1 files changed, 65 insertions, 0 deletions
diff --git a/js/src/frontend/DefaultEmitter.h b/js/src/frontend/DefaultEmitter.h
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+++ b/js/src/frontend/DefaultEmitter.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/. */
+
+#ifndef frontend_DefaultEmitter_h
+#define frontend_DefaultEmitter_h
+
+#include "mozilla/Attributes.h"  // MOZ_STACK_CLASS
+#include "mozilla/Maybe.h"       // Maybe
+
+#include "frontend/IfEmitter.h"  // IfEmitter
+
+namespace js {
+namespace frontend {
+
+struct BytecodeEmitter;
+
+// Class for emitting default parameter or default value.
+//
+// Usage: (check for the return value is omitted for simplicity)
+//
+//   `x = 10` in `function (x = 10) {}`
+//     // the value of arguments[0] is on the stack
+//     DefaultEmitter de(this);
+//     de.prepareForDefault();
+//     emit(10);
+//     de.emitEnd();
+//
+class MOZ_STACK_CLASS DefaultEmitter {
+  BytecodeEmitter* bce_;
+
+  mozilla::Maybe<IfEmitter> ifUndefined_;
+
+#ifdef DEBUG
+  // The state of this emitter.
+  //
+  // +-------+ prepareForDefault +---------+ emitEnd +-----+
+  // | Start |------------------>| Default |-------->| End |
+  // +-------+                   +---------+         +-----+
+  enum class State {
+    // The initial state.
+    Start,
+
+    // After calling prepareForDefault.
+    Default,
+
+    // After calling emitEnd.
+    End
+  };
+  State state_ = State::Start;
+#endif
+
+ public:
+  explicit DefaultEmitter(BytecodeEmitter* bce);
+
+  [[nodiscard]] bool prepareForDefault();
+  [[nodiscard]] bool emitEnd();
+};
+
+} /* namespace frontend */
+} /* namespace js */
+
+#endif /* frontend_LabelEmitter_h */