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"
14 . "internal/types/errors"
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.
22 func (check *Checker) ident(x *operand, e *ast.Ident, def *TypeName, 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, "undefined: %s", e.Name)
45 case universeAny, universeComparable:
46 if !check.verifyVersionf(e, go1_18, "predeclared %s", e.Name) {
47 return // avoid follow-on errors
50 check.recordUse(e, obj)
52 // Type-check the object.
53 // Only call Checker.objDecl if the object doesn't have a type yet
54 // (in which case we must actually determine it) or the object is a
55 // TypeName and we also want a type (in which case we might detect
56 // a cycle which needs to be reported). Otherwise we can skip the
57 // call and avoid a possible cycle error in favor of the more
58 // informative "not a type/value" error that this function's caller
59 // will issue (see go.dev/issue/25790).
61 if _, gotType := obj.(*TypeName); typ == nil || gotType && wantType {
62 check.objDecl(obj, def)
63 typ = obj.Type() // type must have been assigned by Checker.objDecl
67 // The object may have been dot-imported.
68 // If so, mark the respective package as used.
69 // (This code is only needed for dot-imports. Without them,
70 // we only have to mark variables, see *Var case below).
71 if pkgName := check.dotImportMap[dotImportKey{scope, obj.Name()}]; pkgName != nil {
75 switch obj := obj.(type) {
77 check.errorf(e, InvalidPkgUse, "use of package %s not in selector", obj.name)
85 if obj == universeIota {
86 if check.iota == nil {
87 check.error(e, InvalidIota, "cannot use iota outside constant declaration")
98 if !check.enableAlias && check.isBrokenAlias(obj) {
99 check.errorf(e, InvalidDeclCycle, "invalid use of type alias %s in recursive type (see go.dev/issue/50729)", obj.name)
105 // It's ok to mark non-local variables, but ignore variables
106 // from other packages to avoid potential race conditions with
107 // dot-imported variables.
108 if obj.pkg == check.pkg {
111 check.addDeclDep(obj)
118 check.addDeclDep(obj)
135 // typ type-checks the type expression e and returns its type, or Typ[Invalid].
136 // The type must not be an (uninstantiated) generic type.
137 func (check *Checker) typ(e ast.Expr) Type {
138 return check.definedType(e, nil)
141 // varType type-checks the type expression e and returns its type, or Typ[Invalid].
142 // The type must not be an (uninstantiated) generic type and it must not be a
143 // constraint interface.
144 func (check *Checker) varType(e ast.Expr) Type {
145 typ := check.definedType(e, nil)
146 check.validVarType(e, typ)
150 // validVarType reports an error if typ is a constraint interface.
151 // The expression e is used for error reporting, if any.
152 func (check *Checker) validVarType(e ast.Expr, typ Type) {
153 // If we have a type parameter there's nothing to do.
154 if isTypeParam(typ) {
158 // We don't want to call under() or complete interfaces while we are in
159 // the middle of type-checking parameter declarations that might belong
160 // to interface methods. Delay this check to the end of type-checking.
162 if t, _ := under(typ).(*Interface); t != nil {
163 tset := computeInterfaceTypeSet(check, e.Pos(), t) // TODO(gri) is this the correct position?
164 if !tset.IsMethodSet() {
166 check.softErrorf(e, MisplacedConstraintIface, "cannot use type %s outside a type constraint: interface is (or embeds) comparable", typ)
168 check.softErrorf(e, MisplacedConstraintIface, "cannot use type %s outside a type constraint: interface contains type constraints", typ)
172 }).describef(e, "check var type %s", typ)
175 // definedType is like typ but also accepts a type name def.
176 // If def != nil, e is the type specification for the type named def, declared
177 // in a type declaration, and def.typ.underlying will be set to the type of e
178 // before any components of e are type-checked.
179 func (check *Checker) definedType(e ast.Expr, def *TypeName) Type {
180 typ := check.typInternal(e, def)
183 check.errorf(e, WrongTypeArgCount, "cannot use generic type %s without instantiation", typ)
186 check.recordTypeAndValue(e, typexpr, typ, nil)
190 // genericType is like typ but the type must be an (uninstantiated) generic
191 // type. If cause is non-nil and the type expression was a valid type but not
192 // generic, cause will be populated with a message describing the error.
