mkGoEnv: different locations for tools.go and go.mod/sum?

[martinbaillie]

Thanks for the excellent work you've done here! I'm especially interested in the mkGoEnv / tools.go pattern for providing Go tooling via Nix that's clamped to the go.sum.

I've been looking through the code tonight to see if it would be suitable for a monorepo I work in that shares a single go.mod but has many subfolders each with their own shell.nix/tools.go that want to utilise a subset of the go.mod to put some Go-based tools on the developer's path.

I was wondering:

• Is there a way to provide a different location from pwd for the tools.go during mkGoEnv that I missed?
• Will mkGoEnv always build everything in the go.mod even if the tools.go only references a tiny subset of import _ <gitforge>/<user>/<blahprj>/cmd/<blah>