gecko/js/public/CallArgs.h

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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
* vim: set ts=8 sts=4 et sw=4 tw=99:
* 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/. */
/*
* Helper classes encapsulating access to the callee, |this| value, arguments,
* and argument count for a function call.
*
* The intent of JS::CallArgs and JS::CallReceiver is that they be used to
* encapsulate access to the un-abstracted |unsigned argc, Value *vp| arguments
* to a function. 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. It's also possible to use the supported API of JS_CALLEE,
* JS_THIS, JS_ARGV, JS_RVAL and JS_SET_RVAL to the same ends. But neither API
* has the error-handling or moving-GC correctness of CallArgs or CallReceiver.
* New code should use CallArgs and CallReceiver 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 "mozilla/TypeTraits.h"
#include "jstypes.h"
#include "js/RootingAPI.h"
#include "js/Value.h"
/* Typedef for native functions called by the JS VM. */
typedef bool
(* JSNative)(JSContext *cx, unsigned argc, JS::Value *vp);
/*
* Compute |this| for the |vp| inside a JSNative, either boxing primitives or
* replacing with the global object as necessary.
*
* This method will go away at some point: instead use |args.thisv()|. If the
* value is an object, no further work is required. If that value is |null| or
* |undefined|, use |JS_GetGlobalForObject| to compute the global object. If
* the value is some other primitive, use |JS_ValueToObject| to box it.
*/
extern JS_PUBLIC_API(JS::Value)
JS_ComputeThis(JSContext *cx, JS::Value *vp);
namespace JS {
extern JS_PUBLIC_DATA(const HandleValue) UndefinedHandleValue;
/*
* JS::CallReceiver encapsulates access to the callee, |this|, and eventual
* return value for a function call. The principal way to create a
* CallReceiver is using JS::CallReceiverFromVp:
*
* static bool
* FunctionReturningThis(JSContext *cx, unsigned argc, JS::Value *vp)
* {
* JS::CallReceiver rec = JS::CallReceiverFromVp(vp);
*
* // Access to the callee must occur before accessing/setting
* // the return value.
* JSObject &callee = rec.callee();
* rec.rval().set(JS::ObjectValue(callee));
*
* // callee() and calleev() will now assert.
*
* // It's always fine to access thisv().
* HandleValue thisv = rec.thisv();
* rec.rval().set(thisv);
*
* // As the return value was last set to |this|, returns |this|.
* return true;
* }
*
* A note on JS_ComputeThis and JS_THIS_OBJECT: these methods currently aren't
* part of the CallReceiver interface. We will likely add them at some point.
* Until then, you should probably continue using |vp| directly for these two
* cases.
*
* CallReceiver 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.
*/
namespace detail {
#ifdef JS_DEBUG
extern JS_PUBLIC_API(void)
CheckIsValidConstructible(Value v);
#endif
enum UsedRval { IncludeUsedRval, NoUsedRval };
template<UsedRval WantUsedRval>
class MOZ_STACK_CLASS UsedRvalBase;
template<>
class MOZ_STACK_CLASS UsedRvalBase<IncludeUsedRval>
{
protected:
mutable bool usedRval_;
void setUsedRval() const { usedRval_ = true; }
void clearUsedRval() const { usedRval_ = false; }
};
template<>
class MOZ_STACK_CLASS UsedRvalBase<NoUsedRval>
{
protected:
void setUsedRval() const {}
void clearUsedRval() const {}
};
template<UsedRval WantUsedRval>
class MOZ_STACK_CLASS CallReceiverBase : public UsedRvalBase<
#ifdef JS_DEBUG
WantUsedRval
#else
NoUsedRval
#endif
>
{
protected:
Value *argv_;
public:
/*
* Returns the function being called, as an object. Must not be called
* after rval() has been used!
*/
JSObject &callee() const {
MOZ_ASSERT(!this->usedRval_);
return argv_[-2].toObject();
}
/*
* Returns the function being called, as a value. Must not be called after
* rval() has been used!
