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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.rhino.JSDocInfo;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.Token;
import java.util.LinkedHashSet;

/**
 * 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.
 *
 * 
Mode.CHECK is set when checksOnly=true and only collects the externs in the type expressions
 * in JSDoc. Mode.OPTIMIZE is set when checksOnly=false and only collects the externs in AST
 * properties.
 *
 * To optimize build time, we collect only type expression externs in getChecks() and only AST
 * property externs in getOptimizations() instead of collecting all in both.
 */
final class GatherExternProperties implements NodeTraversal.Callback, CompilerPass {
  private final AbstractCompiler compiler;

  private final LinkedHashSet externProperties = new LinkedHashSet<>();

  enum Mode {
    CHECK(true, false),
    OPTIMIZE(false, true),
    CHECK_AND_OPTIMIZE(true, true);

    private final boolean check;
    private final boolean optimize;

    Mode(boolean check, boolean optimize) {
      this.check = check;
      this.optimize = optimize;
    }
  }

  private final Mode mode;

  GatherExternProperties(AbstractCompiler compiler, Mode mode) {
    this.compiler = compiler;
    this.mode = mode;

    if (compiler.getExternProperties() != null) {
      this.externProperties.addAll(compiler.getExternProperties());
    }
  }

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

  @Override
  public boolean shouldTraverse(NodeTraversal t, Node n, Node parent) {
    return !n.isScript() || !NodeUtil.isFromTypeSummary(n);
  }

  @Override
  public void visit(NodeTraversal t, Node n, Node parent) {
    if (this.mode.optimize) {
      switch (n.getToken()) {
        case GETPROP:
          // Gathers "name" from (someObject.name).
          externProperties.add(n.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 && this.mode.check) {
      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);
      }
    }
  }
}