This announcement dropped today:

I realized that this is the missing piece for supporting Go modules in pkgsrc. If you go back and reread the “fetch” section in Supporting Go Modules in pkgsrc, it seems a bit awkward compared to a standard fetch action. The reason is that go mod download re-packs the source into its own zip format archive.

The module proxy (https://proxy.golang.org/) solves this problem and enables a simple solution for modules, very similar to lang/rust/cargo.mk. Basically, a target similar to show-cargo-depends that outputs a Makefile fragment containing the names of modules that the current package depends upon. All these become distfiles fetched from a hypothetical $MASTER_SITES_GOPROXY. Crucially, this means that the distfiles do not have to be stored in a LOCAL_PORTS subdirectory but can use the normal fetch infrastructure.

Now all that remains is implementing this :) There is some more time to do that: Go 1.13 (to be released some time in summer) will use module support by default. What’s more, a bunch of new software (including the various golang.org/x/* repositories) has go.mod files these days, using module-based builds by default.