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 various field and method lookup functions. 6 7 package types 8 9 import ( 10 "bytes" 11 "strings" 12 ) 13 14 // Internal use of LookupFieldOrMethod: If the obj result is a method 15 // associated with a concrete (non-interface) type, the method's signature 16 // may not be fully set up. Call Checker.objDecl(obj, nil) before accessing 17 // the method's type. 18 19 // LookupFieldOrMethod looks up a field or method with given package and name 20 // in T and returns the corresponding *Var or *Func, an index sequence, and a 21 // bool indicating if there were any pointer indirections on the path to the 22 // field or method. If addressable is set, T is the type of an addressable 23 // variable (only matters for method lookups). T must not be nil. 24 // 25 // The last index entry is the field or method index in the (possibly embedded) 26 // type where the entry was found, either: 27 // 28 // 1. the list of declared methods of a named type; or 29 // 2. the list of all methods (method set) of an interface type; or 30 // 3. the list of fields of a struct type. 31 // 32 // The earlier index entries are the indices of the embedded struct fields 33 // traversed to get to the found entry, starting at depth 0. 34 // 35 // If no entry is found, a nil object is returned. In this case, the returned 36 // index and indirect values have the following meaning: 37 // 38 // - If index != nil, the index sequence points to an ambiguous entry 39 // (the same name appeared more than once at the same embedding level). 40 // 41 // - If indirect is set, a method with a pointer receiver type was found 42 // but there was no pointer on the path from the actual receiver type to 43 // the method's formal receiver base type, nor was the receiver addressable. 44 func LookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string) (obj Object, index []int, indirect bool) { 45 if T == nil { 46 panic("LookupFieldOrMethod on nil type") 47 } 48 49 // Methods cannot be associated to a named pointer type. 50 // (spec: "The type denoted by T is called the receiver base type; 51 // it must not be a pointer or interface type and it must be declared 52 // in the same package as the method."). 53 // Thus, if we have a named pointer type, proceed with the underlying 54 // pointer type but discard the result if it is a method since we would 55 // not have found it for T (see also issue 8590). 56 if t, _ := T.(*Named); t != nil { 57 if p, _ := t.Underlying().(*Pointer); p != nil { 58 obj, index, indirect = lookupFieldOrMethod(p, false, pkg, name, false) 59 if _, ok := obj.(*Func); ok { 60 return nil, nil, false 61 } 62 return 63 } 64 } 65 66 obj, index, indirect = lookupFieldOrMethod(T, addressable, pkg, name, false) 67 68 // If we didn't find anything and if we have a type parameter with a core type, 69 // see if there is a matching field (but not a method, those need to be declared 70 // explicitly in the constraint). If the constraint is a named pointer type (see 71 // above), we are ok here because only fields are accepted as results. 72 const enableTParamFieldLookup = false // see issue #51576 73 if enableTParamFieldLookup && obj == nil && isTypeParam(T) { 74 if t := coreType(T); t != nil { 75 obj, index, indirect = lookupFieldOrMethod(t, addressable, pkg, name, false) 76 if _, ok := obj.(*Var); !ok { 77 obj, index, indirect = nil, nil, false // accept fields (variables) only 78 } 79 } 80 } 81 return 82 } 83 84 // lookupFieldOrMethod should only be called by LookupFieldOrMethod and missingMethod. 85 // If foldCase is true, the lookup for methods will include looking for any method 86 // which case-folds to the same as 'name' (used for giving helpful error messages). 87 // 88 // The resulting object may not be fully type-checked. 89 func lookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string, foldCase bool) (obj Object, index []int, indirect bool) { 90 // WARNING: The code in this function is extremely subtle - do not modify casually! 91 92 if name == "_" { 93 return // blank fields/methods are never found 94 } 95 96 typ, isPtr := deref(T) 97 98 // *typ where typ is an interface (incl. a type parameter) has no methods. 99 if isPtr { 100 if _, ok := under(typ).(*Interface); ok { 101 return 102 } 103 } 104 105 // Start with typ as single entry at shallowest depth. 106 current := []embeddedType{{typ, nil, isPtr, false}} 107 108 // seen tracks named types that we have seen already, allocated lazily. 109 // Used to avoid endless searches in case of recursive types. 