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 "go/token" 10 11 // LookupFieldOrMethod looks up a field or method with given package and name 12 // in T and returns the corresponding *Var or *Func, an index sequence, and a 13 // bool indicating if there were any pointer indirections on the path to the 14 // field or method. If addressable is set, T is the type of an addressable 15 // variable (only matters for method lookups). 16 // 17 // The last index entry is the field or method index in the (possibly embedded) 18 // type where the entry was found, either: 19 // 20 // 1) the list of declared methods of a named type; or 21 // 2) the list of all methods (method set) of an interface type; or 22 // 3) the list of fields of a struct type. 23 // 24 // The earlier index entries are the indices of the embedded struct fields 25 // traversed to get to the found entry, starting at depth 0. 26 // 27 // If no entry is found, a nil object is returned. In this case, the returned 28 // index and indirect values have the following meaning: 29 // 30 // - If index != nil, the index sequence points to an ambiguous entry 31 // (the same name appeared more than once at the same embedding level). 32 // 33 // - If indirect is set, a method with a pointer receiver type was found 34 // but there was no pointer on the path from the actual receiver type to 35 // the method's formal receiver base type, nor was the receiver addressable. 36 // 37 func LookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string) (obj Object, index []int, indirect bool) { 38 return (*Checker)(nil).lookupFieldOrMethod(T, addressable, pkg, name) 39 } 40 41 // Internal use of Checker.lookupFieldOrMethod: If the obj result is a method 42 // associated with a concrete (non-interface) type, the method's signature 43 // may not be fully set up. Call Checker.objDecl(obj, nil) before accessing 44 // the method's type. 45 // TODO(gri) Now that we provide the *Checker, we can probably remove this 46 // caveat by calling Checker.objDecl from lookupFieldOrMethod. Investigate. 47 48 // lookupFieldOrMethod is like the external version but completes interfaces 49 // as necessary. 50 func (check *Checker) lookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string) (obj Object, index []int, indirect bool) { 51 // Methods cannot be associated to a named pointer type 52 // (spec: "The type denoted by T is called the receiver base type; 53 // it must not be a pointer or interface type and it must be declared 54 // in the same package as the method."). 55 // Thus, if we have a named pointer type, proceed with the underlying 56 // pointer type but discard the result if it is a method since we would 57 // not have found it for T (see also issue 8590). 58 if t := asNamed(T); t != nil { 59 if p, _ := t.underlying.(*Pointer); p != nil { 60 obj, index, indirect = check.rawLookupFieldOrMethod(p, false, pkg, name) 61 if _, ok := obj.(*Func); ok { 62 return nil, nil, false 63 } 64 return 65 } 66 } 67 68 return check.rawLookupFieldOrMethod(T, addressable, pkg, name) 69 } 70 71 // TODO(gri) The named type consolidation and seen maps below must be 72 // indexed by unique keys for a given type. Verify that named 73 // types always have only one representation (even when imported 74 // indirectly via different packages.) 75 76 // rawLookupFieldOrMethod should only be called by lookupFieldOrMethod and missingMethod. 77 func (check *Checker) rawLookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string) (obj Object, index []int, indirect bool) { 78 // WARNING: The code in this function is extremely subtle - do not modify casually! 79 // This function and NewMethodSet should be kept in sync. 80 81 if name == "_" { 82 return // blank fields/methods are never found 83 } 84 85 typ, isPtr := deref(T) 86 87 // *typ where typ is an interface has no methods. 88 // Be cautious: typ may be nil (issue 39634, crash #3). 89 if typ == nil || isPtr && IsInterface(typ) { 90 return 91 } 92 93 // Start with typ as single entry at shallowest depth. 94 current := []embeddedType{{typ, nil, isPtr, false}} 95 96 // Named types that we have seen already, allocated lazily. 97 // Used to avoid endless searches in case of recursive types. 98 // Since only Named types can be used for recursive types, we 99 // only need to track those. 