1 files changed, 182 insertions, 0 deletions
diff --git a/js/public/GCVariant.h b/js/public/GCVariant.h
new file mode 100644
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--- /dev/null
+++ b/js/public/GCVariant.h
@@ -0,0 +1,182 @@
+/* -*- 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/. */
+
+#ifndef js_GCVariant_h
+#define js_GCVariant_h
+
+#include "mozilla/Variant.h"
+
+#include <type_traits>
+
+#include "js/GCPolicyAPI.h"
+#include "js/RootingAPI.h"
+#include "js/TracingAPI.h"
+
+namespace JS {
+
+// These template specializations allow Variant to be used inside GC wrappers.
+//
+// When matching on GC wrappers around Variants, matching should be done on
+// the wrapper itself. The matcher class's methods should take Handles or
+// MutableHandles. For example,
+//
+//   struct MyMatcher
+//   {
+//        using ReturnType = const char*;
+//        ReturnType match(HandleObject o) { return "object"; }
+//        ReturnType match(HandleScript s) { return "script"; }
+//   };
+//
+//   Rooted<Variant<JSObject*, JSScript*>> v(cx, someScript);
+//   MyMatcher mm;
+//   v.match(mm);
+//
+// If you get compile errors about inability to upcast subclasses (e.g., from
+// NativeObject* to JSObject*) and are inside js/src, be sure to also include
+// "gc/Policy.h".
+
+namespace detail {
+
+template <typename... Ts>
+struct GCVariantImplementation;
+
+// The base case.
+template <typename T>
+struct GCVariantImplementation<T> {
+  template <typename ConcreteVariant>
+  static void trace(JSTracer* trc, ConcreteVariant* v, const char* name) {
+    T& thing = v->template as<T>();
+    GCPolicy<T>::trace(trc, &thing, name);
+  }
+
+  template <typename Matcher, typename ConcreteVariant>
+  static typename Matcher::ReturnType match(Matcher& matcher,
+                                            Handle<ConcreteVariant> v) {
+    const T& thing = v.get().template as<T>();
+    return matcher.match(Handle<T>::fromMarkedLocation(&thing));
+  }
+
+  template <typename Matcher, typename ConcreteVariant>
+  static typename Matcher::ReturnType match(Matcher& matcher,
+                                            MutableHandle<ConcreteVariant> v) {
+    T& thing = v.get().template as<T>();
+    return matcher.match(MutableHandle<T>::fromMarkedLocation(&thing));
+  }
+};
+
+// The inductive case.
+template <typename T, typename... Ts>
+struct GCVariantImplementation<T, Ts...> {
+  using Next = GCVariantImplementation<Ts...>;
+
+  template <typename ConcreteVariant>
+  static void trace(JSTracer* trc, ConcreteVariant* v, const char* name) {
+    if (v->template is<T>()) {
+      T& thing = v->template as<T>();
+      GCPolicy<T>::trace(trc, &thing, name);
+    } else {
+      Next::trace(trc, v, name);
+    }
+  }
+
+  template <typename Matcher, typename ConcreteVariant>
+  static typename Matcher::ReturnType match(Matcher& matcher,
+                                            Handle<ConcreteVariant> v) {
+    if (v.get().template is<T>()) {
+      const T& thing = v.get().template as<T>();
+      return matcher.match(Handle<T>::fromMarkedLocation(&thing));
+    }
+    return Next::match(matcher, v);
+  }
+
+  template <typename Matcher, typename ConcreteVariant>
+  static typename Matcher::ReturnType match(Matcher& matcher,
+                                            MutableHandle<ConcreteVariant> v) {
+    if (v.get().template is<T>()) {
+      T& thing = v.get().template as<T>();
+      return matcher.match(MutableHandle<T>::fromMarkedLocation(&thing));
+    }
+    return Next::match(matcher, v);
+  }
+};
+
+}  // namespace detail
+
+template <typename... Ts>
+struct GCPolicy<mozilla::Variant<Ts...>> {
+  using Impl = detail::GCVariantImplementation<Ts...>;
+
+  static void trace(JSTracer* trc, mozilla::Variant<Ts...>* v,
+                    const char* name) {
+    Impl::trace(trc, v, name);
+  }
+
+  static bool isValid(const mozilla::Variant<Ts...>& v) {
+    return v.match([](auto& v) {
+      return GCPolicy<std::remove_reference_t<decltype(v)>>::isValid(v);
+    });
+  }
+};
+
+}  // namespace JS
+
+namespace js {
+
+template <typename Wrapper, typename... Ts>
+class WrappedPtrOperations<mozilla::Variant<Ts...>, Wrapper> {
+  using Impl = JS::detail::GCVariantImplementation<Ts...>;
+  using Variant = mozilla::Variant<Ts...>;
+
+  const Variant& variant() const {
+    return static_cast<const Wrapper*>(this)->get();
+  }
+
+ public:
+  template <typename T>
+  bool is() const {
+    return variant().template is<T>();
+  }
+
+  template <typename T>
+  JS::Handle<T> as() const {
+    return Handle<T>::fromMarkedLocation(&variant().template as<T>());
+  }
+
+  template <typename Matcher>
+  typename Matcher::ReturnType match(Matcher& matcher) const {
+    return Impl::match(matcher,
+                       JS::Handle<Variant>::fromMarkedLocation(&variant()));
+  }
+};
+
+template <typename Wrapper, typename... Ts>
+class MutableWrappedPtrOperations<mozilla::Variant<Ts...>, Wrapper>
+    : public WrappedPtrOperations<mozilla::Variant<Ts...>, Wrapper> {
+  using Impl = JS::detail::GCVariantImplementation<Ts...>;
+  using Variant = mozilla::Variant<Ts...>;
+
+  const Variant& variant() const {
+    return static_cast<const Wrapper*>(this)->get();
+  }
+  Variant& variant() { return static_cast<Wrapper*>(this)->get(); }
+
+ public:
+  template <typename T>
+  JS::MutableHandle<T> as() {
+    return JS::MutableHandle<T>::fromMarkedLocation(
+        &variant().template as<T>());
+  }
+
+  template <typename Matcher>
+  typename Matcher::ReturnType match(Matcher& matcher) {
+    return Impl::match(
+        matcher, JS::MutableHandle<Variant>::fromMarkedLocation(&variant()));
+  }
+};
+
+}  // namespace js
+
+#endif  // js_GCVariant_h