110 // 111 // We must use a lookup on identity rather than a simple map[*Named]bool as 112 // instantiated types may be identical but not equal. 113 var seen instanceLookup 114 115 // search current depth 116 for len(current) > 0 { 117 var next []embeddedType // embedded types found at current depth 118 119 // look for (pkg, name) in all types at current depth 120 for _, e := range current { 121 typ := e.typ 122 123 // If we have a named type, we may have associated methods. 124 // Look for those first. 125 if named, _ := typ.(*Named); named != nil { 126 if alt := seen.lookup(named); alt != nil { 127 // We have seen this type before, at a more shallow depth 128 // (note that multiples of this type at the current depth 129 // were consolidated before). The type at that depth shadows 130 // this same type at the current depth, so we can ignore 131 // this one. 132 continue 133 } 134 seen.add(named) 135 136 // look for a matching attached method 137 if i, m := named.lookupMethod(pkg, name, foldCase); m != nil { 138 // potential match 139 // caution: method may not have a proper signature yet 140 index = concat(e.index, i) 141 if obj != nil || e.multiples { 142 return nil, index, false // collision 143 } 144 obj = m 145 indirect = e.indirect 146 continue // we can't have a matching field or interface method 147 } 148 } 149 150 switch t := under(typ).(type) { 151 case *Struct: 152 // look for a matching field and collect embedded types 153 for i, f := range t.fields { 154 if f.sameId(pkg, name) { 155 assert(f.typ != nil) 156 index = concat(e.index, i) 157 if obj != nil || e.multiples { 158 return nil, index, false // collision 159 } 160 obj = f 161 indirect = e.indirect 162 continue // we can't have a matching interface method 163 } 164 // Collect embedded struct fields for searching the next 165 // lower depth, but only if we have not seen a match yet 166 // (if we have a match it is either the desired field or 167 // we have a name collision on the same depth; in either 168 // case we don't need to look further). 169 // Embedded fields are always of the form T or *T where 170 // T is a type name. If e.typ appeared multiple times at 171 // this depth, f.typ appears multiple times at the next 172 // depth. 173 if obj == nil && f.embedded { 174 typ, isPtr := deref(f.typ) 175 // TODO(gri) optimization: ignore types that can't 176 // have fields or methods (only Named, Struct, and 177 // Interface types need to be considered). 178 next = append(next, embeddedType{typ, concat(e.index, i), e.indirect || isPtr, e.multiples}) 179 } 180 } 181 182 case *Interface: 183 // look for a matching method (interface may be a type parameter) 184 if i, m := t.typeSet().LookupMethod(pkg, name, foldCase); m != nil { 185 assert(m.typ != nil) 186 index = concat(e.index, i) 187 if obj != nil || e.multiples { 188 return nil, index, false // collision 189 } 190 obj = m 191 indirect = e.indirect 192 } 193 } 194 } 195 196 if obj != nil { 197 // found a potential match 198 // spec: "A method call x.m() is valid if the method set of (the type of) x 199 // contains m and the argument list can be assigned to the parameter 200 // list of m. If x is addressable and &x's method set contains m, x.m() 201 // is shorthand for (&x).m()". 202 if f, _ := obj.(*Func); f != nil { 203 // determine if method has a pointer receiver 204 if f.hasPtrRecv() && !indirect && !addressable { 205 return nil, nil, true // pointer/addressable receiver required 206 } 207 } 208 return 209 } 210 211 current = consolidateMultiples(next) 212 } 213 214 return nil, nil, false // not found 215 } 216 217 // embeddedType represents an embedded type 218 type embeddedType struct { 219 typ Type 220 index []int // embedded field indices, starting with index at depth 0 221 indirect bool // if set, there was a pointer indirection on the path to this field 222 multiples bool // if set, typ appears multiple times at this depth 223 } 224 225 // consolidateMultiples collects multiple list entries with the same type 226 // into a single entry marked as containing multiples. The result is the 227 // consolidated list. 228 func consolidateMultiples(list []embeddedType) []embeddedType { 229 if len(list) <= 1 { 230 return list // at most one entry - nothing to do 231 } 232 233 n := 0 // number of entries w/ unique type 234 prev := make(map[Type]int) // index at which type was previously seen 235 for _, e := range list { 236 if i, found := lookupType(prev, e.typ); found { 237 list[i].multiples = true 238 // ignore this entry 239 } else { 240 