:

Error in path: Unable to load package for @nixpkgs-nodejs_darwin_amd64//:bin/node: The repository '@nixpkgs-nodejs_darwin_amd64' could not be resolved: Repository '@nixpkgs-nodejs_darwin_amd64' is not defined

Probably we have to mimic the behavior that rules_haskell does (thx @ylecornec )

[aherrmann]

@kczulko Thank you for raising and investigating this!

Probably we have to mimic the behavior that rules_haskell does (thx @ylecornec )

The link points to this PR again. Did you mean this?

[kczulko]

@aherrmann @avdv
I think it's ready for the next review round. I think I am also missing some docs about this new way of configuring rules_nodejs under nix. I added rules_nodejs_core as explicit dependency of this project. Otherwise there were some "circular" (?) dependency issues which lead to a failures.

[aherrmann]

Thank you! That looks good!

Otherwise there were some "circular" (?) dependency issues which lead to a failures.

Bazel reports missing external repositories like that sometimes.

I think I am also missing some docs about this new way of configuring rules_nodejs under nix.

A good place to add them would be the docstring of the new nixpkgs_nodejs_configure_platforms and also a docstring in nixpkgs_nodejs_configure pointing to it. (Also a note in the CHANGELOG). You can look at other macros for the format of docstrings.

[aherrmann]

Looks great! Thank @kczulko for pushing this through, great work!
Only one small comment. Feel free to apply and then add the merge-queue label.