100 // (If we ever allow type aliases to construct recursive types, 101 // we must use type identity rather than pointer equality for 102 // the map key comparison, as we do in consolidateMultiples.) 103 var seen map[*Named]bool 104 105 // search current depth 106 for len(current) > 0 { 107 var next []embeddedType // embedded types found at current depth 108 109 // look for (pkg, name) in all types at current depth 110 var tpar *_TypeParam // set if obj receiver is a type parameter 111 for _, e := range current { 112 typ := e.typ 113 114 // If we have a named type, we may have associated methods. 115 // Look for those first. 116 if named := asNamed(typ); named != nil { 117 if seen[named] { 118 // We have seen this type before, at a more shallow depth 119 // (note that multiples of this type at the current depth 120 // were consolidated before). The type at that depth shadows 121 // this same type at the current depth, so we can ignore 122 // this one. 123 continue 124 } 125 if seen == nil { 126 seen = make(map[*Named]bool) 127 } 128 seen[named] = true 129 130 // look for a matching attached method 131 if i, m := lookupMethod(named.methods, pkg, name); m != nil { 132 // potential match 133 // caution: method may not have a proper signature yet 134 index = concat(e.index, i) 135 if obj != nil || e.multiples { 136 return nil, index, false // collision 137 } 138 obj = m 139 indirect = e.indirect 140 continue // we can't have a matching field or interface method 141 } 142 143 // continue with underlying type, but only if it's not a type parameter 144 // TODO(gri) is this what we want to do for type parameters? (spec question) 145 // TODO(#45639) the error message produced as a result of skipping an 146 // underlying type parameter should be improved. 147 typ = named.under() 148 if asTypeParam(typ) != nil { 149 continue 150 } 151 } 152 153 tpar = nil 154 switch t := typ.(type) { 155 case *Struct: 156 // look for a matching field and collect embedded types 157 for i, f := range t.fields { 158 if f.sameId(pkg, name) { 159 assert(f.typ != nil) 160 index = concat(e.index, i) 161 if obj != nil || e.multiples { 162 return nil, index, false // collision 163 } 164 obj = f 165 indirect = e.indirect 166 continue // we can't have a matching interface method 167 } 168 // Collect embedded struct fields for searching the next 169 // lower depth, but only if we have not seen a match yet 170 // (if we have a match it is either the desired field or 171 // we have a name collision on the same depth; in either 172 // case we don't need to look further). 173 // Embedded fields are always of the form T or *T where 174 // T is a type name. If e.typ appeared multiple times at 175 // this depth, f.typ appears multiple times at the next 176 // depth. 177 if obj == nil && f.embedded { 178 typ, isPtr := deref(f.typ) 179 // TODO(gri) optimization: ignore types that can't 180 // have fields or methods (only Named, Struct, and 181 // Interface types need to be considered). 182 next = append(next, embeddedType{typ, concat(e.index, i), e.indirect || isPtr, e.multiples}) 183 } 184 } 185 186 case *Interface: 187 // look for a matching method 188 // TODO(gri) t.allMethods is sorted - use binary search 189 check.completeInterface(token.NoPos, t) 190 if i, m := lookupMethod(t.allMethods, pkg, name); m != nil { 191 assert(m.typ != nil) 192 index = concat(e.index, i) 193 if obj != nil || e.multiples { 194 return nil, index, false // collision 195 } 196 obj = m 197 indirect = e.indirect 198 } 199 200 case *_TypeParam: 201 // only consider explicit methods in the type parameter bound, not 202 // methods that may be common to all types in the type list. 203 if i, m := lookupMethod(t.Bound().allMethods, pkg, name); m != nil { 204 assert(m.typ != nil) 205 index = concat(e.index, i) 206 if obj != nil || e.multiples { 207 return nil, index, false // collision 208 } 209 tpar = t 210 obj = m 211 indirect = e.indirect 212 } 213 } 214 } 215 216 if obj != nil { 217 // found a potential match 218 // spec: "A method call x.m() is valid if the method set of (the type of) x 219 // contains m and the argument list can be assigned to the parameter 220 // list of m. If x is addressable and &x's method set contains m, x.m() 221 // is shorthand for (&x).m()". 222 if f, _ := obj.