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 // 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(nil, 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 environment and set up object environment
182 defer func(env environment) {
183 check.environment = env
185 check.environment = environment{
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 tparCycle := false // if set, the cycle is through a type parameter list
232 nval := 0 // number of (constant or variable) values in the cycle; valid if !generic
233 ndef := 0 // number of type definitions in the cycle; valid if !generic
235 for _, obj := range cycle {
236 switch obj := obj.(type) {
240 // If we reach a generic type that is part of a cycle
241 // and we are in a type parameter list, we have a cycle
242 // through a type parameter list, which is invalid.
243 if check.inTParamList && isGeneric(obj.typ) {
248 // Determine if the type name is an alias or not. For
249 // package-level objects, use the object map which
250 // provides syntactic information (which doesn't rely
251 // on the order in which the objects are set up). For
252 // local objects, we can rely on the order, so use
253 // the object's predicate.
254 // TODO(gri) It would be less fragile to always access
255 // the syntactic information. We should consider storing
256 // this information explicitly in the object.
258 if d := check.objMap[obj]; d != nil {
259 alias = d.tdecl.Alias // package-level object
261 alias = obj.IsAlias() // function local object
273 if check.conf.Trace {
274 check.trace(obj.Pos(), "## cycle detected: objPath = %s->%s (len = %d)", pathString(cycle), obj.Name(), len(cycle))
276 check.trace(obj.Pos(), "## cycle contains: generic type in a type parameter list")
278 check.trace(obj.Pos(), "## cycle contains: %d values, %d type definitions", nval, ndef)
282 check.trace(obj.Pos(), "=> error: cycle is invalid")
288 // A cycle involving only constants and variables is invalid but we
289 // ignore them here because they are reported via the initialization
291 if nval == len(cycle) {
295 // A cycle involving only types (and possibly functions) must have at least
296 // one type definition to be permitted: If there is no type definition, we
297 // have a sequence of alias type names which will expand ad infinitum.
298 if nval == 0 && ndef > 0 {
303 check.cycleError(cycle)
307 // cycleError reports a declaration cycle starting with
308 // the object in cycle that is "first" in the source.
309 func (check *Checker) cycleError(cycle []Object) {
310 // TODO(gri) Should we start with the last (rather than the first) object in the cycle
311 // since that is the earliest point in the source where we start seeing the
312 // cycle? That would be more consistent with other error messages.
313 i := firstInSrc(cycle)
316 if check.conf.CompilerErrorMessages {
317 err.errorf(obj, "invalid recursive type %s", obj.Name())
319 err.errorf(obj, "illegal cycle in declaration of %s", obj.Name())
322 err.errorf(obj, "%s refers to", obj.Name())
329 err.errorf(obj, "%s", obj.Name())
333 // firstInSrc reports the index of the object with the "smallest"
334 // source position in path. path must not be empty.
335 func firstInSrc(path []Object) int {
336 fst, pos := 0, path[0].Pos()
337 for i, t := range path[1:] {
338 if t.Pos().Cmp(pos) < 0 {
339 fst, pos = i+1, t.Pos()
345 func (check *Checker) constDecl(obj *Const, typ, init syntax.Expr, inherited bool) {
346 assert(obj.typ == nil)
348 // use the correct value of iota and errpos
349 defer func(iota constant.Value, errpos syntax.Pos) {
351 check.errpos = errpos
352 }(check.iota, check.errpos)
356 // provide valid constant value under all circumstances
357 obj.val = constant.MakeUnknown()
359 // determine type, if any
363 // don't report an error if the type is an invalid C (defined) type
365 if under(t) != Typ[Invalid] {
366 check.errorf(typ, "invalid constant type %s", t)
368 obj.typ = Typ[Invalid]
374 // check initialization
378 // The initialization expression is inherited from a previous
379 // constant declaration, and (error) positions refer to that
380 // expression and not the current constant declaration. Use
381 // the constant identifier position for any errors during
382 // init expression evaluation since that is all we have
383 // (see issues #42991, #42992).
384 check.errpos = obj.pos
388 check.initConst(obj, &x)
391 func (check *Checker) varDecl(obj *Var, lhs []*Var, typ, init syntax.Expr) {
392 assert(obj.typ == nil)
394 // If we have undefined variable types due to errors,
395 // mark variables as used to avoid follow-on errors.
