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                 // exported basic types go into package unsafe
 102                 // (currently this is just unsafe.Pointer)
 103                 if isExported(t.name) {
 104                         if obj, _ := Unsafe.scope.Lookup(t.name).(*TypeName); obj != nil {
 105                                 writeTypeName(buf, obj, qf)
 106                                 break
 107                         }
 108                 }
 109
 110                 if gcCompatibilityMode {
 111                         // forget the alias names
 112                         switch t.kind {
 113                         case Byte:
 114                                 t = Typ[Uint8]
 115                         case Rune:
 116                                 t = Typ[Int32]
 117                         }
 118                 }
 119                 buf.WriteString(t.name)
 120
 121         case *Array:
 122                 fmt.Fprintf(buf, "[%d]", t.len)
 123                 writeType(buf, t.elem, qf, visited)
 124
 125         case *Slice:
 126                 buf.WriteString("[]")
 127                 writeType(buf, t.elem, qf, visited)
 128
 129         case *Struct:
 130                 buf.WriteString("struct{")
 131                 for i, f := range t.fields {
 132                         if i > 0 {
 133                                 buf.WriteString("; ")
 134                         }
 135                         // This doesn't do the right thing for embedded type
 136                         // aliases where we should print the alias name, not
 137                         // the aliased type (see issue #44410).
 138                         if !f.embedded {
 139                                 buf.WriteString(f.name)
 140                                 buf.WriteByte(' ')
 141                         }
 142                         writeType(buf, f.typ, qf, visited)
 143                         if tag := t.Tag(i); tag != "" {
 144                                 fmt.Fprintf(buf, " %q", tag)
 145                         }
 146                 }
 147                 buf.WriteByte('}')
 148
 149         case *Pointer:
 150                 buf.WriteByte('*')
 151                 writeType(buf, t.base, qf, visited)
 152
 153         case *Tuple:
 154                 writeTuple(buf, t, false, qf, visited)
 155
 156         case *Signature:
 157                 buf.WriteString("func")
 158                 writeSignature(buf, t, qf, visited)
 159
 160         case *Sum:
 161                 writeTypeList(buf, t.types, qf, visited)
 162
 163         case *Union:
 164                 for i, e := range t.terms {
 165                         if i > 0 {
 166                                 buf.WriteString("|")
 167                         }
 168                         if t.tilde[i] {
 169                                 buf.WriteByte('~')
 170                         }
 171                         writeType(buf, e, qf, visited)
 172                 }
 173
 174         case *Interface:
 175                 // We write the source-level methods and embedded types rather
 176                 // than the actual method set since resolved method signatures
 177                 // may have non-printable cycles if parameters have embedded
 178                 // interface types that (directly or indirectly) embed the
 179                 // current interface. For instance, consider the result type
 180                 // of m:
 181                 //
 182                 //     type T interface{
 183                 //         m() interface{ T }
 184                 //     }
 185                 //
 186                 buf.WriteString("interface{")
 187                 empty := true
 188                 if gcCompatibilityMode {
 189                         // print flattened interface
 190                         // (useful to compare against gc-generated interfaces)
 191                         for i, m := range t.allMethods {
 192                                 if i > 0 {
 193                                         buf.WriteString("; ")
 194                                 }
 195                                 buf.WriteString(m.name)
 196                                 writeSignature(buf, m.typ.(*Signature), qf, visited)
 197                                 empty = false
 198                         }
 199                         if !empty && t.allTypes != nil {
 200                                 buf.WriteString("; ")
 201                         }
 202                         if t.allTypes != nil {
 203                                 buf.WriteString("type ")
 204                                 writeType(buf, t.allTypes, qf, visited)
 205                         }
 206                 } else {
 207                         // print explicit interface methods and embedded types
 208                         for i, m := range t.methods {
 209                                 if i > 0 {
