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

   1 // Copyright 2013 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 // This file implements printing of types.
   6
   7 package types2
   8
   9 import (
  10         "bytes"
  11         "fmt"
  12         "unicode/utf8"
  13 )
  14
  15 // A Qualifier controls how named package-level objects are printed in
  16 // calls to TypeString, ObjectString, and SelectionString.
  17 //
  18 // These three formatting routines call the Qualifier for each
  19 // package-level object O, and if the Qualifier returns a non-empty
  20 // string p, the object is printed in the form p.O.
  21 // If it returns an empty string, only the object name O is printed.
  22 //
  23 // Using a nil Qualifier is equivalent to using (*Package).Path: the
  24 // object is qualified by the import path, e.g., "encoding/json.Marshal".
  25 //
  26 type Qualifier func(*Package) string
  27
  28 // RelativeTo returns a Qualifier that fully qualifies members of
  29 // all packages other than pkg.
  30 func RelativeTo(pkg *Package) Qualifier {
  31         if pkg == nil {
  32                 return nil
  33         }
  34         return func(other *Package) string {
  35                 if pkg == other {
  36                         return "" // same package; unqualified
  37                 }
  38                 return other.Path()
  39         }
  40 }
  41
  42 // If gcCompatibilityMode is set, printing of types is modified
  43 // to match the representation of some types in the gc compiler:
  44 //
  45 //      - byte and rune lose their alias name and simply stand for
  46 //        uint8 and int32 respectively
  47 //      - embedded interfaces get flattened (the embedding info is lost,
  48 //        and certain recursive interface types cannot be printed anymore)
  49 //
  50 // This makes it easier to compare packages computed with the type-
  51 // checker vs packages imported from gc export data.
  52 //
  53 // Caution: This flag affects all uses of WriteType, globally.
  54 // It is only provided for testing in conjunction with
  55 // gc-generated data.
  56 //
  57 // This flag is exported in the x/tools/go/types package. We don't
  58 // need it at the moment in the std repo and so we don't export it
  59 // anymore. We should eventually try to remove it altogether.
  60 // TODO(gri) remove this
  61 var gcCompatibilityMode bool
  62
  63 // TypeString returns the string representation of typ.
  64 // The Qualifier controls the printing of
  65 // package-level objects, and may be nil.
  66 func TypeString(typ Type, qf Qualifier) string {
  67         var buf bytes.Buffer
  68         WriteType(&buf, typ, qf)
  69         return buf.String()
  70 }
  71
  72 // WriteType writes the string representation of typ to buf.
  73 // The Qualifier controls the printing of
  74 // package-level objects, and may be nil.
  75 func WriteType(buf *bytes.Buffer, typ Type, qf Qualifier) {
  76         writeType(buf, typ, qf, make([]Type, 0, 8))
  77 }
  78
  79 // instanceMarker is the prefix for an instantiated type
  80 // in "non-evaluated" instance form.
  81 const instanceMarker = '#'
  82
  83 func writeType(buf *bytes.Buffer, typ Type, qf Qualifier, visited []Type) {
  84         // Theoretically, this is a quadratic lookup algorithm, but in
  85         // practice deeply nested composite types with unnamed component
  86         // types are uncommon. This code is likely more efficient than
  87         // using a map.
  88         for _, t := range visited {
  89                 if t == typ {
  90                         fmt.Fprintf(buf, "○%T", goTypeName(typ)) // cycle to typ
  91                         return
  92                 }
  93         }
  94         visited = append(visited, typ)
  95
  96         switch t := typ.(type) {
  97         case nil:
  98                 buf.WriteString("<nil>")
  99
 100         case *Basic:
 101                 if t.kind == UnsafePointer {
 102                         buf.WriteString("unsafe.")
 103                 }
 104                 if gcCompatibilityMode {
 105                         // forget the alias names
 106                         switch t.kind {
 107                         case Byte:
 108                                 t = Typ[Uint8]
 109                         case Rune:
 110                                 t = Typ[Int32]
 111                         }
 112                 }
 113                 buf.WriteString(t.name)
 114
 115         case *Array:
 116                 fmt.Fprintf(buf, "[%d]", t.len)
 117                 writeType(buf, t.elem, qf, visited)
 118
 119         case *Slice:
 120                 buf.WriteString("[]")
 121                 writeType(buf, t.elem, qf, visited)
 122
 123         case *Struct:
 124                 buf.WriteString("struct{")
 125                 for i, f := range t.fields {
 126                         if i > 0 {
 127                                 buf.WriteString("; ")
 128                         }
 129                         // This doesn't do the right thing for embedded type
 130                         // aliases where we should print the alias name, not
 131                         // the aliased type (see issue #44410).
