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Closure Compiler is a JavaScript optimizing compiler. It parses your JavaScript, analyzes it, removes dead code and rewrites and minimizes what's left. It also checks syntax, variable references, and types, and warns about common JavaScript pitfalls. It is used in many of Google's JavaScript apps, including Gmail, Google Web Search, Google Maps, and Google Docs.

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/*
 * Copyright 2015 The Closure Compiler Authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.javascript.jscomp;

import com.google.common.collect.Table;
import com.google.javascript.jscomp.NodeTraversal.AbstractPostOrderCallback;
import com.google.javascript.rhino.Node;

/** Renames references in code. */
final class Es6RenameReferences extends AbstractPostOrderCallback {

  /**
   * Map from the root node of a scope + the original variable name to a new name for the variable.
   *
   * An entry in this map means we should rename a variable that was originally declared in the
   * scope with the given root and had the original variable name to the new name.
   */
  private final Table renameTable;

  Es6RenameReferences(Table renameTable) {
    this.renameTable = renameTable;
  }

  @Override
  public void visit(NodeTraversal t, Node n, Node parent) {
    if (NodeUtil.isReferenceName(n)) {
      renameReference(t, n, n.getString());
    }
  }

  /**
   * @param t The NodeTraversal.
   * @param oldName The root name of a qualified name.
   */
  private void renameReference(NodeTraversal t, Node n, String oldName) {
    Scope current = t.getScope();
    // You should be wondering:
    //
    // Why are we searching up the stack of scopes here instead of just looking up the Var for
    // oldName and getting the scope from that?
    //
    // The answer is:
    //
    // When Es6RewriteBlockScopedDeclaration uses this class, it has already modified the scopes so
    // that `oldName` is no longer declared in its original scope.
    //
    // I don't know if the other users of this class are also modifying the scopes in advance.
    // - [email protected]
    while (current != null) {
      String newName = renameTable.get(current.getRootNode(), oldName);
      if (newName != null) {
        n.setString(newName);
        t.reportCodeChange();
        return;
      } else if (current.hasOwnSlot(oldName)) {
        return;
      } else {
        current = current.getParent();
      }
    }
  }
}