cmd/go: provide a better error message when no modules exist in workspace

[sylr]

What version of Go are you using (go version)?

$ go version
go version devel go1.18-c239790 Sat Nov 13 03:33:55 2021 +0000 darwin/arm64

Does this issue reproduce with the latest release?

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE=""
GOARCH="arm64"
GOBIN="/Users/sylvain/go/bin"
GOCACHE="/Users/sylvain/Library/Caches/go-build"
GOENV="/Users/sylvain/Library/Application Support/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="arm64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/sylvain/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/sylvain/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/opt/homebrew/Cellar/go/1.17.2/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/opt/homebrew/Cellar/go/1.17.2/libexec/pkg/tool/darwin_arm64"
GOVCS=""
GOVERSION="go1.17.2"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/sylvain/git/go-cache/examples/metered/go.mod"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/19/d_hlhyz50bs8pbrg6_xn43km0000gp/T/go-build3653344954=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

Tried to test go mod workspace and ended up with a panic.

$ cd /tmp
$ git clone https://github.com/sylr/go-cache go-work-panic
$ cd go-work-panic
$ git checkout origin/go-work-panic
$ cd examples/metered
$ gotip build .
panic: in workspace mode, but pruning is not workspace in newRequirements

goroutine 1 [running]:
cmd/go/internal/modload.newRequirements(0x0, {0x0?, 0x0, 0x5?}, 0x0)
	/Users/sylvain/sdk/gotip/src/cmd/go/internal/modload/buildlist.go:118 +0x5d8
cmd/go/internal/modload.LoadModFile({0x100bf2f38, 0x140001a4000})
	/Users/sylvain/sdk/gotip/src/cmd/go/internal/modload/init.go:695 +0x538
cmd/go/internal/modload.LoadPackages({0x100bf2f38?, 0x140001a4000}, {{0x0, 0x0}, 0x14000020060, 0x0, {0x0, 0x0}, 0x0, 0x1, ...}, ...)
	/Users/sylvain/sdk/gotip/src/cmd/go/internal/modload/load.go:341 +0x19c
cmd/go/internal/load.PackagesAndErrors({0x100bf2f38?, 0x140001a4000?}, {0x0?, 0x0?, 0x0?}, {0x1400019e170, 0x1, 0x1})
	/Users/sylvain/sdk/gotip/src/cmd/go/internal/load/pkg.go:2647 +0x120
cmd/go/internal/work.runBuild({0x100bf2f38, 0x140001a4000}, 0x1400002c390?, {0x1400019e170, 0x1, 0x1})
	/Users/sylvain/sdk/gotip/src/cmd/go/internal/work/build.go:398 +0x78
main.invoke(0x100ebe440, {0x1400019e160, 0x2, 0x2})
	/Users/sylvain/sdk/gotip/src/cmd/go/main.go:218 +0x2b0
main.main()
	/Users/sylvain/sdk/gotip/src/cmd/go/main.go:175 +0x770

What did you expect to see?

What did you see instead?

[sten4eg]

this is a duplicate #49591

[seankhliao]

Duplicate of #49594

[matloob]

Hi, I haven't had time to look at it, but I'm wondering how we know this is a duplicate of #49591? Do we know that they're happening for the same reason?

[seankhliao]

I assumed they were dups based on the identical panic message and stacktrace

they also both fail with either of go build or go work sync

[matloob]

I will reopen this to provide a better error message.

[gopherbot]

Change https://golang.org/cl/365319 mentions this issue: cmd/go: report a helpful error when there are no modules in workspace