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"
18 // ident type-checks identifier e and initializes x with the value or type of e.
19 // If an error occurred, x.mode is set to invalid.
20 // For the meaning of def, see Checker.definedType, below.
21 // If wantType is set, the identifier e is expected to denote a type.
23 func (check *Checker) ident(x *operand, e *ast.Ident, def *Named, wantType bool) {
27 // Note that we cannot use check.lookup here because the returned scope
28 // may be different from obj.Parent(). See also Scope.LookupParent doc.
29 scope, obj := check.scope.LookupParent(e.Name, check.pos)
33 // Blank identifiers are never declared, but the current identifier may
34 // be a placeholder for a receiver type parameter. In this case we can
35 // resolve its type and object from Checker.recvTParamMap.
36 if tpar := check.recvTParamMap[e]; tpar != nil {
40 check.error(e, _InvalidBlank, "cannot use _ as value or type")
43 check.errorf(e, _UndeclaredName, "undeclared name: %s", e.Name)
46 case universeAny, universeComparable:
47 if !check.allowVersion(check.pkg, 1, 18) {
48 check.errorf(e, _UndeclaredName, "undeclared name: %s (requires version go1.18 or later)", e.Name)
49 return // avoid follow-on errors
52 check.recordUse(e, obj)
54 // Type-check the object.
55 // Only call Checker.objDecl if the object doesn't have a type yet
56 // (in which case we must actually determine it) or the object is a
57 // TypeName and we also want a type (in which case we might detect
58 // a cycle which needs to be reported). Otherwise we can skip the
59 // call and avoid a possible cycle error in favor of the more
60 // informative "not a type/value" error that this function's caller
61 // will issue (see issue #25790).
63 if _, gotType := obj.(*TypeName); typ == nil || gotType && wantType {
64 check.objDecl(obj, def)
65 typ = obj.Type() // type must have been assigned by Checker.objDecl
69 // The object may have been dot-imported.
70 // If so, mark the respective package as used.
71 // (This code is only needed for dot-imports. Without them,
72 // we only have to mark variables, see *Var case below).
73 if pkgName := check.dotImportMap[dotImportKey{scope, obj.Name()}]; pkgName != nil {
77 switch obj := obj.(type) {
79 check.errorf(e, _InvalidPkgUse, "use of package %s not in selector", obj.name)
84 if typ == Typ[Invalid] {
87 if obj == universeIota {
88 if check.iota == nil {
89 check.errorf(e, _InvalidIota, "cannot use iota outside constant declaration")
103 // It's ok to mark non-local variables, but ignore variables
104 // from other packages to avoid potential race conditions with
105 // dot-imported variables.
106 if obj.pkg == check.pkg {
109 check.addDeclDep(obj)
110 if typ == Typ[Invalid] {
116 check.addDeclDep(obj)
133 // typ type-checks the type expression e and returns its type, or Typ[Invalid].
134 // The type must not be an (uninstantiated) generic type.
135 func (check *Checker) typ(e ast.Expr) Type {
136 return check.definedType(e, nil)
139 // varType type-checks the type expression e and returns its type, or Typ[Invalid].
140 // The type must not be an (uninstantiated) generic type and it must not be a
141 // constraint interface.
142 func (check *Checker) varType(e ast.Expr) Type {
143 typ := check.definedType(e, nil)
144 // We don't want to call under() (via toInterface) or complete interfaces while we
145 // are in the middle of type-checking parameter declarations that might belong to
146 // interface methods. Delay this check to the end of type-checking.
148 if t, _ := under(typ).(*Interface); t != nil {
149 tset := computeInterfaceTypeSet(check, e.Pos(), t) // TODO(gri) is this the correct position?
150 if !tset.IsMethodSet() {
152 check.softErrorf(e, _MisplacedConstraintIface, "interface is (or embeds) comparable")
154 check.softErrorf(e, _MisplacedConstraintIface, "interface contains type constraints")
163 // definedType is like typ but also accepts a type name def.
164 // If def != nil, e is the type specification for the defined type def, declared
165 // in a type declaration, and def.underlying will be set to the type of e before
166 // any components of e are type-checked.
168 func (check *Checker) definedType(e ast.Expr, def *Named) Type {
169 typ := check.typInternal(e, def)
172 check.errorf(e, _WrongTypeArgCount, "cannot use generic type %s without instantiation", typ)
175 check.recordTypeAndValue(e, typexpr, typ, nil)
179 // genericType is like typ but the type must be an (uninstantiated) generic
180 // type. If reason is non-nil and the type expression was a valid type but not
181 // generic, reason will be populated with a message describing the error.
182 func (check *Checker) genericType(e ast.Expr, reason *string) Type {
183 typ := check.typInternal(e, nil)
185 if typ != Typ[Invalid] && !isGeneric(typ) {
187 *reason = check.sprintf("%s is not a generic type", typ)
191 // TODO(gri) what is the correct call below?
