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.
5 // This file implements various field and method lookup functions.
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
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).
25 // The last index entry is the field or method index in the (possibly embedded)
26 // type where the entry was found, either:
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.
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.
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:
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).
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.
45 func LookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string) (obj Object, index []int, indirect bool) {
46 // Methods cannot be associated to a named pointer type
47 // (spec: "The type denoted by T is called the receiver base type;
48 // it must not be a pointer or interface type and it must be declared
49 // in the same package as the method.").
50 // Thus, if we have a named pointer type, proceed with the underlying
51 // pointer type but discard the result if it is a method since we would
52 // not have found it for T (see also issue 8590).
53 if t, _ := T.(*Named); t != nil {
54 if p, _ := t.Underlying().(*Pointer); p != nil {
55 obj, index, indirect = lookupFieldOrMethod(p, false, false, pkg, name)
56 if _, ok := obj.(*Func); ok {
57 return nil, nil, false
63 return lookupFieldOrMethod(T, addressable, false, pkg, name)
66 // TODO(gri) The named type consolidation and seen maps below must be
67 // indexed by unique keys for a given type. Verify that named
68 // types always have only one representation (even when imported
69 // indirectly via different packages.)
71 // lookupFieldOrMethod should only be called by LookupFieldOrMethod and missingMethod.
72 // If checkFold is true, the lookup for methods will include looking for any method
73 // which case-folds to the same as 'name' (used for giving helpful error messages).
75 // The resulting object may not be fully type-checked.
76 func lookupFieldOrMethod(T Type, addressable, checkFold bool, pkg *Package, name string) (obj Object, index []int, indirect bool) {
77 // WARNING: The code in this function is extremely subtle - do not modify casually!
80 return // blank fields/methods are never found
83 typ, isPtr := deref(T)
85 // *typ where typ is an interface has no methods.
87 if _, ok := under(typ).(*Interface); ok {
92 // Start with typ as single entry at shallowest depth.
93 current := []embeddedType{{typ, nil, isPtr, false}}
95 // Named types that we have seen already, allocated lazily.
96 // Used to avoid endless searches in case of recursive types.
97 // Since only Named types can be used for recursive types, we
98 // only need to track those.
99 // (If we ever allow type aliases to construct recursive types,
100 // we must use type identity rather than pointer equality for
101 // the map key comparison, as we do in consolidateMultiples.)
102 var seen map[*Named]bool
104 // search current depth
105 for len(current) > 0 {
106 var next []embeddedType // embedded types found at current depth
108 // look for (pkg, name) in all types at current depth
109 var tpar *TypeParam // set if obj receiver is a type parameter
110 for _, e := range current {
113 // If we have a named type, we may have associated methods.
114 // Look for those first.
115 if named, _ := typ.(*Named); named != nil {
117 // We have seen this type before, at a more shallow depth
118 // (note that multiples of this type at the current depth
119 // were consolidated before). The type at that depth shadows
120 // this same type at the current depth, so we can ignore
125 seen = make(map[*Named]bool)
129 // look for a matching attached method
131 if i, m := lookupMethodFold(named.methods, pkg, name, checkFold); m != nil {
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
139 indirect = e.indirect
140 continue // we can't have a matching field or interface method
143 // continue with underlying type
148 switch t := typ.(type) {
150 // look for a matching field and collect embedded types
151 for i, f := range t.fields {
152 if f.sameId(pkg, name) {
154 index = concat(e.index, i)
155 if obj != nil || e.multiples {
156 return nil, index, false // collision
159 indirect = e.indirect
160 continue // we can't have a matching interface method
162 // Collect embedded struct fields for searching the next
163 // lower depth, but only if we have not seen a match yet
164 // (if we have a match it is either the desired field or
165 // we have a name collision on the same depth; in either
166 // case we don't need to look further).
