reintroduce lock

src/lib.rs

@@ -4,6 +4,11 @@ use crate::types::{InputCause, InputTypeFlags, ProcessingResult};
 
 pub mod types;
 
+
+// error out specifically if no backend is chosen
+#[cfg(not(any(feature="backend_piston", feature="backend_gilrs")))]	
+compile_error!("No backend selected, use features=<backend> in Cargo.toml or --features <backend> when building directly.");
+
 #[cfg(feature="backend_piston")]
 pub mod backend_piston;
 #[cfg(feature="backend_gilrs")]