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a128f0c35c
--HG-- extra : rebase_source : b80911e01f984ee9f99fbbc6c4552ef3d2178587
361 lines
11 KiB
C++
361 lines
11 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
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* vim: set ts=8 sts=2 et sw=2 tw=80:
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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/*
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* [SMDOC] JS::CallArgs API
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*
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* Helper classes encapsulating access to the callee, |this| value, arguments,
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* and argument count for a call/construct operation.
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*
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* JS::CallArgs encapsulates access to a JSNative's un-abstracted
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* |unsigned argc, Value* vp| arguments. The principal way to create a
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* JS::CallArgs is using JS::CallArgsFromVp:
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*
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* // If provided no arguments or a non-numeric first argument, return zero.
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* // Otherwise return |this| exactly as given, without boxing.
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* static bool
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* Func(JSContext* cx, unsigned argc, JS::Value* vp)
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* {
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* JS::CallArgs args = JS::CallArgsFromVp(argc, vp);
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*
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* // Guard against no arguments or a non-numeric arg0.
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* if (args.length() == 0 || !args[0].isNumber()) {
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* args.rval().setInt32(0);
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* return true;
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* }
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*
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* // Access to the callee must occur before accessing/setting
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* // the return value.
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* JSObject& callee = args.callee();
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* args.rval().setObject(callee);
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*
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* // callee() and calleev() will now assert.
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*
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* // It's always fine to access thisv().
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* HandleValue thisv = args.thisv();
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* args.rval().set(thisv);
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*
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* // As the return value was last set to |this|, returns |this|.
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* return true;
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* }
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*
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* CallArgs is exposed publicly and used internally. Not all parts of its
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* public interface are meant to be used by embedders! See inline comments to
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* for details.
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*
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* It's possible (albeit deprecated) to manually index into |vp| to access the
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* callee, |this|, and arguments of a function, and to set its return value.
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* This does not have the error-handling or moving-GC correctness of CallArgs.
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* New code should use CallArgs instead whenever possible.
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*
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* The eventual plan is to change JSNative to take |const CallArgs&| directly,
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* for automatic assertion of correct use and to make calling functions more
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* efficient. Embedders should start internally switching away from using
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* |argc| and |vp| directly, except to create a |CallArgs|. Then, when an
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* eventual release making that change occurs, porting efforts will require
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* changing methods' signatures but won't require invasive changes to the
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* methods' implementations, potentially under time pressure.
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*/
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#ifndef js_CallArgs_h
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#define js_CallArgs_h
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#include "mozilla/Assertions.h"
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#include "mozilla/Attributes.h"
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#include "mozilla/TypeTraits.h"
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#include "jstypes.h"
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#include "js/RootingAPI.h"
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#include "js/Value.h"
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/* Typedef for native functions called by the JS VM. */
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using JSNative = bool (*)(JSContext* cx, unsigned argc, JS::Value* vp);
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namespace JS {
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extern JS_PUBLIC_DATA const HandleValue UndefinedHandleValue;
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namespace detail {
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/*
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* Compute |this| for the |vp| inside a JSNative, either boxing primitives or
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* replacing with the global object as necessary.
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*/
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extern JS_PUBLIC_API bool ComputeThis(JSContext* cx, JS::Value* vp,
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MutableHandleObject thisObject);
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#ifdef JS_DEBUG
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extern JS_PUBLIC_API void CheckIsValidConstructible(const Value& v);
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#endif
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class MOZ_STACK_CLASS IncludeUsedRval {
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mutable bool usedRval_;
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public:
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bool usedRval() const { return usedRval_; }
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void setUsedRval() const { usedRval_ = true; }
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void clearUsedRval() const { usedRval_ = false; }
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void assertUnusedRval() const { MOZ_ASSERT(!usedRval_); }
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};
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class MOZ_STACK_CLASS NoUsedRval {
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public:
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bool usedRval() const { return false; }
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void setUsedRval() const {}
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void clearUsedRval() const {}
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void assertUnusedRval() const {}
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};
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template <class WantUsedRval>
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class MOZ_STACK_CLASS CallArgsBase {
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static_assert(mozilla::IsSame<WantUsedRval, IncludeUsedRval>::value ||
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mozilla::IsSame<WantUsedRval, NoUsedRval>::value,
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"WantUsedRval can only be IncludeUsedRval or NoUsedRval");
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protected:
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Value* argv_;
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unsigned argc_;
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bool constructing_ : 1;
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// True if the caller does not use the return value.
