Rewrite go license generator in go (#21078)

This removes the JS dependency in the checks pipeline. JSON output is
different because the previous JS did indent the license data
differently and a JSON key was changed, but the end result is the same
as it gets re-indented by wepack.

Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: zeripath <art27@cantab.net>

build/generate-go-licenses.go

@@ -0,0 +1,74 @@
+// Copyright 2022 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.
+
+//go:build ignore
+
+package main
+
+import (
+	"encoding/json"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"regexp"
+	"sort"
+	"strings"
+)
+
+// regexp is based on go-license, excluding README and NOTICE
+// https://github.com/google/go-licenses/blob/master/licenses/find.go
+var licenseRe = regexp.MustCompile(`^(?i)((UN)?LICEN(S|C)E|COPYING).*$`)
+
+type LicenseEntry struct {
+	Name        string `json:"name"`
+	Path        string `json:"path"`
+	LicenseText string `json:"licenseText"`
+}
+
+func main() {
+	base, out := os.Args[1], os.Args[2]
+
+	paths := []string{}
+	err := filepath.WalkDir(base, func(path string, entry fs.DirEntry, err error) error {
+		if err != nil {
+			return err
+		}
+		if entry.IsDir() || !licenseRe.MatchString(entry.Name()) {
+			return nil
+		}
+		paths = append(paths, path)
+		return nil
+	})
+	if err != nil {
+		panic(err)
+	}
+
+	sort.Strings(paths)
+
+	entries := []LicenseEntry{}
+	for _, path := range paths {
+		licenseText, err := os.ReadFile(path)
+		if err != nil {
+			panic(err)
+		}
+
+		path := strings.Replace(path, base+string(os.PathSeparator), "", 1)
+
+		entries = append(entries, LicenseEntry{
+			Name: filepath.Dir(path),
+			Path: path,
+			LicenseText: string(licenseText),
+		})
+	}
+
+	jsonBytes, err := json.MarshalIndent(entries, "", "  ")
+	if err != nil {
+		panic(err)
+	}
+
+	err = os.WriteFile(out, jsonBytes, 0o644)
+	if err != nil {
+		panic(err)
+	}
+}