Recognize underscore token to avoid slow path

src/lib.rs

@@ -1074,6 +1074,10 @@ macro_rules! quote_token {
         $crate::__private::push_literal(&mut $tokens, stringify!($literal));
     };
 
+    ($tokens:ident _) => {
+        $crate::__private::push_underscore(&mut $tokens);
+    };
+
     ($tokens:ident $other:tt) => {
         $crate::__private::parse(&mut $tokens, stringify!($other));
     };
@@ -1297,6 +1301,10 @@ macro_rules! quote_token_spanned {
         $crate::__private::push_literal_spanned(&mut $tokens, $span, stringify!($literal));
     };
 
+    ($tokens:ident $span:ident _) => {
+        $crate::__private::push_underscore_spanned(&mut $tokens, $span);
+    };
+
     ($tokens:ident $span:ident $other:tt) => {
         $crate::__private::parse_spanned(&mut $tokens, $span, stringify!($other));
     };

src/runtime.rs

@@ -396,6 +396,14 @@ push_punct!(push_star push_star_spanned '*');
 push_punct!(push_sub push_sub_spanned '-');
 push_punct!(push_sub_eq push_sub_eq_spanned '-' '=');
 
+pub fn push_underscore(tokens: &mut TokenStream) {
+    push_underscore_spanned(tokens, Span::call_site());
+}
+
+pub fn push_underscore_spanned(tokens: &mut TokenStream, span: Span) {
+    tokens.append(Ident::new("_", span));
+}
+
 // Helper method for constructing identifiers from the `format_ident!` macro,
 // handling `r#` prefixes.
 //