internal/astutil/clone.go

// Copyright 2023 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package astutil

import (
	"go/ast"
	"reflect"
)

// CloneNode returns a deep copy of a Node.
// It omits pointers to ast.{Scope,Object} variables.
func CloneNode[T ast.Node](n T) T {
	return cloneNode(n).(T)
}

func cloneNode(n ast.Node) ast.Node {
	var clone func(x reflect.Value) reflect.Value
	set := func(dst, src reflect.Value) {
		src = clone(src)
		if src.IsValid() {
			dst.Set(src)
		}
	}
	clone = func(x reflect.Value) reflect.Value {
		switch x.Kind() {
		case reflect.Ptr:
			if x.IsNil() {
				return x
			}
			// Skip fields of types potentially involved in cycles.
			switch x.Interface().(type) {
			case *ast.Object, *ast.Scope:
				return reflect.Zero(x.Type())
			}
			y := reflect.New(x.Type().Elem())
			set(y.Elem(), x.Elem())
			return y

		case reflect.Struct:
			y := reflect.New(x.Type()).Elem()
			for i := 0; i < x.Type().NumField(); i++ {
				set(y.Field(i), x.Field(i))
			}
			return y

		case reflect.Slice:
			if x.IsNil() {
				return x
			}
			y := reflect.MakeSlice(x.Type(), x.Len(), x.Cap())
			for i := 0; i < x.Len(); i++ {
				set(y.Index(i), x.Index(i))
			}
			return y

		case reflect.Interface:
			y := reflect.New(x.Type()).Elem()
			set(y, x.Elem())
			return y

		case reflect.Array, reflect.Chan, reflect.Func, reflect.Map, reflect.UnsafePointer:
			panic(x) // unreachable in AST

		default:
			return x // bool, string, number
		}
	}
	return clone(reflect.ValueOf(n)).Interface().(ast.Node)
}