193 func (check *Checker) genericType(e ast.Expr, cause *string) Type {
194 typ := check.typInternal(e, nil)
196 if isValid(typ) && !isGeneric(typ) {
198 *cause = check.sprintf("%s is not a generic type", typ)
202 // TODO(gri) what is the correct call below?
203 check.recordTypeAndValue(e, typexpr, typ, nil)
207 // goTypeName returns the Go type name for typ and
208 // removes any occurrences of "types." from that name.
209 func goTypeName(typ Type) string {
210 return strings.ReplaceAll(fmt.Sprintf("%T", typ), "types.", "")
213 // typInternal drives type checking of types.
214 // Must only be called by definedType or genericType.
215 func (check *Checker) typInternal(e0 ast.Expr, def *TypeName) (T Type) {
216 if check.conf._Trace {
217 check.trace(e0.Pos(), "-- type %s", e0)
223 // Calling under() here may lead to endless instantiations.
224 // Test case: type T[P any] *T[P]
225 under = safeUnderlying(T)
228 check.trace(e0.Pos(), "=> %s // %s", T, goTypeName(T))
230 check.trace(e0.Pos(), "=> %s (under = %s) // %s", T, under, goTypeName(T))
235 switch e := e0.(type) {
237 // ignore - error reported before
241 check.ident(&x, e, def, true)
249 // ignore - error reported before
251 check.errorf(&x, NotAType, "%s used as type", &x)
253 check.errorf(&x, NotAType, "%s is not a type", &x)
256 case *ast.SelectorExpr:
258 check.selector(&x, e, def, true)
266 // ignore - error reported before
268 check.errorf(&x, NotAType, "%s used as type", &x)
270 check.errorf(&x, NotAType, "%s is not a type", &x)
273 case *ast.IndexExpr, *ast.IndexListExpr:
274 ix := typeparams.UnpackIndexExpr(e)
275 check.verifyVersionf(inNode(e, ix.Lbrack), go1_18, "type instantiation")
276 return check.instantiatedType(ix, def)
279 // Generic types must be instantiated before they can be used in any form.
280 // Consequently, generic types cannot be parenthesized.
281 return check.definedType(e.X, def)
287 typ.elem = check.varType(e.Elt)
293 // Provide a more specific error when encountering a [...] array
294 // rather than leaving it to the handling of the ... expression.
295 if _, ok := e.Len.(*ast.Ellipsis); ok {
296 check.error(e.Len, BadDotDotDotSyntax, "invalid use of [...] array (outside a composite literal)")
299 typ.len = check.arrayLength(e.Len)
301 typ.elem = check.varType(e.Elt)
305 // report error if we encountered [...]
308 // dots are handled explicitly where they are legal
309 // (array composite literals and parameter lists)
310 check.error(e, InvalidDotDotDot, "invalid use of '...'")
313 case *ast.StructType:
316 check.structType(typ, e)
321 typ.base = Typ[Invalid] // avoid nil base in invalid recursive type declaration
323 typ.base = check.varType(e.X)
327 typ := new(Signature)
329 check.funcType(typ, nil, e)
332 case *ast.InterfaceType:
333 typ := check.newInterface()
335 check.interfaceType(typ, e, def)
342 typ.key = check.varType(e.Key)
343 typ.elem = check.varType(e.Value)
345 // spec: "The comparison operators == and != must be fully defined
346 // for operands of the key type; thus the key type must not be a
347 // function, map, or slice."
349 // Delay this check because it requires fully setup types;
350 // it is safe to continue in any case (was go.dev/issue/6667).
352 if !Comparable(typ.key) {
354 if isTypeParam(typ.key) {
355 why = " (missing comparable constraint)"
357 check.errorf(e.Key, IncomparableMapKey, "invalid map key type %s%s", typ.key, why)
359 }).describef(e.Key, "check map key %s", typ.key)
369 case ast.SEND | ast.RECV:
376 check.errorf(e, InvalidSyntaxTree, "unknown channel direction %d", e.Dir)
381 typ.elem = check.varType(e.Value)
385 check.errorf(e0, NotAType, "%s is not a type", e0)
394 func setDefType(def *TypeName, typ Type) {
396 switch t := def.typ.(type) {
398 // t.fromRHS should always be set, either to an invalid type
399 // in the beginning, or to typ in certain cyclic declarations.
