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 for package-local and non-instantiated signatures; nil otherwise
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 // Params returns the parameters of signature s, or nil.
77 func (s *Signature) Params() *Tuple { return s.params }
79 // Results returns the results of signature s, or nil.
80 func (s *Signature) Results() *Tuple { return s.results }
82 // Variadic reports whether the signature s is variadic.
83 func (s *Signature) Variadic() bool { return s.variadic }
85 func (s *Signature) Underlying() Type { return s }
86 func (s *Signature) String() string { return TypeString(s, nil) }
88 // ----------------------------------------------------------------------------
91 // funcType type-checks a function or method type.
92 func (check *Checker) funcType(sig *Signature, recvPar *syntax.Field, tparams []*syntax.Field, ftyp *syntax.FuncType) {
93 check.openScope(ftyp, "function")
94 check.scope.isFunc = true
95 check.recordScope(ftyp, check.scope)
96 sig.scope = check.scope
97 defer check.closeScope()
100 // collect generic receiver type parameters, if any
101 // - a receiver type parameter is like any other type parameter, except that it is declared implicitly
102 // - the receiver specification acts as local declaration for its type parameters, which may be blank
103 _, rname, rparams := check.unpackRecv(recvPar.Type, true)
104 if len(rparams) > 0 {
105 tparams := make([]*TypeParam, len(rparams))
106 for i, rparam := range rparams {
107 tparams[i] = check.declareTypeParam(rparam)
109 sig.rparams = bindTParams(tparams)
110 // Blank identifiers don't get declared, so naive type-checking of the
111 // receiver type expression would fail in Checker.collectParams below,
112 // when Checker.ident cannot resolve the _ to a type.
114 // Checker.recvTParamMap maps these blank identifiers to their type parameter
115 // types, so that they may be resolved in Checker.ident when they fail
116 // lookup in the scope.
117 for i, p := range rparams {
119 if check.recvTParamMap == nil {
120 check.recvTParamMap = make(map[*syntax.Name]*TypeParam)
122 check.recvTParamMap[p] = tparams[i]
125 // determine receiver type to get its type parameters
126 // and the respective type parameter bounds
127 var recvTParams []*TypeParam
129 // recv should be a Named type (otherwise an error is reported elsewhere)
130 // Also: Don't report an error via genericType since it will be reported
131 // again when we type-check the signature.
132 // TODO(gri) maybe the receiver should be marked as invalid instead?
133 if recv, _ := check.genericType(rname, false).(*Named); recv != nil {
134 recvTParams = recv.TypeParams().list()
137 // provide type parameter bounds
138 if len(tparams) == len(recvTParams) {
139 smap := makeRenameMap(recvTParams, tparams)
140 for i, tpar := range tparams {
141 recvTPar := recvTParams[i]
142 check.mono.recordCanon(tpar, recvTPar)
143 // recvTPar.bound is (possibly) parameterized in the context of the
144 // receiver type declaration. Substitute parameters for the current
146 tpar.bound = check.subst(tpar.obj.pos, recvTPar.bound, smap, nil, check.context())
148 } else if len(tparams) < len(recvTParams) {
149 // Reporting an error here is a stop-gap measure to avoid crashes in the
150 // compiler when a type parameter/argument cannot be inferred later. It
151 // may lead to follow-on errors (see issues #51339, #51343).
152 // TODO(gri) find a better solution
153 got := measure(len(tparams), "type parameter")
154 check.errorf(recvPar, "got %s, but receiver base type declares %d", got, len(recvTParams))
160 // The parser will complain about invalid type parameters for methods.
161 check.collectTypeParams(&sig.tparams, tparams)
164 // Value (non-type) parameters' scope starts in the function body. Use a temporary scope for their
165 // declarations and then squash that scope into the parent scope (and report any redeclarations at
167 scope := NewScope(check.scope, nopos, nopos, "function body (temp. scope)")
168 var recvList []*Var // TODO(gri) remove the need for making a list here
170 recvList, _ = check.collectParams(scope, []*syntax.Field{recvPar}, false) // use rewritten receiver type, if any
172 params, variadic := check.collectParams(scope, ftyp.ParamList, true)
173 results, _ := check.collectParams(scope, ftyp.ResultList, false)
174 scope.Squash(func(obj, alt Object) {
176 err.errorf(obj, "%s redeclared in this block", obj.Name())
177 err.recordAltDecl(alt)
182 // recv parameter list present (may be empty)
183 // spec: "The receiver is specified via an extra parameter section preceding the
184 // method name. That parameter section must declare a single parameter, the receiver."
