1 // Copyright 2014 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.
8 "cmd/compile/internal/syntax"
13 func (err *error_) recordAltDecl(obj Object) {
14 if pos := obj.Pos(); pos.IsKnown() {
15 // We use "other" rather than "previous" here because
16 // the first declaration seen may not be textually
17 // earlier in the source.
18 err.errorf(pos, "other declaration of %s", obj.Name())
22 func (check *Checker) declare(scope *Scope, id *syntax.Name, obj Object, pos syntax.Pos) {
23 // spec: "The blank identifier, represented by the underscore
24 // character _, may be used in a declaration like any other
25 // identifier but the declaration does not introduce a new
27 if obj.Name() != "_" {
28 if alt := scope.Insert(obj); alt != nil {
30 err.errorf(obj, "%s redeclared in this block", obj.Name())
31 err.recordAltDecl(alt)
38 check.recordDef(id, obj)
42 // pathString returns a string of the form a->b-> ... ->g for a path [a, b, ... g].
43 func pathString(path []Object) string {
45 for i, p := range path {
54 // objDecl type-checks the declaration of obj in its respective (file) context.
55 // For the meaning of def, see Checker.definedType, in typexpr.go.
56 func (check *Checker) objDecl(obj Object, def *Named) {
57 if check.conf.Trace && obj.Type() == nil {
58 if check.indent == 0 {
59 fmt.Println() // empty line between top-level objects for readability
61 check.trace(obj.Pos(), "-- checking %s (%s, objPath = %s)", obj, obj.color(), pathString(check.objPath))
65 check.trace(obj.Pos(), "=> %s (%s)", obj, obj.color())
69 // Funcs with m.instRecv set have not yet be completed. Complete them now
70 // so that they have a type when objDecl exits.
71 if m, _ := obj.(*Func); m != nil && m.instRecv != nil {
72 check.completeMethod(check.conf.Context, m)
75 // Checking the declaration of obj means inferring its type
76 // (and possibly its value, for constants).
77 // An object's type (and thus the object) may be in one of
78 // three states which are expressed by colors:
80 // - an object whose type is not yet known is painted white (initial color)
81 // - an object whose type is in the process of being inferred is painted grey
82 // - an object whose type is fully inferred is painted black
84 // During type inference, an object's color changes from white to grey
85 // to black (pre-declared objects are painted black from the start).
86 // A black object (i.e., its type) can only depend on (refer to) other black
87 // ones. White and grey objects may depend on white and black objects.
88 // A dependency on a grey object indicates a cycle which may or may not be
91 // When objects turn grey, they are pushed on the object path (a stack);
92 // they are popped again when they turn black. Thus, if a grey object (a
93 // cycle) is encountered, it is on the object path, and all the objects
94 // it depends on are the remaining objects on that path. Color encoding
95 // is such that the color value of a grey object indicates the index of
96 // that object in the object path.
98 // During type-checking, white objects may be assigned a type without
99 // traversing through objDecl; e.g., when initializing constants and
100 // variables. Update the colors of those objects here (rather than
101 // everywhere where we set the type) to satisfy the color invariants.
102 if obj.color() == white && obj.Type() != nil {
109 assert(obj.Type() == nil)
110 // All color values other than white and black are considered grey.
111 // Because black and white are < grey, all values >= grey are grey.
112 // Use those values to encode the object's index into the object path.
113 obj.setColor(grey + color(check.push(obj)))
115 check.pop().setColor(black)
119 assert(obj.Type() != nil)
123 // Color values other than white or black are considered grey.
128 // In the existing code, this is marked by a non-nil type
129 // for the object except for constants and variables whose
130 // type may be non-nil (known), or nil if it depends on the
131 // not-yet known initialization value.
132 // In the former case, set the type to Typ[Invalid] because
133 // we have an initialization cycle. The cycle error will be
134 // reported later, when determining initialization order.
