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 // TypeString returns the string representation of typ.
  43 // The Qualifier controls the printing of
  44 // package-level objects, and may be nil.
  45 func TypeString(typ Type, qf Qualifier) string {
  46         var buf bytes.Buffer
  47         WriteType(&buf, typ, qf)
  48         return buf.String()
  49 }
  50
  51 // WriteType writes the string representation of typ to buf.
  52 // The Qualifier controls the printing of
  53 // package-level objects, and may be nil.
  54 func WriteType(buf *bytes.Buffer, typ Type, qf Qualifier) {
  55         writeType(buf, typ, qf, make([]Type, 0, 8))
  56 }
  57
  58 // instanceMarker is the prefix for an instantiated type
  59 // in "non-evaluated" instance form.
  60 const instanceMarker = '#'
  61
  62 func writeType(buf *bytes.Buffer, typ Type, qf Qualifier, visited []Type) {
  63         // Theoretically, this is a quadratic lookup algorithm, but in
  64         // practice deeply nested composite types with unnamed component
  65         // types are uncommon. This code is likely more efficient than
  66         // using a map.
  67         for _, t := range visited {
  68                 if t == typ {
  69                         fmt.Fprintf(buf, "○%T", goTypeName(typ)) // cycle to typ
  70                         return
  71                 }
  72         }
  73         visited = append(visited, typ)
  74
  75         switch t := typ.(type) {
  76         case nil:
  77                 buf.WriteString("<nil>")
  78
  79         case *Basic:
  80                 // exported basic types go into package unsafe
  81                 // (currently this is just unsafe.Pointer)
  82                 if isExported(t.name) {
  83                         if obj, _ := Unsafe.scope.Lookup(t.name).(*TypeName); obj != nil {
  84                                 writeTypeName(buf, obj, qf)
  85                                 break
  86                         }
  87                 }
  88                 buf.WriteString(t.name)
  89
  90         case *Array:
  91                 fmt.Fprintf(buf, "[%d]", t.len)
  92                 writeType(buf, t.elem, qf, visited)
  93
  94         case *Slice:
  95                 buf.WriteString("[]")
  96                 writeType(buf, t.elem, qf, visited)
  97
  98         case *Struct:
  99                 buf.WriteString("struct{")
 100                 for i, f := range t.fields {
 101                         if i > 0 {
 102                                 buf.WriteString("; ")
 103                         }
 104                         // This doesn't do the right thing for embedded type
 105                         // aliases where we should print the alias name, not
 106                         // the aliased type (see issue #44410).
 107                         if !f.embedded {
 108                                 buf.WriteString(f.name)
 109                                 buf.WriteByte(' ')
 110                         }
 111                         writeType(buf, f.typ, qf, visited)
 112                         if tag := t.Tag(i); tag != "" {
 113                                 fmt.Fprintf(buf, " %q", tag)
 114                         }
 115                 }
 116                 buf.WriteByte('}')
 117
 118         case *Pointer:
 119                 buf.WriteByte('*')
 120                 writeType(buf, t.base, qf, visited)
 121
 122         case *Tuple:
 123                 writeTuple(buf, t, false, qf, visited)
 124
 125         case *Signature:
 126                 buf.WriteString("func")
 127                 writeSignature(buf, t, qf, visited)
 128
 129         case *Union:
 130                 // Unions only appear as (syntactic) embedded elements
 131                 // in interfaces and syntactically cannot be empty.