400 if t.fromRHS != Typ[Invalid] && t.fromRHS != typ {
401 panic(sprintf(nil, nil, true, "t.fromRHS = %s, typ = %s\n", t.fromRHS, typ))
405 assert(t == Typ[Invalid])
409 panic(fmt.Sprintf("unexpected type %T", t))
414 func (check *Checker) instantiatedType(ix *typeparams.IndexExpr, def *TypeName) (res Type) {
415 if check.conf._Trace {
416 check.trace(ix.Pos(), "-- instantiating type %s with %s", ix.X, ix.Indices)
420 // Don't format the underlying here. It will always be nil.
421 check.trace(ix.Pos(), "=> %s", res)
426 gtyp := check.genericType(ix.X, &cause)
428 check.errorf(ix.Orig, NotAGenericType, invalidOp+"%s (%s)", ix.Orig, cause)
431 return gtyp // error already reported
434 orig := asNamed(gtyp)
436 panic(fmt.Sprintf("%v: cannot instantiate %v", ix.Pos(), gtyp))
439 // evaluate arguments
440 targs := check.typeList(ix.Indices)
442 setDefType(def, Typ[Invalid]) // avoid errors later due to lazy instantiation
446 // create the instance
447 inst := asNamed(check.instance(ix.Pos(), orig, targs, nil, check.context()))
448 setDefType(def, inst)
450 // orig.tparams may not be set up, so we need to do expansion later.
452 // This is an instance from the source, not from recursive substitution,
453 // and so it must be resolved during type-checking so that we can report
455 check.recordInstance(ix.Orig, inst.TypeArgs().list(), inst)
457 if check.validateTArgLen(ix.Pos(), inst.TypeParams().Len(), inst.TypeArgs().Len()) {
458 if i, err := check.verify(ix.Pos(), inst.TypeParams().list(), inst.TypeArgs().list(), check.context()); err != nil {
459 // best position for error reporting
461 if i < len(ix.Indices) {
462 pos = ix.Indices[i].Pos()
464 check.softErrorf(atPos(pos), InvalidTypeArg, err.Error())
466 check.mono.recordInstance(check.pkg, ix.Pos(), inst.TypeParams().list(), inst.TypeArgs().list(), ix.Indices)
470 // TODO(rfindley): remove this call: we don't need to call validType here,
471 // as cycles can only occur for types used inside a Named type declaration,
472 // and so it suffices to call validType from declared types.
473 check.validType(inst)
474 }).describef(ix, "resolve instance %s", inst)
479 // arrayLength type-checks the array length expression e
480 // and returns the constant length >= 0, or a value < 0
481 // to indicate an error (and thus an unknown length).
482 func (check *Checker) arrayLength(e ast.Expr) int64 {
483 // If e is an identifier, the array declaration might be an
484 // attempt at a parameterized type declaration with missing
485 // constraint. Provide an error message that mentions array
487 if name, _ := e.(*ast.Ident); name != nil {
488 obj := check.lookup(name.Name)
490 check.errorf(name, InvalidArrayLen, "undefined array length %s or missing type constraint", name.Name)
493 if _, ok := obj.(*Const); !ok {
494 check.errorf(name, InvalidArrayLen, "invalid array length %s", name.Name)
500 check.expr(nil, &x, e)
501 if x.mode != constant_ {
502 if x.mode != invalid {
503 check.errorf(&x, InvalidArrayLen, "array length %s must be constant", &x)
508 if isUntyped(x.typ) || isInteger(x.typ) {
509 if val := constant.ToInt(x.val); val.Kind() == constant.Int {
510 if representableConst(val, check, Typ[Int], nil) {
511 if n, ok := constant.Int64Val(val); ok && n >= 0 {
519 if isInteger(x.typ) {
520 msg = "invalid array length %s"
522 msg = "array length %s must be integer"
524 check.errorf(&x, InvalidArrayLen, msg, &x)
528 // typeList provides the list of types corresponding to the incoming expression list.
529 // If an error occurred, the result is nil, but all list elements were type-checked.
530 func (check *Checker) typeList(list []ast.Expr) []Type {
531 res := make([]Type, len(list)) // res != nil even if len(list) == 0
532 for i, x := range list {
533 t := check.varType(x)