Feature bare cache

[yofreke]

In progress

• [x] cache initialization should validate entries and remove invalid (eg. not bare)
• [x] cache should make use of node-git to bare clone modules in to cache folder
  • [x] if already in cache then fetch inside of bare repo
• [x] run clone in /modules using bare repo as remote
  • [x] swap remotes so that module origin is original and module cache-origin points to cache folder
  • [x] checkout cache-origin/requested-version
  • [ ] todo: use devkit cache for submodules as well?
• [ ] ensure that devkit install <single module> still works as expected (using cache)
• [ ] validate dependencies better (eg failure on "devkit-core": "https://github.com/gameclosure/devkit-core#")

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Rationale for using git bare repos for caching.

Devkit in general has caching, specifically js.io and the build server are built on this idea of having symlinks to the modules so that we can use a cached version to keep network overhead down.

1. Having a bare repo and just cloning that from one folder to another solves this issue and also lets us cache every version in one go using the minimal system file space.
2. We can reuse this so that when any of our engineers call devkit install on a project it doesn't go all the way to github to get the version they want which more importantly then bandwidth is very slow and costs us valuable time. .i.e Money.
3. Non Unix support (i.e windows) should be a lot more viable because symlinks are a massive disaster on that platform (this is not that important but still true). Also because of relying on nodegit instead of the git cli.

Additionally we can then add an option like devkit cache update which updates all the cached bare repos and that way we can bake this into jsio container creation that updates periodically so that when users login to jsio their container always has access to the latest versions of modules.

Other options such as devkit cache list and devkit cache inspect should be added to list all the modules in the cache and to see what the head commit is and the remote and possibly date???

(credit for rationale @martell )

[martell]

@yofreke I assume you had to merge this for the devkit app type for jsio. How is it shaping up? Need help anywhere with the git stuff?

[yofreke]

Would be good to have some tests around the new module cache to make sure it works... other than that not sure