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) environment.
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 // Checking the declaration of obj means inferring its type
70 // (and possibly its value, for constants).
71 // An object's type (and thus the object) may be in one of
72 // three states which are expressed by colors:
74 // - an object whose type is not yet known is painted white (initial color)
75 // - an object whose type is in the process of being inferred is painted grey
76 // - an object whose type is fully inferred is painted black
78 // During type inference, an object's color changes from white to grey
79 // to black (pre-declared objects are painted black from the start).
80 // A black object (i.e., its type) can only depend on (refer to) other black
81 // ones. White and grey objects may depend on white and black objects.
82 // A dependency on a grey object indicates a cycle which may or may not be
85 // When objects turn grey, they are pushed on the object path (a stack);
86 // they are popped again when they turn black. Thus, if a grey object (a
87 // cycle) is encountered, it is on the object path, and all the objects
88 // it depends on are the remaining objects on that path. Color encoding
89 // is such that the color value of a grey object indicates the index of
90 // that object in the object path.
92 // During type-checking, white objects may be assigned a type without
93 // traversing through objDecl; e.g., when initializing constants and
94 // variables. Update the colors of those objects here (rather than
95 // everywhere where we set the type) to satisfy the color invariants.
96 if obj.color() == white && obj.Type() != nil {
103 assert(obj.Type() == nil)
104 // All color values other than white and black are considered grey.
105 // Because black and white are < grey, all values >= grey are grey.
106 // Use those values to encode the object's index into the object path.
107 obj.setColor(grey + color(check.push(obj)))
109 check.pop().setColor(black)
113 assert(obj.Type() != nil)
117 // Color values other than white or black are considered grey.
121 // We have a (possibly invalid) cycle.
122 // In the existing code, this is marked by a non-nil type
123 // for the object except for constants and variables whose
124 // type may be non-nil (known), or nil if it depends on the
125 // not-yet known initialization value.
126 // In the former case, set the type to Typ[Invalid] because
127 // we have an initialization cycle. The cycle error will be
128 // reported later, when determining initialization order.
129 // TODO(gri) Report cycle here and simplify initialization
131 switch obj := obj.(type) {
133 if !check.validCycle(obj) || obj.typ == nil {
134 obj.typ = Typ[Invalid]
138 if !check.validCycle(obj) || obj.typ == nil {
139 obj.typ = Typ[Invalid]
143 if !check.validCycle(obj) {
145 // (without this, calling underlying()
146 // below may lead to an endless loop
147 // if we have a cycle for a defined
149 obj.typ = Typ[Invalid]
153 if !check.validCycle(obj) {
154 // Don't set obj.typ to Typ[Invalid] here
155 // because plenty of code type-asserts that
156 // functions have a *Signature type. Grey
157 // functions have their type set to an empty
158 // signature which makes it impossible to
159 // initialize a variable with the function.
165 assert(obj.Type() != nil)
169 d := check.objMap[obj]
171 check.dump("%v: %s should have been declared", obj.Pos(), obj)
175 // save/restore current environment and set up object environment
176 defer func(env environment) {
177 check.environment = env
179 check.environment = environment{
183 // Const and var declarations must not have initialization
184 // cycles. We track them by remembering the current declaration
185 // in check.decl. Initialization expressions depending on other
186 // consts, vars, or functions, add dependencies to the current
188 switch obj := obj.(type) {
190 check.decl = d // new package-level const decl
191 check.constDecl(obj, d.vtyp, d.init, d.inherited)
193 check.decl = d // new package-level var decl
194 check.varDecl(obj, d.lhs, d.vtyp, d.init)
196 // invalid recursive types are detected via path
197 check.typeDecl(obj, d.tdecl, def)
198 check.collectMethods(obj) // methods can only be added to top-level types
200 // functions may be recursive - no need to track dependencies
201 check.funcDecl(obj, d)
207 // validCycle reports whether the cycle starting with obj is valid and
208 // reports an error if it is not.
