Corral allows bad locators and doesn't error

[SeanTAllen]

I did an add with an incorrect locator and got:

{
"deps": [
{
"locator": "github.com/ponylang/peg",
"version": "0.1.0"
}
],
"info": {}
}

when I run corral fetch I get:

fetch: fetching from /home/sean/code/ponylang/changelog-tool
fetch: fetching dep: github.com/ponylang/peg @ 0.1.0
No dep bundle for: github.com/ponylang/peg

Which is horribly misleading given that the locator doesn't exist at all.

I propose this is addressed in two parts. Fix the bug of it not indicating the error on fetch.
Enhance to validate a locator on addition.

[SeanTAllen]

So the problem here is that the way that Corral determines the VCS to use work like this.

There's a primitive called VCSType that has the following to pick a VCS:

primitive VCSForType
  """
  This factory returns a VCS instance for any given VCS by name.
  """
  fun apply(env: Env, kind: String): VCS val ? =>
    match kind
    | "git" => GitVCS(env)?
    | "hg"  => HgVCS
    | "bzr" => BzrVCS
    | "svn" => SvnVCS
    else
      NoneVCS
    end

So if the VCS is unknown, you get the NoneVCS which NoOps everything. Thus it appearing to "work" in example I gave when opening this.

The match on string comes from vcs on the Deps class:

fun vcs(): String => locator.vcs_suffix.trim(1)

So a locator without a suffix will give you the NoneVCS and NoOps everything.

This seems like a design flaw in how Corral is determining the VCS to use and how the factory works.
Reasonably, there should be no NoneVCS outside of perhaps testing. It's existence is a smell.

At this point, I'm adding the "needs discussion" label to this issue. We need to rework how the VCS is determined and that requires some discussion.