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). T must not be nil.
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) {
46 panic("LookupFieldOrMethod on nil type")
49 // Methods cannot be associated to a named pointer type.
50 // (spec: "The type denoted by T is called the receiver base type;
51 // it must not be a pointer or interface type and it must be declared
52 // in the same package as the method.").
53 // Thus, if we have a named pointer type, proceed with the underlying
54 // pointer type but discard the result if it is a method since we would
55 // not have found it for T (see also issue 8590).
56 if t, _ := T.(*Named); t != nil {
57 if p, _ := t.Underlying().(*Pointer); p != nil {
58 obj, index, indirect = lookupFieldOrMethod(p, false, pkg, name, false)
59 if _, ok := obj.(*Func); ok {
60 return nil, nil, false
66 obj, index, indirect = lookupFieldOrMethod(T, addressable, pkg, name, false)
68 // If we didn't find anything and if we have a type parameter with a structural constraint,
69 // see if there is a matching field (but not a method, those need to be declared explicitly
70 // in the constraint). If the structural constraint is a named pointer type (see above), we
71 // are ok here because only fields are accepted as results.
72 if obj == nil && isTypeParam(T) {
73 if t := structuralType(T); t != nil {
74 obj, index, indirect = lookupFieldOrMethod(t, addressable, pkg, name, false)
75 if _, ok := obj.(*Var); !ok {
76 obj, index, indirect = nil, nil, false // accept fields (variables) only
83 // TODO(gri) The named type consolidation and seen maps below must be
84 // indexed by unique keys for a given type. Verify that named
85 // types always have only one representation (even when imported
86 // indirectly via different packages.)
88 // lookupFieldOrMethod should only be called by LookupFieldOrMethod and missingMethod.
89 // If foldCase is true, the lookup for methods will include looking for any method
90 // which case-folds to the same as 'name' (used for giving helpful error messages).
92 // The resulting object may not be fully type-checked.
93 func lookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string, foldCase bool) (obj Object, index []int, indirect bool) {
94 // WARNING: The code in this function is extremely subtle - do not modify casually!
97 return // blank fields/methods are never found
100 typ, isPtr := deref(T)
102 // *typ where typ is an interface (incl. a type parameter) has no methods.
104 if _, ok := under(typ).(*Interface); ok {
109 // Start with typ as single entry at shallowest depth.
110 current := []embeddedType{{typ, nil, isPtr, false}}
112 // Named types that we have seen already, allocated lazily.
113 // Used to avoid endless searches in case of recursive types.
114 // Since only Named types can be used for recursive types, we
115 // only need to track those.
116 // (If we ever allow type aliases to construct recursive types,
117 // we must use type identity rather than pointer equality for
118 // the map key comparison, as we do in consolidateMultiples.)
119 var seen map[*Named]bool
121 // search current depth
122 for len(current) > 0 {
123 var next []embeddedType // embedded types found at current depth
125 // look for (pkg, name) in all types at current depth
126 for _, e := range current {
129 // If we have a named type, we may have associated methods.
130 // Look for those first.
131 if named, _ := typ.(*Named); named != nil {
133 // We have seen this type before, at a more shallow depth
134 // (note that multiples of this type at the current depth
135 // were consolidated before). The type at that depth shadows
136 // this same type at the current depth, so we can ignore
141 seen = make(map[*Named]bool)
145 // look for a matching attached method
147 if i, m := named.lookupMethod(pkg, name, foldCase); m != nil {
149 // caution: method may not have a proper signature yet
150 index = concat(e.index, i)
151 if obj != nil || e.multiples {
152 return nil, index, false // collision
155 indirect = e.indirect
156 continue // we can't have a matching field or interface method
160 switch t := under(typ).(type) {
162 // look for a matching field and collect embedded types
163 for i, f := range t.fields {
164 if f.sameId(pkg, name) {
166 index = concat(e.index, i)
167 if obj != nil || e.multiples {
168 return nil, index, false // collision
171 indirect = e.indirect
172 continue // we can't have a matching interface method
174 // Collect embedded struct fields for searching the next
175 // lower depth, but only if we have not seen a match yet
176 // (if we have a match it is either the desired field or
177 // we have a name collision on the same depth; in either
178 // case we don't need to look further).
179 // Embedded fields are always of the form T or *T where
180 // T is a type name. If e.typ appeared multiple times at
181 // this depth, f.typ appears multiple times at the next
183 if obj == nil && f.embedded {
184 typ, isPtr := deref(f.typ)
185 // TODO(gri) optimization: ignore types that can't
186 // have fields or methods (only Named, Struct, and
187 // Interface types need to be considered).