135 // TODO(gri) Report cycle here and simplify initialization
137 switch obj := obj.(type) {
139 if check.cycle(obj) || obj.typ == nil {
140 obj.typ = Typ[Invalid]
144 if check.cycle(obj) || obj.typ == nil {
145 obj.typ = Typ[Invalid]
149 if check.cycle(obj) {
151 // (without this, calling underlying()
152 // below may lead to an endless loop
153 // if we have a cycle for a defined
155 obj.typ = Typ[Invalid]
159 if check.cycle(obj) {
160 // Don't set obj.typ to Typ[Invalid] here
161 // because plenty of code type-asserts that
162 // functions have a *Signature type. Grey
163 // functions have their type set to an empty
164 // signature which makes it impossible to
165 // initialize a variable with the function.
171 assert(obj.Type() != nil)
175 d := check.objMap[obj]
177 check.dump("%v: %s should have been declared", obj.Pos(), obj)
181 // save/restore current context and setup object context
182 defer func(ctxt context) {
185 check.context = context{
189 // Const and var declarations must not have initialization
190 // cycles. We track them by remembering the current declaration
191 // in check.decl. Initialization expressions depending on other
192 // consts, vars, or functions, add dependencies to the current
194 switch obj := obj.(type) {
196 check.decl = d // new package-level const decl
197 check.constDecl(obj, d.vtyp, d.init, d.inherited)
199 check.decl = d // new package-level var decl
200 check.varDecl(obj, d.lhs, d.vtyp, d.init)
202 // invalid recursive types are detected via path
203 check.typeDecl(obj, d.tdecl, def)
204 check.collectMethods(obj) // methods can only be added to top-level types
206 // functions may be recursive - no need to track dependencies
207 check.funcDecl(obj, d)
213 // cycle checks if the cycle starting with obj is valid and
214 // reports an error if it is not.
215 func (check *Checker) cycle(obj Object) (isCycle bool) {
216 // The object map contains the package scope objects and the non-interface methods.
218 info := check.objMap[obj]
219 inObjMap := info != nil && (info.fdecl == nil || info.fdecl.Recv == nil) // exclude methods
220 isPkgObj := obj.Parent() == check.pkg.scope
221 if isPkgObj != inObjMap {
222 check.dump("%v: inconsistent object map for %s (isPkgObj = %v, inObjMap = %v)", obj.Pos(), obj, isPkgObj, inObjMap)
227 // Count cycle objects.
228 assert(obj.color() >= grey)
229 start := obj.color() - grey // index of obj in objPath
230 cycle := check.objPath[start:]
231 nval := 0 // number of (constant or variable) values in the cycle
232 ndef := 0 // number of type definitions in the cycle
233 for _, obj := range cycle {
234 switch obj := obj.(type) {
238 // Determine if the type name is an alias or not. For
239 // package-level objects, use the object map which
240 // provides syntactic information (which doesn't rely
241 // on the order in which the objects are set up). For
242 // local objects, we can rely on the order, so use
243 // the object's predicate.
244 // TODO(gri) It would be less fragile to always access
245 // the syntactic information. We should consider storing
246 // this information explicitly in the object.
248 if d := check.objMap[obj]; d != nil {
249 alias = d.tdecl.Alias // package-level object
251 alias = obj.IsAlias() // function local object
263 if check.conf.Trace {
264 check.trace(obj.Pos(), "## cycle detected: objPath = %s->%s (len = %d)", pathString(cycle), obj.Name(), len(cycle))
265 check.trace(obj.Pos(), "## cycle contains: %d values, %d type definitions", nval, ndef)
268 check.trace(obj.Pos(), "=> error: cycle is invalid")
273 // A cycle involving only constants and variables is invalid but we
274 // ignore them here because they are reported via the initialization
276 if nval == len(cycle) {
280 // A cycle involving only types (and possibly functions) must have at least
281 // one type definition to be permitted: If there is no type definition, we
282 // have a sequence of alias type names which will expand ad infinitum.
283 if nval == 0 && ndef > 0 {
284 return false // cycle is permitted
287 check.cycleError(cycle)
294 // validType verifies that the given type does not "expand" infinitely
295 // producing a cycle in the type graph. Cycles are detected by marking
297 // (Cycles involving alias types, as in "type A = [10]A" are detected
298 // earlier, via the objDecl cycle detection mechanism.)
