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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"
)
// Alias is an alias of types.Alias.
type Alias = types.Alias
// Rhs returns the type on the right-hand side of the alias declaration.
func Rhs(alias *Alias) types.Type {
if alias, ok := any(alias).(interface{ Rhs() types.Type }); ok {
return alias.Rhs() // go1.23+
}
// go1.22's Alias didn't have the Rhs method,
// so Unalias is the best we can do.
return Unalias(alias)
}
// TypeParams returns the type parameter list of the alias.
func TypeParams(alias *Alias) *types.TypeParamList {
if alias, ok := any(alias).(interface{ TypeParams() *types.TypeParamList }); ok {
return alias.TypeParams() // go1.23+
}
return nil
}
// SetTypeParams sets the type parameters of the alias type.
func SetTypeParams(alias *Alias, tparams []*types.TypeParam) {
if alias, ok := any(alias).(interface {
SetTypeParams(tparams []*types.TypeParam)
}); ok {
alias.SetTypeParams(tparams) // go1.23+
} else if len(tparams) > 0 {
panic("cannot set type parameters of an Alias type in go1.22")
}
}
// TypeArgs returns the type arguments used to instantiate the Alias type.
func TypeArgs(alias *Alias) *types.TypeList {
if alias, ok := any(alias).(interface{ TypeArgs() *types.TypeList }); ok {
return alias.TypeArgs() // go1.23+
}
return nil // empty (go1.22)
}
// Origin returns the generic Alias type of which alias is an instance.
// If alias is not an instance of a generic alias, Origin returns alias.
func Origin(alias *Alias) *Alias {
if alias, ok := any(alias).(interface{ Origin() *types.Alias }); ok {
return alias.Origin() // go1.23+
}
return alias // not an instance of a generic alias (go1.22)
}
// 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 reports whether [NewAlias] should create [types.Alias] types.
//
// This function is expensive! Call it sparingly.
func Enabled() bool {
// The only reliable way to compute the answer is to invoke go/types.
// We don't parse the GODEBUG environment variable, because
// (a) it's tricky to do so in a manner that is consistent
// with the godebug package; in particular, a simple
// substring check is not good enough. The value is a
// rightmost-wins list of options. But more importantly:
// (b) it is impossible to detect changes to the effective
// setting caused by os.Setenv("GODEBUG"), as happens in
// many tests. Therefore any attempt to cache the result
// is just incorrect.
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)
_, enabled := pkg.Scope().Lookup("A").Type().(*types.Alias)
return enabled
}
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