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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
* vim: set ts=8 sts=2 et sw=2 tw=80:
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
/*
* [SMDOC] JS::CallArgs API
*
* Helper classes encapsulating access to the callee, |this| value, arguments,
* and argument count for a call/construct operation.
*
* JS::CallArgs encapsulates access to a JSNative's un-abstracted
* |unsigned argc, Value* vp| arguments. The principal way to create a
* JS::CallArgs is using JS::CallArgsFromVp:
*
* // If provided no arguments or a non-numeric first argument, return zero.
* // Otherwise return |this| exactly as given, without boxing.
* static bool
* Func(JSContext* cx, unsigned argc, JS::Value* vp)
* {
* JS::CallArgs args = JS::CallArgsFromVp(argc, vp);
*
* // Guard against no arguments or a non-numeric arg0.
* if (args.length() == 0 || !args[0].isNumber()) {
* args.rval().setInt32(0);
* return true;
* }
*
* // Access to the callee must occur before accessing/setting
* // the return value.
* JSObject& callee = args.callee();
* args.rval().setObject(callee);
*
* // callee() and calleev() will now assert.
*
* // It's always fine to access thisv().
* HandleValue thisv = args.thisv();
* args.rval().set(thisv);
*
* // As the return value was last set to |this|, returns |this|.
* return true;
* }
*
* CallArgs is exposed publicly and used internally. Not all parts of its
* public interface are meant to be used by embedders! See inline comments to
* for details.
*
* It's possible (albeit deprecated) to manually index into |vp| to access the
* callee, |this|, and arguments of a function, and to set its return value.
* This does not have the error-handling or moving-GC correctness of CallArgs.
* New code should use CallArgs instead whenever possible.
*
* The eventual plan is to change JSNative to take |const CallArgs&| directly,
* for automatic assertion of correct use and to make calling functions more
* efficient. Embedders should start internally switching away from using
* |argc| and |vp| directly, except to create a |CallArgs|. Then, when an
* eventual release making that change occurs, porting efforts will require
* changing methods' signatures but won't require invasive changes to the
* methods' implementations, potentially under time pressure.
*/
#ifndef js_CallArgs_h
#define js_CallArgs_h
#include "mozilla/Assertions.h"
#include "mozilla/Attributes.h"
#include <type_traits>
#include "jstypes.h"
#include "js/RootingAPI.h"
#include "js/Value.h"
/* Typedef for native functions called by the JS VM. */
using JSNative = bool (*)(JSContext* cx, unsigned argc, JS::Value* vp);
namespace JS {
extern JS_PUBLIC_DATA const HandleValue UndefinedHandleValue;
namespace detail {
/*
* Compute |this| for the |vp| inside a JSNative, either boxing primitives or
* replacing with the global object as necessary.
*/
extern JS_PUBLIC_API bool ComputeThis(JSContext* cx, JS::Value* vp,
MutableHandleObject thisObject);
#ifdef JS_DEBUG
extern JS_PUBLIC_API void CheckIsValidConstructible(const Value& v);
#endif
class MOZ_STACK_CLASS IncludeUsedRval {
mutable bool usedRval_;
public:
bool usedRval() const { return usedRval_; }
void setUsedRval() const { usedRval_ = true; }
void clearUsedRval() const { usedRval_ = false; }
void assertUnusedRval() const { MOZ_ASSERT(!usedRval_); }
};
class MOZ_STACK_CLASS NoUsedRval {
public:
bool usedRval() const { return false; }
void setUsedRval() const {}
void clearUsedRval() const {}
void assertUnusedRval() const {}
};
template <class WantUsedRval>
class MOZ_STACK_CLASS CallArgsBase {
static_assert(std::is_same_v<WantUsedRval, IncludeUsedRval> ||
std::is_same_v<WantUsedRval, NoUsedRval>,
"WantUsedRval can only be IncludeUsedRval or NoUsedRval");
protected:
Value* argv_;
unsigned argc_;
bool constructing_ : 1;
// True if the caller does not use the return value.
bool ignoresReturnValue_ : 1;
#ifdef JS_DEBUG
WantUsedRval wantUsedRval_;
bool usedRval() const { return wantUsedRval_.usedRval(); }
void setUsedRval() const { wantUsedRval_.setUsedRval(); }
void clearUsedRval() const { wantUsedRval_.clearUsedRval(); }
void assertUnusedRval() const { wantUsedRval_.assertUnusedRval(); }
#else
bool usedRval() const { return false; }
void setUsedRval() const {}
void clearUsedRval() const {}
void assertUnusedRval() const {}
#endif
public:
// CALLEE ACCESS
/*
* Returns the function being called, as a value. Must not be called after
* rval() has been used!
*/
HandleValue calleev() const {
this->assertUnusedRval();
return HandleValue::fromMarkedLocation(&argv_[-2]);
}
/*
* Returns the function being called, as an object. Must not be called
* after rval() has been used!
*/
JSObject& callee() const { return calleev().toObject(); }
// CALLING/CONSTRUCTING-DIFFERENTIATIONS
bool isConstructing() const {
if (!argv_[-1].isMagic()) {
return false;
}
#ifdef JS_DEBUG
if (!this->usedRval()) {
CheckIsValidConstructible(calleev());
}
#endif
return true;
}
bool ignoresReturnValue() const { return ignoresReturnValue_; }
MutableHandleValue newTarget() const {
MOZ_ASSERT(constructing_);
return MutableHandleValue::fromMarkedLocation(&this->argv_[argc_]);
}
/*
* Returns the |this| value passed to the function. This method must not
* be called when the function is being called as a constructor via |new|.
