Warn when project constraint is missing in Gopkg.toml

[darkowlzz]

For every project in Gopkg.toml, there should be a constraint (branch, version or revision). A project without any constraint doesn't tell anything useful to dep.

For example, Gopkg.toml with a project:

[[constraint]]
  name = "github.com/x/y"

should result in warning during manifest validation and tell the user to add a branch/version/revision constraint.

[sdboyer]

mmmm, almost - a [[constraint]] is useful if either a version rule OR a source rule is present. but other than that, yeah, this would be good to add 😁

[JackyChiu]

Hey @sdboyer @darkowlzz can I pick this one up?

[darkowlzz]

@JackyChiu go for it! 👍

[carolynvs]

@sdboyer @darkowlzz The importers make entries like this when a constraint version/branch cannot be determined. Here's the original PR where that behavior was introduced #901. If we are going to start warning about config that dep itself is generating, then we'll need to change the importers to do something different.

I can't find the original issue/discussion on why we use gps.any for the constraint, instead of ommitting it, but I thought it had to do with confusion around getting an empty manifest (but populated lock) after importing.

UPDATE: Found them: #149 and I think somewhere in this monster issue #213.

[darkowlzz]

@carolynvs a quick update. I had a discussion with Sam about this and we decided to omit those projects from manifest for which we don't have proper/useful constraints.

[carolynvs]

Thanks for the quick clarification! I've created #1373 to get the importers tweaked to match and flagged it with help wanted.