 210                                         buf.WriteString("; ")
 211                                 }
 212                                 buf.WriteString(m.name)
 213                                 writeSignature(buf, m.typ.(*Signature), qf, visited)
 214                                 empty = false
 215                         }
 216                         if !empty && len(t.embeddeds) > 0 {
 217                                 buf.WriteString("; ")
 218                         }
 219                         for i, typ := range t.embeddeds {
 220                                 if i > 0 {
 221                                         buf.WriteString("; ")
 222                                 }
 223                                 writeType(buf, typ, qf, visited)
 224                                 empty = false
 225                         }
 226                 }
 227                 if debug && (t.allMethods == nil || len(t.methods) > len(t.allMethods)) {
 228                         if !empty {
 229                                 buf.WriteByte(' ')
 230                         }
 231                         buf.WriteString("/* incomplete */")
 232                 }
 233                 buf.WriteByte('}')
 234
 235         case *Map:
 236                 buf.WriteString("map[")
 237                 writeType(buf, t.key, qf, visited)
 238                 buf.WriteByte(']')
 239                 writeType(buf, t.elem, qf, visited)
 240
 241         case *Chan:
 242                 var s string
 243                 var parens bool
 244                 switch t.dir {
 245                 case SendRecv:
 246                         s = "chan "
 247                         // chan (<-chan T) requires parentheses
 248                         if c, _ := t.elem.(*Chan); c != nil && c.dir == RecvOnly {
 249                                 parens = true
 250                         }
 251                 case SendOnly:
 252                         s = "chan<- "
 253                 case RecvOnly:
 254                         s = "<-chan "
 255                 default:
 256                         panic("unreachable")
 257                 }
 258                 buf.WriteString(s)
 259                 if parens {
 260                         buf.WriteByte('(')
 261                 }
 262                 writeType(buf, t.elem, qf, visited)
 263                 if parens {
 264                         buf.WriteByte(')')
 265                 }
 266
 267         case *Named:
 268                 writeTypeName(buf, t.obj, qf)
 269                 if t.targs != nil {
 270                         // instantiated type
 271                         buf.WriteByte('[')
 272                         writeTypeList(buf, t.targs, qf, visited)
 273                         buf.WriteByte(']')
 274                 } else if t.tparams != nil {
 275                         // parameterized type
 276                         writeTParamList(buf, t.tparams, qf, visited)
 277                 }
 278
 279         case *TypeParam:
 280                 s := "?"
 281                 if t.obj != nil {
 282                         // Optionally write out package for typeparams (like Named).
 283                         // TODO(danscales): this is required for import/export, so
 284                         // we maybe need a separate function that won't be changed
 285                         // for debugging purposes.
 286                         if t.obj.pkg != nil {
 287                                 writePackage(buf, t.obj.pkg, qf)
 288                         }
 289                         s = t.obj.name
 290                 }
 291                 buf.WriteString(s + subscript(t.id))
 292
 293         case *instance:
 294                 buf.WriteByte(instanceMarker) // indicate "non-evaluated" syntactic instance
 295                 writeTypeName(buf, t.base.obj, qf)
 296                 buf.WriteByte('[')
 297                 writeTypeList(buf, t.targs, qf, visited)
 298                 buf.WriteByte(']')
 299
 300         case *bottom:
 301                 buf.WriteString("⊥")
 302
 303         case *top:
 304                 buf.WriteString("⊤")
 305
 306         default:
 307                 // For externally defined implementations of Type.
 308                 // Note: In this case cycles won't be caught.
 309                 buf.WriteString(t.String())
 310         }
 311 }
 312
 313 func writeTypeList(buf *bytes.Buffer, list []Type, qf Qualifier, visited []Type) {
 314         for i, typ := range list {
 315                 if i > 0 {
 316                         buf.WriteString(", ")
 317                 }
 318                 writeType(buf, typ, qf, visited)
 319         }
 320 }
 321
 322 func writeTParamList(buf *bytes.Buffer, list []*TypeName, qf Qualifier, visited []Type) {
 323         buf.WriteString("[")
 324         var prev Type
 325         for i, p := range list {
 326                 // TODO(gri) support 'any' sugar here.
