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

$ go version
go version go1.10.3 darwin/amd64

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

$ go env
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/leonard/Library/Caches/go-build"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/leonard/go_projects"
GORACE=""
GOROOT="/usr/local/Cellar/go/1.10.3/libexec"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.10.3/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/xw/fjl2c85x0psg7nm1sth8y_m40000gn/T/go-build892466275=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

Just use the command env CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build -o attacker main.go to build one of my single package to executable binary.

But since I don't want to include this package in my production release, so i use the // +build ignore to ignore it, only when i need to run above build command i remove the // +build ignore flag.

Previously the // +build ignore was working as expected, i mean if i run above command with it i will run into error that "the source was ignored.. bla bla", if i want to build it then i need to remove the // +build ignore, but now with the // +build ignore there, i still can build it!!!, totally cannot recall what was changed to cause this.

What did you expect to see?

With the // +build ignore i should not able to build the source.

What did you see instead?

Even with the // +build ignore there i am still able not build the source and roll out the executable binary!

// +build ignore

package main

import (
	"flag"
	"fmt"
	"math/rand"
	"runtime"
	"sync"
	"time"