1 files changed, 110 insertions, 0 deletions
diff --git a/js/src/builtin/HandlerFunction-inl.h b/js/src/builtin/HandlerFunction-inl.h
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+++ b/js/src/builtin/HandlerFunction-inl.h
@@ -0,0 +1,110 @@
+/* -*- 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/. */
+
+/*
+ * Handler for operations that act on a target object, and possibly upon
+ * an extra value.
+ */
+
+#ifndef builtin_HandlerFunction_inl_h
+#define builtin_HandlerFunction_inl_h
+
+#include <stddef.h>  // size_t
+
+#include "gc/AllocKind.h"   // js::gc::AllocKind
+#include "js/CallArgs.h"    // JS::CallArgs
+#include "js/RootingAPI.h"  // JS::Handle, JS::Rooted
+#include "js/Value.h"       // JS::ObjectValue
+#include "vm/JSContext.h"   // JSContext
+#include "vm/JSFunction.h"  // JSFunction, js::Native, js::NewNativeFunction
+#include "vm/JSObject.h"    // JSObject, js::GenericObject
+#include "vm/StringType.h"  // js::PropertyName
+
+#include "vm/JSContext-inl.h"  // JSContext::check
+
+namespace js {
+
+// Handler functions are extended functions, that close over a target object and
+// (optionally) over an extra object, storing those objects in the function's
+// extended slots.
+constexpr size_t HandlerFunctionSlot_Target = 0;
+constexpr size_t HandlerFunctionSlot_Extra = 1;
+
+static_assert(HandlerFunctionSlot_Extra < FunctionExtended::NUM_EXTENDED_SLOTS,
+              "handler function slots shouldn't exceed available extended "
+              "slots");
+
+[[nodiscard]] inline JSFunction* NewHandler(JSContext* cx, Native handler,
+                                            JS::Handle<JSObject*> target) {
+  cx->check(target);
+
+  JS::Handle<PropertyName*> funName = cx->names().empty;
+  JS::Rooted<JSFunction*> handlerFun(
+      cx, NewNativeFunction(cx, handler, 0, funName,
+                            gc::AllocKind::FUNCTION_EXTENDED, GenericObject));
+  if (!handlerFun) {
+    return nullptr;
+  }
+  handlerFun->setExtendedSlot(HandlerFunctionSlot_Target,
+                              JS::ObjectValue(*target));
+  return handlerFun;
+}
+
+[[nodiscard]] inline JSFunction* NewHandlerWithExtra(
+    JSContext* cx, Native handler, JS::Handle<JSObject*> target,
+    JS::Handle<JSObject*> extra) {
+  cx->check(extra);
+  JSFunction* handlerFun = NewHandler(cx, handler, target);
+  if (handlerFun) {
+    handlerFun->setExtendedSlot(HandlerFunctionSlot_Extra,
+                                JS::ObjectValue(*extra));
+  }
+  return handlerFun;
+}
+
+[[nodiscard]] inline JSFunction* NewHandlerWithExtraValue(
+    JSContext* cx, Native handler, JS::Handle<JSObject*> target,
+    JS::Handle<JS::Value> extra) {
+  cx->check(extra);
+  JSFunction* handlerFun = NewHandler(cx, handler, target);
+  if (handlerFun) {
+    handlerFun->setExtendedSlot(HandlerFunctionSlot_Extra, extra);
+  }
+  return handlerFun;
+}
+
+/**
+ * Within the call of a handler function that "closes over" a target value that
+ * is always a |T*| object (and never a wrapper around one), return that |T*|.
+ */
+template <class T>
+[[nodiscard]] inline T* TargetFromHandler(const JS::CallArgs& args) {
+  JSFunction& func = args.callee().as<JSFunction>();
+  return &func.getExtendedSlot(HandlerFunctionSlot_Target).toObject().as<T>();
+}
+
+/**
+ * Within the call of a handler function that "closes over" a target value and
+ * an extra value, return that extra value.
+ */
+[[nodiscard]] inline JS::Value ExtraValueFromHandler(const JS::CallArgs& args) {
+  JSFunction& func = args.callee().as<JSFunction>();
+  return func.getExtendedSlot(HandlerFunctionSlot_Extra);
+}
+
+/**
+ * Within the call of a handler function that "closes over" a target value and
+ * an extra value, where that extra value is always a |T*| object (and never a
+ * wrapper around one), return that |T*|.
+ */
+template <class T>
+[[nodiscard]] inline T* ExtraFromHandler(const JS::CallArgs& args) {
+  return &ExtraValueFromHandler(args).toObject().as<T>();
+}
+
+}  // namespace js
+
+#endif  // builtin_HandlerFunction_inl_h