* The value may or may not be an object: it is the individual function's
* responsibility to box the value if needed.
*/
HandleValue thisv() const {
// Some internal code uses thisv() in constructing cases, so don't do
// this yet.
// MOZ_ASSERT(!argv_[-1].isMagic(JS_IS_CONSTRUCTING));
return HandleValue::fromMarkedLocation(&argv_[-1]);
}
bool computeThis(JSContext* cx, MutableHandleObject thisObject) const {
if (thisv().isObject()) {
thisObject.set(&thisv().toObject());
return true;
}
return ComputeThis(cx, base(), thisObject);
}
// ARGUMENTS
/* Returns the number of arguments. */
unsigned length() const { return argc_; }
/* Returns the i-th zero-indexed argument. */
MutableHandleValue operator[](unsigned i) const {
MOZ_ASSERT(i < argc_);
return MutableHandleValue::fromMarkedLocation(&this->argv_[i]);
}
/*
* Returns the i-th zero-indexed argument, or |undefined| if there's no
* such argument.
*/
HandleValue get(unsigned i) const {
return i < length() ? HandleValue::fromMarkedLocation(&this->argv_[i])
: UndefinedHandleValue;
}
/*
* Returns true if the i-th zero-indexed argument is present and is not
* |undefined|.
*/
bool hasDefined(unsigned i) const {
return i < argc_ && !this->argv_[i].isUndefined();
}
// RETURN VALUE
/*
* Returns the currently-set return value. The initial contents of this
* value are unspecified. Once this method has been called, callee() and
* calleev() can no longer be used. (If you're compiling against a debug
* build of SpiderMonkey, these methods will assert to aid debugging.)
*
* If the method you're implementing succeeds by returning true, you *must*
* set this. (SpiderMonkey doesn't currently assert this, but it will do
* so eventually.) You don't need to use or change this if your method
* fails.
*/
MutableHandleValue rval() const {
this->setUsedRval();
return MutableHandleValue::fromMarkedLocation(&argv_[-2]);
}
/*
* Returns true if there are at least |required| arguments passed in. If
* false, it reports an error message on the context.
*/
JS_PUBLIC_API inline bool requireAtLeast(JSContext* cx, const char* fnname,
unsigned required) const;
public:
// These methods are publicly exposed, but they are *not* to be used when
// implementing a JSNative method and encapsulating access to |vp| within
// it. You probably don't want to use these!
void setCallee(const Value& aCalleev) const {
this->clearUsedRval();
argv_[-2] = aCalleev;
}
void setThis(const Value& aThisv) const { argv_[-1] = aThisv; }
MutableHandleValue mutableThisv() const {
return MutableHandleValue::fromMarkedLocation(&argv_[-1]);
}
public:
// These methods are publicly exposed, but we're unsure of the interfaces
// (because they're hackish and drop assertions). Avoid using these if you
// can.
Value* array() const { return argv_; }
Value* end() const { return argv_ + argc_ + constructing_; }
public:
// These methods are only intended for internal use. Embedders shouldn't
// use them!
Value* base() const { return argv_ - 2; }
Value* spAfterCall() const {
this->setUsedRval();
return argv_ - 1;
}
};
} // namespace detail
class MOZ_STACK_CLASS CallArgs
: public detail::CallArgsBase<detail::IncludeUsedRval> {
private:
friend CallArgs CallArgsFromVp(unsigned argc, Value* vp);
friend CallArgs CallArgsFromSp(unsigned stackSlots, Value* sp,
bool constructing, bool ignoresReturnValue);
static CallArgs create(unsigned argc, Value* argv, bool constructing,
bool ignoresReturnValue = false) {
CallArgs args;
args.clearUsedRval();
args.argv_ = argv;
args.argc_ = argc;
args.constructing_ = constructing;
args.ignoresReturnValue_ = ignoresReturnValue;
#ifdef DEBUG
AssertValueIsNotGray(args.thisv());
AssertValueIsNotGray(args.calleev());
for (unsigned i = 0; i < argc; ++i) {
AssertValueIsNotGray(argv[i]);
}
#endif
return args;
}
public:
/*
* Helper for requireAtLeast to report the actual exception. Public
* so we can call it from CallArgsBase and not need multiple
* per-template instantiations of it.
*/
static JS_PUBLIC_API void reportMoreArgsNeeded(JSContext* cx,
const char* fnname,
unsigned required,
unsigned actual);
};
namespace detail {
template <class WantUsedRval>
JS_PUBLIC_API inline bool CallArgsBase<WantUsedRval>::requireAtLeast(
JSContext* cx, const char* fnname, unsigned required) const {
if (MOZ_LIKELY(required <= length())) {
return true;
}
CallArgs::reportMoreArgsNeeded(cx, fnname, required, length());
return false;
}
} // namespace detail
MOZ_ALWAYS_INLINE CallArgs CallArgsFromVp(unsigned argc, Value* vp) {
return CallArgs::create(argc, vp + 2, vp[1].isMagic(JS_IS_CONSTRUCTING));
}
// This method is only intended for internal use in SpiderMonkey. We may
// eventually move it to an internal header. Embedders should use
// JS::CallArgsFromVp!
MOZ_ALWAYS_INLINE CallArgs CallArgsFromSp(unsigned stackSlots, Value* sp,
bool constructing = false,
bool ignoresReturnValue = false) {
return CallArgs::create(stackSlots - constructing, sp - stackSlots,
constructing, ignoresReturnValue);
}
} // namespace JS
#endif /* js_CallArgs_h */