src/cmd/compile/internal/types2/signature.go

   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.
   4
   5 package types2
   6
   7 import (
   8         "cmd/compile/internal/syntax"
   9         "fmt"
  10 )
  11
  12 // Disabled by default, but enabled when running tests (via types_test.go).
  13 var acceptMethodTypeParams bool
  14
  15 // funcType type-checks a function or method type.
  16 func (check *Checker) funcType(sig *Signature, recvPar *syntax.Field, tparams []*syntax.Field, ftyp *syntax.FuncType) {
  17         check.openScope(ftyp, "function")
  18         check.scope.isFunc = true
  19         check.recordScope(ftyp, check.scope)
  20         sig.scope = check.scope
  21         defer check.closeScope()
  22
  23         var recvTyp syntax.Expr // rewritten receiver type; valid if != nil
  24         if recvPar != nil {
  25                 // collect generic receiver type parameters, if any
  26                 // - a receiver type parameter is like any other type parameter, except that it is declared implicitly
  27                 // - the receiver specification acts as local declaration for its type parameters, which may be blank
  28                 _, rname, rparams := check.unpackRecv(recvPar.Type, true)
  29                 if len(rparams) > 0 {
  30                         // Blank identifiers don't get declared and regular type-checking of the instantiated
  31                         // parameterized receiver type expression fails in Checker.collectParams of receiver.
  32                         // Identify blank type parameters and substitute each with a unique new identifier named
  33                         // "n_" (where n is the parameter index) and which cannot conflict with any user-defined
  34                         // name.
  35                         var smap map[*syntax.Name]*syntax.Name // substitution map from "_" to "!n" identifiers
  36                         for i, p := range rparams {
  37                                 if p.Value == "_" {
  38                                         new := *p
  39                                         new.Value = fmt.Sprintf("%d_", i)
  40                                         rparams[i] = &new // use n_ identifier instead of _ so it can be looked up
  41                                         if smap == nil {
  42                                                 smap = make(map[*syntax.Name]*syntax.Name)
  43                                         }
  44                                         smap[p] = &new
  45                                 }
  46                         }
  47                         if smap != nil {
  48                                 // blank identifiers were found => use rewritten receiver type
  49                                 recvTyp = isubst(recvPar.Type, smap)
  50                         }
  51                         // TODO(gri) rework declareTypeParams
  52                         sig.rparams = nil
  53                         for _, rparam := range rparams {
  54                                 sig.rparams = check.declareTypeParam(sig.rparams, rparam)
  55                         }
  56                         // determine receiver type to get its type parameters
  57                         // and the respective type parameter bounds
  58                         var recvTParams []*TypeName
  59                         if rname != nil {
  60                                 // recv should be a Named type (otherwise an error is reported elsewhere)
  61                                 // Also: Don't report an error via genericType since it will be reported
  62                                 //       again when we type-check the signature.
  63                                 // TODO(gri) maybe the receiver should be marked as invalid instead?
  64                                 if recv := asNamed(check.genericType(rname, false)); recv != nil {
  65                                         recvTParams = recv.tparams
  66                                 }
  67                         }
  68                         // provide type parameter bounds
  69                         // - only do this if we have the right number (otherwise an error is reported elsewhere)
  70                         if len(sig.rparams) == len(recvTParams) {
  71                                 // We have a list of *TypeNames but we need a list of Types.
  72                                 list := make([]Type, len(sig.rparams))
  73                                 for i, t := range sig.rparams {
  74                                         list[i] = t.typ
  75                                 }
  76                                 smap := makeSubstMap(recvTParams, list)
  77                                 for i, tname := range sig.rparams {
  78                                         bound := recvTParams[i].typ.(*TypeParam).bound
  79                                         // bound is (possibly) parameterized in the context of the
  80                                         // receiver type declaration. Substitute parameters for the
  81                                         // current context.
  82                                         // TODO(gri) should we assume now that bounds always exist?
  83                                         //           (no bound == empty interface)
  84                                         if bound != nil {
  85                                                 bound = check.subst(tname.pos, bound, smap)
  86                                                 tname.typ.(*TypeParam).bound = bound
  87                                         }
  88                                 }
  89                         }
  90                 }
  91         }
  92
  93         if tparams != nil {
  94                 sig.tparams = check.collectTypeParams(tparams)
  95                 // Always type-check method type parameters but complain if they are not enabled.
