When you don't want a Makefile

build.go

package main

import (
	"os"
	"os/exec"
	"reflect"
	"runtime"
)

func main() {
	env := getenv()

	wasm := env
	wasm.GOOS = "js"
	wasm.GOARCH = "wasm"

	var command string
	if len(os.Args) == 2 {
		command = os.Args[1]
	} else {
		command = "build"
	}

	switch command {
	case "build":
		Go(env, "build", "github.com/tauoverpi/example/cmd/levy-server")
		Go(wasm, "build", "github.com/tauoverpi/example/cmd/levy-wasm")
	case "test":
		Go(env, "test", "github.com/tauoverpi/example/cmd/levy-web")
		Go(env, "build", "github.com/tauoverpi/example/cmd/levy-wasm")
	default:
		panic("u wot m8")
	}
}

func Go(env Env, command ...string) {
	cmd := exec.Command("go", command...)
	cmd.Stdin = os.Stdin
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr

	val := reflect.ValueOf(env)
	typ := val.Type()

	for i := 0; i < typ.NumField(); i++ {
		value := val.Field(i).String()
		field := typ.Field(i).Name

		cmd.Env = append(cmd.Env, field+"="+value)
	}
}

type Env struct {
	GOOS           string
	GOARCH         string
	GOCACHE        string
	XDG_CACHE_HOME string
	HOME           string
}

func getenv() Env {
	env := Env{
		GOOS:           os.Getenv("GOOS"),
		GOARCH:         os.Getenv("GOARCH"),
		GOCACHE:        os.Getenv("GOCACHE"),
		XDG_CACHE_HOME: os.Getenv("XDG_CACHE_HOME"),
		HOME:           os.Getenv("HOME"),
	}

	if len(env.GOOS) == 0 {
		env.GOOS = runtime.GOOS
	}

	if len(env.GOARCH) == 0 {
		env.GOARCH = runtime.GOARCH
	}

	if len(env.GOCACHE) == 0 {
		env.GOCACHE = "/tmp/go-cache"
	}

	return env
}