Using npm to install yarn

[MalcolmDwyer]

TLDR: How do I 'npm install yarn', then run 'yarn install' from that yarn?

(Similar to #503)

Motivation

I'm trying to set up a yarn build on an isolated corporate system. We have an internal npm repo, and an internal copy of node_dist. We don't have any internal yarn dist though. By default the 'install-node-and-yarn' execution is getting yarn downloads from https://github.com/yarnpkg/yarn/releases/download/...
However, while there are gzip files reachable there, it's not readable as a directory and therefore, I can't reasonably ask my configuration support people to clone it internally.

I tried pointing the yarnDownloadRoot at our local npm repo. I can find a path where yarn-0.16.0.tgz exists, but the yarnDownloadRoot argument makes incompatible assumptions about how the version number fits into that path.

Requesting either of the following:

1. A way to install yarn given an npm repo path, instead of a dist path
2. A way to run yarn from node_modules. In this scenario (similar to what issue 503 is asking), I would use <goal>install-node-and-npm</goal>, then stick in an extra step to run npm install yarn, then I would need a way in <goal>yarn install</goal> to tell it to use the node_modules/yarn/bin/yarn instead of node/yarn/bin/yarn. If there's a configuration variable to do this, I couldn't find it.

Thanks

[eirslett]

The answer is in #490, I posted an example there.