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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 2017 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.bundle;

import com.google.common.annotations.GwtIncompatible;
import com.google.errorprone.annotations.Immutable;
import com.google.javascript.jscomp.CompilerOptions;
import com.google.javascript.jscomp.CompilerOptions.InstrumentOption;
import com.google.javascript.jscomp.Result;
import com.google.javascript.jscomp.VariableRenamingPolicy;
import java.util.Optional;

/**
 * A source transformer for instrmenting code for coverage data collection.
 */
@GwtIncompatible
@Immutable
public class CoverageInstrumenter extends CompilerBasedTransformer {

  public CoverageInstrumenter(CompilerBasedTransformer.CompilerSupplier compilerSupplier) {
    super(compilerSupplier);
  }
  /**
   * Supply options for coverage.
   */
  public static class CompilerSupplier extends CompilerBasedTransformer.CompilerSupplier {
    @Override
    protected void setOptions(CompilerOptions options) {
      options.coalesceVariableNames = false;
      options.setLanguageOut(CompilerOptions.LanguageMode.ECMASCRIPT5);
      options.setLanguageIn(CompilerOptions.LanguageMode.ECMASCRIPT_NEXT);
      options.setStrictModeInput(false);
      // Setting the path to any non-null value will trigger source map generation.
      // CompilerBasedTransformer attachs the sourcemap to the result.
      options.setSourceMapOutputPath("/dev/null");
      options.setVariableRenaming(VariableRenamingPolicy.OFF);
      options.setInstrumentForCoverageOption(InstrumentOption.LINE_ONLY);
      options.setInstrumentForCoverageOnly(true);
    }

    @Override
    public boolean transformed(Result result) {
      return true;
    }
  }

  @Override
  public Optional getRuntime() {
    return Optional.empty();
  }

  @Override
  public String getTranformationName() {
    return "Coverage Instrumentation";
  }

  public static CoverageInstrumenter.CompilerSupplier compilerSupplier() {
    return new CoverageInstrumenter.CompilerSupplier();
  }

  public static final CoverageInstrumenter INSTRUMENTER =
      new CoverageInstrumenter(CoverageInstrumenter.compilerSupplier());
}