  96                 // (A separate check is needed when type-checking interface method signatures because
  97                 // they don't have a receiver specification.)
  98                 if recvPar != nil && !acceptMethodTypeParams {
  99                         check.error(ftyp, "methods cannot have type parameters")
 100                 }
 101         }
 102
 103         // Value (non-type) parameters' scope starts in the function body. Use a temporary scope for their
 104         // declarations and then squash that scope into the parent scope (and report any redeclarations at
 105         // that time).
 106         scope := NewScope(check.scope, nopos, nopos, "function body (temp. scope)")
 107         var recvList []*Var // TODO(gri) remove the need for making a list here
 108         if recvPar != nil {
 109                 recvList, _ = check.collectParams(scope, []*syntax.Field{recvPar}, recvTyp, false) // use rewritten receiver type, if any
 110         }
 111         params, variadic := check.collectParams(scope, ftyp.ParamList, nil, true)
 112         results, _ := check.collectParams(scope, ftyp.ResultList, nil, false)
 113         scope.Squash(func(obj, alt Object) {
 114                 var err error_
 115                 err.errorf(obj, "%s redeclared in this block", obj.Name())
 116                 err.recordAltDecl(alt)
 117                 check.report(&err)
 118         })
 119
 120         if recvPar != nil {
 121                 // recv parameter list present (may be empty)
 122                 // spec: "The receiver is specified via an extra parameter section preceding the
 123                 // method name. That parameter section must declare a single parameter, the receiver."
 124                 var recv *Var
 125                 switch len(recvList) {
 126                 case 0:
 127                         // error reported by resolver
 128                         recv = NewParam(nopos, nil, "", Typ[Invalid]) // ignore recv below
 129                 default:
 130                         // more than one receiver
 131                         check.error(recvList[len(recvList)-1].Pos(), "method must have exactly one receiver")
 132                         fallthrough // continue with first receiver
 133                 case 1:
 134                         recv = recvList[0]
 135                 }
 136
 137                 // TODO(gri) We should delay rtyp expansion to when we actually need the
 138                 //           receiver; thus all checks here should be delayed to later.
 139                 rtyp, _ := deref(recv.typ)
 140                 rtyp = expand(rtyp)
 141
 142                 // spec: "The receiver type must be of the form T or *T where T is a type name."
 143                 // (ignore invalid types - error was reported before)
 144                 if t := rtyp; t != Typ[Invalid] {
 145                         var err string
 146                         if T := asNamed(t); T != nil {
 147                                 // spec: "The type denoted by T is called the receiver base type; it must not
 148                                 // be a pointer or interface type and it must be declared in the same package
 149                                 // as the method."
 150                                 if T.obj.pkg != check.pkg {
 151                                         err = "type not defined in this package"
 152                                         if check.conf.CompilerErrorMessages {
 153                                                 check.errorf(recv.pos, "cannot define new methods on non-local type %s", recv.typ)
 154                                                 err = ""
 155                                         }
 156                                 } else {
 157                                         switch u := optype(T).(type) {
 158                                         case *Basic:
 159                                                 // unsafe.Pointer is treated like a regular pointer
 160                                                 if u.kind == UnsafePointer {
 161                                                         err = "unsafe.Pointer"
 162                                                 }
 163                                         case *Pointer, *Interface:
 164                                                 err = "pointer or interface type"
 165                                         }
 166                                 }
 167                         } else if T := asBasic(t); T != nil {
 168                                 err = "basic or unnamed type"
 169                                 if check.conf.CompilerErrorMessages {
 170                                         check.errorf(recv.pos, "cannot define new methods on non-local type %s", recv.typ)
 171                                         err = ""
 172                                 }
 173                         } else {
 174                                 check.errorf(recv.pos, "invalid receiver type %s", recv.typ)
 175                         }
 176                         if err != "" {
 177                                 check.errorf(recv.pos, "invalid receiver type %s (%s)", recv.typ, err)
 178                                 // ok to continue
 179                         }
 180                 }
 181                 sig.recv = recv
 182         }
 183
 184         sig.params = NewTuple(params...)
 185         sig.results = NewTuple(results...)
 186         sig.variadic = variadic
 187 }
 188
 189 // collectParams declares the parameters of list in scope and returns the corresponding
 190 // variable list. If type0 != nil, it is used instead of the first type in list.
