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.
9 // Internal use of LookupFieldOrMethod: If the obj result is a method
10 // associated with a concrete (non-interface) type, the method's signature
11 // may not be fully set up. Call Checker.objDecl(obj, nil) before accessing
14 // LookupFieldOrMethod looks up a field or method with given package and name
15 // in T and returns the corresponding *Var or *Func, an index sequence, and a
16 // bool indicating if there were any pointer indirections on the path to the
17 // field or method. If addressable is set, T is the type of an addressable
18 // variable (only matters for method lookups).
20 // The last index entry is the field or method index in the (possibly embedded)
21 // type where the entry was found, either:
23 // 1) the list of declared methods of a named type; or
24 // 2) the list of all methods (method set) of an interface type; or
25 // 3) the list of fields of a struct type.
27 // The earlier index entries are the indices of the embedded struct fields
28 // traversed to get to the found entry, starting at depth 0.
30 // If no entry is found, a nil object is returned. In this case, the returned
31 // index and indirect values have the following meaning:
33 // - If index != nil, the index sequence points to an ambiguous entry
34 // (the same name appeared more than once at the same embedding level).
36 // - If indirect is set, a method with a pointer receiver type was found
37 // but there was no pointer on the path from the actual receiver type to
38 // the method's formal receiver base type, nor was the receiver addressable.
40 func LookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string) (obj Object, index []int, indirect bool) {
41 // Methods cannot be associated to a named pointer type
42 // (spec: "The type denoted by T is called the receiver base type;
43 // it must not be a pointer or interface type and it must be declared
44 // in the same package as the method.").
45 // Thus, if we have a named pointer type, proceed with the underlying
46 // pointer type but discard the result if it is a method since we would
47 // not have found it for T (see also issue 8590).
48 if t := asNamed(T); t != nil {
49 if p, _ := safeUnderlying(t).(*Pointer); p != nil {
50 obj, index, indirect = lookupFieldOrMethod(p, false, pkg, name)
51 if _, ok := obj.(*Func); ok {
52 return nil, nil, false
58 return lookupFieldOrMethod(T, addressable, pkg, name)
61 // TODO(gri) The named type consolidation and seen maps below must be
62 // indexed by unique keys for a given type. Verify that named
63 // types always have only one representation (even when imported
64 // indirectly via different packages.)
66 // lookupFieldOrMethod should only be called by LookupFieldOrMethod and missingMethod.
67 func lookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string) (obj Object, index []int, indirect bool) {
68 // WARNING: The code in this function is extremely subtle - do not modify casually!
71 return // blank fields/methods are never found
74 typ, isPtr := deref(T)
76 // *typ where typ is an interface or type parameter has no methods.
78 // don't look at under(typ) here - was bug (issue #47747)
79 if _, ok := typ.(*TypeParam); ok {
82 if _, ok := under(typ).(*Interface); ok {
87 // Start with typ as single entry at shallowest depth.
88 current := []embeddedType{{typ, nil, isPtr, false}}
90 // Named types that we have seen already, allocated lazily.
91 // Used to avoid endless searches in case of recursive types.
92 // Since only Named types can be used for recursive types, we
93 // only need to track those.
94 // (If we ever allow type aliases to construct recursive types,
95 // we must use type identity rather than pointer equality for
96 // the map key comparison, as we do in consolidateMultiples.)
97 var seen map[*Named]bool
99 // search current depth
100 for len(current) > 0 {
101 var next []embeddedType // embedded types found at current depth
103 // look for (pkg, name) in all types at current depth
104 var tpar *TypeParam // set if obj receiver is a type parameter
105 for _, e := range current {
108 // If we have a named type, we may have associated methods.
109 // Look for those first.
110 if named := asNamed(typ); named != nil {
112 // We have seen this type before, at a more shallow depth
113 // (note that multiples of this type at the current depth
114 // were consolidated before). The type at that depth shadows
115 // this same type at the current depth, so we can ignore
120 seen = make(map[*Named]bool)
124 // look for a matching attached method
126 if i, m := lookupMethod(named.methods, pkg, name); m != nil {
128 // caution: method may not have a proper signature yet
129 index = concat(e.index, i)
130 if obj != nil || e.multiples {
131 return nil, index, false // collision
134 indirect = e.indirect
135 continue // we can't have a matching field or interface method
138 // continue with underlying type, but only if it's not a type parameter
139 // TODO(gri) is this what we want to do for type parameters? (spec question)
141 if asTypeParam(typ) != nil {
147 switch t := typ.(type) {
149 // look for a matching field and collect embedded types
150 for i, f := range t.fields {
151 if f.sameId(pkg, name) {
153 index = concat(e.index, i)
154 if obj != nil || e.multiples {
155 return nil, index, false // collision
158 indirect = e.indirect
159 continue // we can't have a matching interface method
161 // Collect embedded struct fields for searching the next
162 // lower depth, but only if we have not seen a match yet
163 // (if we have a match it is either the desired field or
164 // we have a name collision on the same depth; in either
165 // case we don't need to look further).
