match_ast! takes a pattern to allow underscore usage

crates/syntax/src/lib.rs

@@ -242,7 +242,7 @@ macro_rules! match_ast {
     (match $node:ident { $($tt:tt)* }) => { match_ast!(match ($node) { $($tt)* }) };
 
     (match ($node:expr) {
-        $( ast::$ast:ident($it:ident) => $res:expr, )*
+        $( ast::$ast:ident($it:pat) => $res:expr, )*
         _ => $catch_all:expr $(,)?
     }) => {{
         $( if let Some($it) = ast::$ast::cast($node.clone()) { $res } else )*