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.
13 // Internal use of LookupFieldOrMethod: If the obj result is a method
14 // associated with a concrete (non-interface) type, the method's signature
15 // may not be fully set up. Call Checker.objDecl(obj, nil) before accessing
18 // LookupFieldOrMethod looks up a field or method with given package and name
19 // in T and returns the corresponding *Var or *Func, an index sequence, and a
20 // bool indicating if there were any pointer indirections on the path to the
21 // field or method. If addressable is set, T is the type of an addressable
22 // variable (only matters for method lookups).
24 // The last index entry is the field or method index in the (possibly embedded)
25 // type where the entry was found, either:
27 // 1) the list of declared methods of a named type; or
28 // 2) the list of all methods (method set) of an interface type; or
29 // 3) the list of fields of a struct type.
31 // The earlier index entries are the indices of the embedded struct fields
32 // traversed to get to the found entry, starting at depth 0.
34 // If no entry is found, a nil object is returned. In this case, the returned
35 // index and indirect values have the following meaning:
37 // - If index != nil, the index sequence points to an ambiguous entry
38 // (the same name appeared more than once at the same embedding level).
40 // - If indirect is set, a method with a pointer receiver type was found
41 // but there was no pointer on the path from the actual receiver type to
42 // 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 // Methods cannot be associated to a named pointer type.
46 // (spec: "The type denoted by T is called the receiver base type;
47 // it must not be a pointer or interface type and it must be declared
48 // in the same package as the method.").
49 // Thus, if we have a named pointer type, proceed with the underlying
50 // pointer type but discard the result if it is a method since we would
51 // not have found it for T (see also issue 8590).
52 if t, _ := T.(*Named); t != nil {
53 if p, _ := t.Underlying().(*Pointer); p != nil {
54 obj, index, indirect = lookupFieldOrMethod(p, false, pkg, name)
55 if _, ok := obj.(*Func); ok {
56 return nil, nil, false
62 obj, index, indirect = lookupFieldOrMethod(T, addressable, pkg, name)
64 // If we didn't find anything and if we have a type parameter with a structural constraint,
65 // see if there is a matching field (but not a method, those need to be declared explicitly
66 // in the constraint). If the structural constraint is a named pointer type (see above), we
67 // are ok here because only fields are accepted as results.
68 if obj == nil && isTypeParam(T) {
69 if t := structuralType(T); t != nil {
70 obj, index, indirect = lookupFieldOrMethod(t, addressable, pkg, name)
71 if _, ok := obj.(*Var); !ok {
72 obj, index, indirect = nil, nil, false // accept fields (variables) only
79 // TODO(gri) The named type consolidation and seen maps below must be
80 // indexed by unique keys for a given type. Verify that named
81 // types always have only one representation (even when imported
82 // indirectly via different packages.)
84 // lookupFieldOrMethod should only be called by LookupFieldOrMethod and missingMethod.
86 // The resulting object may not be fully type-checked.
87 func lookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string) (obj Object, index []int, indirect bool) {
88 // WARNING: The code in this function is extremely subtle - do not modify casually!
91 return // blank fields/methods are never found
94 typ, isPtr := deref(T)
96 // *typ where typ is an interface (incl. a type parameter) has no methods.
98 if _, ok := under(typ).(*Interface); ok {
103 // Start with typ as single entry at shallowest depth.
104 current := []embeddedType{{typ, nil, isPtr, false}}
106 // Named types that we have seen already, allocated lazily.
107 // Used to avoid endless searches in case of recursive types.
108 // Since only Named types can be used for recursive types, we
109 // only need to track those.
110 // (If we ever allow type aliases to construct recursive types,
111 // we must use type identity rather than pointer equality for
112 // the map key comparison, as we do in consolidateMultiples.)
113 var seen map[*Named]bool
115 // search current depth
116 for len(current) > 0 {
117 var next []embeddedType // embedded types found at current depth
119 // look for (pkg, name) in all types at current depth
120 for _, e := range current {
123 // If we have a named type, we may have associated methods.
124 // Look for those first.
125 if named, _ := typ.(*Named); named != 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
135 seen = make(map[*Named]bool)
139 // look for a matching attached method
141 if i, m := lookupMethod(named.methods, pkg, name); m != nil {
143 // caution: method may not have a proper signature yet
144 index = concat(e.index, i)
145 if obj != nil || e.multiples {
146 return nil, index, false // collision
149 indirect = e.indirect
150 continue // we can't have a matching field or interface method
154 switch t := under(typ).(type) {
156 // look for a matching field and collect embedded types
157 for i, f := range t.fields {
158 if f.sameId(pkg, name) {
160 index = concat(e.index, i)
161 if obj != nil || e.multiples {
162 return nil, index, false // collision
165 indirect = e.indirect
166 continue // we can't have a matching interface method
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
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})
187 // look for a matching method (interface may be a type parameter)
188 if i, m := t.typeSet().LookupMethod(pkg, name); m != nil {
190 index = concat(e.index, i)
191 if obj != nil || e.multiples {
192 return nil, index, false // collision
195 indirect = e.indirect
201 // found a potential match
202 // spec: "A method call x.m() is valid if the method set of (the type of) x
203 // contains m and the argument list can be assigned to the parameter
204 // list of m. If x is addressable and &x's method set contains m, x.m()
205 // is shorthand for (&x).m()".
