Add version option

.goreleaser.yml

@@ -7,6 +7,9 @@ builds:
       - amd64
       - arm64
       - 386
+    ldflags:
+      - -X main.version={{ .Version }}
+      - -X main.revision={{ .ShortCommit }}
 
 archives:
   - replacements:

main.go

@@ -2,15 +2,91 @@ package main
 
 import (
 	"context"
+	"flag"
+	"fmt"
 	"os"
+	"runtime"
+	"runtime/debug"
 
 	"github.com/kitagry/regols/langserver"
 	"github.com/sourcegraph/jsonrpc2"
 )
 
+const (
+	name = "regols"
+)
+
+var (
+	version  = "v0.0.0"
+	revision = ""
+)
+
+type exitCode int
+
+const (
+	exitCodeOK exitCode = iota
+	exitCodeErr
+)
+
 func main() {
+	os.Exit(int(run(os.Args[1:])))
+}
+
+func run(args []string) exitCode {
+	fs := flag.NewFlagSet(name, flag.ContinueOnError)
+	fs.SetOutput(os.Stderr)
+	fs.Usage = func() {
+		fs.SetOutput(os.Stdout)
+		fmt.Printf(`%[1]s - OPA rego language server
+
+Version: %s (rev: %s/%s)
+
+You can use your favorite lsp client.
+`, name, version, getRevision(), runtime.Version())
+		fs.PrintDefaults()
+	}
+
+	var showVersion bool
+	fs.BoolVar(&showVersion, "version", false, "print version")
+	if err := fs.Parse(args); err != nil {
+		if err == flag.ErrHelp {
+			return exitCodeOK
+		}
+		return exitCodeErr
+	}
+
+	if showVersion {
+		fmt.Printf("%s %s (rev: %s/%s)\n", name, version, getRevision(), runtime.Version())
+		return exitCodeOK
+	}
+
 	handler := langserver.NewHandler()
 	<-jsonrpc2.NewConn(context.Background(), jsonrpc2.NewBufferedStream(stdrwc{}, jsonrpc2.VSCodeObjectCodec{}), handler).DisconnectNotify()
+	return exitCodeOK
+}
+
+func getRevision() string {
+	if revision != "" {
+		return revision
+	}
+	info, ok := debug.ReadBuildInfo()
+	if !ok {
+		return ""
+	}
+	var revision string
+	var modified string
+	for _, s := range info.Settings {
+		switch s.Key {
+		case "vcs.revision":
+			revision = s.Value
+		case "vcs.modified":
+			modified = s.Value
+		}
+	}
+	if modified == "true" {
+		revision += "(modified)"
+	}
+	return revision
 }
 
 type stdrwc struct{}