required function argument handling

[schmurfy]

I have a helper.libsonnet file containing this:

function(a, b)
{ sum: a+b }

I get a "Missing argument error" which is correct but quite useless, how can I give the language server a useable default without having to resort to writing that:

function(a = 0, b = 0)
{ sum: a+b }

it works but I don't want these arguments to be optional, is there a way to do that in a way on visible to the language server maybe ?