Generate Bindata iff TAGS="bindata" and not up-to-date (#10004)

* Only generate bindata if necessary

* Only generate bindata if they are not up-to-date

* generate a hash of the fileinfo and use that to keep up-to-date

* Newer test is redundant

* handle missing bindata and clean

* Only update hash after successful write

* switch to sha1 hash

* Apply suggestions from code review

Co-Authored-By: guillep2k <18600385+guillep2k@users.noreply.github.com>

Co-authored-by: guillep2k <18600385+guillep2k@users.noreply.github.com>

scripts/generate-bindata.go

@@ -0,0 +1,86 @@
+// Copyright 2020 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+// +build ignore
+
+package main
+
+import (
+	"bytes"
+	"crypto/sha1"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"net/http"
+	"os"
+	"path/filepath"
+	"strconv"
+
+	"github.com/shurcooL/vfsgen"
+)
+
+func needsUpdate(dir string, filename string) (bool, []byte) {
+	needRegen := false
+	_, err := os.Stat(filename)
+	if err != nil {
+		needRegen = true
+	}
+
+	oldHash, err := ioutil.ReadFile(filename + ".hash")
+	if err != nil {
+		oldHash = []byte{}
+	}
+
+	hasher := sha1.New()
+
+	err = filepath.Walk(dir, func(path string, info os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+		_, _ = hasher.Write([]byte(info.Name()))
+		_, _ = hasher.Write([]byte(info.ModTime().String()))
+		_, _ = hasher.Write([]byte(strconv.FormatInt(info.Size(), 16)))
+		return nil
+	})
+	if err != nil {
+		return true, oldHash
+	}
+
+	newHash := hasher.Sum([]byte{})
+
+	if bytes.Compare(oldHash, newHash) != 0 {
+
+		return true, newHash
+	}
+
+	return needRegen, newHash
+}
+
+func main() {
+	if len(os.Args) != 4 {
+		log.Fatal("Insufficient number of arguments. Need: directory packageName filename")
+	}
+
+	dir, packageName, filename := os.Args[1], os.Args[2], os.Args[3]
+
+	update, newHash := needsUpdate(dir, filename)
+
+	if !update {
+		fmt.Printf("bindata for %s already up-to-date\n", packageName)
+		return
+	}
+
+	fmt.Printf("generating bindata for %s\n", packageName)
+	var fsTemplates http.FileSystem = http.Dir(dir)
+	err := vfsgen.Generate(fsTemplates, vfsgen.Options{
+		PackageName:  packageName,
+		BuildTags:    "bindata",
+		VariableName: "Assets",
+		Filename:     filename,
+	})
+	if err != nil {
+		log.Fatalf("%v\n", err)
+	}
+	_ = ioutil.WriteFile(filename+".hash", newHash, 0666)
+}