1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
2 * vim: set ts=8 sts=2 et sw=2 tw=80:
3 * This Source Code Form is subject to the terms of the Mozilla Public
4 * License, v. 2.0. If a copy of the MPL was not distributed with this
5 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
8 * [SMDOC] JS::CallArgs API
10 * Helper classes encapsulating access to the callee, |this| value, arguments,
11 * and argument count for a call/construct operation.
13 * JS::CallArgs encapsulates access to a JSNative's un-abstracted
14 * |unsigned argc, Value* vp| arguments. The principal way to create a
15 * JS::CallArgs is using JS::CallArgsFromVp:
17 * // If provided no arguments or a non-numeric first argument, return zero.
18 * // Otherwise return |this| exactly as given, without boxing.
20 * Func(JSContext* cx, unsigned argc, JS::Value* vp)
22 * JS::CallArgs args = JS::CallArgsFromVp(argc, vp);
24 * // Guard against no arguments or a non-numeric arg0.
25 * if (args.length() == 0 || !args[0].isNumber()) {
26 * args.rval().setInt32(0);
30 * // Access to the callee must occur before accessing/setting
31 * // the return value.
32 * JSObject& callee = args.callee();
33 * args.rval().setObject(callee);
35 * // callee() and calleev() will now assert.
37 * // It's always fine to access thisv().
38 * HandleValue thisv = args.thisv();
39 * args.rval().set(thisv);
41 * // As the return value was last set to |this|, returns |this|.
45 * CallArgs is exposed publicly and used internally. Not all parts of its
46 * public interface are meant to be used by embedders! See inline comments to
49 * It's possible (albeit deprecated) to manually index into |vp| to access the
50 * callee, |this|, and arguments of a function, and to set its return value.
51 * This does not have the error-handling or moving-GC correctness of CallArgs.
52 * New code should use CallArgs instead whenever possible.
54 * The eventual plan is to change JSNative to take |const CallArgs&| directly,
55 * for automatic assertion of correct use and to make calling functions more
56 * efficient. Embedders should start internally switching away from using
57 * |argc| and |vp| directly, except to create a |CallArgs|. Then, when an
58 * eventual release making that change occurs, porting efforts will require
59 * changing methods' signatures but won't require invasive changes to the
60 * methods' implementations, potentially under time pressure.
66 #include "mozilla/Assertions.h"
67 #include "mozilla/Attributes.h"
69 #include <type_traits>
73 #include "js/RootingAPI.h"
76 /* Typedef for native functions called by the JS VM. */
77 using JSNative
= bool (*)(JSContext
* cx
, unsigned argc
, JS::Value
* vp
);
81 extern JS_PUBLIC_DATA
const HandleValue UndefinedHandleValue
;
86 * Compute |this| for the |vp| inside a JSNative, either boxing primitives or
87 * replacing with the global object as necessary.
89 extern JS_PUBLIC_API
bool ComputeThis(JSContext
* cx
, JS::Value
* vp
,
90 MutableHandleObject thisObject
);
93 extern JS_PUBLIC_API
void CheckIsValidConstructible(const Value
& v
);
96 class MOZ_STACK_CLASS IncludeUsedRval
{
97 mutable bool usedRval_
= false;
100 bool usedRval() const { return usedRval_
; }
101 void setUsedRval() const { usedRval_
= true; }
102 void clearUsedRval() const { usedRval_
= false; }
103 void assertUnusedRval() const { MOZ_ASSERT(!usedRval_
); }
106 class MOZ_STACK_CLASS NoUsedRval
{
108 bool usedRval() const { return false; }
109 void setUsedRval() const {}
110 void clearUsedRval() const {}
111 void assertUnusedRval() const {}
114 template <class WantUsedRval
>
115 class MOZ_STACK_CLASS CallArgsBase
{
116 static_assert(std::is_same_v
<WantUsedRval
, IncludeUsedRval
> ||
117 std::is_same_v
<WantUsedRval
, NoUsedRval
>,
118 "WantUsedRval can only be IncludeUsedRval or NoUsedRval");
121 Value
* argv_
= nullptr;
123 bool constructing_
: 1;
125 // True if the caller does not use the return value.
126 bool ignoresReturnValue_
: 1;
129 WantUsedRval wantUsedRval_
;
130 bool usedRval() const { return wantUsedRval_
.usedRval(); }
131 void setUsedRval() const { wantUsedRval_
.setUsedRval(); }
132 void clearUsedRval() const { wantUsedRval_
.clearUsedRval(); }
133 void assertUnusedRval() const { wantUsedRval_
.assertUnusedRval(); }
135 bool usedRval() const { return false; }
136 void setUsedRval() const {}
137 void clearUsedRval() const {}
138 void assertUnusedRval() const {}
141 CallArgsBase() : constructing_(false), ignoresReturnValue_(false) {}
147 * Returns the function being called, as a value. Must not be called after
148 * rval() has been used!
150 HandleValue
calleev() const {
151 this->assertUnusedRval();
152 return HandleValue::fromMarkedLocation(&argv_
[-2]);
156 * Returns the function being called, as an object. Must not be called
157 * after rval() has been used!
159 JSObject
& callee() const { return calleev().toObject(); }
161 // CALLING/CONSTRUCTING-DIFFERENTIATIONS
163 bool isConstructing() const {
164 if (!argv_
[-1].isMagic()) {
169 if (!this->usedRval()) {
170 CheckIsValidConstructible(calleev());
177 bool ignoresReturnValue() const { return ignoresReturnValue_
; }
179 MutableHandleValue
newTarget() const {
180 MOZ_ASSERT(constructing_
);
181 return MutableHandleValue::fromMarkedLocation(&this->argv_
[argc_
]);
185 * Returns the |this| value passed to the function. This method must not
186 * be called when the function is being called as a constructor via |new|.
