message: quick fix for components w/ optional jar
  We need tests!
diff: @@ -111,7 +111,7 @@ fn fn_configuration(args: &Args, item_fn: &syn::ItemFn) -> syn::Result<Configura
  }
  fn ingredients_for_impl(args: &Args, struct_ty: &syn::Type) -> syn::ItemImpl {
  - let jar_ty = &args.jar_ty;
  + let jar_ty = args.jar_ty();
  parse_quote! {
  impl salsa::storage::IngredientsFor for #struct_ty {
  type Ingredients = Self;
  @@ -202,7 +202,7 @@ fn ref_getter_fn(
  item_fn: &syn::ItemFn,
  struct_ty: &syn::Type,
  ) -> syn::Result<syn::ItemFn> {
  - let jar_ty = &args.jar_ty;
  + let jar_ty = args.jar_ty();
  let mut ref_getter_fn = item_fn.clone();
  ref_getter_fn.sig.ident = syn::Ident::new("get", item_fn.sig.ident.span());
  ref_getter_fn = make_fn_return_ref(ref_getter_fn)?;
  @@ -226,7 +226,7 @@ fn setter_fn(
  ) -> syn::Result<syn::ImplItemMethod> {
  // The setter has *always* the same signature as the original:
  // but it takes a value arg and has no return type.
  - let jar_ty = &args.jar_ty;
  + let jar_ty = args.jar_ty();
  let (db_var, arg_names) = fn_args(item_fn)?;
  let mut setter_sig = item_fn.sig.clone();
  let value_ty = configuration::value_ty(&item_fn.sig);
  @@ -321,7 +321,7 @@ fn accumulated_fn(
  item_fn: &syn::ItemFn,
  struct_ty: &syn::Type,
  ) -> syn::Result<syn::ItemFn> {
  - let jar_ty = &args.jar_ty;
  + let jar_ty = args.jar_ty();
  let mut accumulated_fn = item_fn.clone();
  accumulated_fn.sig.ident = syn::Ident::new("accumulated", item_fn.sig.ident.span());
  