(*Func); f != nil { 223 // determine if method has a pointer receiver 224 hasPtrRecv := tpar == nil && ptrRecv(f) 225 if hasPtrRecv && !indirect && !addressable { 226 return nil, nil, true // pointer/addressable receiver required 227 } 228 } 229 return 230 } 231 232 current = check.consolidateMultiples(next) 233 } 234 235 return nil, nil, false // not found 236 } 237 238 // embeddedType represents an embedded type 239 type embeddedType struct { 240 typ Type 241 index []int // embedded field indices, starting with index at depth 0 242 indirect bool // if set, there was a pointer indirection on the path to this field 243 multiples bool // if set, typ appears multiple times at this depth 244 } 245 246 // consolidateMultiples collects multiple list entries with the same type 247 // into a single entry marked as containing multiples. The result is the 248 // consolidated list. 249 func (check *Checker) consolidateMultiples(list []embeddedType) []embeddedType { 250 if len(list) <= 1 { 251 return list // at most one entry - nothing to do 252 } 253 254 n := 0 // number of entries w/ unique type 255 prev := make(map[Type]int) // index at which type was previously seen 256 for _, e := range list { 257 if i, found := check.lookupType(prev, e.typ); found { 258 list[i].multiples = true 259 // ignore this entry 260 } else { 261 prev[e.typ] = n 262 list[n] = e 263 n++ 264 } 265 } 266 return list[:n] 267 } 268 269 func (check *Checker) lookupType(m map[Type]int, typ Type) (int, bool) { 270 // fast path: maybe the types are equal 271 if i, found := m[typ]; found { 272 return i, true 273 } 274 275 for t, i := range m { 276 if check.identical(t, typ) { 277 return i, true 278 } 279 } 280 281 return 0, false 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 // 294 func MissingMethod(V Type, T *Interface, static bool) (method *Func, wrongType bool) { 295 m, typ := (*Checker)(nil).missingMethod(V, T, static) 296 return m, typ != nil 297 } 298 299 // missingMethod is like MissingMethod but accepts a *Checker as 300 // receiver and an addressable flag. 301 // The receiver may be nil if missingMethod is invoked through 302 // an exported API call (such as MissingMethod), i.e., when all 303 // methods have been type-checked. 304 // If the type has the correctly named method, but with the wrong 305 // signature, the existing method is returned as well. 306 // To improve error messages, also report the wrong signature 307 // when the method exists on *V instead of V. 308 func (check *Checker) missingMethod(V Type, T *Interface, static bool) (method, wrongType *Func) { 309 check.completeInterface(token.NoPos, T) 310 311 // fast path for common case 312 if T.Empty() { 313 return 314 } 315 316 if ityp := asInterface(V); ityp != nil { 317 check.completeInterface(token.NoPos, ityp) 318 // TODO(gri) allMethods is sorted - can do this more efficiently 319 for _, m := range T.allMethods { 320 _, f := lookupMethod(ityp.allMethods, m.pkg, m.name) 321 322 if f == nil { 323 // if m is the magic method == we're ok (interfaces are comparable) 324 if m.name == "==" || !static { 325 continue 326 } 327 return m, f 328 } 329 330 ftyp := f.typ.(*Signature) 331 mtyp := m.typ.(*Signature) 332 if len(ftyp.tparams) != len(mtyp.tparams) { 333 return m, f 334 } 335 336 // If the methods have type parameters we don't care whether they 337 // are the same or not, as long as they match up. Use unification 338 // to see if they can be made to match. 339 // TODO(gri) is this always correct? what about type bounds? 340 // (Alternative is to rename/subst type parameters and compare.) 341 u := newUnifier(check, true) 342 u.x.init(ftyp.tparams) 343 if !u.unify(ftyp, mtyp) { 344 return m, f 345 } 346 } 347 348 return 349 } 350 351 // A concrete type implements T if it implements all methods of T. 352 Vd, _ := deref(V) 353 Vn := asNamed(Vd) 354 for _, m := range T.allMethods { 355 // TODO(gri) should this be calling lookupFieldOrMethod instead (and why not)? 356 obj, _, _ := check.rawLookupFieldOrMethod(V, false, m.pkg, m.name) 357 358 // Check if *V implements this method of T. 359 if obj == nil { 360 ptr := NewPointer(V) 361 obj, _, _ = check.rawLookupFieldOrMethod(ptr, false, m.pkg, m.name) 362 if obj != nil { 363 return m, obj.(*Func) 364 } 365 } 366 367 // we must have a method (not a field of matching function type) 368 f, _ := obj.