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213 lines
7.7 KiB
C++
213 lines
7.7 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
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* vim: set ts=8 sts=4 et sw=4 tw=99:
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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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#ifndef js_TraceKind_h
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#define js_TraceKind_h
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#include "mozilla/UniquePtr.h"
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#include "js/TypeDecls.h"
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// Forward declarations of all the types a TraceKind can denote.
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namespace js {
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class BaseShape;
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class LazyScript;
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class ObjectGroup;
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class Shape;
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class Scope;
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namespace jit {
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class JitCode;
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} // namespace jit
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} // namespace js
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namespace JS {
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// When tracing a thing, the GC needs to know about the layout of the object it
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// is looking at. There are a fixed number of different layouts that the GC
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// knows about. The "trace kind" is a static map which tells which layout a GC
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// thing has.
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//
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// Although this map is public, the details are completely hidden. Not all of
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// the matching C++ types are exposed, and those that are, are opaque.
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//
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// See Value::gcKind() and JSTraceCallback in Tracer.h for more details.
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enum class TraceKind
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{
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// These trace kinds have a publicly exposed, although opaque, C++ type.
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// Note: The order here is determined by our Value packing. Other users
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// should sort alphabetically, for consistency.
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Object = 0x00,
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String = 0x01,
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Symbol = 0x02,
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Script = 0x03,
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// Shape details are exposed through JS_TraceShapeCycleCollectorChildren.
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Shape = 0x04,
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// ObjectGroup details are exposed through JS_TraceObjectGroupCycleCollectorChildren.
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ObjectGroup = 0x05,
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// The kind associated with a nullptr.
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Null = 0x06,
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// The following kinds do not have an exposed C++ idiom.
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BaseShape = 0x0F,
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JitCode = 0x1F,
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LazyScript = 0x2F,
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Scope = 0x3F
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};
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const static uintptr_t OutOfLineTraceKindMask = 0x07;
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static_assert(uintptr_t(JS::TraceKind::BaseShape) & OutOfLineTraceKindMask, "mask bits are set");
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static_assert(uintptr_t(JS::TraceKind::JitCode) & OutOfLineTraceKindMask, "mask bits are set");
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static_assert(uintptr_t(JS::TraceKind::LazyScript) & OutOfLineTraceKindMask, "mask bits are set");
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static_assert(uintptr_t(JS::TraceKind::Scope) & OutOfLineTraceKindMask, "mask bits are set");
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// When this header is imported inside SpiderMonkey, the class definitions are
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// available and we can query those definitions to find the correct kind
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// directly from the class hierarchy.
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template <typename T>
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struct MapTypeToTraceKind {
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static const JS::TraceKind kind = T::TraceKind;
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};
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// When this header is used outside SpiderMonkey, the class definitions are not
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// available, so the following table containing all public GC types is used.
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#define JS_FOR_EACH_TRACEKIND(D) \
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/* PrettyName TypeName AddToCCKind */ \
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D(BaseShape, js::BaseShape, true) \
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D(JitCode, js::jit::JitCode, true) \
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D(LazyScript, js::LazyScript, true) \
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D(Scope, js::Scope, true) \
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D(Object, JSObject, true) \
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D(ObjectGroup, js::ObjectGroup, true) \
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D(Script, JSScript, true) \
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D(Shape, js::Shape, true) \
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D(String, JSString, false) \
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D(Symbol, JS::Symbol, false)
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// Map from all public types to their trace kind.
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#define JS_EXPAND_DEF(name, type, _) \
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template <> struct MapTypeToTraceKind<type> { \
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static const JS::TraceKind kind = JS::TraceKind::name; \
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};
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JS_FOR_EACH_TRACEKIND(JS_EXPAND_DEF);
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#undef JS_EXPAND_DEF
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// RootKind is closely related to TraceKind. Whereas TraceKind's indices are
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// laid out for convenient embedding as a pointer tag, the indicies of RootKind
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// are designed for use as array keys via EnumeratedArray.
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enum class RootKind : int8_t
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{
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// These map 1:1 with trace kinds.
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#define EXPAND_ROOT_KIND(name, _0, _1) \
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name,
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JS_FOR_EACH_TRACEKIND(EXPAND_ROOT_KIND)
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#undef EXPAND_ROOT_KIND
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// These tagged pointers are special-cased for performance.
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Id,
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Value,
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// Everything else.
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Traceable,
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Limit
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};
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// Most RootKind correspond directly to a trace kind.
