static int joinVariables(@NotNull Document document,
                           @NotNull PsiElement elementAtStartLineEnd,
                           @NotNull PsiVariable firstVar,
                           @NotNull PsiVariable secondVar) {
    PsiTypeElement firstTypeElement = firstVar.getTypeElement();
    if (firstTypeElement == null || firstTypeElement.isInferredType()) return -1;
    PsiTypeElement secondTypeElement = secondVar.getTypeElement();
    if (secondTypeElement == null || secondTypeElement.isInferredType()) return -1;
    if (!PsiEquivalenceUtil.areElementsEquivalent(firstTypeElement, secondTypeElement)) return -1;
    PsiModifierList firstModifiers = firstVar.getModifierList();
    PsiModifierList secondModifiers = secondVar.getModifierList();
    if (firstModifiers == null) {
      if (secondModifiers != null) return -1;
    }
    else {
      if (secondModifiers == null || !PsiEquivalenceUtil.areElementsEquivalent(firstModifiers, secondModifiers)) return -1;
    }

    int startOffset = elementAtStartLineEnd.getTextRange().getStartOffset();
    int endOffset = secondTypeElement.getTextRange().getEndOffset();
    document.replaceString(startOffset, endOffset, ",");
    return startOffset;
  }
static int joinVariables(@NotNull Document document,
                           @NotNull PsiElement elementAtStartLineEnd,
                           @NotNull PsiVariable firstVar,
                           @NotNull PsiVariable secondVar)