// Copyright 2024 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 aliases

import (
	"go/token"
	"go/types"
)

// Package aliases defines backward compatible shims
// for the types.Alias type representation added in 1.22.
// This defines placeholders for x/tools until 1.26.

// NewAlias creates a new TypeName in Package pkg that
// is an alias for the type rhs.
//
// The enabled parameter determines whether the resulting [TypeName]'s
// type is an [types.Alias]. Its value must be the result of a call to
// [Enabled], which computes the effective value of
// GODEBUG=gotypesalias=... by invoking the type checker. The Enabled
// function is expensive and should be called once per task (e.g.
// package import), not once per call to NewAlias.
//
// Precondition: enabled || len(tparams)==0.
// If materialized aliases are disabled, there must not be any type parameters.
func NewAlias(enabled bool, pos token.Pos, pkg *types.Package, name string, rhs types.Type, tparams []*types.TypeParam) *types.TypeName {
	if enabled {
		tname := types.NewTypeName(pos, pkg, name, nil)
		SetTypeParams(types.NewAlias(tname, rhs), tparams)
		return tname
	}
	if len(tparams) > 0 {
		panic("cannot create an alias with type parameters when gotypesalias is not enabled")
	}
	return types.NewTypeName(pos, pkg, name, rhs)
}