doc: Add and use LicenseYear

_docs/gen.go

@@ -27,6 +27,8 @@ import (
 	"regexp"
 	"strconv"
 	"strings"
+
+	"github.com/hajimehoshi/ebiten/internal"
 )
 
 func execute(command string, args ...string) error {
@@ -55,12 +57,7 @@ var (
 )
 
 func init() {
-	b, err := ioutil.ReadFile("../LICENSE")
+	year, err := internal.LicenseYear()
-	if err != nil {
-		panic(err)
-	}
-	license := strings.TrimSpace(string(b))
-	year, err := strconv.Atoi(regexp.MustCompile(`^Copyright (\d+)`).FindStringSubmatch(license)[1])
 	if err != nil {
 		panic(err)
 	}

internal/license.go

@@ -17,7 +17,9 @@ package internal
 import (
 	"io/ioutil"
 	"path/filepath"
+	"regexp"
 	"runtime"
+	"strconv"
 	"strings"
 )
 
@@ -33,3 +35,15 @@ func LicenseComment() (string, error) {
 	license := "// " + strings.Join(lines[:len(lines)-1], "\n// ")
 	return license, nil
 }
+
+func LicenseYear() (int, error) {
+	license, err := LicenseComment()
+	if err != nil {
+		return 0, err
+	}
+	year, err := strconv.Atoi(regexp.MustCompile(`^// Copyright (\d+)`).FindStringSubmatch(license)[1])
+	if err != nil {
+		return 0, err
+	}
+	return year, nil
+}