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