209 func (check *Checker) validCycle(obj Object) (valid bool) {
210 // The object map contains the package scope objects and the non-interface methods.
212 info := check.objMap[obj]
213 inObjMap := info != nil && (info.fdecl == nil || info.fdecl.Recv == nil) // exclude methods
214 isPkgObj := obj.Parent() == check.pkg.scope
215 if isPkgObj != inObjMap {
216 check.dump("%v: inconsistent object map for %s (isPkgObj = %v, inObjMap = %v)", obj.Pos(), obj, isPkgObj, inObjMap)
221 // Count cycle objects.
222 assert(obj.color() >= grey)
223 start := obj.color() - grey // index of obj in objPath
224 cycle := check.objPath[start:]
225 tparCycle := false // if set, the cycle is through a type parameter list
226 nval := 0 // number of (constant or variable) values in the cycle; valid if !generic
227 ndef := 0 // number of type definitions in the cycle; valid if !generic
229 for _, obj := range cycle {
230 switch obj := obj.(type) {
234 // If we reach a generic type that is part of a cycle
235 // and we are in a type parameter list, we have a cycle
236 // through a type parameter list, which is invalid.
237 if check.inTParamList && isGeneric(obj.typ) {
242 // Determine if the type name is an alias or not. For
243 // package-level objects, use the object map which
244 // provides syntactic information (which doesn't rely
245 // on the order in which the objects are set up). For
246 // local objects, we can rely on the order, so use
247 // the object's predicate.
248 // TODO(gri) It would be less fragile to always access
249 // the syntactic information. We should consider storing
250 // this information explicitly in the object.
252 if d := check.objMap[obj]; d != nil {
253 alias = d.tdecl.Alias // package-level object
255 alias = obj.IsAlias() // function local object
267 if check.conf.Trace {
268 check.trace(obj.Pos(), "## cycle detected: objPath = %s->%s (len = %d)", pathString(cycle), obj.Name(), len(cycle))
270 check.trace(obj.Pos(), "## cycle contains: generic type in a type parameter list")
272 check.trace(obj.Pos(), "## cycle contains: %d values, %d type definitions", nval, ndef)
276 check.trace(obj.Pos(), "=> cycle is valid")
278 check.trace(obj.Pos(), "=> error: cycle is invalid")
284 // A cycle involving only constants and variables is invalid but we
285 // ignore them here because they are reported via the initialization
287 if nval == len(cycle) {
291 // A cycle involving only types (and possibly functions) must have at least
292 // one type definition to be permitted: If there is no type definition, we
293 // have a sequence of alias type names which will expand ad infinitum.
294 if nval == 0 && ndef > 0 {
299 check.cycleError(cycle)
303 // cycleError reports a declaration cycle starting with
304 // the object in cycle that is "first" in the source.
305 func (check *Checker) cycleError(cycle []Object) {
306 // TODO(gri) Should we start with the last (rather than the first) object in the cycle
307 // since that is the earliest point in the source where we start seeing the
308 // cycle? That would be more consistent with other error messages.
309 i := firstInSrc(cycle)
311 // If obj is a type alias, mark it as valid (not broken) in order to avoid follow-on errors.
312 tname, _ := obj.(*TypeName)
313 if tname != nil && tname.IsAlias() {
314 check.validAlias(tname, Typ[Invalid])
317 if tname != nil && check.conf.CompilerErrorMessages {
318 err.errorf(obj, "invalid recursive type %s", obj.Name())
320 err.errorf(obj, "illegal cycle in declaration of %s", obj.Name())
323 err.errorf(obj, "%s refers to", obj.Name())
330 err.errorf(obj, "%s", obj.Name())
334 // firstInSrc reports the index of the object with the "smallest"
335 // source position in path. path must not be empty.