167 // Embedded fields are always of the form T or *T where
168 // T is a type name. If e.typ appeared multiple times at
169 // this depth, f.typ appears multiple times at the next
171 if obj == nil && f.embedded {
172 typ, isPtr := deref(f.typ)
173 // TODO(gri) optimization: ignore types that can't
174 // have fields or methods (only Named, Struct, and
175 // Interface types need to be considered).
176 next = append(next, embeddedType{typ, concat(e.index, i), e.indirect || isPtr, e.multiples})
181 // look for a matching method
182 if i, m := lookupMethodFold(t.typeSet().methods, pkg, name, checkFold); m != nil {
184 index = concat(e.index, i)
185 if obj != nil || e.multiples {
186 return nil, index, false // collision
189 indirect = e.indirect
193 if i, m := lookupMethodFold(t.iface().typeSet().methods, pkg, name, checkFold); m != nil {
195 index = concat(e.index, i)
196 if obj != nil || e.multiples {
197 return nil, index, false // collision
201 indirect = e.indirect
204 // At this point we're not (yet) looking into methods
205 // that any underlying type of the types in the type list
207 // TODO(gri) Do we want to specify the language that way?
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 hasPtrRecv := tpar == nil && f.hasPtrRecv()
221 if hasPtrRecv && !indirect && !addressable {
222 return nil, nil, true // pointer/addressable receiver required
228 current = consolidateMultiples(next)
231 return nil, nil, false // not found
234 // embeddedType represents an embedded type
235 type embeddedType struct {
237 index []int // embedded field indices, starting with index at depth 0
238 indirect bool // if set, there was a pointer indirection on the path to this field
239 multiples bool // if set, typ appears multiple times at this depth
242 // consolidateMultiples collects multiple list entries with the same type
243 // into a single entry marked as containing multiples. The result is the
244 // consolidated list.
245 func consolidateMultiples(list []embeddedType) []embeddedType {
247 return list // at most one entry - nothing to do
250 n := 0 // number of entries w/ unique type
251 prev := make(map[Type]int) // index at which type was previously seen
252 for _, e := range list {
253 if i, found := lookupType(prev, e.typ); found {
254 list[i].multiples = true
265 func lookupType(m map[Type]int, typ Type) (int, bool) {
266 // fast path: maybe the types are equal
267 if i, found := m[typ]; found {
271 for t, i := range m {
272 if Identical(t, typ) {
280 // MissingMethod returns (nil, false) if V implements T, otherwise it
281 // returns a missing method required by T and whether it is missing or
282 // just has the wrong type.
284 // For non-interface types V, or if static is set, V implements T if all
285 // methods of T are present in V. Otherwise (V is an interface and static
286 // is not set), MissingMethod only checks that methods of T which are also
287 // present in V have matching types (e.g., for a type assertion x.(T) where
288 // x is of interface type V).
290 func MissingMethod(V Type, T *Interface, static bool) (method *Func, wrongType bool) {
291 m, typ := (*Checker)(nil).missingMethod(V, T, static)
295 // missingMethod is like MissingMethod but accepts a *Checker as
296 // receiver and an addressable flag.
297 // The receiver may be nil if missingMethod is invoked through
298 // an exported API call (such as MissingMethod), i.e., when all
299 // methods have been type-checked.
300 // If the type has the correctly named method, but with the wrong
301 // signature, the existing method is returned as well.
302 // To improve error messages, also report the wrong signature
303 // when the method exists on *V instead of V.
304 func (check *Checker) missingMethod(V Type, T *Interface, static bool) (method, wrongType *Func) {
305 // fast path for common case
310 if ityp, _ := under(V).(*Interface); ityp != nil {
311 // TODO(gri) the methods are sorted - could do this more efficiently
312 for _, m := range T.typeSet().methods {
313 _, f := ityp.typeSet().LookupMethod(m.pkg, m.name)
319 // We don't do any case-fold check if V is an interface.
