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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 com.google.javascript.rhino.jstype.JSType;

/**
 * The different strategies for matching the {@code JSType} of nodes.
 */
public enum TypeMatchingStrategy {

  /**
   * Matches type or any subtype. Matches types with different nullability/voidability. Allows loose
   * matches.
   */
  LOOSE(true, true, true),

  /**
   * Matches type or any subtype. Does not match types with different nullability/voidability.
   * Allows loose matches.
   */
  STRICT_NULLABILITY(true, false, true),

  /**
   * Matches type or any subtype. Does not match types with different nullability/voidability.
   * Does not allow loose matches.
   */
  SUBTYPES(true, false, false),

  /**
   * Does not match subtypes. Does not match types with different nullability/voidability. Does not
   * allow loose matches.
   */
  EXACT(false, false, false);

  private final boolean allowSubtypes;
  private final boolean ignoreNullability;
  private final boolean allowLooseMatches;

  private TypeMatchingStrategy(
      boolean allowSubtypes, boolean ignoreNullability, boolean allowLooseMatches) {
    this.allowSubtypes = allowSubtypes;
    this.ignoreNullability = ignoreNullability;
    this.allowLooseMatches = allowLooseMatches;
  }

  public MatchResult match(JSType templateType, JSType type) {
    if (templateType.isUnknownType()) {
      // If the template type is '?', then any type is a match and this is not considered a loose
      // match.
      return MatchResult.MATCH;
    }

    if (type == null || type.isUnknownType() || type.isAllType()) {
      return allowLooseMatches ? MatchResult.LOOSE_MATCH : MatchResult.NO_MATCH;
    }

    if (allowSubtypes) {
      if (ignoreNullability) {
        type = type.restrictByNotNullOrUndefined();
      }
      if (type.isSubtypeOf(templateType)) {
        return MatchResult.MATCH;
      }
    }

    boolean nullableMismatch = templateType.isNullable() != type.isNullable();
    boolean voidableMismatch = templateType.isVoidable() != type.isVoidable();
    if (!ignoreNullability && (nullableMismatch || voidableMismatch)) {
      return MatchResult.NO_MATCH;
    }

    return type.equals(templateType) ? MatchResult.MATCH : MatchResult.NO_MATCH;
  }

  /**
   * The result of comparing two different {@code JSType} instances.
   */
  public enum MatchResult {
    MATCH,
    NO_MATCH,
    LOOSE_MATCH;


    public boolean isMatch() {
      return this != NO_MATCH;
    }

    public boolean isLooseMatch() {
      return this == LOOSE_MATCH;
    }
  }
}