Protoype: allow constraint.source to be a sub-package of an repo

[sttts]

This prototypes to have non-root packages as constraint.source values:

[[override]]
  name = "k8s.io/apimachinery"
  source = "github.com/sttts/k8s-dep-e2e/internal/_staging/k8s.io/apimachinery"

Compare fabulous-gopher/k8s-dep-e2e#7 as an example repo.

[sdboyer]

hmmm.

so, i'm quite dubious about this, because the invariant that roots are never nested is one that i just accepted quite some time ago, and i've stopped keeping mental notes on what implicitly relies on that invariant. all i have is vague, placeless memories, deep in the weeds of some logic that "boy, this really locks us out from nested roots."

but, this is a more limited scope way of driving at that, and it's possible that it's not as harmful as doing it in general. so, i'm keeping an open mind 😄

[sdboyer]

this strikes me as unnecessary - it's a fairly straightforward manipulation to select a subtree of a PackageTree. as such, this could just be a method on PackageTree itself; we needn't push it into the SourceManager's API.

GetManifestAndLock() is the harder one that may actually need this.

[sttts]

this could just be a method on PackageTree itself;

I actually had that and hit some issues due to the cache. Didn't dig any deeper and just hacked listPackages. You have a better overview for a more elegant implementation.

[sdboyer]

yep, the cache is not designed to parameterize on a subpath. it'd be quite wasteful to inflate the cache with the additional parameter, and applying it as a post-cache transform wouldn't add much value.

better to have e.g. func (ptree PackageTree) Subtree(subpath string) (PackageTree, error), which produces a new PackageTree containing only the subpackages along that subpath. error could be omitted - OTTOMH the only possible error it could express is if the provided subpath didn't match any packages in the receiver PackageTree.

i think this would fit in quite snugly with the other PackageTree methods.

[mvdan]

Dep was officially deprecated earlier this year, and the proposal to archive this repository was accepted. As such, I'm closing outstanding issues before archiving the repository. For any further comments, please use the proposal thread on the Go issue tracker. Thanks!