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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. This binary checks for style issues such as incorrect or missing JSDoc usage, and missing goog.require() statements. It does not do more advanced checks such as typechecking.

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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;

import com.google.javascript.rhino.FunctionTypeI;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.ObjectTypeI;
import com.google.javascript.rhino.TypeI;
import java.util.Iterator;
import java.util.List;
import java.util.Objects;

/**
 * Signals that the first type and the second type have been
 * used interchangeably.
 *
 * Type-based optimizations should take this into account
 * so that they don't wreck code with type warnings.
 */
class TypeMismatch {
  final TypeI typeA;
  final TypeI typeB;
  final JSError src;

  /**
   * It's the responsibility of the class that creates the
   * {@code TypeMismatch} to ensure that {@code a} and {@code b} are
   * non-matching types.
   */
  TypeMismatch(TypeI a, TypeI b, JSError src) {
    this.typeA = a;
    this.typeB = b;
    this.src = src;
  }

  static void registerIfMismatch(
      List mismatches, List implicitInterfaceUses,
      TypeI found, TypeI required, JSError error) {
    if (found != null && required != null && !found.isSubtypeWithoutStructuralTyping(required)) {
      registerMismatch(mismatches, implicitInterfaceUses, found, required, error);
    }
  }

  static void registerMismatch(
      List mismatches, List implicitInterfaceUses,
      TypeI found, TypeI required, JSError error) {
    // Don't register a mismatch for differences in null or undefined or if the
    // code didn't downcast.
    found = removeNullUndefinedAndTemplates(found);
    required = removeNullUndefinedAndTemplates(required);
    if (found.isSubtypeOf(required) || required.isSubtypeOf(found)) {
      boolean strictMismatch =
          !found.isSubtypeWithoutStructuralTyping(required)
          && !required.isSubtypeWithoutStructuralTyping(found);
      if (strictMismatch) {
        implicitInterfaceUses.add(new TypeMismatch(found, required, error));
      }
      return;
    }

    mismatches.add(new TypeMismatch(found, required, error));

    if (found.isFunctionType() && required.isFunctionType()) {
      FunctionTypeI fnTypeA = found.toMaybeFunctionType();
      FunctionTypeI fnTypeB = required.toMaybeFunctionType();
      Iterator paramItA = fnTypeA.getParameterTypes().iterator();
      Iterator paramItB = fnTypeB.getParameterTypes().iterator();
      while (paramItA.hasNext() && paramItB.hasNext()) {
        TypeMismatch.registerIfMismatch(
            mismatches, implicitInterfaceUses, paramItA.next(), paramItB.next(), error);
      }
      TypeMismatch.registerIfMismatch(
          mismatches, implicitInterfaceUses,
          fnTypeA.getReturnType(), fnTypeB.getReturnType(), error);
    }
  }

  static void recordImplicitUseOfNativeObject(
      List mismatches, Node src, TypeI sourceType, TypeI targetType) {
    sourceType = sourceType.restrictByNotNullOrUndefined();
    targetType = targetType.restrictByNotNullOrUndefined();
    if (sourceType.isInstanceofObject()
        && !targetType.isInstanceofObject() && !targetType.isUnknownType()) {
      // We don't report a type error, but we still need to construct a JSError,
      // for people who enable the invalidation diagnostics in DisambiguateProperties.
      String msg = "Implicit use of Object type: " + sourceType + " as type: " + targetType;
      JSError err = JSError.make(src, TypeValidator.TYPE_MISMATCH_WARNING, msg);
      mismatches.add(new TypeMismatch(sourceType, targetType, err));
    }
  }

  static void recordImplicitInterfaceUses(
      List implicitInterfaceUses, Node src, TypeI sourceType, TypeI targetType) {
    sourceType = removeNullUndefinedAndTemplates(sourceType);
    targetType = removeNullUndefinedAndTemplates(targetType);
    if (targetType.isUnknownType()) {
      return;
    }
    boolean strictMismatch =
        !sourceType.isSubtypeWithoutStructuralTyping(targetType)
        && !targetType.isSubtypeWithoutStructuralTyping(sourceType);
    boolean mismatch = !sourceType.isSubtypeOf(targetType) && !targetType.isSubtypeOf(sourceType);
    if (strictMismatch || mismatch) {
      // We don't report a type error, but we still need to construct a JSError,
      // for people who enable the invalidation diagnostics in DisambiguateProperties.
      // Use the empty string as the error string. Creating an actual error message can be slow
      // for large types; we create an error string lazily in DisambiguateProperties.
      JSError err = JSError.make(src, TypeValidator.TYPE_MISMATCH_WARNING, "");
      implicitInterfaceUses.add(new TypeMismatch(sourceType, targetType, err));
    }
  }

  private static TypeI removeNullUndefinedAndTemplates(TypeI t) {
    TypeI result = t.restrictByNotNullOrUndefined();
    ObjectTypeI obj = result.toMaybeObjectType();
    if (obj != null && obj.isGenericObjectType()) {
      return obj.instantiateGenericsWithUnknown();
    }
    return result;
  }

  @Override public boolean equals(Object object) {
    if (object instanceof TypeMismatch) {
      TypeMismatch that = (TypeMismatch) object;
      return (that.typeA.equals(this.typeA) && that.typeB.equals(this.typeB))
          || (that.typeB.equals(this.typeA) && that.typeA.equals(this.typeB));
    }
    return false;
  }

  @Override public int hashCode() {
    return Objects.hash(typeA, typeB);
  }

  @Override public String toString() {
    return "(" + typeA + ", " + typeB + ")";
  }
}