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// Copyright 2014 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef V8_PROTOTYPE_H_
#define V8_PROTOTYPE_H_
#include "src/isolate.h"
#include "src/objects.h"
namespace v8 {
namespace internal {
/**
* A class to uniformly access the prototype of any Object and walk its
* prototype chain.
*
* The PrototypeIterator can either start at the prototype (default), or
* include the receiver itself. If a PrototypeIterator is constructed for a
* Map, it will always start at the prototype.
*
* The PrototypeIterator can either run to the null_value(), the first
* non-hidden prototype, or a given object.
*/
class PrototypeIterator {
public:
enum WhereToEnd { END_AT_NULL, END_AT_NON_HIDDEN };
PrototypeIterator(Isolate* isolate, Handle<JSReceiver> receiver,
WhereToStart where_to_start = kStartAtPrototype,
WhereToEnd where_to_end = END_AT_NULL)
: isolate_(isolate),
object_(nullptr),
handle_(receiver),
where_to_end_(where_to_end),
is_at_end_(false),
seen_proxies_(0) {
CHECK(!handle_.is_null());
if (where_to_start == kStartAtPrototype) Advance();
}
PrototypeIterator(Isolate* isolate, JSReceiver* receiver,
WhereToStart where_to_start = kStartAtPrototype,
WhereToEnd where_to_end = END_AT_NULL)
: isolate_(isolate),
object_(receiver),
where_to_end_(where_to_end),
is_at_end_(false),
seen_proxies_(0) {
if (where_to_start == kStartAtPrototype) Advance();
}
explicit PrototypeIterator(Map* receiver_map,
WhereToEnd where_to_end = END_AT_NULL)
: isolate_(receiver_map->GetIsolate()),
object_(receiver_map->GetPrototypeChainRootMap(isolate_)->prototype()),
where_to_end_(where_to_end),
is_at_end_(object_->IsNull(isolate_)),
seen_proxies_(0) {
if (!is_at_end_ && where_to_end_ == END_AT_NON_HIDDEN) {
DCHECK(object_->IsJSReceiver());
Map* map = JSReceiver::cast(object_)->map();
is_at_end_ = !map->has_hidden_prototype();
}
}
explicit PrototypeIterator(Handle<Map> receiver_map,
WhereToEnd where_to_end = END_AT_NULL)
: isolate_(receiver_map->GetIsolate()),
object_(nullptr),
handle_(receiver_map->GetPrototypeChainRootMap(isolate_)->prototype(),
isolate_),
where_to_end_(where_to_end),
is_at_end_(handle_->IsNull(isolate_)),
seen_proxies_(0) {
if (!is_at_end_ && where_to_end_ == END_AT_NON_HIDDEN) {
DCHECK(handle_->IsJSReceiver());
Map* map = JSReceiver::cast(*handle_)->map();
is_at_end_ = !map->has_hidden_prototype();
}
}
~PrototypeIterator() {}
bool HasAccess() const {
// We can only perform access check in the handlified version of the
// PrototypeIterator.
DCHECK(!handle_.is_null());
if (handle_->IsAccessCheckNeeded()) {
return isolate_->MayAccess(handle(isolate_->context()),
Handle<JSObject>::cast(handle_));
}
return true;
}
template <typename T = Object>
T* GetCurrent() const {
DCHECK(handle_.is_null());
return T::cast(object_);
}
template <typename T = Object>
static Handle<T> GetCurrent(const PrototypeIterator& iterator) {
DCHECK(!iterator.handle_.is_null());
DCHECK_NULL(iterator.object_);
return Handle<T>::cast(iterator.handle_);
}
void Advance() {
if (handle_.is_null() && object_->IsJSProxy()) {
is_at_end_ = true;
object_ = isolate_->heap()->null_value();
return;
} else if (!handle_.is_null() && handle_->IsJSProxy()) {
is_at_end_ = true;
handle_ = isolate_->factory()->null_value();
return;
}
AdvanceIgnoringProxies();
}
void AdvanceIgnoringProxies() {
Object* object = handle_.is_null() ? object_ : *handle_;
Map* map = HeapObject::cast(object)->map();
Object* prototype = map->prototype();
is_at_end_ = where_to_end_ == END_AT_NON_HIDDEN
? !map->has_hidden_prototype()
: prototype->IsNull(isolate_);
if (handle_.is_null()) {
object_ = prototype;
} else {
handle_ = handle(prototype, isolate_);
}
}
// Returns false iff a call to JSProxy::GetPrototype throws.
// TODO(neis): This should probably replace Advance().
MUST_USE_RESULT bool AdvanceFollowingProxies() {
DCHECK(!(handle_.is_null() && object_->IsJSProxy()));
if (!HasAccess()) {
// Abort the lookup if we do not have access to the current object.
handle_ = isolate_->factory()->null_value();
is_at_end_ = true;
return true;
}
return AdvanceFollowingProxiesIgnoringAccessChecks();
}
MUST_USE_RESULT bool AdvanceFollowingProxiesIgnoringAccessChecks() {
if (handle_.is_null() || !handle_->IsJSProxy()) {
AdvanceIgnoringProxies();
return true;
}
// Due to possible __proto__ recursion limit the number of Proxies
// we visit to an arbitrarily chosen large number.
seen_proxies_++;
if (seen_proxies_ > JSProxy::kMaxIterationLimit) {
isolate_->StackOverflow();
return false;
}
MaybeHandle<Object> proto =
JSProxy::GetPrototype(Handle<JSProxy>::cast(handle_));
if (!proto.ToHandle(&handle_)) return false;
is_at_end_ =
where_to_end_ == END_AT_NON_HIDDEN || handle_->IsNull(isolate_);
return true;
}
bool IsAtEnd() const { return is_at_end_; }
Isolate* isolate() const { return isolate_; }
private:
Isolate* isolate_;
Object* object_;
Handle<Object> handle_;
WhereToEnd where_to_end_;
bool is_at_end_;
int seen_proxies_;
DISALLOW_COPY_AND_ASSIGN(PrototypeIterator);
};
} // namespace internal
} // namespace v8
#endif // V8_PROTOTYPE_H_