prev[e.typ] = n 241 list[n] = e 242 n++ 243 } 244 } 245 return list[:n] 246 } 247 248 func lookupType(m map[Type]int, typ Type) (int, bool) { 249 // fast path: maybe the types are equal 250 if i, found := m[typ]; found { 251 return i, true 252 } 253 254 for t, i := range m { 255 if Identical(t, typ) { 256 return i, true 257 } 258 } 259 260 return 0, false 261 } 262 263 type instanceLookup struct { 264 m map[*Named][]*Named 265 } 266 267 func (l *instanceLookup) lookup(inst *Named) *Named { 268 for _, t := range l.m[inst.Origin()] { 269 if Identical(inst, t) { 270 return t 271 } 272 } 273 return nil 274 } 275 276 func (l *instanceLookup) add(inst *Named) { 277 if l.m == nil { 278 l.m = make(map[*Named][]*Named) 279 } 280 insts := l.m[inst.Origin()] 281 l.m[inst.Origin()] = append(insts, inst) 282 } 283 284 // MissingMethod returns (nil, false) if V implements T, otherwise it 285 // returns a missing method required by T and whether it is missing or 286 // just has the wrong type. 287 // 288 // For non-interface types V, or if static is set, V implements T if all 289 // methods of T are present in V. Otherwise (V is an interface and static 290 // is not set), MissingMethod only checks that methods of T which are also 291 // present in V have matching types (e.g., for a type assertion x.(T) where 292 // x is of interface type V). 293 func MissingMethod(V Type, T *Interface, static bool) (method *Func, wrongType bool) { 294 m, alt := (*Checker)(nil).missingMethod(V, T, static) 295 // Only report a wrong type if the alternative method has the same name as m. 296 return m, alt != nil && alt.name == m.name // alt != nil implies m != nil 297 } 298 299 // missingMethod is like MissingMethod but accepts a *Checker as receiver. 300 // The receiver may be nil if missingMethod is invoked through an exported 301 // API call (such as MissingMethod), i.e., when all methods have been type- 302 // checked. 303 // 304 // If a method is missing on T but is found on *T, or if a method is found 305 // on T when looked up with case-folding, this alternative method is returned 306 // as the second result. 307 func (check *Checker) missingMethod(V Type, T *Interface, static bool) (method, alt *Func) { 308 if T.NumMethods() == 0 { 309 return 310 } 311 312 // V is an interface 313 if u, _ := under(V).(*Interface); u != nil { 314 tset := u.typeSet() 315 for _, m := range T.typeSet().methods { 316 _, f := tset.LookupMethod(m.pkg, m.name, false) 317 318 if f == nil { 319 if !static { 320 continue 321 } 322 return m, nil 323 } 324 325 if !Identical(f.typ, m.typ) { 326 return m, f 327 } 328 } 329 330 return 331 } 332 333 // V is not an interface 334 for _, m := range T.typeSet().methods { 335 // TODO(gri) should this be calling LookupFieldOrMethod instead (and why not)? 336 obj, _, _ := lookupFieldOrMethod(V, false, m.pkg, m.name, false) 337 338 // check if m is on *V, or on V with case-folding 339 found := obj != nil 340 if !found { 341 // TODO(gri) Instead of NewPointer(V) below, can we just set the "addressable" argument? 342 obj, _, _ = lookupFieldOrMethod(NewPointer(V), false, m.pkg, m.name, false) 343 if obj == nil { 344 obj, _, _ = lookupFieldOrMethod(V, false, m.pkg, m.name, true /* fold case */) 345 } 346 } 347 348 // we must have a method (not a struct field) 349 f, _ := obj.(*Func) 350 if f == nil { 351 return m, nil 352 } 353 354 // methods may not have a fully set up signature yet 355 if check != nil { 356 check.objDecl(f, nil) 357 } 358 359 if !found || !Identical(f.typ, m.typ) { 360 return m, f 361 } 362 } 363 364 return 365 } 366 367 // missingMethodReason returns a string giving the detailed reason for a missing method m, 368 // where m is missing from V, but required by T. It puts the reason in parentheses, 369 // and may include more have/want info after that. If non-nil, alt is a relevant 370 // method that matches in some way. It may have the correct name, but wrong type, or 371 // it may have a pointer receiver, or it may have the correct name except wrong case. 372 // check may be nil. 373 func (check *Checker) missingMethodReason(V, T Type, m, alt *Func) string { 374 var mname string 375 if check != nil && compilerErrorMessages { 376 mname = m.Name() + " method" 377 } else { 378 mname = "method " + m.Name() 379 } 380 381 if alt != nil { 382 if m.Name() != alt.Name() { 383 return check.sprintf("(missing %s)\n\t\thave %s\n\t\twant %s", 384 mname, check.funcString(alt), check.funcString(m)) 385 } 386 387 if Identical(m.typ, alt.typ) { 388 return check.sprintf("(%s has pointer receiver)", mname) 389 } 390 391 return check.sprintf("(wrong type for %s)\n\t\thave %s\n\t\twant %s", 392 mname, check.funcString(alt), check.funcString(m)) 393 } 394 395 if isInterfacePtr(V) { 396 return "(" + check.interfacePtrError(V) + ")" 397 } 398 399 if isInterfacePtr(T) { 400 return "(" + check.interfacePtrError(T) + ")" 401 } 402 403 return check.sprintf("(missing %s)", mname) 404 } 405 406 func isInterfacePtr(T Type) bool { 407 p, _ := under(T).