cmd/go: inferred GOAMD64 value in go env should be applied to build

[bsdcode]

Go version

go version go1.24.1 freebsd/amd64

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='clang++'
GCCGO='gccgo'
GO111MODULE=''
GOAMD64='v3'
GOARCH='amd64'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/home/user/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/home/user/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build2518763662=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='freebsd'
GOINSECURE=''
GOMOD='/tmp/example/go.mod'
GOMODCACHE='/home/user/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='freebsd'
GOPATH='/home/user/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go124'
GOSUMDB='sum.golang.org'
GOTELEMETRY='off'
GOTELEMETRYDIR='/home/user/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go124/pkg/tool/freebsd_amd64'
GOVCS=''
GOVERSION='go1.24.1'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

Example program:
go.mod:

module example

go 1.24.1

main.go

//go:build amd64.v3

package main

import "fmt"

func main() {
	fmt.Println("Example")
}

Observe the architecture feature GOAMD64='v3' in go env and the buildconstraint //go:build amd64.v3 in main.go. Now try to build the example program with go build.

What did you see happen?

$ go build
package example: build constraints exclude all Go files in /tmp/example

What did you expect to see?

A successfully build example program main.

The feature has to be given explicitly to satisfy the constraint:

$ GOAMD64=v3 go build

[randall77]

What do echo $GOAMD64 and go env GOAMD64 print?

[seankhliao]

and go env -changed

[bsdcode]

$ echo $GOAMD64

$ go env GOAMD64
v3

$ go env -changed
GOAMD64='v3'