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 types2 8 9 import ( 10 "bytes" 11 "cmd/compile/internal/syntax" 12 "strings" 13 ) 14 15 // Internal use of LookupFieldOrMethod: If the obj result is a method 16 // associated with a concrete (non-interface) type, the method's signature 17 // may not be fully set up. Call Checker.objDecl(obj, nil) before accessing 18 // the method's type. 19 20 // LookupFieldOrMethod looks up a field or method with given package and name 21 // in T and returns the corresponding *Var or *Func, an index sequence, and a 22 // bool indicating if there were any pointer indirections on the path to the 23 // field or method. If addressable is set, T is the type of an addressable 24 // variable (only matters for method lookups). T must not be nil. 25 // 26 // The last index entry is the field or method index in the (possibly embedded) 27 // type where the entry was found, either: 28 // 29 // 1. the list of declared methods of a named type; or 30 // 2. the list of all methods (method set) of an interface type; or 31 // 3. the list of fields of a struct type. 32 // 33 // The earlier index entries are the indices of the embedded struct fields 34 // traversed to get to the found entry, starting at depth 0. 35 // 36 // If no entry is found, a nil object is returned. In this case, the returned 37 // index and indirect values have the following meaning: 38 // 39 // - If index != nil, the index sequence points to an ambiguous entry 40 // (the same name appeared more than once at the same embedding level). 41 // 42 // - If indirect is set, a method with a pointer receiver type was found 43 // but there was no pointer on the path from the actual receiver type to 44 // the method's formal receiver base type, nor was the receiver addressable. 45 func LookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string) (obj Object, index []int, indirect bool) { 46 if T == nil { 47 panic("LookupFieldOrMethod on nil type") 48 } 49 50 // Methods cannot be associated to a named pointer type. 51 // (spec: "The type denoted by T is called the receiver base type; 52 // it must not be a pointer or interface type and it must be declared 53 // in the same package as the method."). 54 // Thus, if we have a named pointer type, proceed with the underlying 55 // pointer type but discard the result if it is a method since we would 56 // not have found it for T (see also go.dev/issue/8590). 57 if t := asNamed(T); t != nil { 58 if p, _ := t.Underlying().(*Pointer); p != nil { 59 obj, index, indirect = lookupFieldOrMethodImpl(p, false, pkg, name, false) 60 if _, ok := obj.(*Func); ok { 61 return nil, nil, false 62 } 63 return 64 } 65 } 66 67 obj, index, indirect = lookupFieldOrMethodImpl(T, addressable, pkg, name, false) 68 69 // If we didn't find anything and if we have a type parameter with a core type, 70 // see if there is a matching field (but not a method, those need to be declared 71 // explicitly in the constraint). If the constraint is a named pointer type (see 72 // above), we are ok here because only fields are accepted as results. 73 const enableTParamFieldLookup = false // see go.dev/issue/51576 74 if enableTParamFieldLookup && obj == nil && isTypeParam(T) { 75 if t := coreType(T); t != nil { 76 obj, index, indirect = lookupFieldOrMethodImpl(t, addressable, pkg, name, false) 77 if _, ok := obj.(*Var); !ok { 78 obj, index, indirect = nil, nil, false // accept fields (variables) only 79 } 80 } 81 } 82 return 83 } 84 85 // lookupFieldOrMethodImpl is the implementation of LookupFieldOrMethod. 86 // Notably, in contrast to LookupFieldOrMethod, it won't find struct fields 87 // in base types of defined (*Named) pointer types T. For instance, given 88 // the declaration: 89 // 90 // type T *struct{f int} 91 // 92 // lookupFieldOrMethodImpl won't find the field f in the defined (*Named) type T 93 // (methods on T are not permitted in the first place). 94 // 95 // Thus, lookupFieldOrMethodImpl should only be called by LookupFieldOrMethod 96 // and missingMethod (the latter doesn't care about struct fields). 97 // 98 // If foldCase is true, method names are considered equal if they are equal 99 // with case folding, irrespective of which package they are in. 100 // 101 // The resulting object may not be fully type-checked. 