299 func (check *Checker) validType(typ Type, path []Object) typeInfo {
301 unknown typeInfo = iota
307 switch t := typ.(type) {
309 return check.validType(t.elem, path)
312 for _, f := range t.fields {
313 if check.validType(f.typ, path) == invalid {
319 for _, t := range t.terms {
320 if check.validType(t.typ, path) == invalid {
326 for _, etyp := range t.embeddeds {
327 if check.validType(etyp, path) == invalid {
333 // If t is parameterized, we should be considering the instantiated (expanded)
334 // form of t, but in general we can't with this algorithm: if t is an invalid
335 // type it may be so because it infinitely expands through a type parameter.
336 // Instantiating such a type would lead to an infinite sequence of instantiations.
337 // In general, we need "type flow analysis" to recognize those cases.
338 // Example: type A[T any] struct{ x A[*T] } (issue #48951)
339 // In this algorithm we always only consider the orginal, uninstantiated type.
340 // This won't recognize some invalid cases with parameterized types, but it
344 // don't touch the type if it is from a different package or the Universe scope
345 // (doing so would lead to a race condition - was issue #35049)
346 if t.obj.pkg != check.pkg {
350 // don't report a 2nd error if we already know the type is invalid
351 // (e.g., if a cycle was detected earlier, via under).
352 if t.underlying == Typ[Invalid] {
360 t.info = check.validType(t.fromRHS, append(path, t.obj)) // only types of current package added to path
363 for i, tn := range path {
364 if t.obj.pkg != check.pkg {
365 panic("type cycle via package-external type")
368 check.cycleError(path[i:])
370 t.underlying = Typ[Invalid]
374 panic("cycle start not found")
382 // cycleError reports a declaration cycle starting with
383 // the object in cycle that is "first" in the source.
384 func (check *Checker) cycleError(cycle []Object) {
385 // TODO(gri) Should we start with the last (rather than the first) object in the cycle
386 // since that is the earliest point in the source where we start seeing the
387 // cycle? That would be more consistent with other error messages.
388 i := firstInSrc(cycle)
391 if check.conf.CompilerErrorMessages {
392 err.errorf(obj, "invalid recursive type %s", obj.Name())
394 err.errorf(obj, "illegal cycle in declaration of %s", obj.Name())
397 err.errorf(obj, "%s refers to", obj.Name())
404 err.errorf(obj, "%s", obj.Name())
408 // firstInSrc reports the index of the object with the "smallest"
409 // source position in path. path must not be empty.
410 func firstInSrc(path []Object) int {
411 fst, pos := 0, path[0].Pos()
412 for i, t := range path[1:] {
413 if t.Pos().Cmp(pos) < 0 {
414 fst, pos = i+1, t.Pos()
420 func (check *Checker) constDecl(obj *Const, typ, init syntax.Expr, inherited bool) {
421 assert(obj.typ == nil)
423 // use the correct value of iota and errpos
424 defer func(iota constant.Value, errpos syntax.Pos) {
426 check.errpos = errpos
427 }(check.iota, check.errpos)
431 // provide valid constant value under all circumstances
432 obj.val = constant.MakeUnknown()
434 // determine type, if any
438 // don't report an error if the type is an invalid C (defined) type
440 if under(t) != Typ[Invalid] {
441 check.errorf(typ, "invalid constant type %s", t)
443 obj.typ = Typ[Invalid]
449 // check initialization
453 // The initialization expression is inherited from a previous
454 // constant declaration, and (error) positions refer to that
455 // expression and not the current constant declaration. Use
456 // the constant identifier position for any errors during
457 // init expression evaluation since that is all we have
458 // (see issues #42991, #42992).
459 check.errpos = obj.pos
463 check.initConst(obj, &x)
466 func (check *Checker) varDecl(obj *Var, lhs []*Var, typ, init syntax.Expr) {
467 assert(obj.typ == nil)
469 // If we have undefined variable types due to errors,
470 // mark variables as used to avoid follow-on errors.
471 // Matches compiler behavior.
473 if obj.typ == Typ[Invalid] {
476 for _, lhs := range lhs {
477 if lhs.typ == Typ[Invalid] {
483 // determine type, if any
485 obj.typ = check.varType(typ)
486 // We cannot spread the type to all lhs variables if there
487 // are more than one since that would mark them as checked
488 // (see Checker.objDecl) and the assignment of init exprs,
489 // if any, would not be checked.
