More reasonable version management

Makefile

@@ -6,7 +6,10 @@ CC_BINARIES  := $(shell bash -c "echo -n $(APP_NAME)-{linux,freebsd,openbsd}-{38
 
 GOLANGCI_LINT_VERSION := v1.21.0
 
-COMMON_BUILD_FLAGS := -ldflags="-s -w"
+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)]'"
 
 MOD_ON  := env GO111MODULE=on
 MOD_OFF := env GO111MODULE=auto

main.go

@@ -14,6 +14,8 @@ import (
 	"github.com/9seconds/mtg/utils"
 )
 
+var version = "dev" // has to be set by ldflags
+
 var (
 	app = kingpin.New("mtg", "Simple MTPROTO proxy.")
 
@@ -155,24 +157,23 @@ 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()
+	if version != "dev" {
+		return version
 	}
 
-	return "dev"
+	info, ok := debug.ReadBuildInfo()
+	if !ok {
+		return version
+	}
+
+	builder := strings.Builder{}
+	builder.WriteString(info.Main.Version)
+
+	if info.Main.Sum != "" {
+		builder.WriteString(" (checksum: ")
+		builder.WriteString(info.Main.Sum)
+		builder.WriteRune(')')
+	}
+
+	return builder.String()
 }