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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.javascript.jscomp.parsing.Config.JsDocParsing.INCLUDE_ALL_COMMENTS;

import com.google.common.annotations.GwtIncompatible;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.javascript.jscomp.CompilerOptions.LanguageMode;
import com.google.javascript.jscomp.deps.ModuleLoader.ResolutionMode;
import com.google.javascript.jscomp.parsing.Config.JsDocParsing;
import com.google.javascript.refactoring.ApplySuggestedFixes;
import com.google.javascript.refactoring.FixingErrorManager;
import com.google.javascript.refactoring.SuggestedFix;
import java.io.IOException;
import java.nio.file.Path;
import java.util.Collection;

/**
 * Tool for running just the lint checks which can be run on a single file at a time.
 *
 * Run from {@link LinterMain}
 */
@GwtIncompatible("Unnecessary")
public final class Linter {

  /**
   * Builder for a Linter that allows some customization.
   *
   * Note: A builder is not designed to generate multiple Linters, just a single one. The
   * underlying CompilerOptions it builds is never copied defensively, so futher edits to this
   * builder will affect previously built Linters.
   */
  public static final class Builder {
    private final CompilerOptions options;

    private Builder() {
      options = new CompilerOptions();
      options.setLanguage(LanguageMode.ECMASCRIPT_NEXT);
      options.setParseJsDocDocumentation(JsDocParsing.INCLUDE_ALL_COMMENTS);
      options.setPreserveDetailedSourceInfo(true);

      // These are necessary to make sure that suggested fixes are printed correctly.
      options.setPrettyPrint(true);
      options.setPreserveTypeAnnotations(true);
      options.setPreferSingleQuotes(true);
      options.setEmitUseStrict(false);

      options.setParseJsDocDocumentation(INCLUDE_ALL_COMMENTS);
      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.JSDOC_MISSING_TYPE, CheckLevel.ERROR);
      options.setWarningLevel(DiagnosticGroups.MISPLACED_MSG_ANNOTATION, CheckLevel.WARNING);
      options.setWarningLevel(DiagnosticGroups.LINT_CHECKS, CheckLevel.WARNING);
      options.setWarningLevel(DiagnosticGroups.UNUSED_LOCAL_VARIABLE, CheckLevel.WARNING);
      options.setWarningLevel(DiagnosticGroups.UNUSED_PRIVATE_PROPERTY, CheckLevel.WARNING);
      options.setWarningLevel(DiagnosticGroups.EXTRA_REQUIRE, CheckLevel.ERROR);
      options.setWarningLevel(DiagnosticGroups.MISPLACED_SUPPRESS, CheckLevel.WARNING);
      options.setWarningLevel(DiagnosticGroups.TYPE_IMPORT_CODE_REFERENCES, CheckLevel.ERROR);
      options.setWarningLevel(DiagnosticGroups.MODULE_LOAD, CheckLevel.OFF);
      options.setWarningLevel(DiagnosticGroups.STRICT_MODULE_CHECKS, CheckLevel.WARNING);
      options.setWarningLevel(DiagnosticGroups.UNDERSCORE, CheckLevel.WARNING);
      options.setSummaryDetailLevel(0);
    }

    @CanIgnoreReturnValue
    public Builder withModuleResolutionMode(ResolutionMode moduleResolutionMode) {
      options.setModuleResolutionMode(moduleResolutionMode);
      return this;
    }

    @CanIgnoreReturnValue
    public Builder withBrowserResolverPrefixReplacements(
        ImmutableMap replacements) {
      options.setBrowserResolverPrefixReplacements(replacements);
      return this;
    }

    public Linter build() {
      return new Linter(options);
    }
  }

  // Don't try to apply fixes anymore, after trying this many times.
  // This is to avoid the unlikely event of an infinite loop of fixes.
  static final int MAX_FIXES = 5;

  private final CompilerOptions options;

  private Linter(CompilerOptions options) {
    this.options = options;
  }

  static Builder builder() {
    return new Builder();
  }

  void lint(String filename) {
    lint(Path.of(filename), new Compiler(System.out));
  }

  void lint(Path path, Compiler compiler) {
    SourceFile file = SourceFile.fromFile(path.toString());
    compiler.setPassConfig(new LintPassConfig(options));
    compiler.disableThreads();
    SourceFile externs = SourceFile.fromCode("", "");
    compiler.compile(ImmutableList.of(externs), ImmutableList.of(file), options);
  }

  /**
   * Keep applying fixes to the given file until no more fixes can be found, or until fixes have
   * been applied {@code MAX_FIXES} times.
   */
  void fixRepeatedly(String filename) throws IOException {
    fixRepeatedly(filename, ImmutableSet.of());
  }

  /**
   * Keep applying fixes to the given file until no more fixes can be found, or until fixes have
   * been applied {@code MAX_FIXES} times.
   */
  void fixRepeatedly(String filename, ImmutableSet unfixableErrors)
      throws IOException {
    for (int i = 0; i < MAX_FIXES; i++) {
      if (!fix(filename, unfixableErrors)) {
        break;
      }
    }
  }

  /** @return Whether any fixes were applied. */
  private boolean fix(String filename, ImmutableSet unfixableErrors)
      throws IOException {
    Compiler compiler = new Compiler(System.out);
    FixingErrorManager errorManager = new FixingErrorManager(unfixableErrors);
    compiler.setErrorManager(errorManager);
    errorManager.setCompiler(compiler);

    lint(Path.of(filename), compiler);

    Collection fixes = errorManager.getSureFixes();
    if (!fixes.isEmpty()) {
      ApplySuggestedFixes.applySuggestedFixesToFiles(fixes);
      return true;
    }
    return false;
  }
}