Use buildinfo to get a version

Makefile

@@ -6,10 +6,7 @@ CC_BINARIES  := $(shell bash -c "echo -n $(APP_NAME)-{linux,freebsd,openbsd}-{38
 
 GOLANGCI_LINT_VERSION := v1.21.0
 
-VERSION_GO         := $(shell go version)
-VERSION_DATE       := $(shell date -Ru)
-VERSION_TAG        := $(shell git describe --tags --always)
-COMMON_BUILD_FLAGS := -ldflags="-s -w -X 'main.version=$(VERSION_TAG) ($(VERSION_GO)) [$(VERSION_DATE)]'"
+COMMON_BUILD_FLAGS := -ldflags="-s -w"
 
 MOD_ON  := env GO111MODULE=on
 MOD_OFF := env GO111MODULE=auto

main.go

@@ -3,6 +3,8 @@ package main
 import (
 	"math/rand"
 	"os"
+	"runtime/debug"
+	"strings"
 	"time"
 
 	kingpin "gopkg.in/alecthomas/kingpin.v2"
@@ -12,8 +14,6 @@ import (
 	"github.com/9seconds/mtg/utils"
 )
 
-var version = "dev" // this has to be set by build ld flags
-
 var (
 	app = kingpin.New("MTG", "Simple MTPROTO proxy.")
 
@@ -114,7 +114,7 @@ var (
 
 func main() {
 	rand.Seed(time.Now().UTC().UnixNano())
-	app.Version(version)
+	app.Version(getVersion())
 	app.HelpFlag.Short('h')
 
 	if err := utils.SetLimits(); err != nil {
@@ -153,3 +153,26 @@ func main() {
 		}
 	}
 }
+
+func getVersion() string {
+	if info, ok := debug.ReadBuildInfo(); ok {
+		builder := strings.Builder{}
+		version := info.Main.Version
+
+		if version == "(devel)" {
+			version = "dev"
+		}
+
+		builder.WriteString(version)
+
+		if info.Main.Sum != "" {
+			builder.WriteString(" (checksum: ")
+			builder.WriteString(info.Main.Sum)
+			builder.WriteRune(')')
+		}
+
+		return builder.String()
+	}
+
+	return "dev"
+}