192 check.recordTypeAndValue(e, typexpr, typ, nil)
196 // goTypeName returns the Go type name for typ and
197 // removes any occurrences of "types." from that name.
198 func goTypeName(typ Type) string {
199 return strings.ReplaceAll(fmt.Sprintf("%T", typ), "types.", "")
202 // typInternal drives type checking of types.
203 // Must only be called by definedType or genericType.
205 func (check *Checker) typInternal(e0 ast.Expr, def *Named) (T Type) {
207 check.trace(e0.Pos(), "type %s", e0)
213 // Calling under() here may lead to endless instantiations.
214 // Test case: type T[P any] *T[P]
215 under = safeUnderlying(T)
218 check.trace(e0.Pos(), "=> %s // %s", T, goTypeName(T))
220 check.trace(e0.Pos(), "=> %s (under = %s) // %s", T, under, goTypeName(T))
225 switch e := e0.(type) {
227 // ignore - error reported before
231 check.ident(&x, e, def, true)
236 def.setUnderlying(typ)
239 // ignore - error reported before
241 check.errorf(&x, _NotAType, "%s used as type", &x)
243 check.errorf(&x, _NotAType, "%s is not a type", &x)
246 case *ast.SelectorExpr:
248 check.selector(&x, e)
253 def.setUnderlying(typ)
256 // ignore - error reported before
258 check.errorf(&x, _NotAType, "%s used as type", &x)
260 check.errorf(&x, _NotAType, "%s is not a type", &x)
263 case *ast.IndexExpr, *ast.IndexListExpr:
264 ix := typeparams.UnpackIndexExpr(e)
265 if !check.allowVersion(check.pkg, 1, 18) {
266 check.softErrorf(inNode(e, ix.Lbrack), _UnsupportedFeature, "type instantiation requires go1.18 or later")
268 return check.instantiatedType(ix, def)
271 // Generic types must be instantiated before they can be used in any form.
272 // Consequently, generic types cannot be parenthesized.
273 return check.definedType(e.X, def)
278 def.setUnderlying(typ)
279 typ.elem = check.varType(e.Elt)
284 def.setUnderlying(typ)
285 typ.len = check.arrayLength(e.Len)
286 typ.elem = check.varType(e.Elt)
292 // dots are handled explicitly where they are legal
293 // (array composite literals and parameter lists)
294 check.error(e, _InvalidDotDotDot, "invalid use of '...'")
297 case *ast.StructType:
299 def.setUnderlying(typ)
300 check.structType(typ, e)
305 def.setUnderlying(typ)
306 typ.base = check.varType(e.X)
310 typ := new(Signature)
311 def.setUnderlying(typ)
312 check.funcType(typ, nil, e)
315 case *ast.InterfaceType:
316 typ := new(Interface)
317 def.setUnderlying(typ)
321 check.interfaceType(typ, e, def)
326 def.setUnderlying(typ)
328 typ.key = check.varType(e.Key)
329 typ.elem = check.varType(e.Value)
331 // spec: "The comparison operators == and != must be fully defined
332 // for operands of the key type; thus the key type must not be a
333 // function, map, or slice."
335 // Delay this check because it requires fully setup types;
336 // it is safe to continue in any case (was issue 6667).
338 if !Comparable(typ.key) {
340 if asTypeParam(typ.key) != nil {
341 why = " (missing comparable constraint)"
343 check.errorf(e.Key, _IncomparableMapKey, "incomparable map key type %s%s", typ.key, why)
351 def.setUnderlying(typ)
355 case ast.SEND | ast.RECV:
362 check.invalidAST(e, "unknown channel direction %d", e.Dir)
367 typ.elem = check.varType(e.Value)
371 check.errorf(e0, _NotAType, "%s is not a type", e0)
375 def.setUnderlying(typ)
379 func (check *Checker) instantiatedType(ix *typeparams.IndexExpr, def *Named) (res Type) {
382 check.trace(pos, "-- instantiating %s with %s", ix.X, ix.Indices)
386 // Don't format the underlying here. It will always be nil.
387 check.trace(pos, "=> %s", res)
392 gtyp := check.genericType(ix.X, &reason)
394 check.invalidOp(ix.Orig, _NotAGenericType, "%s (%s)", ix.Orig, reason)
396 if gtyp == Typ[Invalid] {
397 return gtyp // error already reported
400 orig, _ := gtyp.(*Named)
402 panic(fmt.Sprintf("%v: cannot instantiate %v", ix.Pos(), gtyp))
405 // evaluate arguments
406 targs := check.typeList(ix.Indices)
408 def.setUnderlying(Typ[Invalid]) // avoid later errors due to lazy instantiation
412 // determine argument positions
413 posList := make([]token.Pos, len(targs))
414 for i, arg := range ix.Indices {
415 posList[i] = arg.Pos()
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 // origin.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(posList) {
469 check.softErrorf(atPos(pos), _InvalidTypeArg, err.Error())
471 check.mono.recordInstance(check.pkg, pos, inst.tparams.list(), inst.targs.list(), posList)
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] {