Function source_with 

pub fn source_with(
    program: &Program,
    platform: Platform,
    pool_size: usize,
    probe_count: usize,
    sources: &Sources<'_>,
    resolve: impl Fn(&str) -> Option<&'static str>,
) -> String

The exact source text one entry compiles for one host with the world’s files spliced in. resolve lets a hot-reload build prefer the checkout’s copy of the templates over the embedded ones.