1 // Copyright 2013 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.
5 // This file implements type-checking of identifiers and type expressions.
13 "go/internal/typeparams"
17 // ident type-checks identifier e and initializes x with the value or type of e.
18 // If an error occurred, x.mode is set to invalid.
19 // For the meaning of def, see Checker.definedType, below.
20 // If wantType is set, the identifier e is expected to denote a type.
22 func (check *Checker) ident(x *operand, e *ast.Ident, def *Named, wantType bool) {
26 // Note that we cannot use check.lookup here because the returned scope
27 // may be different from obj.Parent(). See also Scope.LookupParent doc.
28 scope, obj := check.scope.LookupParent(e.Name, check.pos)
32 // Blank identifiers are never declared, but the current identifier may
33 // be a placeholder for a receiver type parameter. In this case we can
34 // resolve its type and object from Checker.recvTParamMap.
35 if tpar := check.recvTParamMap[e]; tpar != nil {
39 check.error(e, _InvalidBlank, "cannot use _ as value or type")
42 check.errorf(e, _UndeclaredName, "undeclared name: %s", e.Name)
45 case universeAny, universeComparable:
46 if !check.allowVersion(check.pkg, 1, 18) {
47 check.errorf(e, _UndeclaredName, "undeclared name: %s (requires version go1.18 or later)", e.Name)
48 return // avoid follow-on errors
51 check.recordUse(e, obj)
53 // Type-check the object.
54 // Only call Checker.objDecl if the object doesn't have a type yet
55 // (in which case we must actually determine it) or the object is a
56 // TypeName and we also want a type (in which case we might detect
57 // a cycle which needs to be reported). Otherwise we can skip the
58 // call and avoid a possible cycle error in favor of the more
59 // informative "not a type/value" error that this function's caller
60 // will issue (see issue #25790).
62 if _, gotType := obj.(*TypeName); typ == nil || gotType && wantType {
63 check.objDecl(obj, def)
64 typ = obj.Type() // type must have been assigned by Checker.objDecl
68 // The object may have been dot-imported.
69 // If so, mark the respective package as used.
70 // (This code is only needed for dot-imports. Without them,
71 // we only have to mark variables, see *Var case below).
72 if pkgName := check.dotImportMap[dotImportKey{scope, obj.Name()}]; pkgName != nil {
76 switch obj := obj.(type) {
78 check.errorf(e, _InvalidPkgUse, "use of package %s not in selector", obj.name)
83 if typ == Typ[Invalid] {
86 if obj == universeIota {
87 if check.iota == nil {
88 check.errorf(e, _InvalidIota, "cannot use iota outside constant declaration")
99 if check.isBrokenAlias(obj) {
100 check.errorf(e, _InvalidDeclCycle, "invalid use of type alias %s in recursive type (see issue #50729)", obj.name)
106 // It's ok to mark non-local variables, but ignore variables
107 // from other packages to avoid potential race conditions with
108 // dot-imported variables.
109 if obj.pkg == check.pkg {
112 check.addDeclDep(obj)
113 if typ == Typ[Invalid] {
119 check.addDeclDep(obj)
136 // typ type-checks the type expression e and returns its type, or Typ[Invalid].
137 // The type must not be an (uninstantiated) generic type.
138 func (check *Checker) typ(e ast.Expr) Type {
139 return check.definedType(e, nil)
142 // varType type-checks the type expression e and returns its type, or Typ[Invalid].
143 // The type must not be an (uninstantiated) generic type and it must not be a
144 // constraint interface.
145 func (check *Checker) varType(e ast.Expr) Type {
146 typ := check.definedType(e, nil)
147 check.validVarType(e, typ)
151 // validVarType reports an error if typ is a constraint interface.
152 // The expression e is used for error reporting, if any.
153 func (check *Checker) validVarType(e ast.Expr, typ Type) {
154 // If we have a type parameter there's nothing to do.
155 if isTypeParam(typ) {
159 // We don't want to call under() or complete interfaces while we are in
160 // the middle of type-checking parameter declarations that might belong
161 // to interface methods. Delay this check to the end of type-checking.
163 if t, _ := under(typ).(*Interface); t != nil {
164 tset := computeInterfaceTypeSet(check, e.Pos(), t) // TODO(gri) is this the correct position?
165 if !tset.IsMethodSet() {
167 check.softErrorf(e, _MisplacedConstraintIface, "interface is (or embeds) comparable")
169 check.softErrorf(e, _MisplacedConstraintIface, "interface contains type constraints")
176 // definedType is like typ but also accepts a type name def.
177 // If def != nil, e is the type specification for the defined type def, declared
178 // in a type declaration, and def.underlying will be set to the type of e before
179 // any components of e are type-checked.