187 * The value may or may not be an object: it is the individual function's
188 * responsibility to box the value if needed.
190 HandleValue
thisv() const {
191 // Some internal code uses thisv() in constructing cases, so don't do
193 // MOZ_ASSERT(!argv_[-1].isMagic(JS_IS_CONSTRUCTING));
194 return HandleValue::fromMarkedLocation(&argv_
[-1]);
197 bool computeThis(JSContext
* cx
, MutableHandleObject thisObject
) const {
198 if (thisv().isObject()) {
199 thisObject
.set(&thisv().toObject());
203 return ComputeThis(cx
, base(), thisObject
);
208 /* Returns the number of arguments. */
209 unsigned length() const { return argc_
; }
211 /* Returns the i-th zero-indexed argument. */
212 MutableHandleValue
operator[](unsigned i
) const {
213 MOZ_ASSERT(i
< argc_
);
214 return MutableHandleValue::fromMarkedLocation(&this->argv_
[i
]);
218 * Returns the i-th zero-indexed argument, or |undefined| if there's no
221 HandleValue
get(unsigned i
) const {
222 return i
< length() ? HandleValue::fromMarkedLocation(&this->argv_
[i
])
223 : UndefinedHandleValue
;
227 * Returns true if the i-th zero-indexed argument is present and is not
230 bool hasDefined(unsigned i
) const {
231 return i
< argc_
&& !this->argv_
[i
].isUndefined();
237 * Returns the currently-set return value. The initial contents of this
238 * value are unspecified. Once this method has been called, callee() and
239 * calleev() can no longer be used. (If you're compiling against a debug
240 * build of SpiderMonkey, these methods will assert to aid debugging.)
242 * If the method you're implementing succeeds by returning true, you *must*
243 * set this. (SpiderMonkey doesn't currently assert this, but it will do
244 * so eventually.) You don't need to use or change this if your method
247 MutableHandleValue
rval() const {
249 return MutableHandleValue::fromMarkedLocation(&argv_
[-2]);
253 * Returns true if there are at least |required| arguments passed in. If
254 * false, it reports an error message on the context.
256 JS_PUBLIC_API
inline bool requireAtLeast(JSContext
* cx
, const char* fnname
,
257 unsigned required
) const;
260 // These methods are publicly exposed, but they are *not* to be used when
261 // implementing a JSNative method and encapsulating access to |vp| within
262 // it. You probably don't want to use these!
264 void setCallee(const Value
& aCalleev
) const {
265 this->clearUsedRval();
266 argv_
[-2] = aCalleev
;
269 void setThis(const Value
& aThisv
) const { argv_
[-1] = aThisv
; }
271 MutableHandleValue
mutableThisv() const {
272 return MutableHandleValue::fromMarkedLocation(&argv_
[-1]);
276 // These methods are publicly exposed, but we're unsure of the interfaces
277 // (because they're hackish and drop assertions). Avoid using these if you
280 Value
* array() const { return argv_
; }
281 Value
* end() const { return argv_
+ argc_
+ constructing_
; }
284 // These methods are only intended for internal use. Embedders shouldn't
287 Value
* base() const { return argv_
- 2; }
289 Value
* spAfterCall() const {
295 } // namespace detail
297 class MOZ_STACK_CLASS CallArgs
298 : public detail::CallArgsBase
<detail::IncludeUsedRval
> {
300 friend CallArgs
CallArgsFromVp(unsigned argc
, Value
* vp
);
301 friend CallArgs
CallArgsFromSp(unsigned stackSlots
, Value
* sp
,
302 bool constructing
, bool ignoresReturnValue
);
304 static CallArgs
create(unsigned argc
, Value
* argv
, bool constructing
,
305 bool ignoresReturnValue
= false) {
307 args
.clearUsedRval();
310 args
.constructing_
= constructing
;
311 args
.ignoresReturnValue_
= ignoresReturnValue
;
313 AssertValueIsNotGray(args
.thisv());
314 AssertValueIsNotGray(args
.calleev());
315 for (unsigned i
= 0; i
< argc
; ++i
) {
316 AssertValueIsNotGray(argv
[i
]);
324 * Helper for requireAtLeast to report the actual exception. Public
325 * so we can call it from CallArgsBase and not need multiple
326 * per-template instantiations of it.
328 static JS_PUBLIC_API
void reportMoreArgsNeeded(JSContext
* cx
,
335 template <class WantUsedRval
>
336 JS_PUBLIC_API
inline bool CallArgsBase
<WantUsedRval
>::requireAtLeast(
337 JSContext
* cx
, const char* fnname
, unsigned required
) const {
338 if (MOZ_LIKELY(required
<= length())) {
342 CallArgs::reportMoreArgsNeeded(cx
, fnname
, required
, length());
345 } // namespace detail
347 MOZ_ALWAYS_INLINE CallArgs
CallArgsFromVp(unsigned argc
, Value
* vp
) {
348 return CallArgs::create(argc
, vp
+ 2, vp
[1].isMagic(JS_IS_CONSTRUCTING
));
351 // This method is only intended for internal use in SpiderMonkey. We may
352 // eventually move it to an internal header. Embedders should use
353 // JS::CallArgsFromVp!
354 MOZ_ALWAYS_INLINE CallArgs
CallArgsFromSp(unsigned stackSlots
, Value
* sp
,
355 bool constructing
= false,
356 bool ignoresReturnValue
= false) {
357 return CallArgs::create(stackSlots
- constructing
, sp
- stackSlots
,
358 constructing
, ignoresReturnValue
);
363 #endif /* js_CallArgs_h */