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.
127 // We have a (possibly invalid) cycle.
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.validCycle(obj) || obj.typ == nil {
140 obj.typ = Typ[Invalid]
144 if !check.validCycle(obj) || obj.typ == nil {
145 obj.typ = Typ[Invalid]
149 if !check.validCycle(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.validCycle(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 // validCycle reports whether the cycle starting with obj is valid and
214 // reports an error if it is not.
215 func (check *Checker) validCycle(obj Object) (valid 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 {
287 check.cycleError(cycle)
293 // validType verifies that the given type does not "expand" infinitely
294 // producing a cycle in the type graph. Cycles are detected by marking
296 // (Cycles involving alias types, as in "type A = [10]A" are detected
297 // earlier, via the objDecl cycle detection mechanism.)
298 func (check *Checker) validType(typ Type, path []Object) typeInfo {
300 unknown typeInfo = iota
306 switch t := typ.(type) {
308 return check.validType(t.elem, path)
311 for _, f := range t.fields {
312 if check.validType(f.typ, path) == invalid {
318 for _, t := range t.terms {
319 if check.validType(t.typ, path) == invalid {
325 for _, etyp := range t.embeddeds {
326 if check.validType(etyp, path) == invalid {
332 // If t is parameterized, we should be considering the instantiated (expanded)
333 // form of t, but in general we can't with this algorithm: if t is an invalid
334 // type it may be so because it infinitely expands through a type parameter.
335 // Instantiating such a type would lead to an infinite sequence of instantiations.
336 // In general, we need "type flow analysis" to recognize those cases.
337 // Example: type A[T any] struct{ x A[*T] } (issue #48951)
338 // In this algorithm we always only consider the orginal, uninstantiated type.
339 // This won't recognize some invalid cases with parameterized types, but it
343 // don't touch the type if it is from a different package or the Universe scope
344 // (doing so would lead to a race condition - was issue #35049)
345 if t.obj.pkg != check.pkg {
349 // don't report a 2nd error if we already know the type is invalid
350 // (e.g., if a cycle was detected earlier, via under).
351 if t.underlying == Typ[Invalid] {
359 t.info = check.validType(t.fromRHS, append(path, t.obj)) // only types of current package added to path
362 for i, tn := range path {
363 if t.obj.pkg != check.pkg {
364 panic("type cycle via package-external type")
367 check.cycleError(path[i:])
369 t.underlying = Typ[Invalid]
373 panic("cycle start not found")
381 // cycleError reports a declaration cycle starting with
382 // the object in cycle that is "first" in the source.
383 func (check *Checker) cycleError(cycle []Object) {
384 // TODO(gri) Should we start with the last (rather than the first) object in the cycle
385 // since that is the earliest point in the source where we start seeing the
386 // cycle? That would be more consistent with other error messages.
387 i := firstInSrc(cycle)
390 if check.conf.CompilerErrorMessages {
391 err.errorf(obj, "invalid recursive type %s", obj.Name())
393 err.errorf(obj, "illegal cycle in declaration of %s", obj.Name())
396 err.errorf(obj, "%s refers to", obj.Name())
403 err.errorf(obj, "%s", obj.Name())
407 // firstInSrc reports the index of the object with the "smallest"
408 // source position in path. path must not be empty.
409 func firstInSrc(path []Object) int {
410 fst, pos := 0, path[0].Pos()
411 for i, t := range path[1:] {
412 if t.Pos().Cmp(pos) < 0 {
413 fst, pos = i+1, t.Pos()
419 func (check *Checker) constDecl(obj *Const, typ, init syntax.Expr, inherited bool) {
420 assert(obj.typ == nil)
422 // use the correct value of iota and errpos
423 defer func(iota constant.Value, errpos syntax.Pos) {
425 check.errpos = errpos
426 }(check.iota, check.errpos)
430 // provide valid constant value under all circumstances
431 obj.val = constant.MakeUnknown()
433 // determine type, if any
437 // don't report an error if the type is an invalid C (defined) type
439 if under(t) != Typ[Invalid] {
440 check.errorf(typ, "invalid constant type %s", t)
442 obj.typ = Typ[Invalid]
448 // check initialization
452 // The initialization expression is inherited from a previous
453 // constant declaration, and (error) positions refer to that
454 // expression and not the current constant declaration. Use
455 // the constant identifier position for any errors during
456 // init expression evaluation since that is all we have
457 // (see issues #42991, #42992).
