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diff --git a/js/src/frontend/LexicalScopeEmitter.h b/js/src/frontend/LexicalScopeEmitter.h
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+++ b/js/src/frontend/LexicalScopeEmitter.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_LexicalScopeEmitter_h
+#define frontend_LexicalScopeEmitter_h
+
+#include "mozilla/Assertions.h"  // MOZ_ASSERT
+#include "mozilla/Attributes.h"  // MOZ_STACK_CLASS, MOZ_MUST_USE
+#include "mozilla/Maybe.h"       // Maybe
+
+#include "frontend/EmitterScope.h"   // EmitterScope
+#include "frontend/TDZCheckCache.h"  // TDZCheckCache
+#include "gc/Rooting.h"              // JS::Handle
+#include "vm/Scope.h"                // ScopeKind, LexicalScope
+
+namespace js {
+namespace frontend {
+
+struct BytecodeEmitter;
+
+// Class for emitting bytecode for lexical scope.
+//
+// In addition to emitting code for entering and leaving a scope, this RAII
+// guard affects the code emitted for `break` and other non-structured
+// control flow. See NonLocalExitControl::prepareForNonLocalJump().
+//
+// Usage: (check for the return value is omitted for simplicity)
+//
+//   `{ ... }` -- lexical scope with no bindings
+//     LexicalScopeEmitter lse(this);
+//     lse.emitEmptyScope();
+//     emit(scopeBody);
+//     lse.emitEnd();
+//
+//   `{ let a; body }`
+//     LexicalScopeEmitter lse(this);
+//     lse.emitScope(ScopeKind::Lexical, scopeBinding);
+//     emit(let_and_body);
+//     lse.emitEnd();
+//
+//   `catch (e) { body }`
+//     LexicalScopeEmitter lse(this);
+//     lse.emitScope(ScopeKind::SimpleCatch, scopeBinding);
+//     emit(body);
+//     lse.emitEnd();
+//
+//   `catch ([a, b]) { body }`
+//     LexicalScopeEmitter lse(this);
+//     lse.emitScope(ScopeKind::Catch, scopeBinding);
+//     emit(body);
+//     lse.emitEnd();
+class MOZ_STACK_CLASS LexicalScopeEmitter {
+  BytecodeEmitter* bce_;
+
+  mozilla::Maybe<TDZCheckCache> tdzCache_;
+  mozilla::Maybe<EmitterScope> emitterScope_;
+
+#ifdef DEBUG
+  // The state of this emitter.
+  //
+  // +-------+ emitScope  +-------+ emitEnd  +-----+
+  // | Start |----------->| Scope |--------->| End |
+  // +-------+            +-------+          +-----+
+  enum class State {
+    // The initial state.
+    Start,
+
+    // After calling emitScope/emitEmptyScope.
+    Scope,
+
+    // After calling emitEnd.
+    End,
+  };
+  State state_ = State::Start;
+#endif
+
+ public:
+  explicit LexicalScopeEmitter(BytecodeEmitter* bce);
+
+  // Returns the scope object for non-empty scope.
+  const EmitterScope& emitterScope() const { return *emitterScope_; }
+
+  MOZ_MUST_USE bool emitScope(ScopeKind kind,
+                              LexicalScope::ParserData* bindings);
+  MOZ_MUST_USE bool emitEmptyScope();
+
+  MOZ_MUST_USE bool emitEnd();
+};
+
+} /* namespace frontend */
+} /* namespace js */
+
+#endif /* frontend_LexicalScopeEmitter_h */