336 func firstInSrc(path []Object) int {
337 fst, pos := 0, path[0].Pos()
338 for i, t := range path[1:] {
339 if t.Pos().Cmp(pos) < 0 {
340 fst, pos = i+1, t.Pos()
346 func (check *Checker) constDecl(obj *Const, typ, init syntax.Expr, inherited bool) {
347 assert(obj.typ == nil)
349 // use the correct value of iota and errpos
350 defer func(iota constant.Value, errpos syntax.Pos) {
352 check.errpos = errpos
353 }(check.iota, check.errpos)
357 // provide valid constant value under all circumstances
358 obj.val = constant.MakeUnknown()
360 // determine type, if any
364 // don't report an error if the type is an invalid C (defined) type
366 if under(t) != Typ[Invalid] {
367 check.errorf(typ, "invalid constant type %s", t)
369 obj.typ = Typ[Invalid]
375 // check initialization
379 // The initialization expression is inherited from a previous
380 // constant declaration, and (error) positions refer to that
381 // expression and not the current constant declaration. Use
382 // the constant identifier position for any errors during
383 // init expression evaluation since that is all we have
384 // (see issues #42991, #42992).
385 check.errpos = obj.pos
389 check.initConst(obj, &x)
392 func (check *Checker) varDecl(obj *Var, lhs []*Var, typ, init syntax.Expr) {
393 assert(obj.typ == nil)
395 // If we have undefined variable types due to errors,
396 // mark variables as used to avoid follow-on errors.
397 // Matches compiler behavior.
399 if obj.typ == Typ[Invalid] {
402 for _, lhs := range lhs {
403 if lhs.typ == Typ[Invalid] {
409 // determine type, if any
411 obj.typ = check.varType(typ)
412 // We cannot spread the type to all lhs variables if there
413 // are more than one since that would mark them as checked
414 // (see Checker.objDecl) and the assignment of init exprs,
415 // if any, would not be checked.
417 // TODO(gri) If we have no init expr, we should distribute
418 // a given type otherwise we need to re-evalate the type
419 // expr for each lhs variable, leading to duplicate work.
422 // check initialization
425 // error reported before by arityMatch
426 obj.typ = Typ[Invalid]
431 if lhs == nil || len(lhs) == 1 {
432 assert(lhs == nil || lhs[0] == obj)
435 check.initVar(obj, &x, "variable declaration")
440 // obj must be one of lhs
442 for _, lhs := range lhs {
449 panic("inconsistent lhs")
453 // We have multiple variables on the lhs and one init expr.
454 // Make sure all variables have been given the same type if
455 // one was specified, otherwise they assume the type of the
456 // init expression values (was issue #15755).
458 for _, lhs := range lhs {
463 check.initVars(lhs, []syntax.Expr{init}, nil)
466 // isImportedConstraint reports whether typ is an imported type constraint.
467 func (check *Checker) isImportedConstraint(typ Type) bool {
468 named, _ := typ.(*Named)
469 if named == nil || named.obj.pkg == check.pkg || named.obj.pkg == nil {
472 u, _ := named.under().(*Interface)
473 return u != nil && !u.IsMethodSet()
476 func (check *Checker) typeDecl(obj *TypeName, tdecl *syntax.TypeDecl, def *Named) {
477 assert(obj.typ == nil)
481 if t, _ := obj.typ.(*Named); t != nil { // type may be invalid
484 // If typ is local, an error was already reported where typ is specified/defined.
485 if check.isImportedConstraint(rhs) && !check.allowVersion(check.pkg, 1, 18) {
486 check.versionErrorf(tdecl.Type, "go1.18", "using type constraint %s", rhs)
488 }).describef(obj, "validType(%s)", obj.Name())
491 if alias && tdecl.TParamList != nil {
492 // The parser will ensure this but we may still get an invalid AST.
493 // Complain and continue as regular type definition.
