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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 static com.google.common.base.Preconditions.checkState;
import static com.google.javascript.jscomp.base.JSCompObjects.identical;

import com.google.common.collect.ImmutableList;
import com.google.javascript.jscomp.parsing.ParserRunner;
import com.google.javascript.jscomp.parsing.parser.FeatureSet;
import com.google.javascript.rhino.ErrorReporter;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.InputId;
import com.google.javascript.rhino.Node;
import java.io.IOException;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.function.Supplier;
import org.jspecify.nullness.Nullable;

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

  private final InputId inputId;
  private final SourceFile sourceFile;

  private @Nullable Node root;
  private FeatureSet features;

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

  @Override
  public Node getAstRoot(AbstractCompiler compiler) {
    if (this.isParsed()) {
      return this.root;
    }

    Supplier astRootSource = compiler.getTypedAstDeserializer(this.sourceFile);
    if (astRootSource != null) {
      this.root = astRootSource.get();
      this.features = (FeatureSet) this.root.getProp(Node.FEATURE_SET);
    } else {
      this.parse(compiler);
    }
    checkState(identical(this.root.getStaticSourceFile(), this.sourceFile));
    this.root.setInputId(this.inputId);
    // Clear the cached source after parsing.  It will be re-read for snippet generation if needed.
    sourceFile.clearCachedSource();
    return this.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;
  }

  public FeatureSet getFeatures(AbstractCompiler compiler) {
    getAstRoot(compiler); // parse if required
    return features;
  }

  /** Representation of Rhino parser error. */
  public static class RhinoError implements Serializable {
    private static final long serialVersionUID = 1L;

    public final String message;
    public final String sourceName;
    public final int line;
    public final int lineOffset;

    public RhinoError(String message, String sourceName, int line, int lineOffset) {
      this.message = message;
      this.sourceName = sourceName;
      this.line = line;
      this.lineOffset = lineOffset;
    }
  }

  /** Simple class to share parse results between compilation jobs */
  public static class ParseResult implements Serializable {
    private static final long serialVersionUID = 1L;

    public final ImmutableList errors;
    public final ImmutableList warnings;

    ParseResult(ImmutableList errors, ImmutableList warnings) {
      this.errors = errors;
      this.warnings = warnings;
    }
  }

  private static class RecordingReporterProxy implements ErrorReporter {
    final ArrayList errors = new ArrayList<>();
    final ArrayList warnings = new ArrayList<>();
    private final ErrorReporter delegateReporter;

    RecordingReporterProxy(ErrorReporter delegateReporter) {
      this.delegateReporter = delegateReporter;
    }

    @Override
    public void warning(String message, String sourceName, int line, int lineOffset) {
      warnings.add(new RhinoError(message, sourceName, line, lineOffset));
      delegateReporter.warning(message, sourceName, line, lineOffset);
    }

    @Override
    public void error(String message, String sourceName, int line, int lineOffset) {
      errors.add(new RhinoError(message, sourceName, line, lineOffset));
      delegateReporter.error(message, sourceName, line, lineOffset);
    }
  }

  boolean isParsed() {
    return root != null;
  }

  private void parse(AbstractCompiler compiler) {
    RecordingReporterProxy reporter = new RecordingReporterProxy(
        compiler.getDefaultErrorReporter());

    try {
      ParserRunner.ParseResult result = ParserRunner.parse(
          sourceFile,
          sourceFile.getCode(),
          compiler.getParserConfig(sourceFile.isExtern()
              ? AbstractCompiler.ConfigContext.EXTERNS
              : AbstractCompiler.ConfigContext.DEFAULT),
          reporter);
      root = result.ast;
      features = result.features;

      if (compiler.getOptions().preservesDetailedSourceInfo()) {
        compiler.addComments(sourceFile.getName(), result.comments);
      }
      if (result.sourceMapURL != null && compiler.getOptions().resolveSourceMapAnnotations) {
        boolean parseInline = compiler.getOptions().parseInlineSourceMaps;
        SourceFile sourceMapSourceFile =
            SourceMapResolver.extractSourceMap(sourceFile, result.sourceMapURL, parseInline);
        if (sourceMapSourceFile != null) {
          compiler.addInputSourceMap(sourceFile.getName(), new SourceMapInput(sourceMapSourceFile));
        }
      }
    } catch (IOException e) {
      compiler.report(
          JSError.make(AbstractCompiler.READ_ERROR, sourceFile.getName(), e.getMessage()));
    }

    if (root == null) {
      root = IR.script();
    }

    if (!reporter.errors.isEmpty() || !reporter.warnings.isEmpty()) {
      ParseResult result = new ParseResult(
          ImmutableList.copyOf(reporter.errors),
          ImmutableList.copyOf(reporter.warnings));
      root.putProp(Node.PARSE_RESULTS, result);
    }

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