go/build: GOAMD64 in env file not setting subarch build tags #75452
Description
Go version
go version go1.25.1 linux/amd64
Output of go env in your module/workspace:
AR='ar'
CC='gcc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='g++'
GCCGO='gccgo'
GO111MODULE=''
GOAMD64='v3'
GOARCH='amd64'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/home/gopher/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/home/gopher/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build2805719706=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/home/gopher/amd64v3test/go.mod'
GOMODCACHE='/home/gopher/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/gopher/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/home/gopher/sdk/go1.25.1'
GOSUMDB='sum.golang.org'
GOTELEMETRY='on'
GOTELEMETRYDIR='/home/gopher/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/home/gopher/sdk/go1.25.1/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.25.1'
GOWORK=''
PKG_CONFIG='pkg-config'What did you do?
- Use
go env -w GOAMD64=v3to set theGOAMD64env value user-wide. - Checked that
go env GOAMD64showsv3. (Also in fullgo envoutput) - Created a file requiring the amd64.v3 build constraint:
//go:build amd64.v3
// +build amd64.v3
package main
import "fmt"
func main() {
fmt.Println("GOAMD64=v3: available")
}- Run
go build(or any other command that respects build tags)
What did you see happen?
The toolchain acts as though the GOAMD64 variable wasn't set resulting in the amd64.v3 constraint not being satisfied, excluding the file from the build. When it's the only file:
$ go build
package amd64v3test: build constraints exclude all Go files in /home/gopher/amd64v3testWhat did you expect to see?
I expected to see a successful build that includes the file. It does work if the GOAMD64 environment variable is set in the shell, suggesting I got the build constraint and syntax correct:
$ GOAMD64=v3 go build
// Successful buildSimilarly looking at go list -json shows such files are ignored when the value is set using the config file, but not when set by the environment.
I only tested GOAMD64, but I suspect it may also affect other "subarch" style build constraints (like GOARM).