494 check.error(tdecl, "generic type cannot be alias")
500 if !check.allowVersion(check.pkg, 1, 9) {
501 check.versionErrorf(tdecl, "go1.9", "type aliases")
504 check.brokenAlias(obj)
505 rhs = check.typ(tdecl.Type)
506 check.validAlias(obj, rhs)
510 // type definition or generic type declaration
511 named := check.newNamed(obj, nil, nil, nil)
512 def.setUnderlying(named)
514 if tdecl.TParamList != nil {
515 check.openScope(tdecl, "type parameters")
516 defer check.closeScope()
517 check.collectTypeParams(&named.tparams, tdecl.TParamList)
520 // determine underlying type of named
521 rhs = check.definedType(tdecl.Type, named)
525 // If the underlying type was not set while type-checking the right-hand
526 // side, it is invalid and an error should have been reported elsewhere.
527 if named.underlying == nil {
528 named.underlying = Typ[Invalid]
531 // Disallow a lone type parameter as the RHS of a type declaration (issue #45639).
532 // We don't need this restriction anymore if we make the underlying type of a type
533 // parameter its constraint interface: if the RHS is a lone type parameter, we will
534 // use its underlying type (like we do for any RHS in a type declaration), and its
535 // underlying type is an interface and the type declaration is well defined.
536 if isTypeParam(rhs) {
537 check.error(tdecl.Type, "cannot use a type parameter as RHS in type declaration")
538 named.underlying = Typ[Invalid]
542 func (check *Checker) collectTypeParams(dst **TypeParamList, list []*syntax.Field) {
543 tparams := make([]*TypeParam, len(list))
545 // Declare type parameters up-front.
546 // The scope of type parameters starts at the beginning of the type parameter
547 // list (so we can have mutually recursive parameterized type bounds).
548 for i, f := range list {
549 tparams[i] = check.declareTypeParam(f.Name)
552 // Set the type parameters before collecting the type constraints because
553 // the parameterized type may be used by the constraints (issue #47887).
554 // Example: type T[P T[P]] interface{}
555 *dst = bindTParams(tparams)
557 // Signal to cycle detection that we are in a type parameter list.
558 // We can only be inside one type parameter list at any given time:
559 // function closures may appear inside a type parameter list but they
560 // cannot be generic, and their bodies are processed in delayed and
561 // sequential fashion. Note that with each new declaration, we save
562 // the existing environment and restore it when done; thus inTParamList
563 // is true exactly only when we are in a specific type parameter list.
564 assert(!check.inTParamList)
565 check.inTParamList = true
567 check.inTParamList = false
570 // Keep track of bounds for later validation.
572 for i, f := range list {
573 // Optimization: Re-use the previous type bound if it hasn't changed.
574 // This also preserves the grouped output of type parameter lists
575 // when printing type strings.
576 if i == 0 || f.Type != list[i-1].Type {
577 bound = check.bound(f.Type)
578 if isTypeParam(bound) {
579 // We may be able to allow this since it is now well-defined what
580 // the underlying type and thus type set of a type parameter is.
581 // But we may need some additional form of cycle detection within
582 // type parameter lists.
583 check.error(f.Type, "cannot use a type parameter as constraint")
587 tparams[i].bound = bound
591 func (check *Checker) bound(x syntax.Expr) Type {
592 // A type set literal of the form ~T and A|B may only appear as constraint;
593 // embed it in an implicit interface so that only interface type-checking
594 // needs to take care of such type expressions.
595 if op, _ := x.(*syntax.Operation); op != nil && (op.Op == syntax.Tilde || op.Op == syntax.Or) {
596 t := check.typ(&syntax.InterfaceType{MethodList: []*syntax.Field{{Type: x}}})
597 // mark t as implicit interface if all went well
598 if t, _ := t.(*Interface); t != nil {
606 func (check *Checker) declareTypeParam(name *syntax.Name) *TypeParam {
607 // Use Typ[Invalid] for the type constraint to ensure that a type
608 // is present even if the actual constraint has not been assigned
610 // TODO(gri) Need to systematically review all uses of type parameter
611 // constraints to make sure we don't rely on them if they
612 // are not properly set yet.
