The go module behavior is documented at: https://github.com/golang/go/wiki/Modules
This would change the expected behavior for all current users of modules. I've marked it as a feature request.

/cc @bcmills @jayconrod

go get -u explicitly requests that versions be upgraded. If we were to avoid upgrading v0 dependencies with -u, those dependencies would never get upgraded and fixes to bugs would never be applied: according to the Semantic Versioning spec, at version 0 “[a]nything MAY change at any time”, including from v0.3.1 to v0.3.2, so literally no upgrade at all would be safe.

If you don't want to pull in breaking changes, either don't pass the -u flag or don't depend on modules that are still unstable.

So we essentially created a situation where:

1. There is no safe migration path from dep,
2. There is no safe upgrades for v0 libraries,
3. There is no convergence path?

It seems that -reading that v0 is all fair game- makes it way less useful (specially to safely iterate). 

And I'm not sure what was so "bad" or "wrong" about Dep's approach that it was decided to diverge from? was it maybe considered to propose an update to SemVer to reflect that behavior....

I would like to use this issue to at least document the thought process that went into this decision...

@EngHabu The thought process and design decisions that went into modules are well described in Russ's series of blog posts. In particular, see The Principles of Versioning in Go.