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