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