613 tname := NewTypeName(name.Pos(), check.pkg, name.Value, nil)
614 tpar := check.newTypeParam(tname, Typ[Invalid]) // assigns type to tname as a side-effect
615 check.declare(check.scope, name, tname, check.scope.pos) // TODO(gri) check scope position
619 func (check *Checker) collectMethods(obj *TypeName) {
620 // get associated methods
621 // (Checker.collectObjects only collects methods with non-blank names;
622 // Checker.resolveBaseTypeName ensures that obj is not an alias name
623 // if it has attached methods.)
624 methods := check.methods[obj]
628 delete(check.methods, obj)
629 assert(!check.objMap[obj].tdecl.Alias) // don't use TypeName.IsAlias (requires fully set up object)
631 // use an objset to check for name conflicts
634 // spec: "If the base type is a struct type, the non-blank method
635 // and field names must be distinct."
636 base, _ := obj.typ.(*Named) // shouldn't fail but be conservative
638 assert(base.targs.Len() == 0) // collectMethods should not be called on an instantiated type
640 // See issue #52529: we must delay the expansion of underlying here, as
641 // base may not be fully set-up.
643 check.checkFieldUniqueness(base)
644 }).describef(obj, "verifying field uniqueness for %v", base)
646 // Checker.Files may be called multiple times; additional package files
647 // may add methods to already type-checked types. Add pre-existing methods
648 // so that we can detect redeclarations.
649 for i := 0; i < base.NumMethods(); i++ {
651 assert(m.name != "_")
652 assert(mset.insert(m) == nil)
657 for _, m := range methods {
658 // spec: "For a base type, the non-blank names of methods bound
659 // to it must be unique."
660 assert(m.name != "_")
661 if alt := mset.insert(m); alt != nil {
663 if check.conf.CompilerErrorMessages {
664 err.errorf(m.pos, "%s.%s redeclared in this block", obj.Name(), m.name)
666 err.errorf(m.pos, "method %s already declared for %s", m.name, obj)
668 err.recordAltDecl(alt)
679 func (check *Checker) checkFieldUniqueness(base *Named) {
680 if t, _ := base.under().(*Struct); t != nil {
682 for i := 0; i < base.NumMethods(); i++ {
684 assert(m.name != "_")
685 assert(mset.insert(m) == nil)
688 // Check that any non-blank field names of base are distinct from its
690 for _, fld := range t.fields {
692 if alt := mset.insert(fld); alt != nil {
693 // Struct fields should already be unique, so we should only
694 // encounter an alternate via collision with a method name.
697 // For historical consistency, we report the primary error on the
698 // method, and the alt decl on the field.
700 err.errorf(alt, "field and method with the same name %s", fld.name)
701 err.recordAltDecl(fld)
709 func (check *Checker) funcDecl(obj *Func, decl *declInfo) {
710 assert(obj.typ == nil)
712 // func declarations cannot use iota
713 assert(check.iota == nil)
715 sig := new(Signature)
716 obj.typ = sig // guard against cycles
718 // Avoid cycle error when referring to method while type-checking the signature.
719 // This avoids a nuisance in the best case (non-parameterized receiver type) and
720 // since the method is not a type, we get an error. If we have a parameterized
721 // receiver type, instantiating the receiver type leads to the instantiation of
722 // its methods, and we don't want a cycle error in that case.
723 // TODO(gri) review if this is correct and/or whether we still need this?
