buildGoModule: building Go binaries in two phases

[kalbasit]

Motivation for this change

This change provides a new builder called buildGoModule for building Go packages with go modules support in mind. It does build through two phases:

1. The first phase consists of building the go-modules derivation: go mod download will be executed within the source directory to download all of the dependencies, and store them at $GOPATH/pkg/mod. After removing the impure directory $GOPATH/pkg/mod/cache/vcs, we persist $GOPATH/pkg/mod as the $out of this derivation.
2. The second phase consists of building the actual Go module, and this is done by setting GOPROXY to point to the download directory within ${go-modules}/cache/download which instructs Go to skip any network call, and simply use the already-downloaded dependencies.

The benefit of such infrastructure is that we no longer need tools such as dep2nix or vgo2nix to parse the go.mod and go.sum in order to generate Nix dependency file.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Assured whether relevant documentation is up to date. Rendered.
• Fits CONTRIBUTING.md.
• Converted packages
  • Move over hugo.
  • Move over pet.
  • Move over jx.
  • Move over gotools.
  • Move over terminal-parrot.
  • Move over todoist.
  • Move over hetzner-kube.
• Create new packages
  • Create mod.

---

cc @ehmry @lethalman @fpletz @Mic92 @nlewo

nix run -f https://github.com/kalbasit/nur-packages/archive/master.tar.gz nix-verify -c nix-verify -I nixpkgs=`pwd` --keep-going \
	-A jx \
	-A pet \
	-A hugo \
    -A gotools \
    -A terminal-parrot \
    -A todoist \
    -A hetzner-kube \
    -A mod

[kalbasit]

@GrahamcOfBorg build jx pet hugo gotools

[kalbasit]

@GrahamcOfBorg build jx pet hugo gotools

[kalbasit]

@Mic92 I've addressed your comments. I have also conducted some tests to verify with certainty that the modules downloaded are not affected by changes to the upstream repository, such as with the release of a new verison. This PR is now clear to be merged as well.

PTAL.