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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 2014 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 static com.google.common.base.Preconditions.checkState;

import com.google.common.collect.ImmutableSet;
import com.google.javascript.jscomp.NodeTraversal.AbstractPostOrderCallback;
import com.google.javascript.rhino.JSDocInfo;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.Token;
import java.util.LinkedHashSet;
import java.util.Set;

/**
 * Gathers property names defined in externs.
 *
 * The collection of these property names could easily happen during
 * type checking. However, when exporting local property definitions,
 * the externs may be modified after type checking, and we want to
 * collect the new names as well.
 *
 * NOTE(dimvar): with NTI, we collect the relevant property names
 * during type checking, and we run this pass just to collect new
 * names that come from local exports. The type-visitor part is not
 * executed because getJSType returns null.
 */
class GatherExternProperties extends AbstractPostOrderCallback
    implements CompilerPass {
  private final Set externProperties;
  private final AbstractCompiler compiler;

  public GatherExternProperties(AbstractCompiler compiler) {
    this.compiler = compiler;
    this.externProperties = compiler.getExternProperties() == null
        ? new LinkedHashSet()
        : new LinkedHashSet(compiler.getExternProperties());
  }

  @Override
  public void process(Node externs, Node root) {
    NodeTraversal.traverseEs6(compiler, externs, this);
    compiler.setExternProperties(ImmutableSet.copyOf(externProperties));
  }

  @Override
  public void visit(NodeTraversal t, Node n, Node parent) {
    switch (n.getToken()) {
      case GETPROP:
        // Gathers "name" from (someObject.name).
        Node dest = n.getSecondChild();
        if (dest.isString()) {
          externProperties.add(dest.getString());
        }
        break;
      case STRING_KEY:
        if (parent.isObjectLit()) {
          externProperties.add(n.getString());
        }
        break;
      case MEMBER_FUNCTION_DEF:
        externProperties.add(n.getString());
        break;
      default:
        break;
    }

    JSDocInfo jsDocInfo = n.getJSDocInfo();
    if (jsDocInfo != null) {
      gatherPropertiesFromJSDocInfo(jsDocInfo);
    }
  }

  private void gatherPropertiesFromJSDocInfo(JSDocInfo jsDocInfo) {
    for (Node jsTypeExpressionNode : jsDocInfo.getTypeNodes()) {
      gatherPropertiesFromJsTypeExpressionNode(jsTypeExpressionNode);
    }
  }

  private void gatherPropertiesFromJsTypeExpressionNode(Node jsTypeExpressionNode) {
    switch (jsTypeExpressionNode.getToken()) {
      case LB:
        gatherPropertiesFromJsDocRecordType(jsTypeExpressionNode);
        break;
      default:
        for (Node child = jsTypeExpressionNode.getFirstChild();
            child != null;
            child = child.getNext()) {
          gatherPropertiesFromJsTypeExpressionNode(child);
        }
    }
  }

  private void gatherPropertiesFromJsDocRecordType(Node jsDocRecordNode) {
    checkState(jsDocRecordNode.getToken() == Token.LB, jsDocRecordNode);
    for (Node fieldNode = jsDocRecordNode.getFirstChild();
        fieldNode != null;
        fieldNode = fieldNode.getNext()) {
      Node fieldNameNode;
      Node fieldTypeNode;
      if (fieldNode.getToken() == Token.COLON) {
        fieldNameNode = fieldNode.getFirstChild();
        fieldTypeNode = fieldNameNode.getNext();
      } else {
        fieldNameNode = fieldNode;
        fieldTypeNode = null;
      }
      checkState(fieldNameNode.isStringKey(), fieldNameNode);
      String fieldName = fieldNameNode.getString();
      // TODO(bradfordcsmith): The JSDoc parser should do this.
      if (fieldName.startsWith("'") || fieldName.startsWith("\"")) {
        fieldName = fieldName.substring(1, fieldName.length() - 1);
      }
      externProperties.add(fieldName);
      if (fieldTypeNode != null) {
        gatherPropertiesFromJsTypeExpressionNode(fieldTypeNode);
      }
    }
  }
}