assertUnreachable (#1294)

packages/util/src/assert.ts

@@ -42,3 +42,11 @@ export function assertReturn <T> (value: T | undefined | null, message: string |
 
   return value;
 }
+
+/**
+ * @name assertUnreachable
+ * @description An assertion helper that ensures all codepaths are followed
+ */
+export function assertUnreachable (x: never): never {
+  throw new Error(`This codepath should be unreachable. Unhandled input: ${x as unknown as string}`);
+}