102 func lookupFieldOrMethodImpl(T Type, addressable bool, pkg *Package, name string, foldCase bool) (obj Object, index []int, indirect bool) { 103 // WARNING: The code in this function is extremely subtle - do not modify casually! 104 105 if name == "_" { 106 return // blank fields/methods are never found 107 } 108 109 // Importantly, we must not call under before the call to deref below (nor 110 // does deref call under), as doing so could incorrectly result in finding 111 // methods of the pointer base type when T is a (*Named) pointer type. 112 typ, isPtr := deref(T) 113 114 // *typ where typ is an interface (incl. a type parameter) has no methods. 115 if isPtr { 116 if _, ok := under(typ).(*Interface); ok { 117 return 118 } 119 } 120 121 // Start with typ as single entry at shallowest depth. 122 current := []embeddedType{{typ, nil, isPtr, false}} 123 124 // seen tracks named types that we have seen already, allocated lazily. 125 // Used to avoid endless searches in case of recursive types. 126 // 127 // We must use a lookup on identity rather than a simple map[*Named]bool as 128 // instantiated types may be identical but not equal. 129 var seen instanceLookup 130 131 // search current depth 132 for len(current) > 0 { 133 var next []embeddedType // embedded types found at current depth 134 135 // look for (pkg, name) in all types at current depth 136 for _, e := range current { 137 typ := e.typ 138 139 // If we have a named type, we may have associated methods. 140 // Look for those first. 141 if named := asNamed(typ); named != nil { 142 if alt := seen.lookup(named); alt != nil { 143 // We have seen this type before, at a more shallow depth 144 // (note that multiples of this type at the current depth 145 // were consolidated before). The type at that depth shadows 146 // this same type at the current depth, so we can ignore 147 // this one. 148 continue 149 } 150 seen.add(named) 151 152 // look for a matching attached method 153 if i, m := named.lookupMethod(pkg, name, foldCase); m != nil { 154 // potential match 155 // caution: method may not have a proper signature yet 156 index = concat(e.index, i) 157 if obj != nil || e.multiples { 158 return nil, index, false // collision 159 } 160 obj = m 161 indirect = e.indirect 162 continue // we can't have a matching field or interface method 163 } 164 } 165 166 switch t := under(typ).(type) { 167 case *Struct: 168 // look for a matching field and collect embedded types 169 for i, f := range t.fields { 170 if f.sameId(pkg, name) { 171 assert(f.typ != nil) 172 index = concat(e.index, i) 173 if obj != nil || e.multiples { 174 return nil, index, false // collision 175 } 176 obj = f 177 indirect = e.indirect 178 continue // we can't have a matching interface method 179 } 180 // Collect embedded struct fields for searching the next 181 // lower depth, but only if we have not seen a match yet 182 // (if we have a match it is either the desired field or 183 // we have a name collision on the same depth; in either 184 // case we don't need to look further). 185 // Embedded fields are always of the form T or *T where 186 // T is a type name. If e.typ appeared multiple times at 187 // this depth, f.typ appears multiple times at the next 188 // depth. 189 if obj == nil && f.embedded { 190 typ, isPtr := deref(f.typ) 191 // TODO(gri) optimization: ignore types that can't 192 // have fields or methods (only Named, Struct, and 193 // Interface types need to be considered). 194 next = append(next, embeddedType{typ, concat(e.index, i), e.indirect || isPtr, e.multiples}) 195 } 196 } 197 198 case *Interface: 199 // look for a matching method (interface may be a type parameter) 200 if i, m := t.typeSet().LookupMethod(pkg, name, foldCase); m != nil { 201 assert(m.typ != nil) 202 index = concat(e.index, i) 203 if obj != nil || e.multiples { 204 return nil, index, false // collision 205 } 206 obj = m 207 indirect = e.indirect 208 } 209 } 210 } 211 212 if obj != nil { 213 // found a potential match 214 // spec: "A method call x.m() is valid if the method set of (the type of) x 215 // contains m and the argument list can be assigned to the parameter 216 // list of m. If x is addressable and &x's method set contains m, x.m() 217 // is shorthand for (&x).m()". 