396 // Matches compiler behavior.
398 if obj.typ == Typ[Invalid] {
401 for _, lhs := range lhs {
402 if lhs.typ == Typ[Invalid] {
408 // determine type, if any
410 obj.typ = check.varType(typ)
411 // We cannot spread the type to all lhs variables if there
412 // are more than one since that would mark them as checked
413 // (see Checker.objDecl) and the assignment of init exprs,
414 // if any, would not be checked.
416 // TODO(gri) If we have no init expr, we should distribute
417 // a given type otherwise we need to re-evalate the type
418 // expr for each lhs variable, leading to duplicate work.
421 // check initialization
424 // error reported before by arityMatch
425 obj.typ = Typ[Invalid]
430 if lhs == nil || len(lhs) == 1 {
431 assert(lhs == nil || lhs[0] == obj)
434 check.initVar(obj, &x, "variable declaration")
439 // obj must be one of lhs
441 for _, lhs := range lhs {
448 panic("inconsistent lhs")
452 // We have multiple variables on the lhs and one init expr.
453 // Make sure all variables have been given the same type if
454 // one was specified, otherwise they assume the type of the
455 // init expression values (was issue #15755).
457 for _, lhs := range lhs {
462 check.initVars(lhs, []syntax.Expr{init}, nil)
465 // isImportedConstraint reports whether typ is an imported type constraint.
466 func (check *Checker) isImportedConstraint(typ Type) bool {
467 named, _ := typ.(*Named)
468 if named == nil || named.obj.pkg == check.pkg || named.obj.pkg == nil {
471 u, _ := named.under().(*Interface)
472 return u != nil && !u.IsMethodSet()
475 func (check *Checker) typeDecl(obj *TypeName, tdecl *syntax.TypeDecl, def *Named) {
476 assert(obj.typ == nil)
480 if t, _ := obj.typ.(*Named); t != nil { // type may be invalid
483 // If typ is local, an error was already reported where typ is specified/defined.
484 if check.isImportedConstraint(rhs) && !check.allowVersion(check.pkg, 1, 18) {
485 check.versionErrorf(tdecl.Type, "go1.18", "using type constraint %s", rhs)
487 }).describef(obj, "validType(%s)", obj.Name())
490 if alias && tdecl.TParamList != nil {
491 // The parser will ensure this but we may still get an invalid AST.
492 // Complain and continue as regular type definition.
493 check.error(tdecl, "generic type cannot be alias")
499 if !check.allowVersion(check.pkg, 1, 9) {
500 check.versionErrorf(tdecl, "go1.9", "type aliases")
503 obj.typ = Typ[Invalid]
504 rhs = check.varType(tdecl.Type)
509 // type definition or generic type declaration
510 named := check.newNamed(obj, nil, nil, nil, nil)
511 def.setUnderlying(named)
513 if tdecl.TParamList != nil {
514 check.openScope(tdecl, "type parameters")
515 defer check.closeScope()
516 check.collectTypeParams(&named.tparams, tdecl.TParamList)
519 // determine underlying type of named
520 rhs = check.definedType(tdecl.Type, named)
524 // If the underlying was not set while type-checking the right-hand side, it
525 // is invalid and an error should have been reported elsewhere.
526 if named.underlying == nil {
527 named.underlying = Typ[Invalid]
530 // Disallow a lone type parameter as the RHS of a type declaration (issue #45639).
531 // We don't need this restriction anymore if we make the underlying type of a type
532 // parameter its constraint interface: if the RHS is a lone type parameter, we will
533 // use its underlying type (like we do for any RHS in a type declaration), and its
534 // underlying type is an interface and the type declaration is well defined.
535 if isTypeParam(rhs) {
536 check.error(tdecl.Type, "cannot use a type parameter as RHS in type declaration")
537 named.underlying = Typ[Invalid]
541 func (check *Checker) collectTypeParams(dst **TypeParamList, list []*syntax.Field) {
542 tparams := make([]*TypeParam, len(list))
544 // Declare type parameters up-front.
545 // The scope of type parameters starts at the beginning of the type parameter
546 // list (so we can have mutually recursive parameterized type bounds).
547 for i, f := range list {
548 tparams[i] = check.declareTypeParam(f.Name)
551 // Set the type parameters before collecting the type constraints because
552 // the parameterized type may be used by the constraints (issue #47887).
