Support Go modules

[bhcleek]

To support Go 1.11 fully, vim-go changes need to be made to handle module mode development.

• support for go.mod
• autocompletion (see gocode: switch to https://github.com/mdempsky/gocode #1853 (comment))
• :GoImport tab completion (GoImport autocomplete not working in go mod project #2212)
• others....

Obviously, vim-go will be dependent on a number of tools getting updated to complete the support, but there are a number of changes that will need to be made to vim-go itself.

[aofei]

+1

But I think this plugin is hard to support the Go modules, at least not until golang/go#24661 is fixed.

[AdamSLevy]

At minimum things like syntax highlighting can be added for the go.mod and go.sum files.

[fatih]

Added initial support for :GoModFmt (auto format the go.mod file) and syntax highlighting here: #1931

[rkuska]

Is it expected that things like auto fmt (and go imports) on save doesn't work outside of GOPATH?

[fatih]

@rkuska no, gofmt works on a single file and should work outside GOPATH.

[rkuska]

Sorry for the noise, I had let g:go_fmt_fail_silently = 1 and there was syntax error in my file 🤦‍♂️ but when I cd-ed to my original GOPATH location the syntax error wasn't there and go fmt was working so I assumed the above.

[makkes]

:GoDoc also doesn't seem to work with modules.

[powerman]

:GoDoc also doesn't seem to work with modules.

It's not because of modules, it's just Go 1.11 removed this functionality from godoc. Looks like we should use go doc instead, but it show less information when viewing doc about whole package and thus require request per each single function/method, which means we need very good navigation to make it fast and easier to move between these small chunks of doc. Also I didn't found a way to move from doc to source with go doc. Maybe distributing old godoc binary with vim-go will solve these issues, but it's unclear if old godoc is compatible with modules (unlikely).