323 // both methods must have the same number of type parameters
324 ftyp := f.typ.(*Signature)
325 mtyp := m.typ.(*Signature)
326 if ftyp.TypeParams().Len() != mtyp.TypeParams().Len() {
329 if !acceptMethodTypeParams && ftyp.TypeParams().Len() > 0 {
330 panic("method with type parameters")
333 // If the methods have type parameters we don't care whether they
334 // are the same or not, as long as they match up. Use unification
335 // to see if they can be made to match.
336 // TODO(gri) is this always correct? what about type bounds?
337 // (Alternative is to rename/subst type parameters and compare.)
338 u := newUnifier(true)
339 u.x.init(ftyp.TypeParams().list())
340 if !u.unify(ftyp, mtyp) {
348 // A concrete type implements T if it implements all methods of T.
349 for _, m := range T.typeSet().methods {
350 // TODO(gri) should this be calling LookupFieldOrMethod instead (and why not)?
351 obj, _, _ := lookupFieldOrMethod(V, false, false, m.pkg, m.name)
353 // Check if *V implements this method of T.
356 obj, _, _ = lookupFieldOrMethod(ptr, false, false, m.pkg, m.name)
358 // If we didn't find the exact method (even with pointer
359 // receiver), look to see if there is a method that
360 // matches m.name with case-folding.
361 obj, _, _ = lookupFieldOrMethod(V, false, true, m.pkg, m.name)
364 // methods may not have a fully set up signature yet
366 check.objDecl(obj, nil)
368 return m, obj.(*Func)
372 // we must have a method (not a field of matching function type)
378 // methods may not have a fully set up signature yet
380 check.objDecl(f, nil)
383 // both methods must have the same number of type parameters
384 ftyp := f.typ.(*Signature)
385 mtyp := m.typ.(*Signature)
386 if ftyp.TypeParams().Len() != mtyp.TypeParams().Len() {
389 if !acceptMethodTypeParams && ftyp.TypeParams().Len() > 0 {
390 panic("method with type parameters")
393 // If the methods have type parameters we don't care whether they
394 // are the same or not, as long as they match up. Use unification
395 // to see if they can be made to match.
396 // TODO(gri) is this always correct? what about type bounds?
397 // (Alternative is to rename/subst type parameters and compare.)
398 u := newUnifier(true)
399 if ftyp.TypeParams().Len() > 0 {
400 // We reach here only if we accept method type parameters.
401 // In this case, unification must consider any receiver
402 // and method type parameters as "free" type parameters.
403 assert(acceptMethodTypeParams)
404 // We don't have a test case for this at the moment since
405 // we can't parse method type parameters. Keeping the
406 // unimplemented call so that we test this code if we
407 // enable method type parameters.
409 u.x.init(append(ftyp.RecvTypeParams().list(), ftyp.TypeParams().list()...))
411 u.x.init(ftyp.RecvTypeParams().list())
413 if !u.unify(ftyp, mtyp) {
421 // missingMethodReason returns a string giving the detailed reason for a missing method m,
422 // where m is missing from V, but required by T. It puts the reason in parentheses,
423 // and may include more have/want info after that. If non-nil, wrongType is a relevant
424 // method that matches in some way. It may have the correct name, but wrong type, or
425 // it may have a pointer receiver, or it may have the correct name except wrong case.