186 switch len(recvList) {
188 // error reported by resolver
189 recv = NewParam(nopos, nil, "", Typ[Invalid]) // ignore recv below
191 // more than one receiver
192 check.error(recvList[len(recvList)-1].Pos(), "method must have exactly one receiver")
193 fallthrough // continue with first receiver
199 // Delay validation of receiver type as it may cause premature expansion
200 // of types the receiver type is dependent on (see issues #51232, #51233).
202 // spec: "The receiver type must be of the form T or *T where T is a type name."
203 rtyp, _ := deref(recv.typ)
204 if rtyp == Typ[Invalid] {
205 return // error was reported before
207 // spec: "The type denoted by T is called the receiver base type; it must not
208 // be a pointer or interface type and it must be declared in the same package
210 switch T := rtyp.(type) {
212 // The receiver type may be an instantiated type referred to
213 // by an alias (which cannot have receiver parameters for now).
214 if T.TypeArgs() != nil && sig.RecvTypeParams() == nil {
215 check.errorf(recv, "cannot define new methods on instantiated type %s", rtyp)
218 if T.obj.pkg != check.pkg {
219 check.errorf(recv, "cannot define new methods on non-local type %s", rtyp)
223 switch u := T.under().(type) {
225 // unsafe.Pointer is treated like a regular pointer
226 if u.kind == UnsafePointer {
227 cause = "unsafe.Pointer"
229 case *Pointer, *Interface:
230 cause = "pointer or interface type"
232 // The underlying type of a receiver base type cannot be a
233 // type parameter: "type T[P any] P" is not a valid declaration.
237 check.errorf(recv, "invalid receiver type %s (%s)", rtyp, cause)
240 check.errorf(recv, "cannot define new methods on non-local type %s", rtyp)
242 check.errorf(recv, "invalid receiver type %s", recv.typ)
244 }).describef(recv, "validate receiver %s", recv)
247 sig.params = NewTuple(params...)
248 sig.results = NewTuple(results...)
249 sig.variadic = variadic
252 // collectParams declares the parameters of list in scope and returns the corresponding
254 func (check *Checker) collectParams(scope *Scope, list []*syntax.Field, variadicOk bool) (params []*Var, variadic bool) {
259 var named, anonymous bool
263 for i, field := range list {
265 // type-check type of grouped fields only once
268 if t, _ := ftype.(*syntax.DotsType); t != nil {
270 if variadicOk && i == len(list)-1 {
273 check.softErrorf(t, "can only use ... with final parameter in list")
274 // ignore ... and continue
277 typ = check.varType(ftype)
279 // The parser ensures that f.Tag is nil and we don't
280 // care if a constructed AST contains a non-nil tag.
281 if field.Name != nil {
283 name := field.Name.Value
285 check.error(field.Name, invalidAST+"anonymous parameter")
288 par := NewParam(field.Name.Pos(), check.pkg, name, typ)
289 check.declare(scope, field.Name, par, scope.pos)
290 params = append(params, par)
293 // anonymous parameter
294 par := NewParam(field.Pos(), check.pkg, "", typ)
295 check.recordImplicit(field, par)
296 params = append(params, par)
301 if named && anonymous {
302 check.error(list[0], invalidAST+"list contains both named and anonymous parameters")
306 // For a variadic function, change the last parameter's type from T to []T.
307 // Since we type-checked T rather than ...T, we also need to retro-actively
308 // record the type for ...T.
310 last := params[len(params)-1]
311 last.typ = &Slice{elem: last.typ}
312 check.recordTypeAndValue(list[len(list)-1].Type, typexpr, last.typ, nil)