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// 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.
//go:build go1.22
// +build go1.22
package aliases
import (
"go/ast"
"go/parser"
"go/token"
"go/types"
"os"
"strings"
"sync"
)
// Alias is an alias of types.Alias.
type Alias = types.Alias
// Unalias is a wrapper of types.Unalias.
func Unalias(t types.Type) types.Type { return types.Unalias(t) }
// newAlias is an internal alias around types.NewAlias.
// Direct usage is discouraged as the moment.
// Try to use NewAlias instead.
func newAlias(tname *types.TypeName, rhs types.Type) *Alias {
a := types.NewAlias(tname, rhs)
// TODO(go.dev/issue/65455): Remove kludgy workaround to set a.actual as a side-effect.
Unalias(a)
return a
}
// enabled returns true when types.Aliases are enabled.
func enabled() bool {
// Use the gotypesalias value in GODEBUG if set.
godebug := os.Getenv("GODEBUG")
value := -1 // last set value.
for _, f := range strings.Split(godebug, ",") {
switch f {
case "gotypesalias=1":
value = 1
case "gotypesalias=0":
value = 0
}
}
switch value {
case 0:
return false
case 1:
return true
default:
return aliasesDefault()
}
}
// aliasesDefault reports if aliases are enabled by default.
func aliasesDefault() bool {
// Dynamically check if Aliases will be produced from go/types.
aliasesDefaultOnce.Do(func() {
fset := token.NewFileSet()
f, _ := parser.ParseFile(fset, "a.go", "package p; type A = int", 0)
pkg, _ := new(types.Config).Check("p", fset, []*ast.File{f}, nil)
_, gotypesaliasDefault = pkg.Scope().Lookup("A").Type().(*types.Alias)
})
return gotypesaliasDefault
}
var gotypesaliasDefault bool
var aliasesDefaultOnce sync.Once
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