458 check.errpos = obj.pos
462 check.initConst(obj, &x)
465 func (check *Checker) varDecl(obj *Var, lhs []*Var, typ, init syntax.Expr) {
466 assert(obj.typ == nil)
468 // If we have undefined variable types due to errors,
469 // mark variables as used to avoid follow-on errors.
470 // Matches compiler behavior.
472 if obj.typ == Typ[Invalid] {
475 for _, lhs := range lhs {
476 if lhs.typ == Typ[Invalid] {
482 // determine type, if any
484 obj.typ = check.varType(typ)
485 // We cannot spread the type to all lhs variables if there
486 // are more than one since that would mark them as checked
487 // (see Checker.objDecl) and the assignment of init exprs,
488 // if any, would not be checked.
490 // TODO(gri) If we have no init expr, we should distribute
491 // a given type otherwise we need to re-evalate the type
492 // expr for each lhs variable, leading to duplicate work.
495 // check initialization
498 // error reported before by arityMatch
499 obj.typ = Typ[Invalid]
504 if lhs == nil || len(lhs) == 1 {
505 assert(lhs == nil || lhs[0] == obj)
508 check.initVar(obj, &x, "variable declaration")
513 // obj must be one of lhs
515 for _, lhs := range lhs {
522 panic("inconsistent lhs")
526 // We have multiple variables on the lhs and one init expr.
527 // Make sure all variables have been given the same type if
528 // one was specified, otherwise they assume the type of the
529 // init expression values (was issue #15755).
531 for _, lhs := range lhs {
536 check.initVars(lhs, []syntax.Expr{init}, nopos)
539 // isImportedConstraint reports whether typ is an imported type constraint.
540 func (check *Checker) isImportedConstraint(typ Type) bool {
541 named, _ := typ.(*Named)
542 if named == nil || named.obj.pkg == check.pkg || named.obj.pkg == nil {
545 u, _ := named.under().(*Interface)
546 return u != nil && !u.IsMethodSet()
549 func (check *Checker) typeDecl(obj *TypeName, tdecl *syntax.TypeDecl, def *Named) {
550 assert(obj.typ == nil)
554 check.validType(obj.typ, nil)
555 // If typ is local, an error was already reported where typ is specified/defined.
556 if check.isImportedConstraint(rhs) && !check.allowVersion(check.pkg, 1, 18) {
557 check.versionErrorf(tdecl.Type.Pos(), "go1.18", "using type constraint %s", rhs)
559 }).describef(obj, "validType(%s)", obj.Name())
562 if alias && tdecl.TParamList != nil {
563 // The parser will ensure this but we may still get an invalid AST.
564 // Complain and continue as regular type definition.
565 check.error(tdecl, "generic type cannot be alias")
571 if !check.allowVersion(check.pkg, 1, 9) {
572 check.versionErrorf(tdecl, "go1.9", "type aliases")
575 obj.typ = Typ[Invalid]
576 rhs = check.varType(tdecl.Type)
581 // type definition or generic type declaration
582 named := check.newNamed(obj, nil, nil, nil, nil)
583 def.setUnderlying(named)
585 if tdecl.TParamList != nil {
586 check.openScope(tdecl, "type parameters")
587 defer check.closeScope()
588 check.collectTypeParams(&named.tparams, tdecl.TParamList)
591 // determine underlying type of named
592 rhs = check.definedType(tdecl.Type, named)
596 // If the underlying was not set while type-checking the right-hand side, it
597 // is invalid and an error should have been reported elsewhere.
598 if named.underlying == nil {
599 named.underlying = Typ[Invalid]
602 // Disallow a lone type parameter as the RHS of a type declaration (issue #45639).
603 // We can look directly at named.underlying because even if it is still a *Named
604 // type (underlying not fully resolved yet) it cannot become a type parameter due
605 // to this very restriction.
606 if tpar, _ := named.underlying.(*TypeParam); tpar != nil {
607 check.error(tdecl.Type, "cannot use a type parameter as RHS in type declaration")
608 named.underlying = Typ[Invalid]
612 func (check *Checker) collectTypeParams(dst **TypeParamList, list []*syntax.Field) {
613 tparams := make([]*TypeParam, len(list))
615 // Declare type parameters up-front.
616 // The scope of type parameters starts at the beginning of the type parameter
617 // list (so we can have mutually recursive parameterized type bounds).
