1 // Copyright 2021 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.
7 import "cmd/compile/internal/syntax"
9 // ----------------------------------------------------------------------------
12 // A Signature represents a (non-builtin) function or method type.
13 // The receiver is ignored when comparing signatures for identity.
14 type Signature struct {
15 // We need to keep the scope in Signature (rather than passing it around
16 // and store it in the Func Object) because when type-checking a function
17 // literal we call the general type checker which returns a general Type.
18 // We then unpack the *Signature and use the scope for the literal body.
19 rparams *TypeParamList // receiver type parameters from left to right, or nil
20 tparams *TypeParamList // type parameters from left to right, or nil
21 scope *Scope // function scope, present for package-local signatures
22 recv *Var // nil if not a method
23 params *Tuple // (incoming) parameters from left to right; or nil
24 results *Tuple // (outgoing) results from left to right; or nil
25 variadic bool // true if the last parameter's type is of the form ...T (or string, for append built-in only)
28 // NewSignatureType creates a new function type for the given receiver,
29 // receiver type parameters, type parameters, parameters, and results. If
30 // variadic is set, params must hold at least one parameter and the last
31 // parameter must be of unnamed slice type. If recv is non-nil, typeParams must
32 // be empty. If recvTypeParams is non-empty, recv must be non-nil.
33 func NewSignatureType(recv *Var, recvTypeParams, typeParams []*TypeParam, params, results *Tuple, variadic bool) *Signature {
37 panic("variadic function must have at least one parameter")
39 if _, ok := params.At(n - 1).typ.(*Slice); !ok {
40 panic("variadic parameter must be of unnamed slice type")
43 sig := &Signature{recv: recv, params: params, results: results, variadic: variadic}
44 if len(recvTypeParams) != 0 {
46 panic("function with receiver type parameters must have a receiver")
48 sig.rparams = bindTParams(recvTypeParams)
50 if len(typeParams) != 0 {
52 panic("function with type parameters cannot have a receiver")
54 sig.tparams = bindTParams(typeParams)
59 // Recv returns the receiver of signature s (if a method), or nil if a
60 // function. It is ignored when comparing signatures for identity.
62 // For an abstract method, Recv returns the enclosing interface either
63 // as a *Named or an *Interface. Due to embedding, an interface may
64 // contain methods whose receiver type is a different interface.
65 func (s *Signature) Recv() *Var { return s.recv }
67 // TypeParams returns the type parameters of signature s, or nil.
68 func (s *Signature) TypeParams() *TypeParamList { return s.tparams }
70 // SetTypeParams sets the type parameters of signature s.
71 func (s *Signature) SetTypeParams(tparams []*TypeParam) { s.tparams = bindTParams(tparams) }
73 // RecvTypeParams returns the receiver type parameters of signature s, or nil.
74 func (s *Signature) RecvTypeParams() *TypeParamList { return s.rparams }
76 // SetRecvTypeParams sets the receiver type params of signature s.
77 func (s *Signature) SetRecvTypeParams(rparams []*TypeParam) { s.rparams = bindTParams(rparams) }
79 // Params returns the parameters of signature s, or nil.
80 func (s *Signature) Params() *Tuple { return s.params }
82 // Results returns the results of signature s, or nil.
83 func (s *Signature) Results() *Tuple { return s.results }
85 // Variadic reports whether the signature s is variadic.
86 func (s *Signature) Variadic() bool { return s.variadic }
88 func (s *Signature) Underlying() Type { return s }
89 func (s *Signature) String() string { return TypeString(s, nil) }
91 // ----------------------------------------------------------------------------
94 // Disabled by default, but enabled when running tests (via types_test.go).
95 var acceptMethodTypeParams bool
97 // funcType type-checks a function or method type.
