cmd/go: go tool -n can point to a file that doesn't exist

[iwahbe]

Go version

go version go1.24.1 darwin/arm64

Output of go env in your module/workspace:

AR='ar'
CC='cc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='c++'
GCCGO='gccgo'
GO111MODULE=''
GOARCH='arm64'
GOARM64='v8.0'
GOAUTH='netrc'
GOBIN='/Users/ianwahbe/go/bin'
GOCACHE='/Users/ianwahbe/Library/Caches/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/Users/ianwahbe/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/fg/_1q36r4j6yx0rwz2fbhjd5y40000gn/T/go-build3052038314=/tmp/go-build -gno-record-gcc-switches -fno-common'
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMOD='/Users/ianwahbe/go/src/github.com/example/empty/go.mod'
GOMODCACHE='/Users/ianwahbe/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/ianwahbe/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/opt/homebrew/Cellar/go/1.24.1/libexec'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/Users/ianwahbe/Library/Application Support/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/opt/homebrew/Cellar/go/1.24.1/libexec/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.24.1'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

I was using go tool -n github.com/iwahbe/helpmakego in my Makefile to work around #71733 like this:

HELPMAKEGO := $(shell go tool -n github.com/iwahbe/helpmakego)

# Use the tool as intended - details don't really matter here
$(shell ${HELPMAKEGO} ...)

I noticed that sometimes $(shell ${HELPMAKEGO} ...) would fail unexpectedly, saying that there was no file at ${HELPMAKEGO}.

I can replicate this behavior locally:

$ mkdir repro
$ go mod init
$ go get -tool github.com/iwahbe/helpmakego
$ go tool -n github.com/iwahbe/helpmakego | tee should_exist && rm $(cat should_exist)
/Users/ianwahbe/Library/Caches/go-build/c5/c503c5059f1c48a29b1dc68749074f475aaf82c717ef355e7079f7e9b4116c2b-d/helpmakego
$ go tool -n github.com/iwahbe/helpmakego | tee should_exist && rm $(cat should_exist)
/var/folders/fg/_1q36r4j6yx0rwz2fbhjd5y40000gn/T/go-build1160981703/b001/exe/helpmakego
rm: /var/folders/fg/_1q36r4j6yx0rwz2fbhjd5y40000gn/T/go-build1160981703/b001/exe/helpmakego: No such file or directory
$ go tool -n github.com/iwahbe/helpmakego | tee should_exist && rm $(cat should_exist)
/Users/ianwahbe/Library/Caches/go-build/c5/c503c5059f1c48a29b1dc68749074f475aaf82c717ef355e7079f7e9b4116c2b-d/helpmakego
$ go tool -n github.com/iwahbe/helpmakego | tee should_exist && rm $(cat should_exist)
/var/folders/fg/_1q36r4j6yx0rwz2fbhjd5y40000gn/T/go-build1221207145/b001/exe/helpmakego
rm: /var/folders/fg/_1q36r4j6yx0rwz2fbhjd5y40000gn/T/go-build1221207145/b001/exe/helpmakego: No such file or directory

You will see that every other time go tool -n github.com/iwahbe/helpmakego it points to a file that doesn't exist.

What did you see happen?

$ go tool -n github.com/iwahbe/helpmakego
/var/folders/fg/_1q36r4j6yx0rwz2fbhjd5y40000gn/T/go-build1221207145/b001/exe/helpmakego

What did you expect to see?

I expect that any time go tool -n ... is run, it will point to a runnable executable.

If that isn't true, then go help tool should document what conditions are necessary to ensure that go tool -n ... will point to an executable file.

[gabyhelp]

Related Issues

• affected/package: go install not working #52294 (closed)
• x/tools/godoc: TestCommandLine failed #23192 (closed)
• cmd/go get doesn't validate module arguments #71437 (closed)
• cmd/go: -x flag doesn't print executable output if cgo is used #21427 (closed)
• cmd/go: work use silently ignores nonexistent target #51965
• cmd/go: failed to build if the testdata contains broken symlinks #53305 (closed)
• build: the build of go bootstrap in case of compilation errors does not stop cleanly #45410 (closed)
• x/tools/gopls: make go.mod diagnostics on mismatched requirements available when go.work is used #48920
• cmd/go doesn't recognize forward go directive when tool section is present in go.mod #70949 (closed)

Related Code Changes

• cmd/go: use os.Executable to find GOROOT

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[seankhliao]

seems like when it builds a tool it prints the location of it in the temporary work directory, rather than the final location in the build cache

[ianlancetaylor]

CC @matloob @samthanawalla

[KirtanSoni]

I figured out the cause on the bug. would u mind if i take this issue up and propose a PR