618 for i, f := range list {
619 tparams[i] = check.declareTypeParam(f.Name)
622 // Set the type parameters before collecting the type constraints because
623 // the parameterized type may be used by the constraints (issue #47887).
624 // Example: type T[P T[P]] interface{}
625 *dst = bindTParams(tparams)
627 // Keep track of bounds for later validation.
631 for i, f := range list {
632 // Optimization: Re-use the previous type bound if it hasn't changed.
633 // This also preserves the grouped output of type parameter lists
634 // when printing type strings.
635 if i == 0 || f.Type != list[i-1].Type {
636 bound = check.bound(f.Type)
637 bounds = append(bounds, bound)
638 posers = append(posers, f.Type)
640 tparams[i].bound = bound
644 for i, bound := range bounds {
645 if _, ok := under(bound).(*TypeParam); ok {
646 check.error(posers[i], "cannot use a type parameter as constraint")
649 for _, tpar := range tparams {
650 tpar.iface() // compute type set
655 func (check *Checker) bound(x syntax.Expr) Type {
656 // A type set literal of the form ~T and A|B may only appear as constraint;
657 // embed it in an implicit interface so that only interface type-checking
658 // needs to take care of such type expressions.
659 if op, _ := x.(*syntax.Operation); op != nil && (op.Op == syntax.Tilde || op.Op == syntax.Or) {
660 t := check.typ(&syntax.InterfaceType{MethodList: []*syntax.Field{{Type: x}}})
661 // mark t as implicit interface if all went well
662 if t, _ := t.(*Interface); t != nil {
670 func (check *Checker) declareTypeParam(name *syntax.Name) *TypeParam {
671 // Use Typ[Invalid] for the type constraint to ensure that a type
672 // is present even if the actual constraint has not been assigned
674 // TODO(gri) Need to systematically review all uses of type parameter
675 // constraints to make sure we don't rely on them if they
676 // are not properly set yet.
677 tname := NewTypeName(name.Pos(), check.pkg, name.Value, nil)
678 tpar := check.newTypeParam(tname, Typ[Invalid]) // assigns type to tname as a side-effect
679 check.declare(check.scope, name, tname, check.scope.pos) // TODO(gri) check scope position
683 func (check *Checker) collectMethods(obj *TypeName) {
684 // get associated methods
685 // (Checker.collectObjects only collects methods with non-blank names;
686 // Checker.resolveBaseTypeName ensures that obj is not an alias name
687 // if it has attached methods.)
688 methods := check.methods[obj]
692 delete(check.methods, obj)
693 assert(!check.objMap[obj].tdecl.Alias) // don't use TypeName.IsAlias (requires fully set up object)
695 // use an objset to check for name conflicts
698 // spec: "If the base type is a struct type, the non-blank method
699 // and field names must be distinct."
700 base := asNamed(obj.typ) // shouldn't fail but be conservative
703 if t, _ := u.(*Struct); t != nil {
704 for _, fld := range t.fields {
706 assert(mset.insert(fld) == nil)
711 // Checker.Files may be called multiple times; additional package files
712 // may add methods to already type-checked types. Add pre-existing methods
713 // so that we can detect redeclarations.
714 for _, m := range base.methods {
715 assert(m.name != "_")
716 assert(mset.insert(m) == nil)
721 for _, m := range methods {
722 // spec: "For a base type, the non-blank names of methods bound
723 // to it must be unique."
724 assert(m.name != "_")
725 if alt := mset.insert(m); alt != nil {
729 err.errorf(m.pos, "field and method with the same name %s", m.name)
731 if check.conf.CompilerErrorMessages {
732 err.errorf(m.pos, "%s.%s redeclared in this block", obj.Name(), m.name)
734 err.errorf(m.pos, "method %s already declared for %s", m.name, obj)
739 err.recordAltDecl(alt)
745 base.resolve(nil) // TODO(mdempsky): Probably unnecessary.
746 base.methods = append(base.methods, m)
751 func (check *Checker) funcDecl(obj *Func, decl *declInfo) {
752 assert(obj.typ == nil)
754 // func declarations cannot use iota
755 assert(check.iota == nil)
757 sig := new(Signature)
758 obj.typ = sig // guard against cycles
760 // Avoid cycle error when referring to method while type-checking the signature.
761 // This avoids a nuisance in the best case (non-parameterized receiver type) and
762 // since the method is not a type, we get an error. If we have a parameterized
763 // receiver type, instantiating the receiver type leads to the instantiation of
764 // its methods, and we don't want a cycle error in that case.
