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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 2015 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.collect.ObjectArrays.concat;

import com.google.common.collect.ImmutableList;
import com.google.javascript.jscomp.CompilerOptions.LanguageMode;
import com.google.javascript.refactoring.ApplySuggestedFixes;
import com.google.javascript.refactoring.ErrorToFixMapper;
import com.google.javascript.refactoring.SuggestedFix;

import java.io.IOException;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.List;

/**
 * Minimal binary that just runs the "lint" checks which can be run on a single file at a time.
 * This means some checks in the lintChecks DiagnosticGroup are skipped, since they depend on
 * type information.
 */
public class Linter {
  public static void main(String[] args) throws IOException {
    for (String filename : args) {
      // TODO(tbreisacher): Add a command line flag that causes this
      // to call fix() instead of lint().
      lint(filename);
    }
  }


  static void lint(String filename) throws IOException {
    lint(Paths.get(filename), false);
  }

  static void fix(String filename) throws IOException {
    lint(Paths.get(filename), true);
  }

  private static void lint(Path path, boolean fix) throws IOException {
    SourceFile file = SourceFile.fromFile(path.toString());
    Compiler compiler = new Compiler(System.out);
    CompilerOptions options = new CompilerOptions();
    options.setLanguage(LanguageMode.ECMASCRIPT6_STRICT);

    // For a full compile, this would cause a crash, as the method name implies. But the passes
    // in LintPassConfig can all handle untranspiled ES6.
    options.setSkipTranspilationAndCrash(true);

    options.setIdeMode(true);
    options.setCodingConvention(new GoogleCodingConvention());

    // Even though we're not running the typechecker, enable the checkTypes DiagnosticGroup, since
    // it contains some warnings we do want to report, such as JSDoc parse warnings.
    options.setWarningLevel(DiagnosticGroups.CHECK_TYPES, CheckLevel.WARNING);

    options.setWarningLevel(DiagnosticGroups.LINT_CHECKS, CheckLevel.WARNING);
    options.setWarningLevel(DiagnosticGroups.MISSING_REQUIRE, CheckLevel.WARNING);
    options.setWarningLevel(DiagnosticGroups.EXTRA_REQUIRE, CheckLevel.WARNING);
    compiler.setPassConfig(new LintPassConfig(options));
    compiler.disableThreads();
    SourceFile externs = SourceFile.fromCode("", "");
    compiler.compile(ImmutableList.of(externs), ImmutableList.of(file), options);
    if (fix) {
      List fixes = new ArrayList<>();
      for (JSError warning : concat(compiler.getErrors(), compiler.getWarnings(), JSError.class)) {
        SuggestedFix suggestedFix = ErrorToFixMapper.getFixForJsError(warning, compiler);
        if (suggestedFix != null) {
          fixes.add(suggestedFix);
        }
      }
      ApplySuggestedFixes.applySuggestedFixesToFiles(fixes);
    }
  }
}