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 (
    11  	"fmt"
    12  	"go/token"
    13  )
    14  
    15  // An Alias represents an alias type.
    16  // Whether or not Alias types are created is controlled by the
    17  // gotypesalias setting with the GODEBUG environment variable.
    18  // For gotypesalias=1, alias declarations produce an Alias type.
    19  // Otherwise, the alias information is only in the type name,
    20  // which points directly to the actual (aliased) type.
    21  type Alias struct {
    22  	obj     *TypeName      // corresponding declared alias object
    23  	orig    *Alias         // original, uninstantiated alias
    24  	tparams *TypeParamList // type parameters, or nil
    25  	targs   *TypeList      // type arguments, or nil
    26  	fromRHS Type           // RHS of type alias declaration; may be an alias
    27  	actual  Type           // actual (aliased) type; never an alias
    28  }
    29  
    30  // NewAlias creates a new Alias type with the given type name and rhs.
    31  // rhs must not be nil.
    32  func NewAlias(obj *TypeName, rhs Type) *Alias {
    33  	alias := (*Checker)(nil).newAlias(obj, rhs)
    34  	// Ensure that alias.actual is set (#65455).
    35  	alias.cleanup()
    36  	return alias
    37  }
    38  
    39  // Obj returns the type name for the declaration defining the alias type a.
    40  // For instantiated types, this is same as the type name of the origin type.
    41  func (a *Alias) Obj() *TypeName { return a.orig.obj }
    42  
    43  func (a *Alias) String() string { return TypeString(a, nil) }
    44  
    45  // Underlying returns the [underlying type] of the alias type a, which is the
    46  // underlying type of the aliased type. Underlying types are never Named,
    47  // TypeParam, or Alias types.
    48  //
    49  // [underlying type]: https://go.dev/ref/spec#Underlying_types.
    50  func (a *Alias) Underlying() Type { return unalias(a).Underlying() }
    51  
    52  // Origin returns the generic Alias type of which a is an instance.
    53  // If a is not an instance of a generic alias, Origin returns a.
    54  func (a *Alias) Origin() *Alias { return a.orig }
    55  
    56  // TypeParams returns the type parameters of the alias type a, or nil.
    57  // A generic Alias and its instances have the same type parameters.
    58  func (a *Alias) TypeParams() *TypeParamList { return a.tparams }
    59  
    60  // SetTypeParams sets the type parameters of the alias type a.
    61  // The alias a must not have type arguments.
    62  func (a *Alias) SetTypeParams(tparams []*TypeParam) {
    63  	assert(a.targs == nil)
    64  	a.tparams = bindTParams(tparams)
    65  }
    66  
    67  // TypeArgs returns the type arguments used to instantiate the Alias type.
    68  // If a is not an instance of a generic alias, the result is nil.
    69  func (a *Alias) TypeArgs() *TypeList { return a.targs }
    70  
    71  // Rhs returns the type R on the right-hand side of an alias
    72  // declaration "type A = R", which may be another alias.
    73  func (a *Alias) Rhs() Type { return a.fromRHS }
    74  
    75  // Unalias returns t if it is not an alias type;
    76  // otherwise it follows t's alias chain until it
    77  // reaches a non-alias type which is then returned.
    78  // Consequently, the result is never an alias type.
    79  func Unalias(t Type) Type {
    80  	if a0, _ := t.(*Alias); a0 != nil {
    81  		return unalias(a0)
    82  	}
    83  	return t
    84  }
    85  
    86  func unalias(a0 *Alias) Type {
    87  	if a0.actual != nil {
    88  		return a0.actual
    89  	}
    90  	var t Type
    91  	for a := a0; a != nil; a, _ = t.(*Alias) {
    92  		t = a.fromRHS
    93  	}
    94  	if t == nil {
    95  		panic(fmt.Sprintf("non-terminated alias %s", a0.obj.name))
    96  	}
    97  
    98  	// Memoize the type only if valid.
    99  	// In the presence of unfinished cyclic declarations, Unalias
   100  	// would otherwise latch the invalid value (#66704).
   101  	// TODO(adonovan): rethink, along with checker.typeDecl's use
   102  	// of Invalid to mark unfinished aliases.
   103  	if t != Typ[Invalid] {
   104  		a0.actual = t
   105  	}
   106  
   107  	return t
   108  }
   109  
   110  // asNamed returns t as *Named if that is t's
   111  // actual type. It returns nil otherwise.
   112  func asNamed(t Type) *Named {
   113  	n, _ := Unalias(t).(*Named)
   114  	return n
   115  }
   116  
   117  // newAlias creates a new Alias type with the given type name and rhs.
   118  // rhs must not be nil.
   119  func (check *Checker) newAlias(obj *TypeName, rhs Type) *Alias {
   120  	assert(rhs != nil)
   121  	a := new(Alias)
   122  	a.obj = obj
   123  	a.orig = a
   124  	a.fromRHS = rhs
   125  	if obj.typ == nil {
   126  		obj.typ = a
   127  	}
   128  
   129  	// Ensure that a.actual is set at the end of type checking.
   130  	if check != nil {
   131  		check.needsCleanup(a)
   132  	}
   133  
   134  	return a
   135  }
   136  
   137  // newAliasInstance creates a new alias instance for the given origin and type
   138  // arguments, recording pos as the position of its synthetic object (for error
   139  // reporting).
   140  func (check *Checker) newAliasInstance(pos token.Pos, orig *Alias, targs []Type, expanding *Named, ctxt *Context) *Alias {
   141  	assert(len(targs) > 0)
   142  	obj := NewTypeName(pos, orig.obj.pkg, orig.obj.name, nil)
   143  	rhs := check.subst(pos, orig.fromRHS, makeSubstMap(orig.TypeParams().list(), targs), expanding, ctxt)
   144  	res := check.newAlias(obj, rhs)
   145  	res.orig = orig
   146  	res.tparams = orig.tparams
   147  	res.targs = newTypeList(targs)
   148  	return res
   149  }
   150  
   151  func (a *Alias) cleanup() {
   152  	// Ensure a.actual is set before types are published,
   153  	// so Unalias is a pure "getter", not a "setter".
   154  	actual := Unalias(a)
   155  
   156  	if actual == Typ[Invalid] {
   157  		// We don't set a.actual to Typ[Invalid] during type checking,
   158  		// as it may indicate that the RHS is not fully set up.
   159  		a.actual = actual
   160  	}
   161  }
   162
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