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bool ignoresReturnValue_ : 1;
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#ifdef JS_DEBUG
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WantUsedRval wantUsedRval_;
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bool usedRval() const { return wantUsedRval_.usedRval(); }
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void setUsedRval() const { wantUsedRval_.setUsedRval(); }
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void clearUsedRval() const { wantUsedRval_.clearUsedRval(); }
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void assertUnusedRval() const { wantUsedRval_.assertUnusedRval(); }
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#else
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bool usedRval() const { return false; }
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void setUsedRval() const {}
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void clearUsedRval() const {}
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void assertUnusedRval() const {}
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#endif
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public:
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// CALLEE ACCESS
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/*
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* Returns the function being called, as a value. Must not be called after
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* rval() has been used!
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*/
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HandleValue calleev() const {
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this->assertUnusedRval();
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return HandleValue::fromMarkedLocation(&argv_[-2]);
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}
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/*
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* Returns the function being called, as an object. Must not be called
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* after rval() has been used!
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*/
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JSObject& callee() const { return calleev().toObject(); }
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// CALLING/CONSTRUCTING-DIFFERENTIATIONS
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bool isConstructing() const {
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if (!argv_[-1].isMagic()) {
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return false;
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}
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#ifdef JS_DEBUG
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if (!this->usedRval()) {
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CheckIsValidConstructible(calleev());
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}
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#endif
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return true;
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}
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bool ignoresReturnValue() const { return ignoresReturnValue_; }
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MutableHandleValue newTarget() const {
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MOZ_ASSERT(constructing_);
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return MutableHandleValue::fromMarkedLocation(&this->argv_[argc_]);
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}
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/*
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* Returns the |this| value passed to the function. This method must not
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* be called when the function is being called as a constructor via |new|.
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* The value may or may not be an object: it is the individual function's
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* responsibility to box the value if needed.
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*/
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HandleValue thisv() const {
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// Some internal code uses thisv() in constructing cases, so don't do
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// this yet.
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// MOZ_ASSERT(!argv_[-1].isMagic(JS_IS_CONSTRUCTING));
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return HandleValue::fromMarkedLocation(&argv_[-1]);
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}
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bool computeThis(JSContext* cx, MutableHandleObject thisObject) const {
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if (thisv().isObject()) {
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thisObject.set(&thisv().toObject());
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return true;
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}
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return ComputeThis(cx, base(), thisObject);
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}
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// ARGUMENTS
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/* Returns the number of arguments. */
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unsigned length() const { return argc_; }
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/* Returns the i-th zero-indexed argument. */
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MutableHandleValue operator[](unsigned i) const {
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MOZ_ASSERT(i < argc_);
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return MutableHandleValue::fromMarkedLocation(&this->argv_[i]);
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}
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/*
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* Returns the i-th zero-indexed argument, or |undefined| if there's no
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* such argument.
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*/
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HandleValue get(unsigned i) const {
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return i < length() ? HandleValue::fromMarkedLocation(&this->argv_[i])
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: UndefinedHandleValue;
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}
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/*
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* Returns true if the i-th zero-indexed argument is present and is not
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* |undefined|.
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*/
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bool hasDefined(unsigned i) const {
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return i < argc_ && !this->argv_[i].isUndefined();
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}
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// RETURN VALUE
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/*
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* Returns the currently-set return value. The initial contents of this
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* value are unspecified. Once this method has been called, callee() and
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* calleev() can no longer be used. (If you're compiling against a debug
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* build of SpiderMonkey, these methods will assert to aid debugging.)
