Add workaround for #9562

This treats the consts generated by older synstructure versions like
unnamed consts. We should remove this at some point (at least after
Chalk has switched).

Author: flodiebold

crates/hir_def/src/item_tree/lower.rs

@@ -448,7 +448,12 @@ impl<'a> Ctx<'a> {
     }
 
     fn lower_const(&mut self, konst: &ast::Const) -> FileItemTreeId<Const> {
-        let name = konst.name().map(|it| it.as_name());
+        let mut name = konst.name().map(|it| it.as_name());
+        if name.as_ref().map_or(false, |n| n.to_string().starts_with("_DERIVE_")) {
+            // FIXME: this is a hack to treat consts generated by synstructure as unnamed
+            // remove this some time in the future
+            name = None;
+        }
         let type_ref = self.lower_type_ref_opt(konst.ty());
         let visibility = self.lower_visibility(konst);
         let ast_id = self.source_ast_id_map.ast_id(konst);