 327                 var b Type = &emptyInterface
 328                 if t, _ := p.typ.(*TypeParam); t != nil && t.bound != nil {
 329                         b = t.bound
 330                 }
 331                 if i > 0 {
 332                         if b != prev {
 333                                 // type bound changed - write previous one before advancing
 334                                 buf.WriteByte(' ')
 335                                 writeType(buf, prev, qf, visited)
 336                         }
 337                         buf.WriteString(", ")
 338                 }
 339                 prev = b
 340
 341                 if t, _ := p.typ.(*TypeParam); t != nil {
 342                         writeType(buf, t, qf, visited)
 343                 } else {
 344                         buf.WriteString(p.name)
 345                 }
 346         }
 347         if prev != nil {
 348                 buf.WriteByte(' ')
 349                 writeType(buf, prev, qf, visited)
 350         }
 351         buf.WriteByte(']')
 352 }
 353
 354 func writeTypeName(buf *bytes.Buffer, obj *TypeName, qf Qualifier) {
 355         s := "<Named w/o object>"
 356         if obj != nil {
 357                 if obj.pkg != nil {
 358                         writePackage(buf, obj.pkg, qf)
 359                 }
 360                 // TODO(gri): function-local named types should be displayed
 361                 // differently from named types at package level to avoid
 362                 // ambiguity.
 363                 s = obj.name
 364         }
 365         buf.WriteString(s)
 366 }
 367
 368 func writeTuple(buf *bytes.Buffer, tup *Tuple, variadic bool, qf Qualifier, visited []Type) {
 369         buf.WriteByte('(')
 370         if tup != nil {
 371                 for i, v := range tup.vars {
 372                         if i > 0 {
 373                                 buf.WriteString(", ")
 374                         }
 375                         if v.name != "" {
 376                                 buf.WriteString(v.name)
 377                                 buf.WriteByte(' ')
 378                         }
 379                         typ := v.typ
 380                         if variadic && i == len(tup.vars)-1 {
 381                                 if s, ok := typ.(*Slice); ok {
 382                                         buf.WriteString("...")
 383                                         typ = s.elem
 384                                 } else {
 385                                         // special case:
 386                                         // append(s, "foo"...) leads to signature func([]byte, string...)
 387                                         if t := asBasic(typ); t == nil || t.kind != String {
 388                                                 panic("internal error: string type expected")
 389                                         }
 390                                         writeType(buf, typ, qf, visited)
 391                                         buf.WriteString("...")
 392                                         continue
 393                                 }
 394                         }
 395                         writeType(buf, typ, qf, visited)
 396                 }
 397         }
 398         buf.WriteByte(')')
 399 }
 400
 401 // WriteSignature writes the representation of the signature sig to buf,
 402 // without a leading "func" keyword.
 403 // The Qualifier controls the printing of
 404 // package-level objects, and may be nil.
 405 func WriteSignature(buf *bytes.Buffer, sig *Signature, qf Qualifier) {
 406         writeSignature(buf, sig, qf, make([]Type, 0, 8))
 407 }
 408
 409 func writeSignature(buf *bytes.Buffer, sig *Signature, qf Qualifier, visited []Type) {
 410         if sig.tparams != nil {
 411                 writeTParamList(buf, sig.tparams, qf, visited)
 412         }
 413
 414         writeTuple(buf, sig.params, sig.variadic, qf, visited)
 415
 416         n := sig.results.Len()
 417         if n == 0 {
 418                 // no result
 419                 return
 420         }
 421
 422         buf.WriteByte(' ')
 423         if n == 1 && sig.results.vars[0].name == "" {
 424                 // single unnamed result
 425                 writeType(buf, sig.results.vars[0].typ, qf, visited)
 426                 return
 427         }
 428
 429         // multiple or named result(s)
 430         writeTuple(buf, sig.results, false, qf, visited)
 431 }
 432
 433 // subscript returns the decimal (utf8) representation of x using subscript digits.
 434 func subscript(x uint64) string {
 435         const w = len("₀") // all digits 0...9 have the same utf8 width
 436         var buf [32 * w]byte
 437         i := len(buf)
 438         for {
 439                 i -= w
 440                 utf8.EncodeRune(buf[i:], '₀'+rune(x%10)) // '₀' == U+2080
 441                 x /= 10
 442                 if x == 0 {
 443                         break
 444                 }
 445         }
 446         return string(buf[i:])
 447 }