188 next = append(next, embeddedType{typ, concat(e.index, i), e.indirect || isPtr, e.multiples})
193 // look for a matching method (interface may be a type parameter)
194 if i, m := t.typeSet().LookupMethod(pkg, name, foldCase); m != nil {
196 index = concat(e.index, i)
197 if obj != nil || e.multiples {
198 return nil, index, false // collision
201 indirect = e.indirect
207 // found a potential match
208 // spec: "A method call x.m() is valid if the method set of (the type of) x
209 // contains m and the argument list can be assigned to the parameter
210 // list of m. If x is addressable and &x's method set contains m, x.m()
211 // is shorthand for (&x).m()".
212 if f, _ := obj.(*Func); f != nil {
213 // determine if method has a pointer receiver
214 if f.hasPtrRecv() && !indirect && !addressable {
215 return nil, nil, true // pointer/addressable receiver required
221 current = consolidateMultiples(next)
224 return nil, nil, false // not found
227 // embeddedType represents an embedded type
228 type embeddedType struct {
230 index []int // embedded field indices, starting with index at depth 0
231 indirect bool // if set, there was a pointer indirection on the path to this field
232 multiples bool // if set, typ appears multiple times at this depth
235 // consolidateMultiples collects multiple list entries with the same type
236 // into a single entry marked as containing multiples. The result is the
237 // consolidated list.
238 func consolidateMultiples(list []embeddedType) []embeddedType {
240 return list // at most one entry - nothing to do
243 n := 0 // number of entries w/ unique type
244 prev := make(map[Type]int) // index at which type was previously seen
245 for _, e := range list {
246 if i, found := lookupType(prev, e.typ); found {
247 list[i].multiples = true
258 func lookupType(m map[Type]int, typ Type) (int, bool) {
259 // fast path: maybe the types are equal
260 if i, found := m[typ]; found {
264 for t, i := range m {
265 if Identical(t, typ) {
273 // MissingMethod returns (nil, false) if V implements T, otherwise it
274 // returns a missing method required by T and whether it is missing or
275 // just has the wrong type.
277 // For non-interface types V, or if static is set, V implements T if all
278 // methods of T are present in V. Otherwise (V is an interface and static
279 // is not set), MissingMethod only checks that methods of T which are also
280 // present in V have matching types (e.g., for a type assertion x.(T) where
281 // x is of interface type V).
283 func MissingMethod(V Type, T *Interface, static bool) (method *Func, wrongType bool) {
284 m, alt := (*Checker)(nil).missingMethod(V, T, static)
285 // Only report a wrong type if the alternative method has the same name as m.
286 return m, alt != nil && alt.name == m.name // alt != nil implies m != nil
289 // missingMethod is like MissingMethod but accepts a *Checker as receiver.
290 // The receiver may be nil if missingMethod is invoked through an exported
291 // API call (such as MissingMethod), i.e., when all methods have been type-
294 // If a method is missing on T but is found on *T, or if a method is found
295 // on T when looked up with case-folding, this alternative method is returned
296 // as the second result.
297 // Note: case-folding lookup is currently disabled
298 func (check *Checker) missingMethod(V Type, T *Interface, static bool) (method, alt *Func) {
299 // fast path for common case
304 if ityp, _ := under(V).(*Interface); ityp != nil {
305 for _, m := range T.typeSet().methods {
306 _, f := ityp.typeSet().LookupMethod(m.pkg, m.name, false)
312 // We don't do any case-fold check if V is an interface.
316 if !Identical(f.typ, m.typ) {
324 // A concrete type implements T if it implements all methods of T.
325 for _, m := range T.typeSet().methods {
326 // TODO(gri) should this be calling LookupFieldOrMethod instead (and why not)?
327 obj, _, _ := lookupFieldOrMethod(V, false, m.pkg, m.name, false)
329 // Check if *V implements this method of T.
332 obj, _, _ = lookupFieldOrMethod(ptr, false, m.pkg, m.name, false)
334 // TODO(gri) enable this code
335 // If we didn't find the exact method (even with pointer receiver),
336 // check if there is a matching method using case-folding.
337 // obj, _, _ = lookupFieldOrMethod(V, false, m.pkg, m.name, true)
340 // methods may not have a fully set up signature yet
342 check.objDecl(obj, nil)
344 return m, obj.(*Func)
348 // we must have a method (not a field of matching function type)
354 // methods may not have a fully set up signature yet
356 check.objDecl(f, nil)
359 if !Identical(f.typ, m.typ) {
367 // missingMethodReason returns a string giving the detailed reason for a missing method m,
368 // where m is missing from V, but required by T. It puts the reason in parentheses,
369 // and may include more have/want info after that. If non-nil, wrongType is a relevant
370 // method that matches in some way. It may have the correct name, but wrong type, or
371 // it may have a pointer receiver.
