Program: 27102
Project: 27102
Buggy source:
boolean checkEquivalenceHelper(final JSType that,EquivalenceMethod eqMethod,EqCache eqCache){
  if (this == that) {
    return true;
  }
  if (this.isNoResolvedType() && that.isNoResolvedType()) {
    if (this.isNamedType() && that.isNamedType()) {
      return Objects.equals(((NamedType)this).getReferenceName(),((NamedType)that).getReferenceName());
    }
 else {
      return true;
    }
  }
  boolean thisUnknown=isUnknownType();
  boolean thatUnknown=that.isUnknownType();
  if (thisUnknown || thatUnknown) {
    if (eqMethod == EquivalenceMethod.INVARIANT) {
      return true;
    }
 else     if (eqMethod == EquivalenceMethod.DATA_FLOW) {
      return thisUnknown && thatUnknown;
    }
 else     if (thisUnknown && thatUnknown && (isNominalType() ^ that.isNominalType())) {
      return false;
    }
  }
  if (isUnionType() && that.isUnionType()) {
    return toMaybeUnionType().checkUnionEquivalenceHelper(that.toMaybeUnionType(),eqMethod,eqCache);
  }
  if (isFunctionType() && that.isFunctionType()) {
    return toMaybeFunctionType().checkFunctionEquivalenceHelper(that.toMaybeFunctionType(),eqMethod,eqCache);
  }
  if (!getTemplateTypeMap().checkEquivalenceHelper(that.getTemplateTypeMap(),eqMethod,eqCache,SubtypingMode.NORMAL)) {
    return false;
  }
  if (eqCache.isStructuralTyping() && this.isStructuralType() && that.isStructuralType()) {
    return toMaybeObjectType().checkStructuralEquivalenceHelper(that.toMaybeObjectType(),eqMethod,eqCache);
  }
  if (isNominalType() && that.isNominalType()) {
    return getConcreteNominalTypeName(this.toObjectType()).equals(getConcreteNominalTypeName(that.toObjectType()));
  }
  if (isTemplateType() && that.isTemplateType()) {
    return false;
  }
  if (this instanceof ProxyObjectType) {
    return ((ProxyObjectType)this).getReferencedTypeInternal().checkEquivalenceHelper(that,eqMethod,eqCache);
  }
  if (that instanceof ProxyObjectType) {
    return checkEquivalenceHelper(((ProxyObjectType)that).getReferencedTypeInternal(),eqMethod,eqCache);
  }
  return false;
}

Fixed version (ground truth):
boolean checkEquivalenceHelper(final JSType that,EquivalenceMethod eqMethod,EqCache eqCache){
  if (areIdentical(this,that)) {
    return true;
  }
  if (this.isNoResolvedType() && that.isNoResolvedType()) {
    if (this.isNamedType() && that.isNamedType()) {
      return Objects.equals(((NamedType)this).getReferenceName(),((NamedType)that).getReferenceName());
    }
 else {
      return true;
    }
  }
  boolean thisUnknown=isUnknownType();
  boolean thatUnknown=that.isUnknownType();
  if (thisUnknown || thatUnknown) {
    if (eqMethod == EquivalenceMethod.INVARIANT) {
      return true;
    }
 else     if (eqMethod == EquivalenceMethod.DATA_FLOW) {
      return thisUnknown && thatUnknown;
    }
 else     if (thisUnknown && thatUnknown && (isNominalType() ^ that.isNominalType())) {
      return false;
    }
  }
  if (isUnionType() && that.isUnionType()) {
    return toMaybeUnionType().checkUnionEquivalenceHelper(that.toMaybeUnionType(),eqMethod,eqCache);
  }
  if (isFunctionType() && that.isFunctionType()) {
    return toMaybeFunctionType().checkFunctionEquivalenceHelper(that.toMaybeFunctionType(),eqMethod,eqCache);
  }
  if (!getTemplateTypeMap().checkEquivalenceHelper(that.getTemplateTypeMap(),eqMethod,eqCache,SubtypingMode.NORMAL)) {
    return false;
  }
  if (eqCache.isStructuralTyping() && this.isStructuralType() && that.isStructuralType()) {
    return toMaybeObjectType().checkStructuralEquivalenceHelper(that.toMaybeObjectType(),eqMethod,eqCache);
  }
  if (isNominalType() && that.isNominalType()) {
    return getConcreteNominalTypeName(this.toObjectType()).equals(getConcreteNominalTypeName(that.toObjectType()));
  }
  if (isTemplateType() && that.isTemplateType()) {
    return false;
  }
  if (this instanceof ProxyObjectType) {
    return ((ProxyObjectType)this).getReferencedTypeInternal().checkEquivalenceHelper(that,eqMethod,eqCache);
  }
  if (that instanceof ProxyObjectType) {
    return checkEquivalenceHelper(((ProxyObjectType)that).getReferencedTypeInternal(),eqMethod,eqCache);
  }
  return false;
}