491 // TODO(gri) If we have no init expr, we should distribute
492 // a given type otherwise we need to re-evalate the type
493 // expr for each lhs variable, leading to duplicate work.
496 // check initialization
499 // error reported before by arityMatch
500 obj.typ = Typ[Invalid]
505 if lhs == nil || len(lhs) == 1 {
506 assert(lhs == nil || lhs[0] == obj)
509 check.initVar(obj, &x, "variable declaration")
514 // obj must be one of lhs
516 for _, lhs := range lhs {
523 panic("inconsistent lhs")
527 // We have multiple variables on the lhs and one init expr.
528 // Make sure all variables have been given the same type if
529 // one was specified, otherwise they assume the type of the
530 // init expression values (was issue #15755).
532 for _, lhs := range lhs {
537 check.initVars(lhs, []syntax.Expr{init}, nopos)
540 // isImportedConstraint reports whether typ is an imported type constraint.
541 func (check *Checker) isImportedConstraint(typ Type) bool {
542 named, _ := typ.(*Named)
543 if named == nil || named.obj.pkg == check.pkg || named.obj.pkg == nil {
546 u, _ := named.under().(*Interface)
547 return u != nil && !u.IsMethodSet()
550 func (check *Checker) typeDecl(obj *TypeName, tdecl *syntax.TypeDecl, def *Named) {
551 assert(obj.typ == nil)
555 check.validType(obj.typ, nil)
556 // If typ is local, an error was already reported where typ is specified/defined.
557 if check.isImportedConstraint(rhs) && !check.allowVersion(check.pkg, 1, 18) {
558 check.errorf(tdecl.Type.Pos(), "using type constraint %s requires go1.18 or later", rhs)
560 }).describef(obj, "validType(%s)", obj.Name())
563 if alias && tdecl.TParamList != nil {
564 // The parser will ensure this but we may still get an invalid AST.
565 // Complain and continue as regular type definition.
566 check.error(tdecl, "generic type cannot be alias")
572 if !check.allowVersion(check.pkg, 1, 9) {
573 if check.conf.CompilerErrorMessages {
574 check.error(tdecl, "type aliases only supported as of -lang=go1.9")
576 check.error(tdecl, "type aliases requires go1.9 or later")
580 obj.typ = Typ[Invalid]
581 rhs = check.varType(tdecl.Type)
586 // type definition or generic type declaration
587 named := check.newNamed(obj, nil, nil, nil, nil)
588 def.setUnderlying(named)
590 if tdecl.TParamList != nil {
591 check.openScope(tdecl, "type parameters")
592 defer check.closeScope()
593 check.collectTypeParams(&named.tparams, tdecl.TParamList)
596 // determine underlying type of named
597 rhs = check.definedType(tdecl.Type, named)
600 // The underlying type of named may be itself a named type that is
609 // The type of C is the (named) type of A which is incomplete,
610 // and which has as its underlying type the named type B.
611 // Determine the (final, unnamed) underlying type by resolving
612 // any forward chain.
613 // TODO(gri) Investigate if we can just use named.fromRHS here
614 // and rely on lazy computation of the underlying type.
615 named.underlying = under(named)
617 // If the RHS is a type parameter, it must be from this type declaration.
618 if tpar, _ := named.underlying.(*TypeParam); tpar != nil && tparamIndex(named.TypeParams().list(), tpar) < 0 {
619 check.errorf(tdecl.Type, "cannot use function type parameter %s as RHS in type declaration", tpar)
620 named.underlying = Typ[Invalid]
624 func (check *Checker) collectTypeParams(dst **TypeParamList, list []*syntax.Field) {
625 tparams := make([]*TypeParam, len(list))
627 // Declare type parameters up-front.
628 // The scope of type parameters starts at the beginning of the type parameter
629 // list (so we can have mutually recursive parameterized type bounds).
630 for i, f := range list {
631 tparams[i] = check.declareTypeParam(f.Name)
634 // Set the type parameters before collecting the type constraints because
635 // the parameterized type may be used by the constraints (issue #47887).
636 // Example: type T[P T[P]] interface{}
637 *dst = bindTParams(tparams)
639 // Keep track of bounds for later validation.
643 for i, f := range list {
644 // Optimization: Re-use the previous type bound if it hasn't changed.
645 // This also preserves the grouped output of type parameter lists
646 // when printing type strings.
