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). T must not be nil.
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) {
47 panic("LookupFieldOrMethod on nil type")
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 issue 8590).
57 if t, _ := T.(*Named); t != nil {
58 if p, _ := t.Underlying().(*Pointer); p != nil {
59 obj, index, indirect = lookupFieldOrMethod(p, false, pkg, name, false)
60 if _, ok := obj.(*Func); ok {
61 return nil, nil, false
67 obj, index, indirect = lookupFieldOrMethod(T, addressable, pkg, name, false)
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 issue #51576
74 if enableTParamFieldLookup && obj == nil && isTypeParam(T) {
75 if t := coreType(T); t != nil {
76 obj, index, indirect = lookupFieldOrMethod(t, addressable, pkg, name, false)
77 if _, ok := obj.(*Var); !ok {
78 obj, index, indirect = nil, nil, false // accept fields (variables) only
85 // TODO(gri) The named type consolidation and seen maps below must be
86 // indexed by unique keys for a given type. Verify that named
87 // types always have only one representation (even when imported
88 // indirectly via different packages.)
90 // lookupFieldOrMethod should only be called by LookupFieldOrMethod and missingMethod.
91 // If foldCase is true, the lookup for methods will include looking for any method
92 // which case-folds to the same as 'name' (used for giving helpful error messages).
94 // The resulting object may not be fully type-checked.
95 func lookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string, foldCase bool) (obj Object, index []int, indirect bool) {
96 // WARNING: The code in this function is extremely subtle - do not modify casually!
99 return // blank fields/methods are never found
102 typ, isPtr := deref(T)
104 // *typ where typ is an interface (incl. a type parameter) has no methods.
106 if _, ok := under(typ).(*Interface); ok {
111 // Start with typ as single entry at shallowest depth.
112 current := []embeddedType{{typ, nil, isPtr, false}}
114 // Named types that we have seen already, allocated lazily.
115 // Used to avoid endless searches in case of recursive types.
116 // Since only Named types can be used for recursive types, we
117 // only need to track those.
118 // (If we ever allow type aliases to construct recursive types,
119 // we must use type identity rather than pointer equality for
120 // the map key comparison, as we do in consolidateMultiples.)
121 var seen map[*Named]bool
123 // search current depth
124 for len(current) > 0 {
125 var next []embeddedType // embedded types found at current depth
127 // look for (pkg, name) in all types at current depth
128 for _, e := range current {
131 // If we have a named type, we may have associated methods.
132 // Look for those first.
133 if named, _ := typ.(*Named); named != nil {
135 // We have seen this type before, at a more shallow depth
136 // (note that multiples of this type at the current depth
137 // were consolidated before). The type at that depth shadows
138 // this same type at the current depth, so we can ignore
143 seen = make(map[*Named]bool)
147 // look for a matching attached method
149 if i, m := named.lookupMethod(pkg, name, foldCase); m != nil {
151 // caution: method may not have a proper signature yet
152 index = concat(e.index, i)
153 if obj != nil || e.multiples {
154 return nil, index, false // collision
157 indirect = e.indirect
158 continue // we can't have a matching field or interface method
162 switch t := under(typ).(type) {
164 // look for a matching field and collect embedded types
165 for i, f := range t.fields {
166 if f.sameId(pkg, name) {
168 index = concat(e.index, i)
169 if obj != nil || e.multiples {
170 return nil, index, false // collision
173 indirect = e.indirect
174 continue // we can't have a matching interface method
176 // Collect embedded struct fields for searching the next
177 // lower depth, but only if we have not seen a match yet
178 // (if we have a match it is either the desired field or
179 // we have a name collision on the same depth; in either
180 // case we don't need to look further).
181 // Embedded fields are always of the form T or *T where
182 // T is a type name. If e.typ appeared multiple times at
183 // this depth, f.typ appears multiple times at the next
185 if obj == nil && f.embedded {
186 typ, isPtr := deref(f.typ)
187 // TODO(gri) optimization: ignore types that can't
188 // have fields or methods (only Named, Struct, and
189 // Interface types need to be considered).