218 if f, _ := obj.(*Func); f != nil { 219 // determine if method has a pointer receiver 220 if f.hasPtrRecv() && !indirect && !addressable { 221 return nil, nil, true // pointer/addressable receiver required 222 } 223 } 224 return 225 } 226 227 current = consolidateMultiples(next) 228 } 229 230 return nil, nil, false // not found 231 } 232 233 // embeddedType represents an embedded type 234 type embeddedType struct { 235 typ Type 236 index []int // embedded field indices, starting with index at depth 0 237 indirect bool // if set, there was a pointer indirection on the path to this field 238 multiples bool // if set, typ appears multiple times at this depth 239 } 240 241 // consolidateMultiples collects multiple list entries with the same type 242 // into a single entry marked as containing multiples. The result is the 243 // consolidated list. 244 func consolidateMultiples(list []embeddedType) []embeddedType { 245 if len(list) <= 1 { 246 return list // at most one entry - nothing to do 247 } 248 249 n := 0 // number of entries w/ unique type 250 prev := make(map[Type]int) // index at which type was previously seen 251 for _, e := range list { 252 if i, found := lookupType(prev, e.typ); found { 253 list[i].multiples = true 254 // ignore this entry 255 } else { 256 prev[e.typ] = n 257 list[n] = e 258 n++ 259 } 260 } 261 return list[:n] 262 } 263 264 func lookupType(m map[Type]int, typ Type) (int, bool) { 265 // fast path: maybe the types are equal 266 if i, found := m[typ]; found { 267 return i, true 268 } 269 270 for t, i := range m { 271 if Identical(t, typ) { 272 return i, true 273 } 274 } 275 276 return 0, false 277 } 278 279 type instanceLookup struct { 280 // buf is used to avoid allocating the map m in the common case of a small 281 // number of instances. 282 buf [3]*Named 283 m map[*Named][]*Named 284 } 285 286 func (l *instanceLookup) lookup(inst *Named) *Named { 287 for _, t := range l.buf { 288 if t != nil && Identical(inst, t) { 289 return t 290 } 291 } 292 for _, t := range l.m[inst.Origin()] { 293 if Identical(inst, t) { 294 return t 295 } 296 } 297 return nil 298 } 299 300 func (l *instanceLookup) add(inst *Named) { 301 for i, t := range l.buf { 302 if t == nil { 303 l.buf[i] = inst 304 return 305 } 306 } 307 if l.m == nil { 308 l.m = make(map[*Named][]*Named) 309 } 310 insts := l.m[inst.Origin()] 311 l.m[inst.Origin()] = append(insts, inst) 312 } 313 314 // MissingMethod returns (nil, false) if V implements T, otherwise it 315 // returns a missing method required by T and whether it is missing or 316 // just has the wrong type: either a pointer receiver or wrong signature. 317 // 318 // For non-interface types V, or if static is set, V implements T if all 319 // methods of T are present in V. Otherwise (V is an interface and static 320 // is not set), MissingMethod only checks that methods of T which are also 321 // present in V have matching types (e.g., for a type assertion x.(T) where 322 // x is of interface type V). 323 func MissingMethod(V Type, T *Interface, static bool) (method *Func, wrongType bool) { 324 return (*Checker)(nil).missingMethod(V, T, static, Identical, nil) 325 } 326 327 // missingMethod is like MissingMethod but accepts a *Checker as receiver, 328 // a comparator equivalent for type comparison, and a *string for error causes. 329 // The receiver may be nil if missingMethod is invoked through an exported 330 // API call (such as MissingMethod), i.e., when all methods have been type- 331 // checked. 332 // The underlying type of T must be an interface; T (rather than its under- 333 // lying type) is used for better error messages (reported through *cause). 334 // The comparator is used to compare signatures. 335 // If a method is missing and cause is not nil, *cause describes the error. 336 func (check *Checker) missingMethod(V, T Type, static bool, equivalent func(x, y Type) bool, cause *string) (method *Func, wrongType bool) { 337 methods := under(T).