166 // Embedded fields are always of the form T or *T where
167 // T is a type name. If e.typ appeared multiple times at
168 // this depth, f.typ appears multiple times at the next
170 if obj == nil && f.embedded {
171 typ, isPtr := deref(f.typ)
172 // TODO(gri) optimization: ignore types that can't
173 // have fields or methods (only Named, Struct, and
174 // Interface types need to be considered).
175 next = append(next, embeddedType{typ, concat(e.index, i), e.indirect || isPtr, e.multiples})
180 // look for a matching method
181 if i, m := t.typeSet().LookupMethod(pkg, name); m != nil {
183 index = concat(e.index, i)
184 if obj != nil || e.multiples {
185 return nil, index, false // collision
188 indirect = e.indirect
192 if i, m := t.iface().typeSet().LookupMethod(pkg, name); m != nil {
194 index = concat(e.index, i)
195 if obj != nil || e.multiples {
196 return nil, index, false // collision
200 indirect = e.indirect
203 // At this point we're not (yet) looking into methods
204 // that any underlying type of the types in the type list
206 // TODO(gri) Do we want to specify the language that way?
212 // found a potential match
213 // spec: "A method call x.m() is valid if the method set of (the type of) x
214 // contains m and the argument list can be assigned to the parameter
215 // list of m. If x is addressable and &x's method set contains m, x.m()
216 // is shorthand for (&x).m()".
217 if f, _ := obj.(*Func); f != nil {
218 // determine if method has a pointer receiver
219 hasPtrRecv := tpar == nil && ptrRecv(f)
220 if hasPtrRecv && !indirect && !addressable {
221 return nil, nil, true // pointer/addressable receiver required
227 current = consolidateMultiples(next)
230 return nil, nil, false // not found
233 // embeddedType represents an embedded type
234 type embeddedType struct {
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
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 {
246 return list // at most one entry - nothing to do
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
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 {
270 for t, i := range m {
271 if Identical(t, typ) {
279 // MissingMethod returns (nil, false) if V implements T, otherwise it
280 // returns a missing method required by T and whether it is missing or
281 // just has the wrong type.
283 // For non-interface types V, or if static is set, V implements T if all
284 // methods of T are present in V. Otherwise (V is an interface and static
285 // is not set), MissingMethod only checks that methods of T which are also
286 // present in V have matching types (e.g., for a type assertion x.(T) where
287 // x is of interface type V).
289 func MissingMethod(V Type, T *Interface, static bool) (method *Func, wrongType bool) {
290 m, typ := (*Checker)(nil).missingMethod(V, T, static)
294 // missingMethod is like MissingMethod but accepts a *Checker as
295 // receiver and an addressable flag.
296 // The receiver may be nil if missingMethod is invoked through
297 // an exported API call (such as MissingMethod), i.e., when all
298 // methods have been type-checked.
299 // If the type has the correctly named method, but with the wrong
300 // signature, the existing method is returned as well.
301 // To improve error messages, also report the wrong signature
302 // when the method exists on *V instead of V.
303 func (check *Checker) missingMethod(V Type, T *Interface, static bool) (method, wrongType *Func) {
304 // fast path for common case
309 if ityp := asInterface(V); ityp != nil {
310 // TODO(gri) the methods are sorted - could do this more efficiently
311 for _, m := range T.typeSet().methods {
312 _, f := ityp.typeSet().LookupMethod(m.pkg, m.name)
321 // both methods must have the same number of type parameters
322 ftyp := f.typ.(*Signature)
323 mtyp := m.typ.(*Signature)
324 if ftyp.TypeParams().Len() != mtyp.TypeParams().Len() {
327 if !acceptMethodTypeParams && ftyp.TypeParams().Len() > 0 {
328 panic("method with type parameters")
331 // If the methods have type parameters we don't care whether they
332 // are the same or not, as long as they match up. Use unification
333 // to see if they can be made to match.
334 // TODO(gri) is this always correct? what about type bounds?
335 // (Alternative is to rename/subst type parameters and compare.)
336 u := newUnifier(true)
337 u.x.init(ftyp.TypeParams().list())
338 if !u.unify(ftyp, mtyp) {
346 // 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, m.pkg, m.name)
353 // Check if *V implements this method of T.