765 // TODO(gri) review if this is correct and/or whether we still need this?
769 check.funcType(sig, fdecl.Recv, fdecl.TParamList, fdecl.Type)
772 if len(fdecl.TParamList) > 0 && fdecl.Body == nil {
773 check.softErrorf(fdecl, "parameterized function is missing function body")
776 // function body must be type-checked after global declarations
777 // (functions implemented elsewhere have no body)
778 if !check.conf.IgnoreFuncBodies && fdecl.Body != nil {
780 check.funcBody(decl, obj.name, sig, fdecl.Body, nil)
785 func (check *Checker) declStmt(list []syntax.Decl) {
788 first := -1 // index of first ConstDecl in the current group, or -1
789 var last *syntax.ConstDecl // last ConstDecl with init expressions, or nil
790 for index, decl := range list {
791 if _, ok := decl.(*syntax.ConstDecl); !ok {
792 first = -1 // we're not in a constant declaration
795 switch s := decl.(type) {
796 case *syntax.ConstDecl:
797 top := len(check.delayed)
799 // iota is the index of the current constDecl within the group
800 if first < 0 || list[index-1].(*syntax.ConstDecl).Group != s.Group {
804 iota := constant.MakeInt64(int64(index - first))
806 // determine which initialization expressions to use
809 case s.Type != nil || s.Values != nil:
813 last = new(syntax.ConstDecl) // make sure last exists
817 // declare all constants
818 lhs := make([]*Const, len(s.NameList))
819 values := unpackExpr(last.Values)
820 for i, name := range s.NameList {
821 obj := NewConst(name.Pos(), pkg, name.Value, nil, iota)
829 check.constDecl(obj, last.Type, init, inherited)
832 // Constants must always have init values.
833 check.arity(s.Pos(), s.NameList, values, true, inherited)
835 // process function literals in init expressions before scope changes
836 check.processDelayed(top)
838 // spec: "The scope of a constant or variable identifier declared
839 // inside a function begins at the end of the ConstSpec or VarSpec
840 // (ShortVarDecl for short variable declarations) and ends at the
841 // end of the innermost containing block."
842 scopePos := syntax.EndPos(s)
843 for i, name := range s.NameList {
844 check.declare(check.scope, name, lhs[i], scopePos)
847 case *syntax.VarDecl:
848 top := len(check.delayed)
850 lhs0 := make([]*Var, len(s.NameList))
851 for i, name := range s.NameList {
852 lhs0[i] = NewVar(name.Pos(), pkg, name.Value, nil)
855 // initialize all variables
856 values := unpackExpr(s.Values)
857 for i, obj := range lhs0 {
861 case len(s.NameList):
865 // rhs is expected to be a multi-valued expression
873 check.varDecl(obj, lhs, s.Type, init)
874 if len(values) == 1 {
875 // If we have a single lhs variable we are done either way.
876 // If we have a single rhs expression, it must be a multi-
877 // valued expression, in which case handling the first lhs
878 // variable will cause all lhs variables to have a type
879 // assigned, and we are done as well.
881 for _, obj := range lhs0 {
882 assert(obj.typ != nil)
889 // If we have no type, we must have values.
890 if s.Type == nil || values != nil {
891 check.arity(s.Pos(), s.NameList, values, false, false)
894 // process function literals in init expressions before scope changes
895 check.processDelayed(top)
897 // declare all variables
898 // (only at this point are the variable scopes (parents) set)
899 scopePos := syntax.EndPos(s) // see constant declarations
900 for i, name := range s.NameList {
901 // see constant declarations
902 check.declare(check.scope, name, lhs0[i], scopePos)
905 case *syntax.TypeDecl:
906 obj := NewTypeName(s.Name.Pos(), pkg, s.Name.Value, nil)
907 // spec: "The scope of a type identifier declared inside a function
908 // begins at the identifier in the TypeSpec and ends at the end of
909 // the innermost containing block."
910 scopePos := s.Name.Pos()
911 check.declare(check.scope, s.Name, obj, scopePos)
912 // mark and unmark type before calling typeDecl; its type is still nil (see Checker.objDecl)
913 obj.setColor(grey + color(check.push(obj)))
914 check.typeDecl(obj, s, nil)
915 check.pop().setColor(black)
918 check.errorf(s, invalidAST+"unknown syntax.Decl node %T", s)