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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_ = false;
+
+ 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_ = nullptr;
+ unsigned argc_ = 0;
+ 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
+
+ CallArgsBase() : constructing_(false), ignoresReturnValue_(false) {}
+
+ 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].isMagicNoReleaseCheck(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 */