(*Interface).typeSet().methods // T must be an interface 338 if len(methods) == 0 { 339 return nil, false 340 } 341 342 const ( 343 ok = iota 344 notFound 345 wrongName 346 unexported 347 wrongSig 348 ambigSel 349 ptrRecv 350 field 351 ) 352 353 state := ok 354 var m *Func // method on T we're trying to implement 355 var f *Func // method on V, if found (state is one of ok, wrongName, wrongSig) 356 357 if u, _ := under(V).(*Interface); u != nil { 358 tset := u.typeSet() 359 for _, m = range methods { 360 _, f = tset.LookupMethod(m.pkg, m.name, false) 361 362 if f == nil { 363 if !static { 364 continue 365 } 366 state = notFound 367 break 368 } 369 370 if !equivalent(f.typ, m.typ) { 371 state = wrongSig 372 break 373 } 374 } 375 } else { 376 for _, m = range methods { 377 obj, index, indirect := lookupFieldOrMethodImpl(V, false, m.pkg, m.name, false) 378 379 // check if m is ambiguous, on *V, or on V with case-folding 380 if obj == nil { 381 switch { 382 case index != nil: 383 state = ambigSel 384 case indirect: 385 state = ptrRecv 386 default: 387 state = notFound 388 obj, _, _ = lookupFieldOrMethodImpl(V, false, m.pkg, m.name, true /* fold case */) 389 f, _ = obj.(*Func) 390 if f != nil { 391 state = wrongName 392 if f.name == m.name { 393 // If the names are equal, f must be unexported 394 // (otherwise the package wouldn't matter). 395 state = unexported 396 } 397 } 398 } 399 break 400 } 401 402 // we must have a method (not a struct field) 403 f, _ = obj.(*Func) 404 if f == nil { 405 state = field 406 break 407 } 408 409 // methods may not have a fully set up signature yet 410 if check != nil { 411 check.objDecl(f, nil) 412 } 413 414 if !equivalent(f.typ, m.typ) { 415 state = wrongSig 416 break 417 } 418 } 419 } 420 421 if state == ok { 422 return nil, false 423 } 424 425 if cause != nil { 426 if f != nil { 427 // This method may be formatted in funcString below, so must have a fully 428 // set up signature. 429 if check != nil { 430 check.objDecl(f, nil) 431 } 432 } 433 switch state { 434 case notFound: 435 switch { 436 case isInterfacePtr(V): 437 *cause = "(" + check.interfacePtrError(V) + ")" 438 case isInterfacePtr(T): 439 *cause = "(" + check.interfacePtrError(T) + ")" 440 default: 441 *cause = check.sprintf("(missing method %s)", m.Name()) 442 } 443 case wrongName: 444 fs, ms := check.funcString(f, false), check.funcString(m, false) 445 *cause = check.sprintf("(missing method %s)\n\t\thave %s\n\t\twant %s", m.Name(), fs, ms) 446 case unexported: 447 *cause = check.sprintf("(unexported method %s)", m.Name()) 448 case wrongSig: 449 fs, ms := check.funcString(f, false), check.funcString(m, false) 450 if fs == ms { 451 // Don't report "want Foo, have Foo". 452 // Add package information to disambiguate (go.dev/issue/54258). 453 fs, ms = check.funcString(f, true), check.funcString(m, true) 454 } 455 if fs == ms { 456 // We still have "want Foo, have Foo". 457 // This is most likely due to different type parameters with 458 // the same name appearing in the instantiated signatures 459 // (go.dev/issue/61685). 460 // Rather than reporting this misleading error cause, for now 461 // just point out that the method signature is incorrect. 462 // TODO(gri) should find a good way to report the root cause 463 *cause = check.sprintf("(wrong type for method %s)", m.Name()) 464 break 465 } 466 *cause = check.sprintf("(wrong type for method %s)\n\t\thave %s\n\t\twant %s", m.Name(), fs, ms) 467 case ambigSel: 468 *cause = check.sprintf("(ambiguous selector %s.%s)", V, m.Name()) 469 case ptrRecv: 470 *cause = check.sprintf("(method %s has pointer receiver)", m.Name()) 471 case field: 472 *cause = check.sprintf("(%s.%s is a field, not a method)", V, m.Name()) 473 default: 474 unreachable() 475 } 476 } 477 478 return m, state == wrongSig || state == ptrRecv 479 } 480 481 func isInterfacePtr(T Type) bool { 482 p, _ := under(T).(*Pointer) 483 return p != nil && IsInterface(p.base) 484 } 485 486 // check may be nil. 487 func (check *Checker) interfacePtrError(T Type) string { 488 assert(isInterfacePtr(T)) 489 if p, _ := under(T).