Add generic set type (#21408)

This PR adds a generic set type to get rid of maps used as sets.

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/container/set.go

@@ -0,0 +1,57 @@
+// 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.
+
+package container
+
+type Set[T comparable] map[T]struct{}
+
+// SetOf creates a set and adds the specified elements to it.
+func SetOf[T comparable](values ...T) Set[T] {
+	s := make(Set[T], len(values))
+	s.AddMultiple(values...)
+	return s
+}
+
+// Add adds the specified element to a set.
+// Returns true if the element is added; false if the element is already present.
+func (s Set[T]) Add(value T) bool {
+	if _, has := s[value]; !has {
+		s[value] = struct{}{}
+		return true
+	}
+	return false
+}
+
+// AddMultiple adds the specified elements to a set.
+func (s Set[T]) AddMultiple(values ...T) {
+	for _, value := range values {
+		s.Add(value)
+	}
+}
+
+// Contains determines whether a set contains the specified element.
+// Returns true if the set contains the specified element; otherwise, false.
+func (s Set[T]) Contains(value T) bool {
+	_, has := s[value]
+	return has
+}
+
+// Remove removes the specified element.
+// Returns true if the element is successfully found and removed; otherwise, false.
+func (s Set[T]) Remove(value T) bool {
+	if _, has := s[value]; has {
+		delete(s, value)
+		return true
+	}
+	return false
+}
+
+// Values gets a list of all elements in the set.
+func (s Set[T]) Values() []T {
+	keys := make([]T, 0, len(s))
+	for k := range s {
+		keys = append(keys, k)
+	}
+	return keys
+}