 191 func (check *Checker) collectParams(scope *Scope, list []*syntax.Field, type0 syntax.Expr, variadicOk bool) (params []*Var, variadic bool) {
 192         if list == nil {
 193                 return
 194         }
 195
 196         var named, anonymous bool
 197
 198         var typ Type
 199         var prev syntax.Expr
 200         for i, field := range list {
 201                 ftype := field.Type
 202                 // type-check type of grouped fields only once
 203                 if ftype != prev {
 204                         prev = ftype
 205                         if i == 0 && type0 != nil {
 206                                 ftype = type0
 207                         }
 208                         if t, _ := ftype.(*syntax.DotsType); t != nil {
 209                                 ftype = t.Elem
 210                                 if variadicOk && i == len(list)-1 {
 211                                         variadic = true
 212                                 } else {
 213                                         check.softErrorf(t, "can only use ... with final parameter in list")
 214                                         // ignore ... and continue
 215                                 }
 216                         }
 217                         typ = check.varType(ftype)
 218                 }
 219                 // The parser ensures that f.Tag is nil and we don't
 220                 // care if a constructed AST contains a non-nil tag.
 221                 if field.Name != nil {
 222                         // named parameter
 223                         name := field.Name.Value
 224                         if name == "" {
 225                                 check.error(field.Name, invalidAST+"anonymous parameter")
 226                                 // ok to continue
 227                         }
 228                         par := NewParam(field.Name.Pos(), check.pkg, name, typ)
 229                         check.declare(scope, field.Name, par, scope.pos)
 230                         params = append(params, par)
 231                         named = true
 232                 } else {
 233                         // anonymous parameter
 234                         par := NewParam(field.Pos(), check.pkg, "", typ)
 235                         check.recordImplicit(field, par)
 236                         params = append(params, par)
 237                         anonymous = true
 238                 }
 239         }
 240
 241         if named && anonymous {
 242                 check.error(list[0], invalidAST+"list contains both named and anonymous parameters")
 243                 // ok to continue
 244         }
 245
 246         // For a variadic function, change the last parameter's type from T to []T.
 247         // Since we type-checked T rather than ...T, we also need to retro-actively
 248         // record the type for ...T.
 249         if variadic {
 250                 last := params[len(params)-1]
 251                 last.typ = &Slice{elem: last.typ}
 252                 check.recordTypeAndValue(list[len(list)-1].Type, typexpr, last.typ, nil)
 253         }
 254
 255         return
 256 }
 257
 258 // isubst returns an x with identifiers substituted per the substitution map smap.
 259 // isubst only handles the case of (valid) method receiver type expressions correctly.
 260 func isubst(x syntax.Expr, smap map[*syntax.Name]*syntax.Name) syntax.Expr {
 261         switch n := x.(type) {
 262         case *syntax.Name:
 263                 if alt := smap[n]; alt != nil {
 264                         return alt
 265                 }
 266         // case *syntax.StarExpr:
 267         //      X := isubst(n.X, smap)
 268         //      if X != n.X {
 269         //              new := *n
 270         //              new.X = X
 271         //              return &new
 272         //      }
 273         case *syntax.Operation:
 274                 if n.Op == syntax.Mul && n.Y == nil {
 275                         X := isubst(n.X, smap)
 276                         if X != n.X {
 277                                 new := *n
 278                                 new.X = X
 279                                 return &new
 280                         }
 281                 }
 282         case *syntax.IndexExpr:
 283                 Index := isubst(n.Index, smap)
 284                 if Index != n.Index {
 285                         new := *n
 286                         new.Index = Index
 287                         return &new
 288                 }
 289         case *syntax.ListExpr:
 290                 var elems []syntax.Expr
 291                 for i, elem := range n.ElemList {
 292                         new := isubst(elem, smap)
 293                         if new != elem {
 294                                 if elems == nil {
 295                                         elems = make([]syntax.Expr, len(n.ElemList))
 296                                         copy(elems, n.ElemList)
 297                                 }
 298                                 elems[i] = new
 299                         }
 300                 }
 301                 if elems != nil {
 302                         new := *n
 303                         new.ElemList = elems
 304                         return &new
 305                 }
 306         case *syntax.ParenExpr:
 307                 return isubst(n.X, smap) // no need to keep parentheses
 308         default:
 309                 // Other receiver type expressions are invalid.
 310                 // It's fine to ignore those here as they will
 311                 // be checked elsewhere.
 312         }
 313         return x
 314 }