98 func (check *Checker) funcType(sig *Signature, recvPar *syntax.Field, tparams []*syntax.Field, ftyp *syntax.FuncType) {
99 check.openScope(ftyp, "function")
100 check.scope.isFunc = true
101 check.recordScope(ftyp, check.scope)
102 sig.scope = check.scope
103 defer check.closeScope()
106 // collect generic receiver type parameters, if any
107 // - a receiver type parameter is like any other type parameter, except that it is declared implicitly
108 // - the receiver specification acts as local declaration for its type parameters, which may be blank
109 _, rname, rparams := check.unpackRecv(recvPar.Type, true)
110 if len(rparams) > 0 {
111 tparams := make([]*TypeParam, len(rparams))
112 for i, rparam := range rparams {
113 tparams[i] = check.declareTypeParam(rparam)
115 sig.rparams = bindTParams(tparams)
116 // Blank identifiers don't get declared, so naive type-checking of the
117 // receiver type expression would fail in Checker.collectParams below,
118 // when Checker.ident cannot resolve the _ to a type.
120 // Checker.recvTParamMap maps these blank identifiers to their type parameter
121 // types, so that they may be resolved in Checker.ident when they fail
122 // lookup in the scope.
123 for i, p := range rparams {
125 tpar := sig.rparams.At(i)
126 if check.recvTParamMap == nil {
127 check.recvTParamMap = make(map[*syntax.Name]*TypeParam)
129 check.recvTParamMap[p] = tpar
132 // determine receiver type to get its type parameters
133 // and the respective type parameter bounds
134 var recvTParams []*TypeParam
136 // recv should be a Named type (otherwise an error is reported elsewhere)
137 // Also: Don't report an error via genericType since it will be reported
138 // again when we type-check the signature.
139 // TODO(gri) maybe the receiver should be marked as invalid instead?
140 if recv, _ := check.genericType(rname, false).(*Named); recv != nil {
141 recvTParams = recv.TypeParams().list()
144 // provide type parameter bounds
145 // - only do this if we have the right number (otherwise an error is reported elsewhere)
146 if sig.RecvTypeParams().Len() == len(recvTParams) {
147 // We have a list of *TypeNames but we need a list of Types.
148 list := make([]Type, sig.RecvTypeParams().Len())
149 for i, t := range sig.RecvTypeParams().list() {
151 check.mono.recordCanon(t, recvTParams[i])
153 smap := makeSubstMap(recvTParams, list)
154 for i, tpar := range sig.RecvTypeParams().list() {
155 bound := recvTParams[i].bound
156 // bound is (possibly) parameterized in the context of the
157 // receiver type declaration. Substitute parameters for the
159 tpar.bound = check.subst(tpar.obj.pos, bound, smap, nil)
166 check.collectTypeParams(&sig.tparams, tparams)
167 // Always type-check method type parameters but complain if they are not enabled.
168 // (A separate check is needed when type-checking interface method signatures because
169 // they don't have a receiver specification.)
170 if recvPar != nil && !acceptMethodTypeParams {
171 check.error(ftyp, "methods cannot have type parameters")
175 // Value (non-type) parameters' scope starts in the function body. Use a temporary scope for their
176 // declarations and then squash that scope into the parent scope (and report any redeclarations at
178 scope := NewScope(check.scope, nopos, nopos, "function body (temp. scope)")
179 var recvList []*Var // TODO(gri) remove the need for making a list here
181 recvList, _ = check.collectParams(scope, []*syntax.Field{recvPar}, false) // use rewritten receiver type, if any
183 params, variadic := check.collectParams(scope, ftyp.ParamList, true)
184 results, _ := check.collectParams(scope, ftyp.ResultList, false)
185 scope.Squash(func(obj, alt Object) {
187 err.errorf(obj, "%s redeclared in this block", obj.Name())
188 err.recordAltDecl(alt)
193 // recv parameter list present (may be empty)
194 // spec: "The receiver is specified via an extra parameter section preceding the
195 // method name. That parameter section must declare a single parameter, the receiver."
