Decouple proc-macro server protocol from the server implementation

crates/span/src/lib.rs

@@ -358,6 +358,18 @@ impl HirFileId {
     }
 }
 
+/// Legacy span type, only defined here as it is still used by the proc-macro server.
+/// While rust-analyzer doesn't use this anymore at all, RustRover relies on the legacy type for
+/// proc-macro expansion.
+#[derive(Clone, Copy, PartialEq, Eq, Hash)]
+pub struct TokenId(pub u32);
+
+impl std::fmt::Debug for TokenId {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        self.0.fmt(f)
+    }
+}
+
 #[cfg(not(feature = "ra-salsa"))]
 mod intern_id_proxy {
     use std::fmt;