Implement version flag

.github/workflows/ci-go.yml

@@ -16,7 +16,7 @@ jobs:
         with:
           go-version-file: 'go.mod'
           cache-dependency-path: 'go.sum'
-      - run: go build -v
+      - run: go build -v -race
   lint:
     runs-on: ubuntu-latest
     steps:

CONTRIBUTING.md

@@ -0,0 +1,20 @@
+# How to develop
+
+## Setup
+
+1. Install [Nix](https://nixos.org/) package manager
+2. Run `nix-shell` or `nix-shell --command 'zsh'`
+3. You can use development tools
+
+```console
+> nix-shell
+(prepared bash)
+
+> go version
+go version go1.20.4 linux/amd64
+
+> dprint --version
+dprint 0.36.1
+
+> go build -ldflags "-X main.revision=$(git rev-parse --short HEAD)"
+```

nix-headbump.go

@@ -2,14 +2,28 @@ package main
 
 import (
 	"encoding/json"
+	"flag"
+	"fmt"
 	"io"
 	"log"
 	"net/http"
 	"os"
 	"regexp"
 )
 
+const version string = "0.1.0"
+
+var revision string
+
 func main() {
+	versionFlag := flag.Bool("version", false, "print the version of this program")
+	flag.Parse()
+
+	if *versionFlag {
+		fmt.Printf("%s\n", version+"("+revision+")")
+		return
+	}
+
 	path := "default.nix"
 	isNixFileExist := true
 	if _, err := os.Stat(path); os.IsNotExist(err) {