553 // Example: type T[P T[P]] interface{}
554 *dst = bindTParams(tparams)
556 // Signal to cycle detection that we are in a type parameter list.
557 // We can only be inside one type parameter list at any given time:
558 // function closures may appear inside a type parameter list but they
559 // cannot be generic, and their bodies are processed in delayed and
560 // sequential fashion. Note that with each new declaration, we save
561 // the existing environment and restore it when done; thus inTParamList
562 // is true exactly only when we are in a specific type parameter list.
563 assert(!check.inTParamList)
564 check.inTParamList = true
566 check.inTParamList = false
569 // 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")
586 bounds = append(bounds, bound)
588 tparams[i].bound = bound
592 func (check *Checker) bound(x syntax.Expr) Type {
593 // A type set literal of the form ~T and A|B may only appear as constraint;
594 // embed it in an implicit interface so that only interface type-checking
595 // needs to take care of such type expressions.
596 if op, _ := x.(*syntax.Operation); op != nil && (op.Op == syntax.Tilde || op.Op == syntax.Or) {
597 t := check.typ(&syntax.InterfaceType{MethodList: []*syntax.Field{{Type: x}}})
598 // mark t as implicit interface if all went well
599 if t, _ := t.(*Interface); t != nil {
607 func (check *Checker) declareTypeParam(name *syntax.Name) *TypeParam {
608 // Use Typ[Invalid] for the type constraint to ensure that a type
609 // is present even if the actual constraint has not been assigned
611 // TODO(gri) Need to systematically review all uses of type parameter
612 // constraints to make sure we don't rely on them if they
613 // are not properly set yet.
614 tname := NewTypeName(name.Pos(), check.pkg, name.Value, nil)
615 tpar := check.newTypeParam(tname, Typ[Invalid]) // assigns type to tname as a side-effect
616 check.declare(check.scope, name, tname, check.scope.pos) // TODO(gri) check scope position
620 func (check *Checker) collectMethods(obj *TypeName) {
621 // get associated methods
622 // (Checker.collectObjects only collects methods with non-blank names;
623 // Checker.resolveBaseTypeName ensures that obj is not an alias name
624 // if it has attached methods.)
625 methods := check.methods[obj]
629 delete(check.methods, obj)
630 assert(!check.objMap[obj].tdecl.Alias) // don't use TypeName.IsAlias (requires fully set up object)
632 // use an objset to check for name conflicts
635 // spec: "If the base type is a struct type, the non-blank method
636 // and field names must be distinct."
637 base, _ := obj.typ.(*Named) // shouldn't fail but be conservative
640 if t, _ := u.(*Struct); t != nil {
641 for _, fld := range t.fields {
643 assert(mset.insert(fld) == nil)
648 // Checker.Files may be called multiple times; additional package files
649 // may add methods to already type-checked types. Add pre-existing methods
650 // so that we can detect redeclarations.
651 for _, m := range base.methods {
652 assert(m.name != "_")
653 assert(mset.insert(m) == nil)
658 for _, m := range methods {
659 // spec: "For a base type, the non-blank names of methods bound
660 // to it must be unique."
661 assert(m.name != "_")
662 if alt := mset.insert(m); alt != nil {
666 err.errorf(m.pos, "field and method with the same name %s", m.name)
668 if check.conf.CompilerErrorMessages {
669 err.errorf(m.pos, "%s.%s redeclared in this block", obj.Name(), m.name)
671 err.errorf(m.pos, "method %s already declared for %s", m.name, obj)
676 err.recordAltDecl(alt)
682 base.resolve(nil) // TODO(mdempsky): Probably unnecessary.
683 base.methods = append(base.methods, m)
688 func (check *Checker) funcDecl(obj *Func, decl *declInfo) {
689 assert(obj.typ == nil)
691 // func declarations cannot use iota
692 assert(check.iota == nil)
694 sig := new(Signature)
695 obj.typ = sig // guard against cycles
697 // Avoid cycle error when referring to method while type-checking the signature.
698 // This avoids a nuisance in the best case (non-parameterized receiver type) and
699 // since the method is not a type, we get an error. If we have a parameterized
700 // receiver type, instantiating the receiver type leads to the instantiation of
701 // its methods, and we don't want a cycle error in that case.