727 check.funcType(sig, fdecl.Recv, fdecl.TParamList, fdecl.Type)
730 if len(fdecl.TParamList) > 0 && fdecl.Body == nil {
731 check.softErrorf(fdecl, "parameterized function is missing function body")
734 // function body must be type-checked after global declarations
735 // (functions implemented elsewhere have no body)
736 if !check.conf.IgnoreFuncBodies && fdecl.Body != nil {
738 check.funcBody(decl, obj.name, sig, fdecl.Body, nil)
739 }).describef(obj, "func %s", obj.name)
743 func (check *Checker) declStmt(list []syntax.Decl) {
746 first := -1 // index of first ConstDecl in the current group, or -1
747 var last *syntax.ConstDecl // last ConstDecl with init expressions, or nil
748 for index, decl := range list {
749 if _, ok := decl.(*syntax.ConstDecl); !ok {
750 first = -1 // we're not in a constant declaration
753 switch s := decl.(type) {
754 case *syntax.ConstDecl:
755 top := len(check.delayed)
757 // iota is the index of the current constDecl within the group
758 if first < 0 || s.Group == nil || list[index-1].(*syntax.ConstDecl).Group != s.Group {
762 iota := constant.MakeInt64(int64(index - first))
764 // determine which initialization expressions to use
767 case s.Type != nil || s.Values != nil:
771 last = new(syntax.ConstDecl) // make sure last exists
775 // declare all constants
776 lhs := make([]*Const, len(s.NameList))
777 values := unpackExpr(last.Values)
778 for i, name := range s.NameList {
779 obj := NewConst(name.Pos(), pkg, name.Value, nil, iota)
787 check.constDecl(obj, last.Type, init, inherited)
790 // Constants must always have init values.
791 check.arity(s.Pos(), s.NameList, values, true, inherited)
793 // process function literals in init expressions before scope changes
794 check.processDelayed(top)
796 // spec: "The scope of a constant or variable identifier declared
797 // inside a function begins at the end of the ConstSpec or VarSpec
798 // (ShortVarDecl for short variable declarations) and ends at the
799 // end of the innermost containing block."
800 scopePos := syntax.EndPos(s)
801 for i, name := range s.NameList {
802 check.declare(check.scope, name, lhs[i], scopePos)
805 case *syntax.VarDecl:
806 top := len(check.delayed)
808 lhs0 := make([]*Var, len(s.NameList))
809 for i, name := range s.NameList {
810 lhs0[i] = NewVar(name.Pos(), pkg, name.Value, nil)
813 // initialize all variables
814 values := unpackExpr(s.Values)
815 for i, obj := range lhs0 {
819 case len(s.NameList):
823 // rhs is expected to be a multi-valued expression
831 check.varDecl(obj, lhs, s.Type, init)
832 if len(values) == 1 {
833 // If we have a single lhs variable we are done either way.
834 // If we have a single rhs expression, it must be a multi-
835 // valued expression, in which case handling the first lhs
836 // variable will cause all lhs variables to have a type
837 // assigned, and we are done as well.
839 for _, obj := range lhs0 {
840 assert(obj.typ != nil)
847 // If we have no type, we must have values.
848 if s.Type == nil || values != nil {
849 check.arity(s.Pos(), s.NameList, values, false, false)
852 // process function literals in init expressions before scope changes
853 check.processDelayed(top)
855 // declare all variables
856 // (only at this point are the variable scopes (parents) set)
857 scopePos := syntax.EndPos(s) // see constant declarations
858 for i, name := range s.NameList {
859 // see constant declarations
860 check.declare(check.scope, name, lhs0[i], scopePos)
863 case *syntax.TypeDecl:
864 obj := NewTypeName(s.Name.Pos(), pkg, s.Name.Value, nil)
865 // spec: "The scope of a type identifier declared inside a function
866 // begins at the identifier in the TypeSpec and ends at the end of
867 // the innermost containing block."
868 scopePos := s.Name.Pos()
869 check.declare(check.scope, s.Name, obj, scopePos)
870 // mark and unmark type before calling typeDecl; its type is still nil (see Checker.objDecl)
871 obj.setColor(grey + color(check.push(obj)))
872 check.typeDecl(obj, s, nil)
873 check.pop().setColor(black)
876 check.errorf(s, invalidAST+"unknown syntax.Decl node %T", s)