Patching Go software

[Jonathan Perkin <jperkin%mnx.io@localhost>]

Packaging golang software is becoming increasingly frustrating.  One of 
the main problems we have with the current setup is that it appears to 
be impossible to patch dependencies.

As an example I'm updating gitea but need to patch one of the deps. 
After 'bmake extract' I have the following file in WRKDIR:

  work/github.com/sassoftware/go-rpmutils@v0.2.0/fileutil/fileutil_unix.go

In older golang/pkgsrc setups it used to be possible to patch these 
files, at least we still have some "patch-.._github.com..." patches 
across pkgsrc.

However, it appears that all of these extracted files are completely 
redundant.  During the build go will unpack its own copies from GOPROXY 
into ${WRKDIR}/.gopath:

  work/.gopath/pkg/mod/github.com/sassoftware/go-rpmutils@v0.2.0/fileutil/fileutil_unix.go

and even if I try to patch that file after the build fails, go just 
extracts a brand new unmodified version in place.

Do we have anyone who understands go who can answer why we unpack 
GO_MODULE_FILES into WRKDIR if they're just going to be ignored, and 
ideally how we can patch vendor dependencies?

As a comparison, OmniOS does not have the same problems with their gitea 
build and happily patch the dependency, but they do not have the same 
strict distfile requirements that we do, so it must be related to our 
GOPROXY usage.

Being unable to patch them results in the process being significantly 
harder, as you then need to fork entire dependencies on github.com, 
create your own releases, then ship patches for the brittle 'go mod 
replace' dance.  This causes problems with updates as other committers 
aren't interested or don't have the permissions to update the forks.

It's not helped by golang upstreams becoming increasingly hostile 
towards non-Linux platforms, so this is only going to get worse.

Thanks,

--
Jonathan Perkin   -   mnx.io   -   pkgsrc.smartos.org
Open Source Complete Cloud   www.tritondatacenter.com