Add loading yaml label template files (#22976)

Extract from #11669 and enhancement to #22585 to support exclusive
scoped labels in label templates

* Move label template functionality to label module
* Fix handling of color codes
* Add Advanced label template

modules/label/parser.go

@@ -0,0 +1,126 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package label
+
+import (
+	"errors"
+	"fmt"
+	"strings"
+
+	"code.gitea.io/gitea/modules/options"
+
+	"gopkg.in/yaml.v3"
+)
+
+type labelFile struct {
+	Labels []*Label `yaml:"labels"`
+}
+
+// ErrTemplateLoad represents a "ErrTemplateLoad" kind of error.
+type ErrTemplateLoad struct {
+	TemplateFile  string
+	OriginalError error
+}
+
+// IsErrTemplateLoad checks if an error is a ErrTemplateLoad.
+func IsErrTemplateLoad(err error) bool {
+	_, ok := err.(ErrTemplateLoad)
+	return ok
+}
+
+func (err ErrTemplateLoad) Error() string {
+	return fmt.Sprintf("Failed to load label template file '%s': %v", err.TemplateFile, err.OriginalError)
+}
+
+// GetTemplateFile loads the label template file by given name,
+// then parses and returns a list of name-color pairs and optionally description.
+func GetTemplateFile(name string) ([]*Label, error) {
+	data, err := options.GetRepoInitFile("label", name+".yaml")
+	if err == nil && len(data) > 0 {
+		return parseYamlFormat(name+".yaml", data)
+	}
+
+	data, err = options.GetRepoInitFile("label", name+".yml")
+	if err == nil && len(data) > 0 {
+		return parseYamlFormat(name+".yml", data)
+	}
+
+	data, err = options.GetRepoInitFile("label", name)
+	if err != nil {
+		return nil, ErrTemplateLoad{name, fmt.Errorf("GetRepoInitFile: %w", err)}
+	}
+
+	return parseLegacyFormat(name, data)
+}
+
+func parseYamlFormat(name string, data []byte) ([]*Label, error) {
+	lf := &labelFile{}
+
+	if err := yaml.Unmarshal(data, lf); err != nil {
+		return nil, err
+	}
+
+	// Validate label data and fix colors
+	for _, l := range lf.Labels {
+		l.Color = strings.TrimSpace(l.Color)
+		if len(l.Name) == 0 || len(l.Color) == 0 {
+			return nil, ErrTemplateLoad{name, errors.New("label name and color are required fields")}
+		}
+		color, err := NormalizeColor(l.Color)
+		if err != nil {
+			return nil, ErrTemplateLoad{name, fmt.Errorf("bad HTML color code '%s' in label: %s", l.Color, l.Name)}
+		}
+		l.Color = color
+	}
+
+	return lf.Labels, nil
+}
+
+func parseLegacyFormat(name string, data []byte) ([]*Label, error) {
+	lines := strings.Split(string(data), "\n")
+	list := make([]*Label, 0, len(lines))
+	for i := 0; i < len(lines); i++ {
+		line := strings.TrimSpace(lines[i])
+		if len(line) == 0 {
+			continue
+		}
+
+		parts, description, _ := strings.Cut(line, ";")
+
+		color, name, ok := strings.Cut(parts, " ")
+		if !ok {
+			return nil, ErrTemplateLoad{name, fmt.Errorf("line is malformed: %s", line)}
+		}
+
+		color, err := NormalizeColor(color)
+		if err != nil {
+			return nil, ErrTemplateLoad{name, fmt.Errorf("bad HTML color code '%s' in line: %s", color, line)}
+		}
+
+		list = append(list, &Label{
+			Name:        strings.TrimSpace(name),
+			Color:       color,
+			Description: strings.TrimSpace(description),
+		})
+	}
+
+	return list, nil
+}
+
+// LoadFormatted loads the labels' list of a template file as a string separated by comma
+func LoadFormatted(name string) (string, error) {
+	var buf strings.Builder
+	list, err := GetTemplateFile(name)
+	if err != nil {
+		return "", err
+	}
+
+	for i := 0; i < len(list); i++ {
+		if i > 0 {
+			buf.WriteString(", ")
+		}
+		buf.WriteString(list[i].Name)
+	}
+	return buf.String(), nil
+}