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*
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* If the method you're implementing succeeds by returning true, you *must*
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* set this. (SpiderMonkey doesn't currently assert this, but it will do
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* so eventually.) You don't need to use or change this if your method
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* fails.
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*/
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MutableHandleValue rval() const {
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this->setUsedRval();
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return MutableHandleValue::fromMarkedLocation(&argv_[-2]);
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}
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/*
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* Returns true if there are at least |required| arguments passed in. If
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* false, it reports an error message on the context.
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*/
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JS_PUBLIC_API inline bool requireAtLeast(JSContext* cx, const char* fnname,
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unsigned required) const;
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public:
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// These methods are publicly exposed, but they are *not* to be used when
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// implementing a JSNative method and encapsulating access to |vp| within
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// it. You probably don't want to use these!
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void setCallee(const Value& aCalleev) const {
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this->clearUsedRval();
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argv_[-2] = aCalleev;
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}
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void setThis(const Value& aThisv) const { argv_[-1] = aThisv; }
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MutableHandleValue mutableThisv() const {
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return MutableHandleValue::fromMarkedLocation(&argv_[-1]);
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}
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public:
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// These methods are publicly exposed, but we're unsure of the interfaces
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// (because they're hackish and drop assertions). Avoid using these if you
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// can.
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Value* array() const { return argv_; }
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Value* end() const { return argv_ + argc_ + constructing_; }
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public:
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// These methods are only intended for internal use. Embedders shouldn't
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// use them!
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Value* base() const { return argv_ - 2; }
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Value* spAfterCall() const {
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this->setUsedRval();
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return argv_ - 1;
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}
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};
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} // namespace detail
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class MOZ_STACK_CLASS CallArgs
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: public detail::CallArgsBase<detail::IncludeUsedRval> {
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private:
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friend CallArgs CallArgsFromVp(unsigned argc, Value* vp);
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friend CallArgs CallArgsFromSp(unsigned stackSlots, Value* sp,
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bool constructing, bool ignoresReturnValue);
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static CallArgs create(unsigned argc, Value* argv, bool constructing,
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bool ignoresReturnValue = false) {
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CallArgs args;
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args.clearUsedRval();
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args.argv_ = argv;
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args.argc_ = argc;
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args.constructing_ = constructing;
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args.ignoresReturnValue_ = ignoresReturnValue;
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#ifdef DEBUG
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AssertValueIsNotGray(args.thisv());
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AssertValueIsNotGray(args.calleev());
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for (unsigned i = 0; i < argc; ++i) {
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AssertValueIsNotGray(argv[i]);
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}
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#endif
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return args;
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}
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public:
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/*
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* Helper for requireAtLeast to report the actual exception. Public
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* so we can call it from CallArgsBase and not need multiple
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* per-template instantiations of it.
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*/
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static JS_PUBLIC_API void reportMoreArgsNeeded(JSContext* cx,
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const char* fnname,
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unsigned required,
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unsigned actual);
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};
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namespace detail {
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template <class WantUsedRval>
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JS_PUBLIC_API inline bool CallArgsBase<WantUsedRval>::requireAtLeast(
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JSContext* cx, const char* fnname, unsigned required) const {
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if (MOZ_LIKELY(required <= length())) {
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return true;
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}
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CallArgs::reportMoreArgsNeeded(cx, fnname, required, length());
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return false;
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}
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} // namespace detail
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MOZ_ALWAYS_INLINE CallArgs CallArgsFromVp(unsigned argc, Value* vp) {
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return CallArgs::create(argc, vp + 2, vp[1].isMagic(JS_IS_CONSTRUCTING));
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}
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// This method is only intended for internal use in SpiderMonkey. We may
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// eventually move it to an internal header. Embedders should use
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// JS::CallArgsFromVp!
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MOZ_ALWAYS_INLINE CallArgs CallArgsFromSp(unsigned stackSlots, Value* sp,
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bool constructing = false,
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bool ignoresReturnValue = false) {
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return CallArgs::create(stackSlots - constructing, sp - stackSlots,
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constructing, ignoresReturnValue);
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}
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} // namespace JS
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#endif /* js_CallArgs_h */
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