Function derive_deftly_engine_func_macro 

pub fn derive_deftly_engine_func_macro(
    input: TokenStream,
) -> Result<TokenStream>

derive_deftly_engine! – implements the actual template engine

In my design, the input contains, firstly, literally the definition that #[derive(Deftly)] was applied to (see NOTES.txt). Using the literal input, rather than some pre-parsed version, is slower, but means that we aren’t inventing a nontrivial data format which potentially crosses crate boundaries with semver implications.