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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 2009 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.base.Preconditions;

import com.google.javascript.jscomp.parsing.ParserRunner;

import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.InputId;
import com.google.javascript.rhino.Node;
import java.io.IOException;

import java.util.logging.Logger;

/**
 * Generates an AST for a JavaScript source file.
 *
 */
public class JsAst implements SourceAst {
  private static final Logger logger_ = Logger.getLogger(JsAst.class.getName());
  private static final long serialVersionUID = 1L;

  private transient InputId inputId;
  private transient SourceFile sourceFile;
  private String fileName;
  private Node root;

  public JsAst(SourceFile sourceFile) {
    this.inputId = new InputId(sourceFile.getName());
    this.sourceFile = sourceFile;
    this.fileName = sourceFile.getName();
  }

  @Override
  public Node getAstRoot(AbstractCompiler compiler) {
    if (root == null) {
      parse(compiler);
      root.setInputId(inputId);
    }
    return root;
  }

  @Override
  public void clearAst() {
    root = null;
    // While we're at it, clear out any saved text in the source file on
    // the assumption that if we're dumping the parse tree, then we probably
    // assume regenerating everything else is a smart idea also.
    sourceFile.clearCachedSource();
  }

  @Override
  public InputId getInputId() {
    return inputId;
  }

  @Override
  public SourceFile getSourceFile() {
    return sourceFile;
  }

  @Override
  public void setSourceFile(SourceFile file) {
    Preconditions.checkState(fileName.equals(file.getName()));
    sourceFile = file;
  }

  private void parse(AbstractCompiler compiler) {
    try {
      logger_.fine("Parsing: " + sourceFile.getName());
      root = ParserRunner.parse(sourceFile, sourceFile.getCode(),
          compiler.getParserConfig(),
          compiler.getDefaultErrorReporter(),
          logger_);
    } catch (IOException e) {
      compiler.report(
          JSError.make(AbstractCompiler.READ_ERROR, sourceFile.getName()));
    }

    if (root == null || compiler.hasHaltingErrors()) {
      // There was a parse error or IOException, so use a dummy block.
      root = IR.script();
    } else {
      compiler.prepareAst(root);
    }

    // Set the source name so that the compiler passes can track
    // the source file and module.
    root.setStaticSourceFile(sourceFile);
  }
}