 132                 if t.Len() == 0 {
 133                         panic("empty union")
 134                 }
 135                 for i, t := range t.terms {
 136                         if i > 0 {
 137                                 buf.WriteByte('|')
 138                         }
 139                         if t.tilde {
 140                                 buf.WriteByte('~')
 141                         }
 142                         writeType(buf, t.typ, qf, visited)
 143                 }
 144
 145         case *Interface:
 146                 buf.WriteString("interface{")
 147                 first := true
 148                 for _, m := range t.methods {
 149                         if !first {
 150                                 buf.WriteString("; ")
 151                         }
 152                         first = false
 153                         buf.WriteString(m.name)
 154                         writeSignature(buf, m.typ.(*Signature), qf, visited)
 155                 }
 156                 for _, typ := range t.embeddeds {
 157                         if !first {
 158                                 buf.WriteString("; ")
 159                         }
 160                         first = false
 161                         writeType(buf, typ, qf, visited)
 162                 }
 163                 buf.WriteByte('}')
 164
 165         case *Map:
 166                 buf.WriteString("map[")
 167                 writeType(buf, t.key, qf, visited)
 168                 buf.WriteByte(']')
 169                 writeType(buf, t.elem, qf, visited)
 170
 171         case *Chan:
 172                 var s string
 173                 var parens bool
 174                 switch t.dir {
 175                 case SendRecv:
 176                         s = "chan "
 177                         // chan (<-chan T) requires parentheses
 178                         if c, _ := t.elem.(*Chan); c != nil && c.dir == RecvOnly {
 179                                 parens = true
 180                         }
 181                 case SendOnly:
 182                         s = "chan<- "
 183                 case RecvOnly:
 184                         s = "<-chan "
 185                 default:
 186                         unreachable()
 187                 }
 188                 buf.WriteString(s)
 189                 if parens {
 190                         buf.WriteByte('(')
 191                 }
 192                 writeType(buf, t.elem, qf, visited)
 193                 if parens {
 194                         buf.WriteByte(')')
 195                 }
 196
 197         case *Named:
 198                 if t.instance != nil {
 199                         buf.WriteByte(instanceMarker)
 200                 }
 201                 writeTypeName(buf, t.obj, qf)
 202                 if t.targs != nil {
 203                         // instantiated type
 204                         buf.WriteByte('[')
 205                         writeTypeList(buf, t.targs, qf, visited)
 206                         buf.WriteByte(']')
 207                 } else if t.TParams().Len() != 0 {
 208                         // parameterized type
 209                         writeTParamList(buf, t.TParams().list(), qf, visited)
 210                 }
 211
 212         case *TypeParam:
 213                 s := "?"
 214                 if t.obj != nil {
 215                         // Optionally write out package for typeparams (like Named).
 216                         // TODO(danscales): this is required for import/export, so
 217                         // we maybe need a separate function that won't be changed
 218                         // for debugging purposes.
 219                         if t.obj.pkg != nil {
 220                                 writePackage(buf, t.obj.pkg, qf)
 221                         }
 222                         s = t.obj.name
 223                 }
 224                 buf.WriteString(s + subscript(t.id))
 225
 226         case *top:
 227                 buf.WriteString("⊤")
 228
 229         default:
 230                 // For externally defined implementations of Type.
 231                 // Note: In this case cycles won't be caught.
 232                 buf.WriteString(t.String())
 233         }
 234 }
 235
 236 func writeTypeList(buf *bytes.Buffer, list []Type, qf Qualifier, visited []Type) {
 237         for i, typ := range list {
 238                 if i > 0 {
 239                         buf.WriteString(", ")
 240                 }
 241                 writeType(buf, typ, qf, visited)
 242         }
 243 }
 244
 245 func writeTParamList(buf *bytes.Buffer, list []*TypeParam, qf Qualifier, visited []Type) {
 246         buf.WriteString("[")
 247         var prev Type
 248         for i, tpar := range list {
 249                 // Determine the type parameter and its constraint.
 250                 // list is expected to hold type parameter names,
 251                 // but don't crash if that's not the case.
 252                 var bound Type
 253                 if tpar != nil {
 254                         bound = tpar.bound // should not be nil but we want to see it if it is
 255                 }
 256
 257                 if i > 0 {
 258                         if bound != prev {
 259                                 // bound changed - write previous one before advancing
 260                                 buf.WriteByte(' ')
 261                                 writeType(buf, prev, qf, visited)
 262                         }
 263                         buf.WriteString(", ")
 264                 }
 265                 prev = bound
 266
 267                 if tpar != nil {
 268                         writeType(buf, tpar, qf, visited)
 269                 } else {
 270                         buf.WriteString(tpar.obj.name)
 271                 }
 272         }
 273         if prev != nil {
 274                 buf.WriteByte(' ')
 275                 writeType(buf, prev, qf, visited)
 276         }
 277         buf.WriteByte(']')
 278 }
 279
 280 func writeTypeName(buf *bytes.Buffer, obj *TypeName, qf Qualifier) {
 281         if obj == nil {
 282                 buf.WriteString("<Named w/o object>")
 283                 return
 284         }
 285         if obj.pkg != nil {
 286                 writePackage(buf, obj.pkg, qf)
 287         }
 288         buf.WriteString(obj.name)
 289
 290         if instanceHashing != 0 {
 291                 // For local defined types, use the (original!) TypeName's scope
 292                 // numbers to disambiguate.
