Function ffi_build 

pub unsafe fn ffi_build<F>(
    schema_ptr: *const u8,
    schema_len: usize,
    config_ptr: *const u8,
    config_len: usize,
    build_fn: F,
) -> *mut u8
where
    F: Fn(Schema, JSON, &Utils) -> Vec<OutputFile>,

Helper for implementing _build WASM export

Safety

This function is unsafe because it works with raw pointers from WASM.