wrap unimplemented ser/de branches with internal macro

Signed-off-by: Jason Volk <jason@zemos.net>

src/database/util.rs

@@ -1,6 +1,29 @@
 use conduit::{err, Result};
 use rocksdb::{Direction, IteratorMode};
 
+//#[cfg(debug_assertions)]
+macro_rules! unhandled {
+	($msg:literal) => {
+		unimplemented!($msg)
+	};
+}
+
+// activate when stable; we're not ready for this yet
+#[cfg(disable)] // #[cfg(not(debug_assertions))]
+macro_rules! unhandled {
+	($msg:literal) => {
+		// SAFETY: Eliminates branches for serializing and deserializing types never
+		// encountered in the codebase. This can promote optimization and reduce
+		// codegen. The developer must verify for every invoking callsite that the
+		// unhandled type is in no way involved and could not possibly be encountered.
+		unsafe {
+			std::hint::unreachable_unchecked();
+		}
+	};
+}
+
+pub(crate) use unhandled;
+
 #[inline]
 pub(crate) fn _into_direction(mode: &IteratorMode<'_>) -> Direction {
 	use Direction::{Forward, Reverse};