181 func (check *Checker) definedType(e ast.Expr, def *Named) Type {
182 typ := check.typInternal(e, def)
185 check.errorf(e, _WrongTypeArgCount, "cannot use generic type %s without instantiation", typ)
188 check.recordTypeAndValue(e, typexpr, typ, nil)
192 // genericType is like typ but the type must be an (uninstantiated) generic
193 // type. If reason is non-nil and the type expression was a valid type but not
194 // generic, reason will be populated with a message describing the error.
195 func (check *Checker) genericType(e ast.Expr, reason *string) Type {
196 typ := check.typInternal(e, nil)
198 if typ != Typ[Invalid] && !isGeneric(typ) {
200 *reason = check.sprintf("%s is not a generic type", typ)
204 // TODO(gri) what is the correct call below?
205 check.recordTypeAndValue(e, typexpr, typ, nil)
209 // goTypeName returns the Go type name for typ and
210 // removes any occurrences of "types." from that name.
211 func goTypeName(typ Type) string {
212 return strings.ReplaceAll(fmt.Sprintf("%T", typ), "types.", "")
215 // typInternal drives type checking of types.
216 // Must only be called by definedType or genericType.
218 func (check *Checker) typInternal(e0 ast.Expr, def *Named) (T Type) {
220 check.trace(e0.Pos(), "-- type %s", e0)
226 // Calling under() here may lead to endless instantiations.
227 // Test case: type T[P any] *T[P]
228 under = safeUnderlying(T)
231 check.trace(e0.Pos(), "=> %s // %s", T, goTypeName(T))
233 check.trace(e0.Pos(), "=> %s (under = %s) // %s", T, under, goTypeName(T))
238 switch e := e0.(type) {
240 // ignore - error reported before
244 check.ident(&x, e, def, true)
249 def.setUnderlying(typ)
252 // ignore - error reported before
254 check.errorf(&x, _NotAType, "%s used as type", &x)
256 check.errorf(&x, _NotAType, "%s is not a type", &x)
259 case *ast.SelectorExpr:
261 check.selector(&x, e, def)
266 def.setUnderlying(typ)
269 // ignore - error reported before
271 check.errorf(&x, _NotAType, "%s used as type", &x)
273 check.errorf(&x, _NotAType, "%s is not a type", &x)
276 case *ast.IndexExpr, *ast.IndexListExpr:
277 ix := typeparams.UnpackIndexExpr(e)
278 if !check.allowVersion(check.pkg, 1, 18) {
279 check.softErrorf(inNode(e, ix.Lbrack), _UnsupportedFeature, "type instantiation requires go1.18 or later")
281 return check.instantiatedType(ix, def)
284 // Generic types must be instantiated before they can be used in any form.
285 // Consequently, generic types cannot be parenthesized.
286 return check.definedType(e.X, def)
291 def.setUnderlying(typ)
292 typ.elem = check.varType(e.Elt)
297 def.setUnderlying(typ)
298 typ.len = check.arrayLength(e.Len)
299 typ.elem = check.varType(e.Elt)
305 // dots are handled explicitly where they are legal
306 // (array composite literals and parameter lists)
307 check.error(e, _InvalidDotDotDot, "invalid use of '...'")
310 case *ast.StructType:
312 def.setUnderlying(typ)
313 check.structType(typ, e)
318 typ.base = Typ[Invalid] // avoid nil base in invalid recursive type declaration
319 def.setUnderlying(typ)
320 typ.base = check.varType(e.X)
324 typ := new(Signature)
325 def.setUnderlying(typ)
326 check.funcType(typ, nil, e)
329 case *ast.InterfaceType:
330 typ := check.newInterface()
331 def.setUnderlying(typ)
332 check.interfaceType(typ, e, def)
337 def.setUnderlying(typ)
339 typ.key = check.varType(e.Key)
340 typ.elem = check.varType(e.Value)
342 // spec: "The comparison operators == and != must be fully defined
343 // for operands of the key type; thus the key type must not be a
344 // function, map, or slice."
346 // Delay this check because it requires fully setup types;
347 // it is safe to continue in any case (was issue 6667).
349 if !Comparable(typ.key) {
351 if isTypeParam(typ.key) {
352 why = " (missing comparable constraint)"
354 check.errorf(e.Key, _IncomparableMapKey, "incomparable map key type %s%s", typ.key, why)
362 def.setUnderlying(typ)
366 case ast.SEND | ast.RECV:
373 check.invalidAST(e, "unknown channel direction %d", e.Dir)
378 typ.elem = check.varType(e.Value)
382 check.errorf(e0, _NotAType, "%s is not a type", e0)
386 def.setUnderlying(typ)
390 func (check *Checker) instantiatedType(ix *typeparams.IndexExpr, def *Named) (res Type) {
393 check.trace(pos, "-- instantiating %s with %s", ix.X, ix.Indices)
397 // Don't format the underlying here. It will always be nil.