190 next = append(next, embeddedType{typ, concat(e.index, i), e.indirect || isPtr, e.multiples})
195 // look for a matching method (interface may be a type parameter)
196 if i, m := t.typeSet().LookupMethod(pkg, name, foldCase); m != nil {
198 index = concat(e.index, i)
199 if obj != nil || e.multiples {
200 return nil, index, false // collision
203 indirect = e.indirect
209 // found a potential match
210 // spec: "A method call x.m() is valid if the method set of (the type of) x
211 // contains m and the argument list can be assigned to the parameter
212 // list of m. If x is addressable and &x's method set contains m, x.m()
213 // is shorthand for (&x).m()".
214 if f, _ := obj.(*Func); f != nil {
215 // determine if method has a pointer receiver
216 if f.hasPtrRecv() && !indirect && !addressable {
217 return nil, nil, true // pointer/addressable receiver required
223 current = consolidateMultiples(next)
226 return nil, nil, false // not found
229 // embeddedType represents an embedded type
230 type embeddedType struct {
232 index []int // embedded field indices, starting with index at depth 0
233 indirect bool // if set, there was a pointer indirection on the path to this field
234 multiples bool // if set, typ appears multiple times at this depth
237 // consolidateMultiples collects multiple list entries with the same type
238 // into a single entry marked as containing multiples. The result is the
239 // consolidated list.
240 func consolidateMultiples(list []embeddedType) []embeddedType {
242 return list // at most one entry - nothing to do
245 n := 0 // number of entries w/ unique type
246 prev := make(map[Type]int) // index at which type was previously seen
247 for _, e := range list {
248 if i, found := lookupType(prev, e.typ); found {
249 list[i].multiples = true
260 func lookupType(m map[Type]int, typ Type) (int, bool) {
261 // fast path: maybe the types are equal
262 if i, found := m[typ]; found {
266 for t, i := range m {
267 if Identical(t, typ) {
275 // MissingMethod returns (nil, false) if V implements T, otherwise it
276 // returns a missing method required by T and whether it is missing or
277 // just has the wrong type.
279 // For non-interface types V, or if static is set, V implements T if all
280 // methods of T are present in V. Otherwise (V is an interface and static
281 // is not set), MissingMethod only checks that methods of T which are also
282 // present in V have matching types (e.g., for a type assertion x.(T) where
283 // x is of interface type V).
285 func MissingMethod(V Type, T *Interface, static bool) (method *Func, wrongType bool) {
286 m, alt := (*Checker)(nil).missingMethod(V, T, static)
287 // Only report a wrong type if the alternative method has the same name as m.
288 return m, alt != nil && alt.name == m.name // alt != nil implies m != nil
291 // missingMethod is like MissingMethod but accepts a *Checker as receiver.
292 // The receiver may be nil if missingMethod is invoked through an exported
293 // API call (such as MissingMethod), i.e., when all methods have been type-
296 // If a method is missing on T but is found on *T, or if a method is found
297 // on T when looked up with case-folding, this alternative method is returned
298 // as the second result.
299 func (check *Checker) missingMethod(V Type, T *Interface, static bool) (method, alt *Func) {
300 if T.NumMethods() == 0 {
305 if u, _ := under(V).(*Interface); u != nil {
307 for _, m := range T.typeSet().methods {
308 _, f := tset.LookupMethod(m.pkg, m.name, false)
317 if !Identical(f.typ, m.typ) {
325 // V is not an interface
326 for _, m := range T.typeSet().methods {
327 // TODO(gri) should this be calling LookupFieldOrMethod instead (and why not)?
328 obj, _, _ := lookupFieldOrMethod(V, false, m.pkg, m.name, false)
330 // check if m is on *V, or on V with case-folding
333 // TODO(gri) Instead of NewPointer(V) below, can we just set the "addressable" argument?
334 obj, _, _ = lookupFieldOrMethod(NewPointer(V), false, m.pkg, m.name, false)
336 obj, _, _ = lookupFieldOrMethod(V, false, m.pkg, m.name, true /* fold case */)
340 // we must have a method (not a struct field)
346 // methods may not have a fully set up signature yet
348 check.objDecl(f, nil)
351 if !found || !Identical(f.typ, m.typ) {
359 // missingMethodReason returns a string giving the detailed reason for a missing method m,
360 // where m is missing from V, but required by T. It puts the reason in parentheses,
361 // and may include more have/want info after that. If non-nil, alt is a relevant
362 // method that matches in some way. It may have the correct name, but wrong type, or
363 // it may have a pointer receiver, or it may have the correct name except wrong case.