372 func (check *Checker) missingMethodReason(V, T Type, m, wrongType *Func) string {
375 if compilerErrorMessages {
376 mname = m.Name() + " method"
378 mname = "method " + m.Name()
380 if wrongType != nil {
381 if m.Name() != wrongType.Name() {
382 // Note: this case can't happen because we don't look for alternative
383 // method spellings, unlike types2. Keep for symmetry with types2.
384 r = check.sprintf("(missing %s)\n\t\thave %s^^%s\n\t\twant %s^^%s",
385 mname, wrongType.Name(), wrongType.typ, m.Name(), m.typ)
386 } else if Identical(m.typ, wrongType.typ) {
387 r = check.sprintf("(%s has pointer receiver)", mname)
389 if compilerErrorMessages {
390 r = check.sprintf("(wrong type for %s)\n\t\thave %s^^%s\n\t\twant %s^^%s",
391 mname, wrongType.Name(), wrongType.typ, m.Name(), m.typ)
393 r = check.sprintf("(wrong type for %s)\n\thave %s\n\twant %s",
394 mname, wrongType.typ, m.typ)
397 // This is a hack to print the function type without the leading
398 // 'func' keyword in the have/want printouts. We could change to have
399 // an extra formatting option for types2.Type that doesn't print out
401 r = strings.Replace(r, "^^func", "", -1)
402 } else if IsInterface(T) {
403 if isInterfacePtr(V) {
404 r = "(" + check.interfacePtrError(V) + ")"
406 } else if isInterfacePtr(T) {
407 r = "(" + check.interfacePtrError(T) + ")"
410 r = check.sprintf("(missing %s)", mname)
415 func isInterfacePtr(T Type) bool {
416 p, _ := under(T).(*Pointer)
417 return p != nil && IsInterface(p.base)
420 func (check *Checker) interfacePtrError(T Type) string {
421 assert(isInterfacePtr(T))
422 if p, _ := under(T).(*Pointer); isTypeParam(p.base) {
423 return check.sprintf("type %s is pointer to type parameter, not type parameter", T)
425 return check.sprintf("type %s is pointer to interface, not interface", T)
428 // assertableTo reports whether a value of type V can be asserted to have type T.
429 // It returns (nil, false) as affirmative answer. Otherwise it returns a missing
430 // method required by V and whether it is missing or just has the wrong type.
431 // The receiver may be nil if assertableTo is invoked through an exported API call
432 // (such as AssertableTo), i.e., when all methods have been type-checked.
433 // If the global constant forceStrict is set, assertions that are known to fail
434 // are not permitted.
435 func (check *Checker) assertableTo(V *Interface, T Type) (method, wrongType *Func) {
436 // no static check is required if T is an interface
437 // spec: "If T is an interface type, x.(T) asserts that the
438 // dynamic type of x implements the interface T."
439 if IsInterface(T) && !forceStrict {
442 return check.missingMethod(T, V, false)
445 // deref dereferences typ if it is a *Pointer and returns its base and true.
446 // Otherwise it returns (typ, false).
447 func deref(typ Type) (Type, bool) {
448 if p, _ := typ.(*Pointer); p != nil {
449 // p.base should never be nil, but be conservative
452 panic("pointer with nil base type (possibly due to an invalid cyclic declaration)")
454 return Typ[Invalid], true
461 // derefStructPtr dereferences typ if it is a (named or unnamed) pointer to a
462 // (named or unnamed) struct and returns its base. Otherwise it returns typ.
463 func derefStructPtr(typ Type) Type {
464 if p, _ := under(typ).(*Pointer); p != nil {
465 if _, ok := under(p.base).(*Struct); ok {
472 // concat returns the result of concatenating list and i.
473 // The result does not share its underlying array with list.
474 func concat(list []int, i int) []int {
476 t = append(t, list...)
480 // fieldIndex returns the index for the field with matching package and name, or a value < 0.
481 func fieldIndex(fields []*Var, pkg *Package, name string) int {
483 for i, f := range fields {
484 if f.sameId(pkg, name) {
492 // lookupMethod returns the index of and method with matching package and name, or (-1, nil).
493 // If foldCase is true, method names are considered equal if they are equal with case folding.
494 func lookupMethod(methods []*Func, pkg *Package, name string, foldCase bool) (int, *Func) {
496 for i, m := range methods {
497 if (m.name == name || foldCase && strings.EqualFold(m.name, name)) && m.sameId(pkg, m.name) {