*/
HandleValue calleev() const {
MOZ_ASSERT(!this->usedRval_);
return HandleValue::fromMarkedLocation(&argv_[-2]);
}
/*
* 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]);
}
Value computeThis(JSContext *cx) const {
if (thisv().isObject())
return thisv();
return JS_ComputeThis(cx, base());
}
bool isConstructing() const {
#ifdef JS_DEBUG
if (this->usedRval_)
CheckIsValidConstructible(calleev());
#endif
return argv_[-1].isMagic();
}
/*
* 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]);
}
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;
}
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(Value aCalleev) const {
this->clearUsedRval();
argv_[-2] = aCalleev;
}
void setThis(Value aThisv) const {
argv_[-1] = aThisv;
}
MutableHandleValue mutableThisv() const {
return MutableHandleValue::fromMarkedLocation(&argv_[-1]);
}
};
} // namespace detail
class MOZ_STACK_CLASS CallReceiver : public detail::CallReceiverBase<detail::IncludeUsedRval>
{
private:
friend CallReceiver CallReceiverFromVp(Value *vp);
friend CallReceiver CallReceiverFromArgv(Value *argv);
};
MOZ_ALWAYS_INLINE CallReceiver
CallReceiverFromArgv(Value *argv)
{
CallReceiver receiver;
receiver.clearUsedRval();
receiver.argv_ = argv;
return receiver;
}
MOZ_ALWAYS_INLINE CallReceiver
CallReceiverFromVp(Value *vp)
{
return CallReceiverFromArgv(vp + 2);
}
/*
* JS::CallArgs encapsulates everything JS::CallReceiver does, plus access to
* the function call's arguments. The principal way to create a CallArgs is
* like so, using JS::CallArgsFromVp:
*
* static bool
* FunctionReturningArgcTimesArg0(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;
* }
*
* args.rval().set(JS::NumberValue(args.length() * args[0].toNumber()));
* 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.
*/
namespace detail {
template<UsedRval WantUsedRval>
class MOZ_STACK_CLASS CallArgsBase :
public mozilla::Conditional<WantUsedRval == detail::IncludeUsedRval,
CallReceiver,
CallReceiverBase<NoUsedRval> >::Type
{
protected:
unsigned argc_;
public:
/* 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();
}
public:
// These methods are publicly exposed, but we're less sure of the interface
// here than we'd like (because they're hackish and drop assertions). Try
// to avoid using these if you can.
Value *array() const { return this->argv_; }
Value *end() const { return this->argv_ + argc_; }
};
} // namespace detail
class MOZ_STACK_CLASS CallArgs : public detail::CallArgsBase<detail::IncludeUsedRval>
{
private:
friend CallArgs CallArgsFromVp(unsigned argc, Value *vp);
friend CallArgs CallArgsFromSp(unsigned argc, Value *sp);
static CallArgs create(unsigned argc, Value *argv) {
CallArgs args;
args.clearUsedRval();
args.argv_ = argv;
args.argc_ = argc;
return args;
}
public:
/*
* Returns true if there are at least |required| arguments passed in. If
* false, it reports an error message on the context.
*/
bool requireAtLeast(JSContext *cx, const char *fnname, unsigned required);
};
MOZ_ALWAYS_INLINE CallArgs
CallArgsFromVp(unsigned argc, Value *vp)
{
return CallArgs::create(argc, vp + 2);
}
// 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 argc, Value *sp)
{
return CallArgs::create(argc, sp - argc);
}
} // namespace JS
/*
* Macros to hide interpreter stack layout details from a JSNative using its
* JS::Value *vp parameter. DO NOT USE THESE! Instead use JS::CallArgs and
* friends, above. These macros will be removed when we change JSNative to
* take a const JS::CallArgs&.
*/
#define JS_THIS_OBJECT(cx,vp) (JS_THIS(cx,vp).toObjectOrNull())
/*
* Note: if this method returns null, an error has occurred and must be
* propagated or caught.
*/
MOZ_ALWAYS_INLINE JS::Value
JS_THIS(JSContext *cx, JS::Value *vp)
{
return vp[1].isPrimitive() ? JS_ComputeThis(cx, vp) : vp[1];
}
/*
* |this| is passed to functions in ES5 without change. Functions themselves
* do any post-processing they desire to box |this|, compute the global object,
* &c. This macro retrieves a function's unboxed |this| value.
*
* This macro must not be used in conjunction with JS_THIS or JS_THIS_OBJECT,
* or vice versa. Either use the provided this value with this macro, or
* compute the boxed |this| value using those. JS_THIS_VALUE must not be used
* if the function is being called as a constructor.
*
* But: DO NOT USE THIS! Instead use JS::CallArgs::thisv(), above.
*
*/
#define JS_THIS_VALUE(cx,vp) ((vp)[1])
#endif /* js_CallArgs_h */