(*Pointer) 408 return p != nil && IsInterface(p.base) 409 } 410 411 // check may be nil. 412 func (check *Checker) interfacePtrError(T Type) string { 413 assert(isInterfacePtr(T)) 414 if p, _ := under(T).(*Pointer); isTypeParam(p.base) { 415 return check.sprintf("type %s is pointer to type parameter, not type parameter", T) 416 } 417 return check.sprintf("type %s is pointer to interface, not interface", T) 418 } 419 420 // check may be nil. 421 func (check *Checker) funcString(f *Func) string { 422 buf := bytes.NewBufferString(f.name) 423 var qf Qualifier 424 if check != nil { 425 qf = check.qualifier 426 } 427 WriteSignature(buf, f.typ.(*Signature), qf) 428 return buf.String() 429 } 430 431 // assertableTo reports whether a value of type V can be asserted to have type T. 432 // It returns (nil, false) as affirmative answer. Otherwise it returns a missing 433 // method required by V and whether it is missing or just has the wrong type. 434 // The receiver may be nil if assertableTo is invoked through an exported API call 435 // (such as AssertableTo), i.e., when all methods have been type-checked. 436 // TODO(gri) replace calls to this function with calls to newAssertableTo. 437 func (check *Checker) assertableTo(V *Interface, T Type) (method, wrongType *Func) { 438 // no static check is required if T is an interface 439 // spec: "If T is an interface type, x.(T) asserts that the 440 // dynamic type of x implements the interface T." 441 if IsInterface(T) { 442 return 443 } 444 // TODO(gri) fix this for generalized interfaces 445 return check.missingMethod(T, V, false) 446 } 447 448 // newAssertableTo reports whether a value of type V can be asserted to have type T. 449 // It also implements behavior for interfaces that currently are only permitted 450 // in constraint position (we have not yet defined that behavior in the spec). 451 func (check *Checker) newAssertableTo(V *Interface, T Type) error { 452 // no static check is required if T is an interface 453 // spec: "If T is an interface type, x.(T) asserts that the 454 // dynamic type of x implements the interface T." 455 if IsInterface(T) { 456 return nil 457 } 458 return check.implements(T, V) 459 } 460 461 // deref dereferences typ if it is a *Pointer and returns its base and true. 462 // Otherwise it returns (typ, false). 463 func deref(typ Type) (Type, bool) { 464 if p, _ := typ.(*Pointer); p != nil { 465 // p.base should never be nil, but be conservative 466 if p.base == nil { 467 if debug { 468 panic("pointer with nil base type (possibly due to an invalid cyclic declaration)") 469 } 470 return Typ[Invalid], true 471 } 472 return p.base, true 473 } 474 return typ, false 475 } 476 477 // derefStructPtr dereferences typ if it is a (named or unnamed) pointer to a 478 // (named or unnamed) struct and returns its base. Otherwise it returns typ. 479 func derefStructPtr(typ Type) Type { 480 if p, _ := under(typ).(*Pointer); p != nil { 481 if _, ok := under(p.base).(*Struct); ok { 482 return p.base 483 } 484 } 485 return typ 486 } 487 488 // concat returns the result of concatenating list and i. 489 // The result does not share its underlying array with list. 490 func concat(list []int, i int) []int { 491 var t []int 492 t = append(t, list...) 493 return append(t, i) 494 } 495 496 // fieldIndex returns the index for the field with matching package and name, or a value < 0. 497 func fieldIndex(fields []*Var, pkg *Package, name string) int { 498 if name != "_" { 499 for i, f := range fields { 500 if f.sameId(pkg, name) { 501 return i 502 } 503 } 504 } 505 return -1 506 } 507 508 // lookupMethod returns the index of and method with matching package and name, or (-1, nil). 509 // If foldCase is true, method names are considered equal if they are equal with case folding. 510 func lookupMethod(methods []*Func, pkg *Package, name string, foldCase bool) (int, *Func) { 511 if name != "_" { 512 for i, m := range methods { 513 if (m.name == name || foldCase && strings.EqualFold(m.name, name)) && m.sameId(pkg, m.name) { 514 return i, m 515 } 516 } 517 } 518 return -1, nil 519 } 520