 132                         if !f.embedded {
 133                                 buf.WriteString(f.name)
 134                                 buf.WriteByte(' ')
 135                         }
 136                         writeType(buf, f.typ, qf, visited)
 137                         if tag := t.Tag(i); tag != "" {
 138                                 fmt.Fprintf(buf, " %q", tag)
 139                         }
 140                 }
 141                 buf.WriteByte('}')
 142
 143         case *Pointer:
 144                 buf.WriteByte('*')
 145                 writeType(buf, t.base, qf, visited)
 146
 147         case *Tuple:
 148                 writeTuple(buf, t, false, qf, visited)
 149
 150         case *Signature:
 151                 buf.WriteString("func")
 152                 writeSignature(buf, t, qf, visited)
 153
 154         case *Sum:
 155                 for i, t := range t.types {
 156                         if i > 0 {
 157                                 buf.WriteString(", ")
 158                         }
 159                         writeType(buf, t, qf, visited)
 160                 }
 161
 162         case *Interface:
 163                 // We write the source-level methods and embedded types rather
 164                 // than the actual method set since resolved method signatures
 165                 // may have non-printable cycles if parameters have embedded
 166                 // interface types that (directly or indirectly) embed the
 167                 // current interface. For instance, consider the result type
 168                 // of m:
 169                 //
 170                 //     type T interface{
 171                 //         m() interface{ T }
 172                 //     }
 173                 //
 174                 buf.WriteString("interface{")
 175                 empty := true
 176                 if gcCompatibilityMode {
 177                         // print flattened interface
 178                         // (useful to compare against gc-generated interfaces)
 179                         for i, m := range t.allMethods {
 180                                 if i > 0 {
 181                                         buf.WriteString("; ")
 182                                 }
 183                                 buf.WriteString(m.name)
 184                                 writeSignature(buf, m.typ.(*Signature), qf, visited)
 185                                 empty = false
 186                         }
 187                         if !empty && t.allTypes != nil {
 188                                 buf.WriteString("; ")
 189                         }
 190                         if t.allTypes != nil {
 191                                 buf.WriteString("type ")
 192                                 writeType(buf, t.allTypes, qf, visited)
 193                         }
 194                 } else {
 195                         // print explicit interface methods and embedded types
 196                         for i, m := range t.methods {
 197                                 if i > 0 {
 198                                         buf.WriteString("; ")
 199                                 }
 200                                 buf.WriteString(m.name)
 201                                 writeSignature(buf, m.typ.(*Signature), qf, visited)
 202                                 empty = false
 203                         }
 204                         if !empty && t.types != nil {
 205                                 buf.WriteString("; ")
 206                         }
 207                         if t.types != nil {
 208                                 buf.WriteString("type ")
 209                                 writeType(buf, t.types, qf, visited)
 210                                 empty = false
 211                         }
 212                         if !empty && len(t.embeddeds) > 0 {
 213                                 buf.WriteString("; ")
 214                         }
 215                         for i, typ := range t.embeddeds {
 216                                 if i > 0 {
 217                                         buf.WriteString("; ")
 218                                 }
 219                                 writeType(buf, typ, qf, visited)
 220                                 empty = false
 221                         }
 222                 }
 223                 if t.allMethods == nil || len(t.methods) > len(t.allMethods) {
 224                         if !empty {
 225                                 buf.WriteByte(' ')
 226                         }
 227                         buf.WriteString("/* incomplete */")
 228                 }
 229                 buf.WriteByte('}')
 230
 231         case *Map:
 232                 buf.WriteString("map[")
 233                 writeType(buf, t.key, qf, visited)
 234                 buf.WriteByte(']')
 235                 writeType(buf, t.elem, qf, visited)
 236
 237         case *Chan:
 238                 var s string
 239                 var parens bool
 240                 switch t.dir {
 241                 case SendRecv:
 242                         s = "chan "
 243                         // chan (<-chan T) requires parentheses
 244                         if c, _ := t.elem.(*Chan); c != nil && c.dir == RecvOnly {
 245                                 parens = true
 246                         }
 247                 case SendOnly:
 248                         s = "chan<- "
 249                 case RecvOnly:
 250                         s = "<-chan "
 251                 default:
 252                         panic("unreachable")
 253                 }
 254                 buf.WriteString(s)
 255                 if parens {
 256                         buf.WriteByte('(')
 257                 }
 258                 writeType(buf, t.elem, qf, visited)
 259                 if parens {
 260                         buf.WriteByte(')')
 261                 }
 262
 263         case *Named:
 264                 writeTypeName(buf, t.obj, qf)
 265                 if t.targs != nil {
 266                         // instantiated type
 267                         buf.WriteByte('[')
 268                         writeTypeList(buf, t.targs, qf, visited)
 269                         buf.WriteByte(']')
 270                 } else if t.tparams != nil {
 271                         // parameterized type
 272                         writeTParamList(buf, t.tparams, qf, visited)
 273                 }
 274
 275         case *TypeParam:
 276                 s := "?"
 277                 if t.obj != nil {
 278                         s = t.obj.name
 279                 }
 280                 buf.WriteString(s + subscript(t.id))
 281
 282         case *instance:
 283                 buf.WriteByte(instanceMarker) // indicate "non-evaluated" syntactic instance
 284                 writeTypeName(buf, t.base.obj, qf)
 285                 buf.WriteByte('[')
 286                 writeTypeList(buf, t.targs, qf, visited)
 287                 buf.WriteByte(']')
 288
 289         case *bottom:
 290                 buf.WriteString("⊥")
 291
 292         case *top:
 293                 buf.WriteString("⊤")
 294
 295         default:
 296                 // For externally defined implementations of Type.
