Enable extra warnings required by rust-lang/rust

crates/hir-expand/src/lib.rs

@@ -4,6 +4,8 @@
 //! tree originates not from the text of some `FileId`, but from some macro
 //! expansion.
 
+#![warn(rust_2018_idioms, unused_lifetimes, semicolon_in_expressions_from_macros)]
+
 pub mod db;
 pub mod ast_id_map;
 pub mod name;