702 // TODO(gri) review if this is correct and/or whether we still need this?
706 check.funcType(sig, fdecl.Recv, fdecl.TParamList, fdecl.Type)
709 if len(fdecl.TParamList) > 0 && fdecl.Body == nil {
710 check.softErrorf(fdecl, "parameterized function is missing function body")
713 // function body must be type-checked after global declarations
714 // (functions implemented elsewhere have no body)
715 if !check.conf.IgnoreFuncBodies && fdecl.Body != nil {
717 check.funcBody(decl, obj.name, sig, fdecl.Body, nil)
722 func (check *Checker) declStmt(list []syntax.Decl) {
725 first := -1 // index of first ConstDecl in the current group, or -1
726 var last *syntax.ConstDecl // last ConstDecl with init expressions, or nil
727 for index, decl := range list {
728 if _, ok := decl.(*syntax.ConstDecl); !ok {
729 first = -1 // we're not in a constant declaration
732 switch s := decl.(type) {
733 case *syntax.ConstDecl:
734 top := len(check.delayed)
736 // iota is the index of the current constDecl within the group
737 if first < 0 || list[index-1].(*syntax.ConstDecl).Group != s.Group {
741 iota := constant.MakeInt64(int64(index - first))
743 // determine which initialization expressions to use
746 case s.Type != nil || s.Values != nil:
750 last = new(syntax.ConstDecl) // make sure last exists
754 // declare all constants
755 lhs := make([]*Const, len(s.NameList))
756 values := unpackExpr(last.Values)
757 for i, name := range s.NameList {
758 obj := NewConst(name.Pos(), pkg, name.Value, nil, iota)
766 check.constDecl(obj, last.Type, init, inherited)
769 // Constants must always have init values.
770 check.arity(s.Pos(), s.NameList, values, true, inherited)
772 // process function literals in init expressions before scope changes
773 check.processDelayed(top)
775 // spec: "The scope of a constant or variable identifier declared
776 // inside a function begins at the end of the ConstSpec or VarSpec
777 // (ShortVarDecl for short variable declarations) and ends at the
778 // end of the innermost containing block."
779 scopePos := syntax.EndPos(s)
780 for i, name := range s.NameList {
781 check.declare(check.scope, name, lhs[i], scopePos)
784 case *syntax.VarDecl:
785 top := len(check.delayed)
787 lhs0 := make([]*Var, len(s.NameList))
788 for i, name := range s.NameList {
789 lhs0[i] = NewVar(name.Pos(), pkg, name.Value, nil)
792 // initialize all variables
793 values := unpackExpr(s.Values)
794 for i, obj := range lhs0 {
798 case len(s.NameList):
802 // rhs is expected to be a multi-valued expression
810 check.varDecl(obj, lhs, s.Type, init)
811 if len(values) == 1 {
812 // If we have a single lhs variable we are done either way.
813 // If we have a single rhs expression, it must be a multi-
814 // valued expression, in which case handling the first lhs
815 // variable will cause all lhs variables to have a type
816 // assigned, and we are done as well.
818 for _, obj := range lhs0 {
819 assert(obj.typ != nil)
826 // If we have no type, we must have values.
827 if s.Type == nil || values != nil {
828 check.arity(s.Pos(), s.NameList, values, false, false)
831 // process function literals in init expressions before scope changes
832 check.processDelayed(top)
834 // declare all variables
835 // (only at this point are the variable scopes (parents) set)
836 scopePos := syntax.EndPos(s) // see constant declarations
837 for i, name := range s.NameList {
838 // see constant declarations
839 check.declare(check.scope, name, lhs0[i], scopePos)
842 case *syntax.TypeDecl:
843 obj := NewTypeName(s.Name.Pos(), pkg, s.Name.Value, nil)
844 // spec: "The scope of a type identifier declared inside a function
845 // begins at the identifier in the TypeSpec and ends at the end of
846 // the innermost containing block."
847 scopePos := s.Name.Pos()
848 check.declare(check.scope, s.Name, obj, scopePos)
849 // mark and unmark type before calling typeDecl; its type is still nil (see Checker.objDecl)
850 obj.setColor(grey + color(check.push(obj)))
851 check.typeDecl(obj, s, nil)
852 check.pop().setColor(black)
855 check.errorf(s, invalidAST+"unknown syntax.Decl node %T", s)