398 check.trace(pos, "=> %s", res)
403 gtyp := check.genericType(ix.X, &reason)
405 check.invalidOp(ix.Orig, _NotAGenericType, "%s (%s)", ix.Orig, reason)
407 if gtyp == Typ[Invalid] {
408 return gtyp // error already reported
411 orig, _ := gtyp.(*Named)
413 panic(fmt.Sprintf("%v: cannot instantiate %v", ix.Pos(), gtyp))
416 // evaluate arguments
417 targs := check.typeList(ix.Indices)
419 def.setUnderlying(Typ[Invalid]) // avoid errors later due to lazy instantiation
423 // enableTypeTypeInference controls whether to infer missing type arguments
424 // using constraint type inference. See issue #51527.
425 const enableTypeTypeInference = false
427 // create the instance
428 ctxt := check.bestContext(nil)
429 h := ctxt.instanceHash(orig, targs)
430 // targs may be incomplete, and require inference. In any case we should de-duplicate.
431 inst, _ := ctxt.lookup(h, orig, targs).(*Named)
432 // If inst is non-nil, we can't just return here. Inst may have been
433 // constructed via recursive substitution, in which case we wouldn't do the
434 // validation below. Ensure that the validation (and resulting errors) runs
435 // for each instantiated type in the source.
437 // x may be a selector for an imported type; use its start pos rather than x.Pos().
438 tname := NewTypeName(ix.Pos(), orig.obj.pkg, orig.obj.name, nil)
439 inst = check.newNamed(tname, orig, nil, nil, nil) // underlying, methods and tparams are set when named is resolved
440 inst.targs = newTypeList(targs)
441 inst = ctxt.update(h, orig, targs, inst).(*Named)
443 def.setUnderlying(inst)
445 inst.resolver = func(ctxt *Context, n *Named) (*TypeParamList, Type, *methodList) {
446 tparams := n.orig.TypeParams().list()
448 targs := n.targs.list()
449 if enableTypeTypeInference && len(targs) < len(tparams) {
450 // If inference fails, len(inferred) will be 0, and inst.underlying will
451 // be set to Typ[Invalid] in expandNamed.
452 inferred := check.infer(ix.Orig, tparams, targs, nil, nil)
453 if len(inferred) > len(targs) {
454 n.targs = newTypeList(inferred)
458 return expandNamed(ctxt, n, pos)
461 // orig.tparams may not be set up, so we need to do expansion later.
463 // This is an instance from the source, not from recursive substitution,
464 // and so it must be resolved during type-checking so that we can report
467 // Since check is non-nil, we can still mutate inst. Unpinning the resolver
468 // frees some memory.
470 check.recordInstance(ix.Orig, inst.TypeArgs().list(), inst)
472 if check.validateTArgLen(pos, inst.tparams.Len(), inst.targs.Len()) {
473 if i, err := check.verify(pos, inst.tparams.list(), inst.targs.list()); err != nil {
474 // best position for error reporting
476 if i < len(ix.Indices) {
477 pos = ix.Indices[i].Pos()
479 check.softErrorf(atPos(pos), _InvalidTypeArg, err.Error())
481 check.mono.recordInstance(check.pkg, pos, inst.tparams.list(), inst.targs.list(), ix.Indices)
485 check.validType(inst)
491 // arrayLength type-checks the array length expression e
492 // and returns the constant length >= 0, or a value < 0
493 // to indicate an error (and thus an unknown length).
494 func (check *Checker) arrayLength(e ast.Expr) int64 {
495 // If e is an identifier, the array declaration might be an
496 // attempt at a parameterized type declaration with missing
497 // constraint. Provide an error message that mentions array
499 if name, _ := e.(*ast.Ident); name != nil {
500 obj := check.lookup(name.Name)
502 check.errorf(name, _InvalidArrayLen, "undeclared name %s for array length", name.Name)
505 if _, ok := obj.(*Const); !ok {
506 check.errorf(name, _InvalidArrayLen, "invalid array length %s", name.Name)
513 if x.mode != constant_ {
514 if x.mode != invalid {
515 check.errorf(&x, _InvalidArrayLen, "array length %s must be constant", &x)
520 if isUntyped(x.typ) || isInteger(x.typ) {
521 if val := constant.ToInt(x.val); val.Kind() == constant.Int {
522 if representableConst(val, check, Typ[Int], nil) {
523 if n, ok := constant.Int64Val(val); ok && n >= 0 {
526 check.errorf(&x, _InvalidArrayLen, "invalid array length %s", &x)
532 check.errorf(&x, _InvalidArrayLen, "array length %s must be integer", &x)
536 // typeList provides the list of types corresponding to the incoming expression list.
537 // If an error occurred, the result is nil, but all list elements were type-checked.
538 func (check *Checker) typeList(list []ast.Expr) []Type {
539 res := make([]Type, len(list)) // res != nil even if len(list) == 0
540 for i, x := range list {
541 t := check.varType(x)
542 if t == Typ[Invalid] {