I'm one of the people responsible for the choice of versioning for the Go protobuf module. (Sorry!) The original Go protobuf implementation is in the module "g

I'm one of the people responsible for the choice of versioning for the Go protobuf module. (Sorry!) The original Go protobuf implementation is in the module "github.com/golang/protobuf". A couple years back, we decided that it was time to do a major overhaul of the protobuf implementation. Protobufs were one of the first major pieces of Go code outside the standard library (the second post ever on the Go blog is about it), and there were a number of design decisions that made sense at the time but which we wanted to go back and revisit. Doing all of this was not going to be possible while preserving API compatibility. Given that, we needed a new module path. That's the core of Go modules and API changes: You change the module path when you make an incompatible change. You can do this by bumping the major version of the module (since the module path includes the version), or by changing the module path entirely. (There's another option, which I think doesn't get enough attention: You can just make the change, and force your users to deal with it. If you're okay with breaking your users when they upgrade, nothing stops you from doing this. We take backwards compatibility very seriously, so that wasn't an option for us.) Given that we needed a new module path anyway, we took advantage of the opportunity to move to a path that isn't specific to a particular code hosting provider: "google.golang.org/protobuf". GitHub is great, we love GitHib, but we'd much rather have a provider-agnostic name for the module. So we have a new module path. The question then was: What version do we tag the new module as when we release it? Remember that there has never been any version of "google.golang.org/protobuf" at this point; it's a completely new module. One option was to tag it as v1.0.0. But that might be confusing, because this is "version 2" of the protobuf implementation, even if it's under a different module path. Also, if someone complains about a problem with "v1.2.0" and doesn't mention which module they're using, we won't have any way to tell which one they're talking about. Another option was to tag it as v2.0.0. But that might be confusing, because there's never been a v1 of this package. Also, this would likely cause unnecessary confusion with "proto2" and "proto3" (versions of the protocol buffer language). We waffled for quite a while, and eventually settled on v1.20.0, which avoids the missing v1 weirdness but also ensures that there is no overlap in versions between the two modules. That confused people. Alas. Perhaps every option would have led to confusion. In retrospect, perhaps we should have gone with v2.0.0 (and a module name of "google.golang.org/protobuf/v2"). Too late now; oh, well. If this was the worst decision we made in the new implementation (and so far, it looks like it may have been), I'll be quite happy.