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")
102 // It's ok to mark non-local variables, but ignore variables
103 // from other packages to avoid potential race conditions with
104 // dot-imported variables.
105 if obj.pkg == check.pkg {
108 check.addDeclDep(obj)
109 if typ == Typ[Invalid] {
115 check.addDeclDep(obj)
132 // typ type-checks the type expression e and returns its type, or Typ[Invalid].
133 // The type must not be an (uninstantiated) generic type.
134 func (check *Checker) typ(e ast.Expr) Type {
135 return check.definedType(e, nil)
138 // varType type-checks the type expression e and returns its type, or Typ[Invalid].
139 // The type must not be an (uninstantiated) generic type and it must not be a
140 // constraint interface.
141 func (check *Checker) varType(e ast.Expr) Type {
142 typ := check.definedType(e, nil)
144 // If we have a type parameter there's nothing to do.
145 if isTypeParam(typ) {
149 // We don't want to call under() or complete interfaces while we are in
150 // the middle of type-checking parameter declarations that might belong
151 // to interface methods. Delay this check to the end of type-checking.
153 if t, _ := under(typ).(*Interface); t != nil {
154 tset := computeInterfaceTypeSet(check, e.Pos(), t) // TODO(gri) is this the correct position?
155 if !tset.IsMethodSet() {
157 check.softErrorf(e, _MisplacedConstraintIface, "interface is (or embeds) comparable")
159 check.softErrorf(e, _MisplacedConstraintIface, "interface contains type constraints")
168 // definedType is like typ but also accepts a type name def.
169 // If def != nil, e is the type specification for the defined type def, declared
170 // in a type declaration, and def.underlying will be set to the type of e before
171 // any components of e are type-checked.
173 func (check *Checker) definedType(e ast.Expr, def *Named) Type {
174 typ := check.typInternal(e, def)
177 check.errorf(e, _WrongTypeArgCount, "cannot use generic type %s without instantiation", typ)
180 check.recordTypeAndValue(e, typexpr, typ, nil)
184 // genericType is like typ but the type must be an (uninstantiated) generic
185 // type. If reason is non-nil and the type expression was a valid type but not
186 // generic, reason will be populated with a message describing the error.
187 func (check *Checker) genericType(e ast.Expr, reason *string) Type {
188 typ := check.typInternal(e, nil)
190 if typ != Typ[Invalid] && !isGeneric(typ) {
192 *reason = check.sprintf("%s is not a generic type", typ)
196 // TODO(gri) what is the correct call below?
197 check.recordTypeAndValue(e, typexpr, typ, nil)
201 // goTypeName returns the Go type name for typ and
202 // removes any occurrences of "types." from that name.
203 func goTypeName(typ Type) string {
204 return strings.ReplaceAll(fmt.Sprintf("%T", typ), "types.", "")
207 // typInternal drives type checking of types.
208 // Must only be called by definedType or genericType.
210 func (check *Checker) typInternal(e0 ast.Expr, def *Named) (T Type) {
212 check.trace(e0.Pos(), "type %s", e0)
218 // Calling under() here may lead to endless instantiations.
219 // Test case: type T[P any] *T[P]
220 under = safeUnderlying(T)
223 check.trace(e0.Pos(), "=> %s // %s", T, goTypeName(T))
225 check.trace(e0.Pos(), "=> %s (under = %s) // %s", T, under, goTypeName(T))
230 switch e := e0.(type) {
232 // ignore - error reported before
236 check.ident(&x, e, def, true)
241 def.setUnderlying(typ)
244 // ignore - error reported before
246 check.errorf(&x, _NotAType, "%s used as type", &x)
248 check.errorf(&x, _NotAType, "%s is not a type", &x)
251 case *ast.SelectorExpr:
253 check.selector(&x, e)
258 def.setUnderlying(typ)
261 // ignore - error reported before
263 check.errorf(&x, _NotAType, "%s used as type", &x)
265 check.errorf(&x, _NotAType, "%s is not a type", &x)
268 case *ast.IndexExpr, *ast.IndexListExpr:
269 ix := typeparams.UnpackIndexExpr(e)
270 if !check.allowVersion(check.pkg, 1, 18) {
271 check.softErrorf(inNode(e, ix.Lbrack), _UnsupportedFeature, "type instantiation requires go1.18 or later")
273 return check.instantiatedType(ix, def)
276 // Generic types must be instantiated before they can be used in any form.
277 // Consequently, generic types cannot be parenthesized.
278 return check.definedType(e.X, def)
283 def.setUnderlying(typ)
284 typ.elem = check.varType(e.Elt)
289 def.setUnderlying(typ)
290 typ.len = check.arrayLength(e.Len)
291 typ.elem = check.varType(e.Elt)
297 // dots are handled explicitly where they are legal
298 // (array composite literals and parameter lists)
299 check.error(e, _InvalidDotDotDot, "invalid use of '...'")
302 case *ast.StructType:
304 def.setUnderlying(typ)
305 check.structType(typ, e)
310 typ.base = Typ[Invalid] // avoid nil base in invalid recursive type declaration
311 def.setUnderlying(typ)
312 typ.base = check.varType(e.X)
316 typ := new(Signature)
317 def.setUnderlying(typ)
318 check.funcType(typ, nil, e)
321 case *ast.InterfaceType:
322 typ := new(Interface)
323 def.setUnderlying(typ)
327 check.interfaceType(typ, e, def)
332 def.setUnderlying(typ)
334 typ.key = check.varType(e.Key)
335 typ.elem = check.varType(e.Value)
337 // spec: "The comparison operators == and != must be fully defined
338 // for operands of the key type; thus the key type must not be a
339 // function, map, or slice."
