alias.go

     1  // Code generated by "go test -run=Generate -write=all"; DO NOT EDIT.
     2  // Source: ../../cmd/compile/internal/types2/alias.go
     3  
     4  // Copyright 2023 The Go Authors. All rights reserved.
     5  // Use of this source code is governed by a BSD-style
     6  // license that can be found in the LICENSE file.
     7  
     8  package types
     9  
    10  import "fmt"
    11  
    12  // An Alias represents an alias type.
    13  // Whether or not Alias types are created is controlled by the
    14  // gotypesalias setting with the GODEBUG environment variable.
    15  // For gotypesalias=1, alias declarations produce an Alias type.
    16  // Otherwise, the alias information is only in the type name,
    17  // which points directly to the actual (aliased) type.
    18  type Alias struct {
    19  	obj     *TypeName      // corresponding declared alias object
    20  	tparams *TypeParamList // type parameters, or nil
    21  	fromRHS Type           // RHS of type alias declaration; may be an alias
    22  	actual  Type           // actual (aliased) type; never an alias
    23  }
    24  
    25  // NewAlias creates a new Alias type with the given type name and rhs.
    26  // rhs must not be nil.
    27  func NewAlias(obj *TypeName, rhs Type) *Alias {
    28  	alias := (*Checker)(nil).newAlias(obj, rhs)
    29  	// Ensure that alias.actual is set (#65455).
    30  	alias.cleanup()
    31  	return alias
    32  }
    33  
    34  func (a *Alias) Obj() *TypeName   { return a.obj }
    35  func (a *Alias) Underlying() Type { return unalias(a).Underlying() }
    36  func (a *Alias) String() string   { return TypeString(a, nil) }
    37  
    38  // Rhs returns the type R on the right-hand side of an alias
    39  // declaration "type A = R", which may be another alias.
    40  func (a *Alias) Rhs() Type { return a.fromRHS }
    41  
    42  // Unalias returns t if it is not an alias type;
    43  // otherwise it follows t's alias chain until it
    44  // reaches a non-alias type which is then returned.
    45  // Consequently, the result is never an alias type.
    46  func Unalias(t Type) Type {
    47  	if a0, _ := t.(*Alias); a0 != nil {
    48  		return unalias(a0)
    49  	}
    50  	return t
    51  }
    52  
    53  func unalias(a0 *Alias) Type {
    54  	if a0.actual != nil {
    55  		return a0.actual
    56  	}
    57  	var t Type
    58  	for a := a0; a != nil; a, _ = t.(*Alias) {
    59  		t = a.fromRHS
    60  	}
    61  	if t == nil {
    62  		panic(fmt.Sprintf("non-terminated alias %s", a0.obj.name))
    63  	}
    64  
    65  	// Memoize the type only if valid.
    66  	// In the presence of unfinished cyclic declarations, Unalias
    67  	// would otherwise latch the invalid value (#66704).
    68  	// TODO(adonovan): rethink, along with checker.typeDecl's use
    69  	// of Invalid to mark unfinished aliases.
    70  	if t != Typ[Invalid] {
    71  		a0.actual = t
    72  	}
    73  
    74  	return t
    75  }
    76  
    77  // asNamed returns t as *Named if that is t's
    78  // actual type. It returns nil otherwise.
    79  func asNamed(t Type) *Named {
    80  	n, _ := Unalias(t).(*Named)
    81  	return n
    82  }
    83  
    84  // newAlias creates a new Alias type with the given type name and rhs.
    85  // rhs must not be nil.
    86  func (check *Checker) newAlias(obj *TypeName, rhs Type) *Alias {
    87  	assert(rhs != nil)
    88  	a := &Alias{obj, nil, rhs, nil}
    89  	if obj.typ == nil {
    90  		obj.typ = a
    91  	}
    92  
    93  	// Ensure that a.actual is set at the end of type checking.
    94  	if check != nil {
    95  		check.needsCleanup(a)
    96  	}
    97  
    98  	return a
    99  }
   100  
   101  func (a *Alias) cleanup() {
   102  	// Ensure a.actual is set before types are published,
   103  	// so Unalias is a pure "getter", not a "setter".
   104  	actual := Unalias(a)
   105  
   106  	if actual == Typ[Invalid] {
   107  		// We don't set a.actual to Typ[Invalid] during type checking,
   108  		// as it may indicate that the RHS is not fully set up.
   109  		a.actual = actual
   110  	}
   111  }
   112
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