 293                 typ := obj.typ.(*Named)
 294                 // TODO(gri) Figure out why typ.orig != typ.orig.orig sometimes
 295                 //           and whether the loop can iterate more than twice.
 296                 //           (It seems somehow connected to instance types.)
 297                 for typ.orig != typ {
 298                         typ = typ.orig
 299                 }
 300                 writeScopeNumbers(buf, typ.obj.parent)
 301         }
 302 }
 303
 304 // writeScopeNumbers writes the number sequence for this scope to buf
 305 // in the form ".i.j.k" where i, j, k, etc. stand for scope numbers.
 306 // If a scope is nil or has no parent (such as a package scope), nothing
 307 // is written.
 308 func writeScopeNumbers(buf *bytes.Buffer, s *Scope) {
 309         if s != nil && s.number > 0 {
 310                 writeScopeNumbers(buf, s.parent)
 311                 fmt.Fprintf(buf, ".%d", s.number)
 312         }
 313 }
 314
 315 func writeTuple(buf *bytes.Buffer, tup *Tuple, variadic bool, qf Qualifier, visited []Type) {
 316         buf.WriteByte('(')
 317         if tup != nil {
 318                 for i, v := range tup.vars {
 319                         if i > 0 {
 320                                 buf.WriteString(", ")
 321                         }
 322                         if v.name != "" {
 323                                 buf.WriteString(v.name)
 324                                 buf.WriteByte(' ')
 325                         }
 326                         typ := v.typ
 327                         if variadic && i == len(tup.vars)-1 {
 328                                 if s, ok := typ.(*Slice); ok {
 329                                         buf.WriteString("...")
 330                                         typ = s.elem
 331                                 } else {
 332                                         // special case:
 333                                         // append(s, "foo"...) leads to signature func([]byte, string...)
 334                                         if t := asBasic(typ); t == nil || t.kind != String {
 335                                                 panic("expected string type")
 336                                         }
 337                                         writeType(buf, typ, qf, visited)
 338                                         buf.WriteString("...")
 339                                         continue
 340                                 }
 341                         }
 342                         writeType(buf, typ, qf, visited)
 343                 }
 344         }
 345         buf.WriteByte(')')
 346 }
 347
 348 // WriteSignature writes the representation of the signature sig to buf,
 349 // without a leading "func" keyword.
 350 // The Qualifier controls the printing of
 351 // package-level objects, and may be nil.
 352 func WriteSignature(buf *bytes.Buffer, sig *Signature, qf Qualifier) {
 353         writeSignature(buf, sig, qf, make([]Type, 0, 8))
 354 }
 355
 356 func writeSignature(buf *bytes.Buffer, sig *Signature, qf Qualifier, visited []Type) {
 357         if sig.TParams().Len() != 0 {
 358                 writeTParamList(buf, sig.TParams().list(), qf, visited)
 359         }
 360
 361         writeTuple(buf, sig.params, sig.variadic, qf, visited)
 362
 363         n := sig.results.Len()
 364         if n == 0 {
 365                 // no result
 366                 return
 367         }
 368
 369         buf.WriteByte(' ')
 370         if n == 1 && sig.results.vars[0].name == "" {
 371                 // single unnamed result
 372                 writeType(buf, sig.results.vars[0].typ, qf, visited)
 373                 return
 374         }
 375
 376         // multiple or named result(s)
 377         writeTuple(buf, sig.results, false, qf, visited)
 378 }
 379
 380 // subscript returns the decimal (utf8) representation of x using subscript digits.
 381 func subscript(x uint64) string {
 382         const w = len("₀") // all digits 0...9 have the same utf8 width
 383         var buf [32 * w]byte
 384         i := len(buf)
 385         for {
 386                 i -= w
 387                 utf8.EncodeRune(buf[i:], '₀'+rune(x%10)) // '₀' == U+2080
 388                 x /= 10
 389                 if x == 0 {
 390                         break
 391                 }
 392         }
 393         return string(buf[i:])
 394 }