(*Func) 369 if f == nil { 370 // if m is the magic method == and V is comparable, we're ok 371 if m.name == "==" && Comparable(V) { 372 continue 373 } 374 return m, nil 375 } 376 377 // methods may not have a fully set up signature yet 378 if check != nil { 379 check.objDecl(f, nil) 380 } 381 382 // both methods must have the same number of type parameters 383 ftyp := f.typ.(*Signature) 384 mtyp := m.typ.(*Signature) 385 if len(ftyp.tparams) != len(mtyp.tparams) { 386 return m, f 387 } 388 389 // If V is a (instantiated) generic type, its methods are still 390 // parameterized using the original (declaration) receiver type 391 // parameters (subst simply copies the existing method list, it 392 // does not instantiate the methods). 393 // In order to compare the signatures, substitute the receiver 394 // type parameters of ftyp with V's instantiation type arguments. 395 // This lazily instantiates the signature of method f. 396 if Vn != nil && len(Vn.tparams) > 0 { 397 // Be careful: The number of type arguments may not match 398 // the number of receiver parameters. If so, an error was 399 // reported earlier but the length discrepancy is still 400 // here. Exit early in this case to prevent an assertion 401 // failure in makeSubstMap. 402 // TODO(gri) Can we avoid this check by fixing the lengths? 403 if len(ftyp.rparams) != len(Vn.targs) { 404 return 405 } 406 ftyp = check.subst(token.NoPos, ftyp, makeSubstMap(ftyp.rparams, Vn.targs)).(*Signature) 407 } 408 409 // If the methods have type parameters we don't care whether they 410 // are the same or not, as long as they match up. Use unification 411 // to see if they can be made to match. 412 // TODO(gri) is this always correct? what about type bounds? 413 // (Alternative is to rename/subst type parameters and compare.) 414 u := newUnifier(check, true) 415 u.x.init(ftyp.tparams) 416 if !u.unify(ftyp, mtyp) { 417 return m, f 418 } 419 } 420 421 return 422 } 423 424 // assertableTo reports whether a value of type V can be asserted to have type T. 425 // It returns (nil, false) as affirmative answer. Otherwise it returns a missing 426 // method required by V and whether it is missing or just has the wrong type. 427 // The receiver may be nil if assertableTo is invoked through an exported API call 428 // (such as AssertableTo), i.e., when all methods have been type-checked. 429 // If the global constant forceStrict is set, assertions that are known to fail 430 // are not permitted. 431 func (check *Checker) assertableTo(V *Interface, T Type) (method, wrongType *Func) { 432 // no static check is required if T is an interface 433 // spec: "If T is an interface type, x.(T) asserts that the 434 // dynamic type of x implements the interface T." 435 if asInterface(T) != nil && !forceStrict { 436 return 437 } 438 return check.missingMethod(T, V, false) 439 } 440 441 // deref dereferences typ if it is a *Pointer and returns its base and true. 442 // Otherwise it returns (typ, false). 443 func deref(typ Type) (Type, bool) { 444 if p, _ := typ.(*Pointer); p != nil { 445 return p.base, true 446 } 447 return typ, false 448 } 449 450 // derefStructPtr dereferences typ if it is a (named or unnamed) pointer to a 451 // (named or unnamed) struct and returns its base. Otherwise it returns typ. 452 func derefStructPtr(typ Type) Type { 453 if p := asPointer(typ); p != nil { 454 if asStruct(p.base) != nil { 455 return p.base 456 } 457 } 458 return typ 459 } 460 461 // concat returns the result of concatenating list and i. 462 // The result does not share its underlying array with list. 463 func concat(list []int, i int) []int { 464 var t []int 465 t = append(t, list...) 466 return append(t, i) 467 } 468 469 // fieldIndex returns the index for the field with matching package and name, or a value < 0. 470 func fieldIndex(fields []*Var, pkg *Package, name string) int { 471 if name != "_" { 472 for i, f := range fields { 473 if f.sameId(pkg, name) { 474 return i 475 } 476 } 477 } 478 return -1 479 } 480 481 // lookupMethod returns the index of and method with matching package and name, or (-1, nil). 482 func lookupMethod(methods []*Func, pkg *Package, name string) (int, *Func) { 483 if name != "_" { 484 for i, m := range methods { 485 if m.sameId(pkg, name) { 486 return i, m 487 } 488 } 489 } 490 return -1, nil 491 } 492