197 switch len(recvList) {
199 // error reported by resolver
200 recv = NewParam(nopos, nil, "", Typ[Invalid]) // ignore recv below
202 // more than one receiver
203 check.error(recvList[len(recvList)-1].Pos(), "method must have exactly one receiver")
204 fallthrough // continue with first receiver
209 // TODO(gri) We should delay rtyp expansion to when we actually need the
210 // receiver; thus all checks here should be delayed to later.
211 rtyp, _ := deref(recv.typ)
213 // spec: "The receiver type must be of the form T or *T where T is a type name."
214 // (ignore invalid types - error was reported before)
215 if rtyp != Typ[Invalid] {
217 switch T := rtyp.(type) {
219 T.resolve(check.conf.Context)
220 // The receiver type may be an instantiated type referred to
221 // by an alias (which cannot have receiver parameters for now).
222 if T.TypeArgs() != nil && sig.RecvTypeParams() == nil {
223 check.errorf(recv.pos, "cannot define methods on instantiated type %s", recv.typ)
226 // spec: "The type denoted by T is called the receiver base type; it must not
227 // be a pointer or interface type and it must be declared in the same package
229 if T.obj.pkg != check.pkg {
230 err = "type not defined in this package"
231 if check.conf.CompilerErrorMessages {
232 check.errorf(recv.pos, "cannot define new methods on non-local type %s", recv.typ)
236 // The underlying type of a receiver base type can be a type parameter;
237 // e.g. for methods with a generic receiver T[P] with type T[P any] P.
238 underIs(T, func(u Type) bool {
239 switch u := u.(type) {
241 // unsafe.Pointer is treated like a regular pointer
242 if u.kind == UnsafePointer {
243 err = "unsafe.Pointer"
246 case *Pointer, *Interface:
247 err = "pointer or interface type"
254 err = "basic or unnamed type"
255 if check.conf.CompilerErrorMessages {
256 check.errorf(recv.pos, "cannot define new methods on non-local type %s", recv.typ)
260 check.errorf(recv.pos, "invalid receiver type %s", recv.typ)
263 check.errorf(recv.pos, "invalid receiver type %s (%s)", recv.typ, err)
270 sig.params = NewTuple(params...)
271 sig.results = NewTuple(results...)
272 sig.variadic = variadic
275 // collectParams declares the parameters of list in scope and returns the corresponding
277 func (check *Checker) collectParams(scope *Scope, list []*syntax.Field, variadicOk bool) (params []*Var, variadic bool) {
282 var named, anonymous bool
286 for i, field := range list {
288 // type-check type of grouped fields only once
291 if t, _ := ftype.(*syntax.DotsType); t != nil {
293 if variadicOk && i == len(list)-1 {
296 check.softErrorf(t, "can only use ... with final parameter in list")
297 // ignore ... and continue
300 typ = check.varType(ftype)
302 // The parser ensures that f.Tag is nil and we don't
303 // care if a constructed AST contains a non-nil tag.
304 if field.Name != nil {
306 name := field.Name.Value
308 check.error(field.Name, invalidAST+"anonymous parameter")
311 par := NewParam(field.Name.Pos(), check.pkg, name, typ)
312 check.declare(scope, field.Name, par, scope.pos)
313 params = append(params, par)
316 // anonymous parameter
317 par := NewParam(field.Pos(), check.pkg, "", typ)
318 check.recordImplicit(field, par)
319 params = append(params, par)
324 if named && anonymous {
325 check.error(list[0], invalidAST+"list contains both named and anonymous parameters")
329 // For a variadic function, change the last parameter's type from T to []T.
330 // Since we type-checked T rather than ...T, we also need to retro-actively
331 // record the type for ...T.
333 last := params[len(params)-1]
334 last.typ = &Slice{elem: last.typ}
335 check.recordTypeAndValue(list[len(list)-1].Type, typexpr, last.typ, nil)