add automatic version string based on git-describe (tags)

Makefile

@@ -120,10 +120,10 @@ dep:
 
 # Build binary
 build:
-	GO111MODULE=on go build
+	GO111MODULE=on go build -ldflags="-X github.com/zcash/lightwalletd/common.Version=`git describe --tags`"
 
 build_rel:
-	GO111MODULE=on GOOS=linux go build
+	GO111MODULE=on GOOS=linux go build -ldflags="-X github.com/zcash/lightwalletd/common.Version=`git describe --tags`"
 
 # Install binaries into Go path
 install:

cmd/root.go

@@ -182,7 +182,7 @@ func startServer(opts *common.Options) error {
 		os.Exit(1)
 	}()
 
-	common.Log.Infof("Starting gRPC server on %s", opts.BindAddr)
+	common.Log.Infof("Starting gRPC server version %s on %s", common.Version, opts.BindAddr)
 
 	err = server.Serve(listener)
 	if err != nil {

cmd/version.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 
 	"github.com/spf13/cobra"
+	"github.com/zcash/lightwalletd/common"
 )
 
 // versionCmd represents the version command
@@ -12,6 +13,6 @@ var versionCmd = &cobra.Command{
 	Short: "Dispaly lightwalletd version",
 	Long:  `Dispaly lightwalletd version.`,
 	Run: func(cmd *cobra.Command, args []string) {
-		fmt.Println("lightwalletd version v0.2.0")
+		fmt.Println("lightwalletd version", common.Version)
 	},
 }

common/common.go

@@ -16,6 +16,9 @@ import (
 	"github.com/zcash/lightwalletd/walletrpc"
 )
 
+// 'make build' will overwrite this string with the output of git-describe (tag)
+var Version = "v0.0.0.0-dev"
+
 type Options struct {
 	BindAddr          string `json:"bind_address,omitempty"`
 	TLSCertPath       string `json:"tls_cert_path,omitempty"`