365 func (check *Checker) missingMethodReason(V, T Type, m, alt *Func) string {
367 if check != nil && compilerErrorMessages {
368 mname = m.Name() + " method"
370 mname = "method " + m.Name()
374 if m.Name() != alt.Name() {
375 return check.sprintf("(missing %s)\n\t\thave %s\n\t\twant %s",
376 mname, check.funcString(alt), check.funcString(m))
379 if Identical(m.typ, alt.typ) {
380 return check.sprintf("(%s has pointer receiver)", mname)
383 return check.sprintf("(wrong type for %s)\n\t\thave %s\n\t\twant %s",
384 mname, check.funcString(alt), check.funcString(m))
387 if isInterfacePtr(V) {
388 return "(" + check.interfacePtrError(V) + ")"
391 if isInterfacePtr(T) {
392 return "(" + check.interfacePtrError(T) + ")"
395 return check.sprintf("(missing %s)", mname)
398 func isInterfacePtr(T Type) bool {
399 p, _ := under(T).(*Pointer)
400 return p != nil && IsInterface(p.base)
404 func (check *Checker) interfacePtrError(T Type) string {
405 assert(isInterfacePtr(T))
406 if p, _ := under(T).(*Pointer); isTypeParam(p.base) {
407 return check.sprintf("type %s is pointer to type parameter, not type parameter", T)
409 return check.sprintf("type %s is pointer to interface, not interface", T)
413 func (check *Checker) funcString(f *Func) string {
414 buf := bytes.NewBufferString(f.name)
419 WriteSignature(buf, f.typ.(*Signature), qf)
423 // assertableTo reports whether a value of type V can be asserted to have type T.
424 // It returns (nil, false) as affirmative answer. Otherwise it returns a missing
425 // method required by V and whether it is missing or just has the wrong type.
426 // The receiver may be nil if assertableTo is invoked through an exported API call
427 // (such as AssertableTo), i.e., when all methods have been type-checked.
428 // TODO(gri) replace calls to this function with calls to newAssertableTo.
429 func (check *Checker) assertableTo(V *Interface, T Type) (method, wrongType *Func) {
430 // no static check is required if T is an interface
431 // spec: "If T is an interface type, x.(T) asserts that the
432 // dynamic type of x implements the interface T."
436 // TODO(gri) fix this for generalized interfaces
437 return check.missingMethod(T, V, false)
440 // newAssertableTo reports whether a value of type V can be asserted to have type T.
441 // It also implements behavior for interfaces that currently are only permitted
442 // in constraint position (we have not yet defined that behavior in the spec).
443 func (check *Checker) newAssertableTo(V *Interface, T Type) error {
444 // no static check is required if T is an interface
445 // spec: "If T is an interface type, x.(T) asserts that the
446 // dynamic type of x implements the interface T."
450 return check.implements(T, V)
453 // deref dereferences typ if it is a *Pointer and returns its base and true.
454 // Otherwise it returns (typ, false).
455 func deref(typ Type) (Type, bool) {
456 if p, _ := typ.(*Pointer); p != nil {
457 // p.base should never be nil, but be conservative
460 panic("pointer with nil base type (possibly due to an invalid cyclic declaration)")
462 return Typ[Invalid], true
469 // derefStructPtr dereferences typ if it is a (named or unnamed) pointer to a
470 // (named or unnamed) struct and returns its base. Otherwise it returns typ.
471 func derefStructPtr(typ Type) Type {
472 if p, _ := under(typ).(*Pointer); p != nil {
473 if _, ok := under(p.base).(*Struct); ok {
480 // concat returns the result of concatenating list and i.
481 // The result does not share its underlying array with list.
482 func concat(list []int, i int) []int {
484 t = append(t, list...)
488 // fieldIndex returns the index for the field with matching package and name, or a value < 0.
489 func fieldIndex(fields []*Var, pkg *Package, name string) int {
491 for i, f := range fields {
492 if f.sameId(pkg, name) {
500 // lookupMethod returns the index of and method with matching package and name, or (-1, nil).
501 // If foldCase is true, method names are considered equal if they are equal with case folding.
502 func lookupMethod(methods []*Func, pkg *Package, name string, foldCase bool) (int, *Func) {
504 for i, m := range methods {
505 if (m.name == name || foldCase && strings.EqualFold(m.name, name)) && m.sameId(pkg, m.name) {