356 obj, _, _ = lookupFieldOrMethod(ptr, false, m.pkg, m.name)
358 return m, obj.(*Func)
362 // we must have a method (not a field of matching function type)
368 // methods may not have a fully set up signature yet
370 check.objDecl(f, nil)
373 // both methods must have the same number of type parameters
374 ftyp := f.typ.(*Signature)
375 mtyp := m.typ.(*Signature)
376 if ftyp.TypeParams().Len() != mtyp.TypeParams().Len() {
379 if !acceptMethodTypeParams && ftyp.TypeParams().Len() > 0 {
380 panic("method with type parameters")
383 // If V is a (instantiated) generic type, its methods are still
384 // parameterized using the original (declaration) receiver type
385 // parameters (subst simply copies the existing method list, it
386 // does not instantiate the methods).
387 // In order to compare the signatures, substitute the receiver
388 // type parameters of ftyp with V's instantiation type arguments.
389 // This lazily instantiates the signature of method f.
390 if Vn != nil && Vn.TypeParams().Len() > 0 {
391 // Be careful: The number of type arguments may not match
392 // the number of receiver parameters. If so, an error was
393 // reported earlier but the length discrepancy is still
394 // here. Exit early in this case to prevent an assertion
395 // failure in makeSubstMap.
396 // TODO(gri) Can we avoid this check by fixing the lengths?
397 if len(ftyp.RecvTypeParams().list()) != Vn.targs.Len() {
400 ftyp = check.subst(nopos, ftyp, makeSubstMap(ftyp.RecvTypeParams().list(), Vn.targs.list()), nil).(*Signature)
403 // If the methods have type parameters we don't care whether they
404 // are the same or not, as long as they match up. Use unification
405 // to see if they can be made to match.
406 // TODO(gri) is this always correct? what about type bounds?
407 // (Alternative is to rename/subst type parameters and compare.)
408 u := newUnifier(true)
409 if ftyp.TypeParams().Len() > 0 {
410 // We reach here only if we accept method type parameters.
411 // In this case, unification must consider any receiver
412 // and method type parameters as "free" type parameters.
413 assert(acceptMethodTypeParams)
414 // We don't have a test case for this at the moment since
415 // we can't parse method type parameters. Keeping the
416 // unimplemented call so that we test this code if we
417 // enable method type parameters.
419 u.x.init(append(ftyp.RecvTypeParams().list(), ftyp.TypeParams().list()...))
421 u.x.init(ftyp.RecvTypeParams().list())
423 if !u.unify(ftyp, mtyp) {
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 // If the global constant forceStrict is set, assertions that are known to fail
437 // are not permitted.
438 func (check *Checker) assertableTo(V *Interface, T Type) (method, wrongType *Func) {
439 // no static check is required if T is an interface
440 // spec: "If T is an interface type, x.(T) asserts that the
441 // dynamic type of x implements the interface T."
442 if asInterface(T) != nil && !forceStrict {
445 return check.missingMethod(T, V, false)
448 // deref dereferences typ if it is a *Pointer and returns its base and true.
449 // Otherwise it returns (typ, false).
450 func deref(typ Type) (Type, bool) {
451 if p, _ := typ.(*Pointer); p != nil {
457 // derefStructPtr dereferences typ if it is a (named or unnamed) pointer to a
458 // (named or unnamed) struct and returns its base. Otherwise it returns typ.
459 func derefStructPtr(typ Type) Type {
460 if p := asPointer(typ); p != nil {
461 if asStruct(p.base) != nil {
468 // concat returns the result of concatenating list and i.
469 // The result does not share its underlying array with list.
470 func concat(list []int, i int) []int {
472 t = append(t, list...)
476 // fieldIndex returns the index for the field with matching package and name, or a value < 0.
477 func fieldIndex(fields []*Var, pkg *Package, name string) int {
479 for i, f := range fields {
480 if f.sameId(pkg, name) {
488 // lookupMethod returns the index of and method with matching package and name, or (-1, nil).
489 func lookupMethod(methods []*Func, pkg *Package, name string) (int, *Func) {
491 for i, m := range methods {
492 if m.sameId(pkg, name) {
500 // ptrRecv reports whether the receiver is of the form *T.
501 func ptrRecv(f *Func) bool {
502 // If a method's receiver type is set, use that as the source of truth for the receiver.
503 // Caution: Checker.funcDecl (decl.go) marks a function by setting its type to an empty
504 // signature. We may reach here before the signature is fully set up: we must explicitly
505 // check if the receiver is set (we cannot just look for non-nil f.typ).
506 if sig, _ := f.typ.(*Signature); sig != nil && sig.recv != nil {
507 _, isPtr := deref(sig.recv.typ)
511 // If a method's type is not set it may be a method/function that is:
512 // 1) client-supplied (via NewFunc with no signature), or
513 // 2) internally created but not yet type-checked.
514 // For case 1) we can't do anything; the client must know what they are doing.
515 // For case 2) we can use the information gathered by the resolver.