cmd/go/internal/modfetch: version before would have negative patch number: found an example.

In go.mod in github.com/moby/buildkit, I found this line:

github.com/containerd/containerd v1.4.0-0.20191014053712-acdcf13d5eaf

This is an invalid psedo version: It is in the form of "vX.Y.(Z+1)-0.yyyymmddhhmmss-abcdefabcdef" but (Z+1)=0. It is rejected by go tools.

I came through a comment in cmd/go/internal/modfetch/pseudo.go, saying interested in examples of invalid pseudo versions "vX.0.0-0". Though this is not exactly the case, I think it may still be of interests of determining futher development.

[bcmills]

Thanks for the report! I've inquired about the origin of this version string on the GitHub page for the commit that introduced it (moby/buildkit@c6641fb).

I've seen other invalid versions within docker and moby projects originating from hand-edited go.mod files, so I suspect that the same happened here.