341 // Delay this check because it requires fully setup types;
342 // it is safe to continue in any case (was issue 6667).
344 if !Comparable(typ.key) {
346 if isTypeParam(typ.key) {
347 why = " (missing comparable constraint)"
349 check.errorf(e.Key, _IncomparableMapKey, "incomparable map key type %s%s", typ.key, why)
357 def.setUnderlying(typ)
361 case ast.SEND | ast.RECV:
368 check.invalidAST(e, "unknown channel direction %d", e.Dir)
373 typ.elem = check.varType(e.Value)
377 check.errorf(e0, _NotAType, "%s is not a type", e0)
381 def.setUnderlying(typ)
385 func (check *Checker) instantiatedType(ix *typeparams.IndexExpr, def *Named) (res Type) {
388 check.trace(pos, "-- instantiating %s with %s", ix.X, ix.Indices)
392 // Don't format the underlying here. It will always be nil.
393 check.trace(pos, "=> %s", res)
398 gtyp := check.genericType(ix.X, &reason)
400 check.invalidOp(ix.Orig, _NotAGenericType, "%s (%s)", ix.Orig, reason)
402 if gtyp == Typ[Invalid] {
403 return gtyp // error already reported
406 orig, _ := gtyp.(*Named)
408 panic(fmt.Sprintf("%v: cannot instantiate %v", ix.Pos(), gtyp))
411 // evaluate arguments
412 targs := check.typeList(ix.Indices)
414 def.setUnderlying(Typ[Invalid]) // avoid later errors due to lazy instantiation
418 // create the instance
419 ctxt := check.bestContext(nil)
420 h := ctxt.instanceHash(orig, targs)
421 // targs may be incomplete, and require inference. In any case we should de-duplicate.
422 inst, _ := ctxt.lookup(h, orig, targs).(*Named)
423 // If inst is non-nil, we can't just return here. Inst may have been
424 // constructed via recursive substitution, in which case we wouldn't do the
425 // validation below. Ensure that the validation (and resulting errors) runs
426 // for each instantiated type in the source.
428 tname := NewTypeName(ix.X.Pos(), orig.obj.pkg, orig.obj.name, nil)
429 inst = check.newNamed(tname, orig, nil, nil, nil) // underlying, methods and tparams are set when named is resolved
430 inst.targs = NewTypeList(targs)
431 inst = ctxt.update(h, orig, targs, inst).(*Named)
433 def.setUnderlying(inst)
435 inst.resolver = func(ctxt *Context, n *Named) (*TypeParamList, Type, []*Func) {
436 tparams := orig.TypeParams().list()
439 if len(targs) < len(tparams) {
440 // If inference fails, len(inferred) will be 0, and inst.underlying will
441 // be set to Typ[Invalid] in expandNamed.
442 inferred = check.infer(ix.Orig, tparams, targs, nil, nil)
443 if len(inferred) > len(targs) {
444 inst.targs = NewTypeList(inferred)
448 check.recordInstance(ix.Orig, inferred, inst)
449 return expandNamed(ctxt, n, pos)
452 // orig.tparams may not be set up, so we need to do expansion later.
454 // This is an instance from the source, not from recursive substitution,
455 // and so it must be resolved during type-checking so that we can report
458 // Since check is non-nil, we can still mutate inst. Unpinning the resolver
459 // frees some memory.
462 if check.validateTArgLen(pos, inst.tparams.Len(), inst.targs.Len()) {
463 if i, err := check.verify(pos, inst.tparams.list(), inst.targs.list()); err != nil {
464 // best position for error reporting
466 if i < len(ix.Indices) {
467 pos = ix.Indices[i].Pos()
469 check.softErrorf(atPos(pos), _InvalidTypeArg, err.Error())
471 check.mono.recordInstance(check.pkg, pos, inst.tparams.list(), inst.targs.list(), ix.Indices)
475 check.validType(inst, nil)
481 // arrayLength type-checks the array length expression e
482 // and returns the constant length >= 0, or a value < 0
483 // to indicate an error (and thus an unknown length).
484 func (check *Checker) arrayLength(e ast.Expr) int64 {
485 // If e is an undeclared identifier, the array declaration might be an
486 // attempt at a parameterized type declaration with missing constraint.
487 // Provide a better error message than just "undeclared name: X".
488 if name, _ := e.(*ast.Ident); name != nil && check.lookup(name.Name) == nil {
489 check.errorf(name, _InvalidArrayLen, "undeclared name %s for array length", name.Name)
495 if x.mode != constant_ {
496 if x.mode != invalid {
497 check.errorf(&x, _InvalidArrayLen, "array length %s must be constant", &x)
502 if isUntyped(x.typ) || isInteger(x.typ) {
503 if val := constant.ToInt(x.val); val.Kind() == constant.Int {
504 if representableConst(val, check, Typ[Int], nil) {
505 if n, ok := constant.Int64Val(val); ok && n >= 0 {
508 check.errorf(&x, _InvalidArrayLen, "invalid array length %s", &x)
514 check.errorf(&x, _InvalidArrayLen, "array length %s must be integer", &x)
518 // typeList provides the list of types corresponding to the incoming expression list.
519 // If an error occurred, the result is nil, but all list elements were type-checked.
520 func (check *Checker) typeList(list []ast.Expr) []Type {
521 res := make([]Type, len(list)) // res != nil even if len(list) == 0
522 for i, x := range list {
523 t := check.varType(x)
524 if t == Typ[Invalid] {