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template <TraceKind traceKind> struct MapTraceKindToRootKind {};
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#define JS_EXPAND_DEF(name, _0, _1) \
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template <> struct MapTraceKindToRootKind<JS::TraceKind::name> { \
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static const JS::RootKind kind = JS::RootKind::name; \
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};
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JS_FOR_EACH_TRACEKIND(JS_EXPAND_DEF)
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#undef JS_EXPAND_DEF
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// Specify the RootKind for all types. Value and jsid map to special cases;
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// pointer types we can derive directly from the TraceKind; everything else
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// should go in the Traceable list and use GCPolicy<T>::trace for tracing.
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template <typename T>
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struct MapTypeToRootKind {
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static const JS::RootKind kind = JS::RootKind::Traceable;
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};
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template <typename T>
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struct MapTypeToRootKind<T*> {
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static const JS::RootKind kind =
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JS::MapTraceKindToRootKind<JS::MapTypeToTraceKind<T>::kind>::kind;
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};
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template <typename T>
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struct MapTypeToRootKind<mozilla::UniquePtr<T>> {
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static const JS::RootKind kind = JS::MapTypeToRootKind<T>::kind;
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};
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template <> struct MapTypeToRootKind<JS::Value> {
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static const JS::RootKind kind = JS::RootKind::Value;
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};
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template <> struct MapTypeToRootKind<jsid> {
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static const JS::RootKind kind = JS::RootKind::Id;
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};
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template <> struct MapTypeToRootKind<JSFunction*> : public MapTypeToRootKind<JSObject*> {};
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// Fortunately, few places in the system need to deal with fully abstract
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// cells. In those places that do, we generally want to move to a layout
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// templated function as soon as possible. This template wraps the upcast
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// for that dispatch.
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//
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// Given a call:
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//
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// DispatchTraceKindTyped(f, thing, traceKind, ... args)
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//
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// Downcast the |void *thing| to the specific type designated by |traceKind|,
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// and pass it to the functor |f| along with |... args|, forwarded. Pass the
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// type designated by |traceKind| as the functor's template argument. The
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// |thing| parameter is optional; without it, we simply pass through |... args|.
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// VS2017+, GCC and Clang require an explicit template declaration in front of
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// the specialization of operator() because it is a dependent template. VS2015,
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// on the other hand, gets very confused if we have a |template| token there.
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// The clang-cl front end defines _MSC_VER, but still requires the explicit
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// template declaration, so we must test for __clang__ here as well.
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#if (defined(_MSC_VER) && _MSC_VER < 1910) && !defined(__clang__)
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# define JS_DEPENDENT_TEMPLATE_HINT
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#else
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# define JS_DEPENDENT_TEMPLATE_HINT template
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#endif
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template <typename F, typename... Args>
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auto
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DispatchTraceKindTyped(F f, JS::TraceKind traceKind, Args&&... args)
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-> decltype(f. JS_DEPENDENT_TEMPLATE_HINT operator()<JSObject>(mozilla::Forward<Args>(args)...))
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{
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switch (traceKind) {
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#define JS_EXPAND_DEF(name, type, _) \
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case JS::TraceKind::name: \
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return f. JS_DEPENDENT_TEMPLATE_HINT operator()<type>(mozilla::Forward<Args>(args)...);
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JS_FOR_EACH_TRACEKIND(JS_EXPAND_DEF);
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#undef JS_EXPAND_DEF
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default:
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MOZ_CRASH("Invalid trace kind in DispatchTraceKindTyped.");
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}
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}
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#undef JS_DEPENDENT_TEMPLATE_HINT
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template <typename F, typename... Args>
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auto
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DispatchTraceKindTyped(F f, void* thing, JS::TraceKind traceKind, Args&&... args)
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-> decltype(f(static_cast<JSObject*>(nullptr), mozilla::Forward<Args>(args)...))
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{
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switch (traceKind) {
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#define JS_EXPAND_DEF(name, type, _) \
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case JS::TraceKind::name: \
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return f(static_cast<type*>(thing), mozilla::Forward<Args>(args)...);
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JS_FOR_EACH_TRACEKIND(JS_EXPAND_DEF);
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#undef JS_EXPAND_DEF
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default:
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MOZ_CRASH("Invalid trace kind in DispatchTraceKindTyped.");
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}
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}
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} // namespace JS
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#endif // js_TraceKind_h
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