647 if i == 0 || f.Type != list[i-1].Type {
648 bound = check.bound(f.Type)
649 bounds = append(bounds, bound)
650 posers = append(posers, f.Type)
652 tparams[i].bound = bound
656 for i, bound := range bounds {
657 if _, ok := under(bound).(*TypeParam); ok {
658 check.error(posers[i], "cannot use a type parameter as constraint")
661 for _, tpar := range tparams {
662 tpar.iface() // compute type set
667 func (check *Checker) bound(x syntax.Expr) Type {
668 // A type set literal of the form ~T and A|B may only appear as constraint;
669 // embed it in an implicit interface so that only interface type-checking
670 // needs to take care of such type expressions.
671 if op, _ := x.(*syntax.Operation); op != nil && (op.Op == syntax.Tilde || op.Op == syntax.Or) {
672 t := check.typ(&syntax.InterfaceType{MethodList: []*syntax.Field{{Type: x}}})
673 // mark t as implicit interface if all went well
674 if t, _ := t.(*Interface); t != nil {
682 func (check *Checker) declareTypeParam(name *syntax.Name) *TypeParam {
683 // Use Typ[Invalid] for the type constraint to ensure that a type
684 // is present even if the actual constraint has not been assigned
686 // TODO(gri) Need to systematically review all uses of type parameter
687 // constraints to make sure we don't rely on them if they
688 // are not properly set yet.
689 tname := NewTypeName(name.Pos(), check.pkg, name.Value, nil)
690 tpar := check.newTypeParam(tname, Typ[Invalid]) // assigns type to tname as a side-effect
691 check.declare(check.scope, name, tname, check.scope.pos) // TODO(gri) check scope position
695 func (check *Checker) collectMethods(obj *TypeName) {
696 // get associated methods
697 // (Checker.collectObjects only collects methods with non-blank names;
698 // Checker.resolveBaseTypeName ensures that obj is not an alias name
699 // if it has attached methods.)
700 methods := check.methods[obj]
704 delete(check.methods, obj)
705 assert(!check.objMap[obj].tdecl.Alias) // don't use TypeName.IsAlias (requires fully set up object)
707 // use an objset to check for name conflicts
710 // spec: "If the base type is a struct type, the non-blank method
711 // and field names must be distinct."
712 base := asNamed(obj.typ) // shouldn't fail but be conservative
714 u := safeUnderlying(base) // base should be expanded, but use safeUnderlying to be conservative
715 if t, _ := u.(*Struct); t != nil {
716 for _, fld := range t.fields {
718 assert(mset.insert(fld) == nil)
723 // Checker.Files may be called multiple times; additional package files
724 // may add methods to already type-checked types. Add pre-existing methods
725 // so that we can detect redeclarations.
726 for _, m := range base.methods {
727 assert(m.name != "_")
728 assert(mset.insert(m) == nil)
733 for _, m := range methods {
734 // spec: "For a base type, the non-blank names of methods bound
735 // to it must be unique."
736 assert(m.name != "_")
737 if alt := mset.insert(m); alt != nil {
741 err.errorf(m.pos, "field and method with the same name %s", m.name)
743 if check.conf.CompilerErrorMessages {
744 err.errorf(m.pos, "%s.%s redeclared in this block", obj.Name(), m.name)
746 err.errorf(m.pos, "method %s already declared for %s", m.name, obj)
751 err.recordAltDecl(alt)
757 base.resolve(nil) // TODO(mdempsky): Probably unnecessary.
758 base.methods = append(base.methods, m)
763 func (check *Checker) funcDecl(obj *Func, decl *declInfo) {
764 assert(obj.typ == nil)
766 // func declarations cannot use iota
767 assert(check.iota == nil)
769 sig := new(Signature)
770 obj.typ = sig // guard against cycles
772 // Avoid cycle error when referring to method while type-checking the signature.
773 // This avoids a nuisance in the best case (non-parameterized receiver type) and
774 // since the method is not a type, we get an error. If we have a parameterized
775 // receiver type, instantiating the receiver type leads to the instantiation of
776 // its methods, and we don't want a cycle error in that case.
777 // TODO(gri) review if this is correct and/or whether we still need this?
