buildGoModule: binaries return an empty string for runtime.GOROOT()

[leonklingele]

Describe the bug

Binaries built using buildGoModule return an empty string for runtime.GOROOT(). This will change behavior and most likely break all apps relying on GOROOT.

I noticed that swag init (see go-swag) was producing inconsistent results based on whether it was installed through nix-shell --pure -p go-swag, installed using go install github.com/swaggo/swag/cmd/swag@latest or build manually from the GitHub repo.

go-swag relies on runtime.GOROOT() to ignore files from the Go stdlib: https://github.com/swaggo/swag/blob/e67c96576bc94cbb0acc8026885ed53e0b08ad04/packages.go#L96

This prefix-check always returns true due to runtime.GOROOT() == "", effectively ignoring all files.

As it is unknown if this breaks other apps (due to them depending directly on GOROOT, or one of their dependencies), this should be fixed in buildGoModule and not only for the go-swag nixpkg.

Steps To Reproduce

Minimal reproducible here: https://git.helsinki.tools/leon.klingele/nix-buildgomodule-bug
Build it using buildGoModule. Running it will output something similar to

[..]
runtime.GOROOT() == "" true

Expected behavior

I don't have a nix system at hand so I can't tell the exact output. But that one line which says true in the output above should say false instead.

Notify maintainers

Sorry for the spam. I'm going to mentioning all users who have contributed to the Go compiler package this year.

@dotlambda @zowoq @Stunkymonkey @zhaofengli @trofi @yu-re-ka

Metadata

s.a., will update tomorrow if required.

[trofi]

Let's pull in golang team:

map (x: "@${x.github}") lib.teams.golang.members expands to: @c00w @kalbasit @Mic92 @zowoq @qbit

[mtoohey31]

I believe this is a result of the program being compiled with the -trimpath argument. This can be disabled by passing allowGoReference to buildGoModule. Having allowGoReference = false is desirable so that Go programs' closures don't include the Go compiler by default.

[06kellyjac]

It uses the GOROOT environment variable, if set at process start, or else the root used during the Go build.

Yep either drop -trimpath or provide a GOROOT env var either when running the command or use a wrapper.

---

Although in this case I think this a bug that go-swag needs to resolve. It should check if the GOROOT function actually gives a value & not just ignore everything. Then it wouldn't matter if we're using -trimpath

[leonklingele]

Any news on this?

The same issue just struck us again with go-licenses which doesn't work at all due to the use of go/build.Default.GOROOT here: https://github.com/google/go-licenses/blob/150520fc5b3aaf07a90ff6cc50f7227abda448f8/licenses/library.go#L303

[06kellyjac]

What resolution do you expect?

trimpath is default and allowGoReference removes trimpath for cases where you need GOROOT or other stuff trimpath removes.
Does that still not resolve the issue for go-licenses?