Add a special function that evaluates nicely with undefined arguments.

[gusega]

Hi

I have the following policy:

allow if count(errs) == 0
valid_document if {
...
}
errs contains sprintf("document must be %v but is %v", ["expected", input.document.something]) if {
    not valid_document
}

Unfortuntaly, if input.document.something is undefined, then errs is empty.

Could you please add a function that allows passing undefined documents and does something nice with them, like replace their value with <undefined> or something like that.

For example:
if input.document.something is undefined then

undef.sprintf("document must be %v but is %v", ["expected", input.document.something])

returns document must be expected but is <undefined>

Thank you.

[anderseknert]

Hi there! There are a few ways you can achieve that with existing language constructs, but if you're looking for a built-in function specifically, object.get would be one to reach for here.

errs contains sprintf("document must be %v but is %v", ["expected", something]) if {
    not valid_document
    something := object.get(input, ["document", "something"], "<undefined>")
}