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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 2010 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.checkNotNull;

import com.google.javascript.jscomp.JsAst.ParseResult;
import com.google.javascript.jscomp.JsAst.RhinoError;
import com.google.javascript.rhino.ErrorReporter;
import com.google.javascript.rhino.InputId;
import com.google.javascript.rhino.Node;
import org.jspecify.nullness.Nullable;

/**
 * An implementation of {@link SourceAst} that avoids re-creating the AST unless it was manually
 * cleared. This creates a single defensive copy of the AST; however, it is not safe for multiple
 * compilations to use this simultaneously, as all compilations mutate this. Since this class copies
 * the tree, you instead should create a central RecoverableJsAst that does the caching across
 * compilations, and create new RecoverableJsAst's that act as copying proxies around the original.
 */
public class RecoverableJsAst implements SourceAst {

  // The AST copy that will be kept around.
  private @Nullable Node root = null;

  // This is the actual SourceAst this caching wrapper wraps around.
  private final SourceAst realSource;

  private final boolean reportParseErrors;

  /** Wraps around an existing SourceAst that provides caching between compilations. */
  public RecoverableJsAst(SourceAst realSource, boolean reportParseErrors) {
    checkNotNull(realSource);
    this.realSource = realSource;
    this.reportParseErrors = reportParseErrors;
  }

  @Override
  public synchronized Node getAstRoot(AbstractCompiler compiler) {
    if (root == null) {
      // The original source (generally SourceAst) might not be thread-safe;
      // synchronize on it.
      synchronized (realSource) {
        root = realSource.getAstRoot(compiler).cloneTree(true);

        // Maybe replay parse error
        ParseResult result = (ParseResult) root.getProp(Node.PARSE_RESULTS);
        if (reportParseErrors && result != null) {
          replay(compiler, result);
        }
      }
    }
    return checkNotNull(root);
  }

  private void replay(AbstractCompiler compiler, ParseResult result) {
    ErrorReporter reporter = compiler.getDefaultErrorReporter();
    for (RhinoError error : result.errors) {
      reporter.error(error.message, error.sourceName, error.line, error.lineOffset);
    }
    for (RhinoError warning : result.warnings) {
      reporter.warning(warning.message, warning.sourceName, warning.line, warning.lineOffset);
    }
  }

  @Override
  public void clearAst() {
    // Just do a shallow clear; don't re-parse the input.
    this.root = null;
  }

  @Override
  public InputId getInputId() {
    synchronized (realSource) {
      return realSource.getInputId();
    }
  }

  @Override
  public SourceFile getSourceFile() {
    synchronized (realSource) {
      return realSource.getSourceFile();
    }
  }
}