(*Pointer); isTypeParam(p.base) { 490 return check.sprintf("type %s is pointer to type parameter, not type parameter", T) 491 } 492 return check.sprintf("type %s is pointer to interface, not interface", T) 493 } 494 495 // funcString returns a string of the form name + signature for f. 496 // check may be nil. 497 func (check *Checker) funcString(f *Func, pkgInfo bool) string { 498 buf := bytes.NewBufferString(f.name) 499 var qf Qualifier 500 if check != nil && !pkgInfo { 501 qf = check.qualifier 502 } 503 w := newTypeWriter(buf, qf) 504 w.pkgInfo = pkgInfo 505 w.paramNames = false 506 w.signature(f.typ.(*Signature)) 507 return buf.String() 508 } 509 510 // assertableTo reports whether a value of type V can be asserted to have type T. 511 // The receiver may be nil if assertableTo is invoked through an exported API call 512 // (such as AssertableTo), i.e., when all methods have been type-checked. 513 // The underlying type of V must be an interface. 514 // If the result is false and cause is not nil, *cause describes the error. 515 // TODO(gri) replace calls to this function with calls to newAssertableTo. 516 func (check *Checker) assertableTo(V, T Type, cause *string) bool { 517 // no static check is required if T is an interface 518 // spec: "If T is an interface type, x.(T) asserts that the 519 // dynamic type of x implements the interface T." 520 if IsInterface(T) { 521 return true 522 } 523 // TODO(gri) fix this for generalized interfaces 524 m, _ := check.missingMethod(T, V, false, Identical, cause) 525 return m == nil 526 } 527 528 // newAssertableTo reports whether a value of type V can be asserted to have type T. 529 // It also implements behavior for interfaces that currently are only permitted 530 // in constraint position (we have not yet defined that behavior in the spec). 531 // The underlying type of V must be an interface. 532 // If the result is false and cause is not nil, *cause is set to the error cause. 533 func (check *Checker) newAssertableTo(pos syntax.Pos, V, T Type, cause *string) bool { 534 // no static check is required if T is an interface 535 // spec: "If T is an interface type, x.(T) asserts that the 536 // dynamic type of x implements the interface T." 537 if IsInterface(T) { 538 return true 539 } 540 return check.implements(pos, T, V, false, cause) 541 } 542 543 // deref dereferences typ if it is a *Pointer (but not a *Named type 544 // with an underlying pointer type!) and returns its base and true. 545 // Otherwise it returns (typ, false). 546 func deref(typ Type) (Type, bool) { 547 if p, _ := Unalias(typ).(*Pointer); p != nil { 548 // p.base should never be nil, but be conservative 549 if p.base == nil { 550 if debug { 551 panic("pointer with nil base type (possibly due to an invalid cyclic declaration)") 552 } 553 return Typ[Invalid], true 554 } 555 return p.base, true 556 } 557 return typ, false 558 } 559 560 // derefStructPtr dereferences typ if it is a (named or unnamed) pointer to a 561 // (named or unnamed) struct and returns its base. Otherwise it returns typ. 562 func derefStructPtr(typ Type) Type { 563 if p, _ := under(typ).(*Pointer); p != nil { 564 if _, ok := under(p.base).(*Struct); ok { 565 return p.base 566 } 567 } 568 return typ 569 } 570 571 // concat returns the result of concatenating list and i. 572 // The result does not share its underlying array with list. 573 func concat(list []int, i int) []int { 574 var t []int 575 t = append(t, list...) 576 return append(t, i) 577 } 578 579 // fieldIndex returns the index for the field with matching package and name, or a value < 0. 580 func fieldIndex(fields []*Var, pkg *Package, name string) int { 581 if name != "_" { 582 for i, f := range fields { 583 if f.sameId(pkg, name) { 584 return i 585 } 586 } 587 } 588 return -1 589 } 590 591 // lookupMethod returns the index of and method with matching package and name, or (-1, nil). 592 // If foldCase is true, method names are considered equal if they are equal with case folding 593 // and their packages are ignored (e.g., pkg1.m, pkg1.M, pkg2.m, and pkg2.M are all equal). 594 func lookupMethod(methods []*Func, pkg *Package, name string, foldCase bool) (int, *Func) { 595 if name != "_" { 596 for i, m := range methods { 597 if m.sameId(pkg, name) || foldCase && strings.EqualFold(m.name, name) { 598 return i, m 599 } 600 } 601 } 602 return -1, nil 603 } 604