 297                 buf.WriteString(t.String())
 298         }
 299 }
 300
 301 func writeTypeList(buf *bytes.Buffer, list []Type, qf Qualifier, visited []Type) {
 302         for i, typ := range list {
 303                 if i > 0 {
 304                         buf.WriteString(", ")
 305                 }
 306                 writeType(buf, typ, qf, visited)
 307         }
 308 }
 309
 310 func writeTParamList(buf *bytes.Buffer, list []*TypeName, qf Qualifier, visited []Type) {
 311         buf.WriteString("[")
 312         var prev Type
 313         for i, p := range list {
 314                 // TODO(gri) support 'any' sugar here.
 315                 var b Type = &emptyInterface
 316                 if t, _ := p.typ.(*TypeParam); t != nil && t.bound != nil {
 317                         b = t.bound
 318                 }
 319                 if i > 0 {
 320                         if b != prev {
 321                                 // type bound changed - write previous one before advancing
 322                                 buf.WriteByte(' ')
 323                                 writeType(buf, prev, qf, visited)
 324                         }
 325                         buf.WriteString(", ")
 326                 }
 327                 prev = b
 328
 329                 if t, _ := p.typ.(*TypeParam); t != nil {
 330                         writeType(buf, t, qf, visited)
 331                 } else {
 332                         buf.WriteString(p.name)
 333                 }
 334         }
 335         if prev != nil {
 336                 buf.WriteByte(' ')
 337                 writeType(buf, prev, qf, visited)
 338         }
 339         buf.WriteByte(']')
 340 }
 341
 342 func writeTypeName(buf *bytes.Buffer, obj *TypeName, qf Qualifier) {
 343         s := "<Named w/o object>"
 344         if obj != nil {
 345                 if obj.pkg != nil {
 346                         writePackage(buf, obj.pkg, qf)
 347                 }
 348                 // TODO(gri): function-local named types should be displayed
 349                 // differently from named types at package level to avoid
 350                 // ambiguity.
 351                 s = obj.name
 352         }
 353         buf.WriteString(s)
 354 }
 355
 356 func writeTuple(buf *bytes.Buffer, tup *Tuple, variadic bool, qf Qualifier, visited []Type) {
 357         buf.WriteByte('(')
 358         if tup != nil {
 359                 for i, v := range tup.vars {
 360                         if i > 0 {
 361                                 buf.WriteString(", ")
 362                         }
 363                         if v.name != "" {
 364                                 buf.WriteString(v.name)
 365                                 buf.WriteByte(' ')
 366                         }
 367                         typ := v.typ
 368                         if variadic && i == len(tup.vars)-1 {
 369                                 if s, ok := typ.(*Slice); ok {
 370                                         buf.WriteString("...")
 371                                         typ = s.elem
 372                                 } else {
 373                                         // special case:
 374                                         // append(s, "foo"...) leads to signature func([]byte, string...)
 375                                         if t := asBasic(typ); t == nil || t.kind != String {
 376                                                 panic("internal error: string type expected")
 377                                         }
 378                                         writeType(buf, typ, qf, visited)
 379                                         buf.WriteString("...")
 380                                         continue
 381                                 }
 382                         }
 383                         writeType(buf, typ, qf, visited)
 384                 }
 385         }
 386         buf.WriteByte(')')
 387 }
 388
 389 // WriteSignature writes the representation of the signature sig to buf,
 390 // without a leading "func" keyword.
 391 // The Qualifier controls the printing of
 392 // package-level objects, and may be nil.
 393 func WriteSignature(buf *bytes.Buffer, sig *Signature, qf Qualifier) {
 394         writeSignature(buf, sig, qf, make([]Type, 0, 8))
 395 }
 396
 397 func writeSignature(buf *bytes.Buffer, sig *Signature, qf Qualifier, visited []Type) {
 398         if sig.tparams != nil {
 399                 writeTParamList(buf, sig.tparams, qf, visited)
 400         }
 401
 402         writeTuple(buf, sig.params, sig.variadic, qf, visited)
 403
 404         n := sig.results.Len()
 405         if n == 0 {
 406                 // no result
 407                 return
 408         }
 409
 410         buf.WriteByte(' ')
 411         if n == 1 && sig.results.vars[0].name == "" {
 412                 // single unnamed result
 413                 writeType(buf, sig.results.vars[0].typ, qf, visited)
 414                 return
 415         }
 416
 417         // multiple or named result(s)
 418         writeTuple(buf, sig.results, false, qf, visited)
 419 }
 420
 421 // subscript returns the decimal (utf8) representation of x using subscript digits.
 422 func subscript(x uint64) string {
 423         const w = len("₀") // all digits 0...9 have the same utf8 width
 424         var buf [32 * w]byte
 425         i := len(buf)
 426         for {
 427                 i -= w
 428                 utf8.EncodeRune(buf[i:], '₀'+rune(x%10)) // '₀' == U+2080
 429                 x /= 10
 430                 if x == 0 {
 431                         break
 432                 }
 433         }
 434         return string(buf[i:])
 435 }