aliases_go122.go

     1  // Copyright 2024 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  //go:build go1.22
     6  // +build go1.22
     7  
     8  package aliases
     9  
    10  import (
    11  	"go/ast"
    12  	"go/parser"
    13  	"go/token"
    14  	"go/types"
    15  )
    16  
    17  // Alias is an alias of types.Alias.
    18  type Alias = types.Alias
    19  
    20  // Rhs returns the type on the right-hand side of the alias declaration.
    21  func Rhs(alias *Alias) types.Type {
    22  	if alias, ok := any(alias).(interface{ Rhs() types.Type }); ok {
    23  		return alias.Rhs() // go1.23+
    24  	}
    25  
    26  	// go1.22's Alias didn't have the Rhs method,
    27  	// so Unalias is the best we can do.
    28  	return Unalias(alias)
    29  }
    30  
    31  // Unalias is a wrapper of types.Unalias.
    32  func Unalias(t types.Type) types.Type { return types.Unalias(t) }
    33  
    34  // newAlias is an internal alias around types.NewAlias.
    35  // Direct usage is discouraged as the moment.
    36  // Try to use NewAlias instead.
    37  func newAlias(tname *types.TypeName, rhs types.Type) *Alias {
    38  	a := types.NewAlias(tname, rhs)
    39  	// TODO(go.dev/issue/65455): Remove kludgy workaround to set a.actual as a side-effect.
    40  	Unalias(a)
    41  	return a
    42  }
    43  
    44  // Enabled reports whether [NewAlias] should create [types.Alias] types.
    45  //
    46  // This function is expensive! Call it sparingly.
    47  func Enabled() bool {
    48  	// The only reliable way to compute the answer is to invoke go/types.
    49  	// We don't parse the GODEBUG environment variable, because
    50  	// (a) it's tricky to do so in a manner that is consistent
    51  	//     with the godebug package; in particular, a simple
    52  	//     substring check is not good enough. The value is a
    53  	//     rightmost-wins list of options. But more importantly:
    54  	// (b) it is impossible to detect changes to the effective
    55  	//     setting caused by os.Setenv("GODEBUG"), as happens in
    56  	//     many tests. Therefore any attempt to cache the result
    57  	//     is just incorrect.
    58  	fset := token.NewFileSet()
    59  	f, _ := parser.ParseFile(fset, "a.go", "package p; type A = int", 0)
    60  	pkg, _ := new(types.Config).Check("p", fset, []*ast.File{f}, nil)
    61  	_, enabled := pkg.Scope().Lookup("A").Type().(*types.Alias)
    62  	return enabled
    63  }
    64
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