Add version information

Fixes #10

.goreleaser.yml

@@ -29,3 +29,5 @@ release:
   github:
     owner: breml
     name: errchkjson
+gomod:
+  proxy: true

cmd/errchkjson/main.go

@@ -1,11 +1,42 @@
 package main
 
 import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"runtime"
+	"runtime/debug"
+
 	"github.com/breml/errchkjson"
 
 	"golang.org/x/tools/go/analysis/singlechecker"
 )
 
+var (
+	version = "development"
+	commit  = ""
+	date    = ""
+)
+
 func main() {
+	errchkjson.Version = buildVersion()
+
 	singlechecker.Main(errchkjson.NewAnalyzer())
 }
+
+func buildVersion() string {
+	result := fmt.Sprintf("%s version %s", filepath.Base(os.Args[0]), version)
+
+	if commit != "" {
+		result = fmt.Sprintf("%s\ncommit: %s", result, commit)
+	}
+	if date != "" {
+		result = fmt.Sprintf("%s\nbuilt at: %s", result, date)
+	}
+	if info, ok := debug.ReadBuildInfo(); ok && info.Main.Sum != "" {
+		result = fmt.Sprintf("%s\nmodule version: %s, checksum: %s", result, info.Main.Version, info.Main.Sum)
+	}
+	result = fmt.Sprintf("%s\ngoos: %s\ngoarch: %s", result, runtime.GOOS, runtime.GOARCH)
+
+	return result
+}

errchkjson.go

@@ -32,6 +32,7 @@ func NewAnalyzer() *analysis.Analyzer {
 	a.Flags.Init("errchkjson", flag.ExitOnError)
 	a.Flags.BoolVar(&errchkjson.omitSafe, "omit-safe", false, "if omit-safe is true, checking of safe returns is omitted")
 	a.Flags.BoolVar(&errchkjson.reportNoExported, "report-no-exported", false, "if report-no-exported is true, encoding a struct without exported fields is reported as issue")
+	a.Flags.Var(versionFlag{}, "V", "print version and exit")
 
 	return a
 }

version.go

@@ -0,0 +1,19 @@
+package errchkjson
+
+import (
+	"fmt"
+	"os"
+)
+
+var Version = "errchkjson version dev"
+
+type versionFlag struct{}
+
+func (versionFlag) IsBoolFlag() bool { return true }
+func (versionFlag) Get() interface{} { return nil }
+func (versionFlag) String() string   { return "" }
+func (versionFlag) Set(s string) error {
+	fmt.Println(Version)
+	os.Exit(0)
+	return nil
+}