206 if f, _ := obj.(*Func); f != nil {
207 // determine if method has a pointer receiver
208 if f.hasPtrRecv() && !indirect && !addressable {
209 return nil, nil, true // pointer/addressable receiver required
215 current = consolidateMultiples(next)
218 return nil, nil, false // not found
221 // embeddedType represents an embedded type
222 type embeddedType struct {
224 index []int // embedded field indices, starting with index at depth 0
225 indirect bool // if set, there was a pointer indirection on the path to this field
226 multiples bool // if set, typ appears multiple times at this depth
229 // consolidateMultiples collects multiple list entries with the same type
230 // into a single entry marked as containing multiples. The result is the
231 // consolidated list.
232 func consolidateMultiples(list []embeddedType) []embeddedType {
234 return list // at most one entry - nothing to do
237 n := 0 // number of entries w/ unique type
238 prev := make(map[Type]int) // index at which type was previously seen
239 for _, e := range list {
240 if i, found := lookupType(prev, e.typ); found {
241 list[i].multiples = true
252 func lookupType(m map[Type]int, typ Type) (int, bool) {
253 // fast path: maybe the types are equal
254 if i, found := m[typ]; found {
258 for t, i := range m {
259 if Identical(t, typ) {
267 // MissingMethod returns (nil, false) if V implements T, otherwise it
268 // returns a missing method required by T and whether it is missing or
269 // just has the wrong type.
271 // For non-interface types V, or if static is set, V implements T if all
272 // methods of T are present in V. Otherwise (V is an interface and static
273 // is not set), MissingMethod only checks that methods of T which are also
274 // present in V have matching types (e.g., for a type assertion x.(T) where
275 // x is of interface type V).
277 func MissingMethod(V Type, T *Interface, static bool) (method *Func, wrongType bool) {
278 m, typ := (*Checker)(nil).missingMethod(V, T, static)
282 // missingMethod is like MissingMethod but accepts a *Checker as
283 // receiver and an addressable flag.
284 // The receiver may be nil if missingMethod is invoked through
285 // an exported API call (such as MissingMethod), i.e., when all
286 // methods have been type-checked.
287 // If the type has the correctly named method, but with the wrong
288 // signature, the existing method is returned as well.
289 // To improve error messages, also report the wrong signature
290 // when the method exists on *V instead of V.
291 func (check *Checker) missingMethod(V Type, T *Interface, static bool) (method, wrongType *Func) {
292 // fast path for common case
297 if ityp, _ := under(V).(*Interface); ityp != nil {
298 // TODO(gri) the methods are sorted - could do this more efficiently
299 for _, m := range T.typeSet().methods {
300 _, f := ityp.typeSet().LookupMethod(m.pkg, m.name)
309 // both methods must have the same number of type parameters
310 ftyp := f.typ.(*Signature)
311 mtyp := m.typ.(*Signature)
312 if ftyp.TypeParams().Len() != mtyp.TypeParams().Len() {
315 if ftyp.TypeParams().Len() > 0 {
316 panic("method with type parameters")
319 // If the methods have type parameters we don't care whether they
320 // are the same or not, as long as they match up. Use unification
321 // to see if they can be made to match.
322 // TODO(gri) is this always correct? what about type bounds?
323 // (Alternative is to rename/subst type parameters and compare.)
324 u := newUnifier(true)
325 u.x.init(ftyp.TypeParams().list())
326 if !u.unify(ftyp, mtyp) {
334 // A concrete type implements T if it implements all methods of T.
335 for _, m := range T.typeSet().methods {
336 // TODO(gri) should this be calling lookupFieldOrMethod instead (and why not)?
337 obj, _, _ := lookupFieldOrMethod(V, false, m.pkg, m.name)
339 // Check if *V implements this method of T.
342 obj, _, _ = lookupFieldOrMethod(ptr, false, m.pkg, m.name)
345 // methods may not have a fully set up signature yet
347 check.objDecl(obj, nil)
349 return m, obj.(*Func)
353 // we must have a method (not a field of matching function type)
359 // methods may not have a fully set up signature yet
361 check.objDecl(f, nil)
364 // both methods must have the same number of type parameters
365 ftyp := f.typ.(*Signature)
366 mtyp := m.typ.(*Signature)
367 if ftyp.TypeParams().Len() != mtyp.TypeParams().Len() {
370 if ftyp.TypeParams().Len() > 0 {
371 panic("method with type parameters")
374 // If the methods have type parameters we don't care whether they
375 // are the same or not, as long as they match up. Use unification
376 // to see if they can be made to match.
