1 files changed, 66 insertions, 0 deletions
diff --git a/dom/bindings/BindingCallContext.h b/dom/bindings/BindingCallContext.h
new file mode 100644
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+++ b/dom/bindings/BindingCallContext.h
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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/. */
+
+/**
+ * A struct that encapsulates a JSContex and information about
+ * which binding method was called.  The idea is to automatically annotate
+ * exceptions thrown via the BindingCallContext with the method name.
+ */
+
+#ifndef mozilla_dom_BindingCallContext_h
+#define mozilla_dom_BindingCallContext_h
+
+#include <utility>
+
+#include "js/TypeDecls.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/ErrorResult.h"
+
+namespace mozilla::dom {
+
+class MOZ_NON_TEMPORARY_CLASS MOZ_STACK_CLASS BindingCallContext {
+ public:
+  // aCx is allowed to be null.  If it is, the BindingCallContext should
+  // generally act like a null JSContext*: test false when tested as a boolean
+  // and produce nullptr when used as a JSContext*.
+  //
+  // aMethodDescription should be something with longer lifetime than this
+  // BindingCallContext.  Most simply, a string literal.  nullptr or "" is
+  // allowed if we want to not have any particular message description.  This
+  // argument corresponds to the "context" string used for DOM error codes that
+  // support one.  See Errors.msg and the documentation for
+  // ErrorResult::MaybeSetPendingException for details on he context arg.
+  BindingCallContext(JSContext* aCx, const char* aMethodDescription)
+      : mCx(aCx), mDescription(aMethodDescription) {}
+
+  ~BindingCallContext() = default;
+
+  // Allow passing a BindingCallContext as a JSContext*, as needed.
+  operator JSContext*() const { return mCx; }
+
+  // Allow testing a BindingCallContext for falsiness, just like a
+  // JSContext* could be tested.
+  explicit operator bool() const { return !!mCx; }
+
+  // Allow throwing an error message, if it has a context.
+  template <dom::ErrNum errorNumber, typename... Ts>
+  bool ThrowErrorMessage(Ts&&... aMessageArgs) const {
+    static_assert(ErrorFormatHasContext[errorNumber],
+                  "We plan to add a context; it better be expected!");
+    MOZ_ASSERT(mCx);
+    return dom::ThrowErrorMessage<errorNumber>(
+        mCx, mDescription, std::forward<Ts>(aMessageArgs)...);
+  }
+
+ private:
+  JSContext* const mCx;
+  const char* const mDescription;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_BindingCallContext_h