WIX check if a file exists during build time

I'm looking for a way to check if a file exists while building an MSI with WIX.

Here is a similar question but in contrast, I don't have a variable with the information yet but am looking for a WIX command which can do the check at compile time rather than checking somewhere else and putting the result in a variable like in the question linked.

If there's none, what would be the simplest option?