781 check.funcType(sig, fdecl.Recv, fdecl.TParamList, fdecl.Type)
784 if len(fdecl.TParamList) > 0 && fdecl.Body == nil {
785 check.softErrorf(fdecl, "parameterized function is missing function body")
788 // function body must be type-checked after global declarations
789 // (functions implemented elsewhere have no body)
790 if !check.conf.IgnoreFuncBodies && fdecl.Body != nil {
792 check.funcBody(decl, obj.name, sig, fdecl.Body, nil)
797 func (check *Checker) declStmt(list []syntax.Decl) {
800 first := -1 // index of first ConstDecl in the current group, or -1
801 var last *syntax.ConstDecl // last ConstDecl with init expressions, or nil
802 for index, decl := range list {
803 if _, ok := decl.(*syntax.ConstDecl); !ok {
804 first = -1 // we're not in a constant declaration
807 switch s := decl.(type) {
808 case *syntax.ConstDecl:
809 top := len(check.delayed)
811 // iota is the index of the current constDecl within the group
812 if first < 0 || list[index-1].(*syntax.ConstDecl).Group != s.Group {
816 iota := constant.MakeInt64(int64(index - first))
818 // determine which initialization expressions to use
821 case s.Type != nil || s.Values != nil:
825 last = new(syntax.ConstDecl) // make sure last exists
829 // declare all constants
830 lhs := make([]*Const, len(s.NameList))
831 values := unpackExpr(last.Values)
832 for i, name := range s.NameList {
833 obj := NewConst(name.Pos(), pkg, name.Value, nil, iota)
841 check.constDecl(obj, last.Type, init, inherited)
844 // Constants must always have init values.
845 check.arity(s.Pos(), s.NameList, values, true, inherited)
847 // process function literals in init expressions before scope changes
848 check.processDelayed(top)
850 // spec: "The scope of a constant or variable identifier declared
851 // inside a function begins at the end of the ConstSpec or VarSpec
852 // (ShortVarDecl for short variable declarations) and ends at the
853 // end of the innermost containing block."
854 scopePos := syntax.EndPos(s)
855 for i, name := range s.NameList {
856 check.declare(check.scope, name, lhs[i], scopePos)
859 case *syntax.VarDecl:
860 top := len(check.delayed)
862 lhs0 := make([]*Var, len(s.NameList))
863 for i, name := range s.NameList {
864 lhs0[i] = NewVar(name.Pos(), pkg, name.Value, nil)
867 // initialize all variables
868 values := unpackExpr(s.Values)
869 for i, obj := range lhs0 {
873 case len(s.NameList):
877 // rhs is expected to be a multi-valued expression
885 check.varDecl(obj, lhs, s.Type, init)
886 if len(values) == 1 {
887 // If we have a single lhs variable we are done either way.
888 // If we have a single rhs expression, it must be a multi-
889 // valued expression, in which case handling the first lhs
890 // variable will cause all lhs variables to have a type
891 // assigned, and we are done as well.
893 for _, obj := range lhs0 {
894 assert(obj.typ != nil)
901 // If we have no type, we must have values.
902 if s.Type == nil || values != nil {
903 check.arity(s.Pos(), s.NameList, values, false, false)
906 // process function literals in init expressions before scope changes
907 check.processDelayed(top)
909 // declare all variables
910 // (only at this point are the variable scopes (parents) set)
911 scopePos := syntax.EndPos(s) // see constant declarations
912 for i, name := range s.NameList {
913 // see constant declarations
914 check.declare(check.scope, name, lhs0[i], scopePos)
917 case *syntax.TypeDecl:
918 obj := NewTypeName(s.Name.Pos(), pkg, s.Name.Value, nil)
919 // spec: "The scope of a type identifier declared inside a function
920 // begins at the identifier in the TypeSpec and ends at the end of
921 // the innermost containing block."
922 scopePos := s.Name.Pos()
923 check.declare(check.scope, s.Name, obj, scopePos)
924 // mark and unmark type before calling typeDecl; its type is still nil (see Checker.objDecl)
925 obj.setColor(grey + color(check.push(obj)))
926 check.typeDecl(obj, s, nil)
927 check.pop().setColor(black)
930 check.errorf(s, invalidAST+"unknown syntax.Decl node %T", s)