377 // TODO(gri) is this always correct? what about type bounds?
378 // (Alternative is to rename/subst type parameters and compare.)
379 u := newUnifier(true)
380 u.x.init(ftyp.RecvTypeParams().list())
381 if !u.unify(ftyp, mtyp) {
389 // missingMethodReason returns a string giving the detailed reason for a missing method m,
390 // where m is missing from V, but required by T. It puts the reason in parentheses,
391 // and may include more have/want info after that. If non-nil, wrongType is a relevant
392 // method that matches in some way. It may have the correct name, but wrong type, or
393 // it may have a pointer receiver.
394 func (check *Checker) missingMethodReason(V, T Type, m, wrongType *Func) string {
397 if compilerErrorMessages {
398 mname = m.Name() + " method"
400 mname = "method " + m.Name()
402 if wrongType != nil {
403 if Identical(m.typ, wrongType.typ) {
404 if m.Name() == wrongType.Name() {
405 r = check.sprintf("(%s has pointer receiver)", mname)
407 r = check.sprintf("(missing %s)\n\t\thave %s^^%s\n\t\twant %s^^%s",
408 mname, wrongType.Name(), wrongType.typ, m.Name(), m.typ)
411 if compilerErrorMessages {
412 r = check.sprintf("(wrong type for %s)\n\t\thave %s^^%s\n\t\twant %s^^%s",
413 mname, wrongType.Name(), wrongType.typ, m.Name(), m.typ)
415 r = check.sprintf("(wrong type for %s: have %s, want %s)",
416 mname, wrongType.typ, m.typ)
419 // This is a hack to print the function type without the leading
420 // 'func' keyword in the have/want printouts. We could change to have
421 // an extra formatting option for types2.Type that doesn't print out
423 r = strings.Replace(r, "^^func", "", -1)
424 } else if IsInterface(T) {
425 if isInterfacePtr(V) {
426 r = "(" + check.interfacePtrError(V) + ")"
428 } else if isInterfacePtr(T) {
429 r = "(" + check.interfacePtrError(T) + ")"
432 r = check.sprintf("(missing %s)", mname)
437 func isInterfacePtr(T Type) bool {
438 p, _ := under(T).(*Pointer)
439 return p != nil && IsInterface(p.base)
442 func (check *Checker) interfacePtrError(T Type) string {
443 assert(isInterfacePtr(T))
444 if p, _ := under(T).(*Pointer); isTypeParam(p.base) {
445 return check.sprintf("type %s is pointer to type parameter, not type parameter", T)
447 return check.sprintf("type %s is pointer to interface, not interface", T)
450 // assertableTo reports whether a value of type V can be asserted to have type T.
451 // It returns (nil, false) as affirmative answer. Otherwise it returns a missing
452 // method required by V and whether it is missing or just has the wrong type.
453 // The receiver may be nil if assertableTo is invoked through an exported API call
454 // (such as AssertableTo), i.e., when all methods have been type-checked.
455 // If the global constant forceStrict is set, assertions that are known to fail
456 // are not permitted.
457 func (check *Checker) assertableTo(V *Interface, T Type) (method, wrongType *Func) {
458 // no static check is required if T is an interface
459 // spec: "If T is an interface type, x.(T) asserts that the
460 // dynamic type of x implements the interface T."
461 if IsInterface(T) && !forceStrict {
464 return check.missingMethod(T, V, false)
467 // deref dereferences typ if it is a *Pointer and returns its base and true.
468 // Otherwise it returns (typ, false).
469 func deref(typ Type) (Type, bool) {
470 if p, _ := typ.(*Pointer); p != nil {
471 // p.base should never be nil, but be conservative
474 panic("pointer with nil base type (possibly due to an invalid cyclic declaration)")
476 return Typ[Invalid], true
483 // derefStructPtr dereferences typ if it is a (named or unnamed) pointer to a
484 // (named or unnamed) struct and returns its base. Otherwise it returns typ.
485 func derefStructPtr(typ Type) Type {
486 if p, _ := under(typ).(*Pointer); p != nil {
487 if _, ok := under(p.base).(*Struct); ok {
494 // concat returns the result of concatenating list and i.
495 // The result does not share its underlying array with list.
496 func concat(list []int, i int) []int {
498 t = append(t, list...)
502 // fieldIndex returns the index for the field with matching package and name, or a value < 0.
503 func fieldIndex(fields []*Var, pkg *Package, name string) int {
505 for i, f := range fields {
506 if f.sameId(pkg, name) {
514 // lookupMethod returns the index of and method with matching package and name, or (-1, nil).
515 func lookupMethod(methods []*Func, pkg *Package, name string) (int, *Func) {
517 for i, m := range methods {
518 if m.sameId(pkg, name) {