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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.parsing;

import com.google.auto.value.AutoValue;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import com.google.errorprone.annotations.Immutable;
import com.google.javascript.jscomp.parsing.parser.FeatureSet;

/**
 * Configuration for the AST factory. Should be shared across AST creation for all files of a
 * compilation process.
 */
@Immutable @AutoValue @AutoValue.CopyAnnotations
public abstract class Config {

  /**
   * Level of language strictness required for the input source code.
   */
  public enum StrictMode {
    STRICT, SLOPPY;

    public boolean isStrict() {
      return this == STRICT;
    }
  }

  /** JavaScript mode */
  public enum LanguageMode {

    // Note that minimumRequiredFor() relies on these being defined in order from fewest features to
    // most features, and _STRICT versions should be supplied after unspecified strictness.
    ECMASCRIPT3(FeatureSet.ES3),
    ECMASCRIPT5(FeatureSet.ES5),
    ECMASCRIPT_2015(FeatureSet.ES2015_MODULES),
    ECMASCRIPT_2016(FeatureSet.ES2016_MODULES),
    ECMASCRIPT_2017(FeatureSet.ES2017_MODULES),
    ECMASCRIPT_2018(FeatureSet.ES2018_MODULES),
    ECMASCRIPT_2019(FeatureSet.ES2019_MODULES),
    ECMASCRIPT_2020(FeatureSet.ES2020_MODULES),
    ECMASCRIPT_2021(FeatureSet.ES2021_MODULES),
    ES_NEXT(FeatureSet.ES_NEXT),
    UNSTABLE(FeatureSet.ES_UNSTABLE),
    UNSUPPORTED(FeatureSet.ES_UNSUPPORTED);

    public final FeatureSet featureSet;

    LanguageMode(FeatureSet featureSet) {
      this.featureSet = featureSet;
    }

    /**
     * Returns the lowest {@link LanguageMode} that supports the specified feature.
     */
    public static LanguageMode minimumRequiredFor(FeatureSet.Feature feature) {
      // relies on the LanguageMode enums being in the right order
      for (LanguageMode mode : LanguageMode.values()) {
        if (mode.featureSet.has(feature)) {
          return mode;
        }
      }
      throw new IllegalStateException("No input language mode supports feature: " + feature);
    }

    /** Returns the lowest {@link LanguageMode} that supports the specified feature set. */
    public static LanguageMode minimumRequiredForSet(FeatureSet featureSet) {
      for (LanguageMode mode : LanguageMode.values()) {
        if (mode.featureSet.contains(featureSet)) {
          return mode;
        }
      }
      throw new IllegalStateException("No input language mode supports feature set: " + featureSet);
    }

    public static LanguageMode latestEcmaScript() {
      return ECMASCRIPT_2020;
    }
  }

  /**
   * Whether to parse the descriptions of JsDoc comments.
   */
  public enum JsDocParsing {
    TYPES_ONLY,
    INCLUDE_DESCRIPTIONS_NO_WHITESPACE,
    INCLUDE_DESCRIPTIONS_WITH_WHITESPACE,
    INCLUDE_ALL_COMMENTS;

    boolean shouldParseDescriptions() {
      return this != TYPES_ONLY;
    }

    boolean shouldPreserveWhitespace() {
      return this == INCLUDE_DESCRIPTIONS_WITH_WHITESPACE || this == INCLUDE_ALL_COMMENTS;
    }
  }

  /**
   * Whether to keep going after encountering a parse error.
   */
  public enum RunMode {
    STOP_AFTER_ERROR,
    KEEP_GOING,
  }

  /** Language level to accept. */
  public abstract LanguageMode languageMode();

  /** Whether to assume input is strict mode compliant. */
  public abstract StrictMode strictMode();

  /** How to parse the descriptions of JsDoc comments. */
  public abstract JsDocParsing jsDocParsingMode();

  /** Whether to keep going after encountering a parse error. */
  public abstract RunMode runMode();

  /** Recognized JSDoc annotations, mapped from their name to their internal representation. */
  public abstract ImmutableMap annotations();

  /** Set of recognized names in a {@code @suppress} tag. */
  public abstract ImmutableSet suppressionNames();

  /** Set of recognized names in a {@code @closurePrimitive} tag. */
  abstract ImmutableSet closurePrimitiveNames();

  /** Whether to parse inline source maps (//# sourceMappingURL=data:...). */
  public abstract boolean parseInlineSourceMaps();

  final ImmutableSet annotationNames() {
    return annotations().keySet();
  }

  public static Builder builder() {
    return new AutoValue_Config.Builder()
        .setLanguageMode(LanguageMode.UNSUPPORTED)
        .setStrictMode(StrictMode.STRICT)
        .setJsDocParsingMode(JsDocParsing.TYPES_ONLY)
        .setRunMode(RunMode.STOP_AFTER_ERROR)
        .setExtraAnnotationNames(ImmutableSet.of())
        .setSuppressionNames(ImmutableSet.of())
        .setClosurePrimitiveNames(ImmutableSet.of())
        .setParseInlineSourceMaps(false);
  }

  /** Builder for a Config. */
  @AutoValue.Builder
  public abstract static class Builder {
    public abstract Builder setLanguageMode(LanguageMode mode);

    public abstract Builder setStrictMode(StrictMode mode);

    public abstract Builder setJsDocParsingMode(JsDocParsing mode);

    public abstract Builder setRunMode(RunMode mode);

    public abstract Builder setParseInlineSourceMaps(boolean parseInlineSourceMaps);

    public abstract Builder setSuppressionNames(Iterable names);

    abstract Builder setClosurePrimitiveNames(Iterable names);

    final Builder setExtraAnnotationNames(Iterable names) {
      return setAnnotations(buildAnnotations(names));
    }

    public abstract Config build();

    // The following is intended to be used internally only (but isn't private due to AutoValue).
    public abstract Builder setAnnotations(ImmutableMap names);
  }

  /** Create the annotation names from the user-specified annotation allowlist. */
  private static ImmutableMap buildAnnotations(Iterable allowlist) {
    ImmutableMap.Builder annotationsBuilder = ImmutableMap.builder();
    annotationsBuilder.putAll(Annotation.recognizedAnnotations);
    for (String unrecognizedAnnotation : allowlist) {
      if (!unrecognizedAnnotation.isEmpty()
          && !Annotation.recognizedAnnotations.containsKey(unrecognizedAnnotation)) {
        annotationsBuilder.put(unrecognizedAnnotation, Annotation.NOT_IMPLEMENTED);
      }
    }
    return annotationsBuilder.buildOrThrow();
  }
}