cmd/go: internal error in `go work sync`

[trajan0x]

Go version

go version go1.21.5 darwin/arm64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='arm64'
GOBIN=''
GOCACHE='/Users/trajan0x/Library/Caches/go-build'
GOENV='/Users/trajan0x/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Users/trajan0x/go/pkg/mod'
GONOPROXY='github.com/synapsecns/*'
GONOSUMDB='github.com/synapsecns/*'
GOOS='darwin'
GOPATH='/Users/trajan0x/go'
GOPRIVATE='github.com/synapsecns/*'
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/opt/homebrew/Cellar/go/1.21.5/libexec'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/opt/homebrew/Cellar/go/1.21.5/libexec/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.21.5'
GCCGO='gccgo'
AR='ar'
CC='cc'
CXX='c++'
CGO_ENABLED='1'
GOMOD='/dev/null'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/12/8xtw48x951g0vv4z_ctcr2hr0000gn/T/go-build1424252971=/tmp/go-build -gno-record-gcc-switches -fno-common'

What did you do?

1. git clone https://github.com/synapsecns/sanguine
2. go work sync
3. git checkout 995354fca4e89c0931ea5f6f0a77f170aac2f13e (this is happening across a couple commits and I found it on Add native ETH support to relayer synapsecns/sanguine#1840, just providing a single commit on master for reproducibility)

(Note: recipe won't work for this kinda bug, but I created a repl of the repo here and ran the command just for ease of debugging.

What did you see happen?

go: cloud.google.com/go@v0.110.7 requires
        github.com/google/s2a-go@v0.1.4
panic: internal error: found a version conflict, but no constraint it violates

goroutine 1 [running]:
cmd/go/internal/modload.editRequirements({0x1010edbd0, 0x1014830a0}, 0x14013bbaaa0, {0x0, 0x0, 0x1400bb7e828?}, {0x14007bac000, 0x108, 0x1400bb7e800?})
        /opt/homebrew/Cellar/go/1.21.5/libexec/src/cmd/go/internal/modload/edit.go:336 +0x2bc0
cmd/go/internal/modload.EditBuildList({0x1010edbd0, 0x1014830a0}, {0x0, 0x0, 0x0}, {0x14007bac000, 0x108, 0x200})
        /opt/homebrew/Cellar/go/1.21.5/libexec/src/cmd/go/internal/modload/buildlist.go:640 +0x64
cmd/go/internal/workcmd.runSync({0x1010edbd0, 0x1014830a0}, 0x140000265b8?, {0x14?, 0x1010248c0?, 0x100adbc6c?})
        /opt/homebrew/Cellar/go/1.21.5/libexec/src/cmd/go/internal/workcmd/sync.go:117 +0x4d0
main.invoke(0x10143fd80, {0x140000201a0, 0x1, 0x1})
        /opt/homebrew/Cellar/go/1.21.5/libexec/src/cmd/go/main.go:268 +0x4f0
main.main()
        /opt/homebrew/Cellar/go/1.21.5/libexec/src/cmd/go/main.go:186 +0x754

What did you expect to see?

Success, another error, but not a panic.

The fact that this isn't handled gracefully tells me it's probably unintended behavior. But I'm a little unsure based on the context in edit.go

[bcmills]

Some notes:

1. This does appear to be perfectly reproducible in synapsecns/sanguine@995354f.
2. github.com/google/s2a-go@v0.1.4 is at go 1.16 and therefore unpruned. It is required directly by several of the modules in the workspace.

When a pruned module has a requirement on another root module, and that root is unpruned, we need to transition from the pruned side of the module graph to the unpruned side. I suspect that isn't happening when it needs to in dqTracker.path.

[gopherbot]

Change https://go.dev/cl/571800 mentions this issue: cmd/go/internal/modload: follow dependencies of unpruned roots in dqTracker.path

[bcmills]

The bug is triggering in the contrib/terraform-provider-helmproxy module, and the conflict is coming about because the workspace-selected version of github.com/google/pprof is ending up lower than the module-selected version — but github.com/google/pprof isn't relevant to this module anyway.

sanguine/contrib/terraform-provider-helmproxy$ go list -m github.com/google/pprof
github.com/google/pprof v0.0.0-20210506205249-923b5ab0fc1a

sanguine/contrib/terraform-provider-helmproxy$ GOWORK=off go list -m github.com/google/pprof
github.com/google/pprof v0.0.0-20210720184732-4bb14d4b1be1