426 func (check *Checker) missingMethodReason(V, T Type, m, wrongType *Func) string {
429 if check.conf.CompilerErrorMessages {
430 mname = m.Name() + " method"
432 mname = "method " + m.Name()
434 if wrongType != nil {
435 if Identical(m.typ, wrongType.typ) {
436 if m.Name() == wrongType.Name() {
437 r = fmt.Sprintf("(%s has pointer receiver)", mname)
439 r = fmt.Sprintf("(missing %s)\n\t\thave %s^^%s\n\t\twant %s^^%s",
440 mname, wrongType.Name(), wrongType.typ, m.Name(), m.typ)
443 if check.conf.CompilerErrorMessages {
444 r = fmt.Sprintf("(wrong type for %s)\n\t\thave %s^^%s\n\t\twant %s^^%s",
445 mname, wrongType.Name(), wrongType.typ, m.Name(), m.typ)
447 r = fmt.Sprintf("(wrong type for %s: have %s, want %s)",
448 mname, wrongType.typ, m.typ)
451 // This is a hack to print the function type without the leading
452 // 'func' keyword in the have/want printouts. We could change to have
453 // an extra formatting option for types2.Type that doesn't print out
455 r = strings.Replace(r, "^^func", "", -1)
456 } else if IsInterface(T) && !isTypeParam(T) {
457 if isInterfacePtr(V) {
458 r = fmt.Sprintf("(%s is pointer to interface, not interface)", V)
460 } else if isInterfacePtr(T) && !isTypeParam(T) {
461 r = fmt.Sprintf("(%s is pointer to interface, not interface)", T)
464 r = fmt.Sprintf("(missing %s)", mname)
469 func isInterfacePtr(T Type) bool {
470 p, _ := under(T).(*Pointer)
471 return p != nil && IsInterface(p.base) && !isTypeParam(p.base)
474 // assertableTo reports whether a value of type V can be asserted to have type T.
475 // It returns (nil, false) as affirmative answer. Otherwise it returns a missing
476 // method required by V and whether it is missing or just has the wrong type.
477 // The receiver may be nil if assertableTo is invoked through an exported API call
478 // (such as AssertableTo), i.e., when all methods have been type-checked.
479 // If the global constant forceStrict is set, assertions that are known to fail
480 // are not permitted.
481 func (check *Checker) assertableTo(V *Interface, T Type) (method, wrongType *Func) {
482 // no static check is required if T is an interface
483 // spec: "If T is an interface type, x.(T) asserts that the
484 // dynamic type of x implements the interface T."
485 if IsInterface(T) && !forceStrict {
488 return check.missingMethod(T, V, false)
491 // deref dereferences typ if it is a *Pointer and returns its base and true.
492 // Otherwise it returns (typ, false).
493 func deref(typ Type) (Type, bool) {
494 if p, _ := typ.(*Pointer); p != nil {
495 // p.base should never be nil, but be conservative
498 panic("pointer with nil base type (possibly due to an invalid cyclic declaration)")
500 return Typ[Invalid], true
507 // derefStructPtr dereferences typ if it is a (named or unnamed) pointer to a
508 // (named or unnamed) struct and returns its base. Otherwise it returns typ.
509 func derefStructPtr(typ Type) Type {
510 if p, _ := under(typ).(*Pointer); p != nil {
511 if _, ok := under(p.base).(*Struct); ok {
518 // concat returns the result of concatenating list and i.
519 // The result does not share its underlying array with list.
520 func concat(list []int, i int) []int {
522 t = append(t, list...)
526 // fieldIndex returns the index for the field with matching package and name, or a value < 0.
527 func fieldIndex(fields []*Var, pkg *Package, name string) int {
529 for i, f := range fields {
530 if f.sameId(pkg, name) {
538 // lookupMethod returns the index of and method with matching package and name, or (-1, nil).
539 func lookupMethod(methods []*Func, pkg *Package, name string) (int, *Func) {
541 for i, m := range methods {
542 if m.sameId(pkg, name) {
550 // lookupMethodFold is like lookupMethod, but if checkFold is true, it matches a method
551 // name if the names are equal with case folding.
552 func lookupMethodFold(methods []*Func, pkg *Package, name string, checkFold bool) (int, *Func) {
554 for i, m := range methods {
555 if m.name != name && !(checkFold && strings.EqualFold(m.name, name)) {
558 // Use m.name, since we've already checked that m.name and
559 // name are equal with folding.
560 if m.sameId(pkg, m.name) {