[destructuring] Implement basic binding destructuring infrastructure

src/pattern-rewriter.h

+// Copyright 2015 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef V8_PATTERN_MATCHER_H_
+#define V8_PATTERN_MATCHER_H_
+
+#include "src/ast.h"
+#include "src/parser.h"
+
+namespace v8 {
+
+namespace internal {
+
+class Parser::PatternRewriter : private AstVisitor {
+ public:
+  struct DeclarationDescriptor {
+    Parser* parser;
+    Scope* declaration_scope;
+    Scope* scope;
+    int initializer_position;
+    VariableMode mode;
+    ZoneList<const AstRawString*>* names;
+    bool is_const;
+    Block* block;
+    bool needs_init;
+    int pos;
+    Token::Value init_op;
+  };
+
+  explicit PatternRewriter(const DeclarationDescriptor* decl,
+                           Expression* pattern)
+      : decl_(decl),
+        pattern_(pattern),
+        current_value_(nullptr),
+        ok_(nullptr),
+        nvars_(nullptr) {}
+
+  PatternRewriter()
+      : decl_(nullptr),
+        pattern_(nullptr),
+        current_value_(nullptr),
+        ok_(nullptr),
+        nvars_(nullptr) {}
+
+  bool IsSingleVariableBinding() const;
+  const AstRawString* SingleName() const;
+
+  void DeclareAndInitializeVariables(Expression* value, int* nvars, bool* ok);
+
+ private:
+#define DECLARE_VISIT(type) void Visit##type(v8::internal::type* node) override;
+  // Visiting functions for AST nodes make this an AstVisitor.
+  AST_NODE_LIST(DECLARE_VISIT)
+#undef DECLARE_VISIT
+  virtual void Visit(AstNode* node) override;
+
+  void RecurseIntoSubpattern(AstNode* pattern, Expression* value) {
+    Expression* old_value = current_value_;
+    current_value_ = value;
+    pattern->Accept(this);
+    current_value_ = old_value;
+  }
+
+  AstNodeFactory* factory() const { return decl_->parser->factory(); }
+  AstValueFactory* ast_value_factory() const {
+    return decl_->parser->ast_value_factory();
+  }
+  bool inside_with() const { return decl_->parser->inside_with(); }
+  Zone* zone() const { return decl_->parser->zone(); }
+
+  const DeclarationDescriptor* decl_;
+  Expression* pattern_;
+  Expression* current_value_;
+  bool* ok_;
+  int* nvars_;
+};
+}
+}  // namespace v8::internal
+
+
+#endif  // V8_PATTERN_MATCHER_H_