Comment ext::tt::transcribe

src/libsyntax/ext/tt/macro_parser.rs

@@ -554,7 +554,10 @@ fn inner_parse_loop<'root, 'tt>(
             match item.top_elts.get_tt(idx) {
                 // Need to descend into a sequence
                 TokenTree::Sequence(sp, seq) => {
-                    // Examine the case where there are 0 matches of this sequence
+                    // Examine the case where there are 0 matches of this sequence. We are
+                    // implicitly disallowing OneOrMore from having 0 matches here. Thus, that will
+                    // result in a "no rules expected token" error by virtue of this matcher not
+                    // working.
                     if seq.op == quoted::KleeneOp::ZeroOrMore
                         || seq.op == quoted::KleeneOp::ZeroOrOne
                     {

src/libsyntax/ext/tt/macro_rules.rs

@@ -151,7 +151,7 @@ fn generic_extension<'cx>(cx: &'cx mut ExtCtxt<'_>,
 
                 let rhs_spans = rhs.iter().map(|t| t.span()).collect::<Vec<_>>();
                 // rhs has holes ( `$id` and `$(...)` that need filled)
-                let mut tts = transcribe(cx, Some(named_matches), rhs);
+                let mut tts = transcribe(cx, &named_matches, rhs);
 
                 // Replace all the tokens for the corresponding positions in the macro, to maintain
                 // proper positions in error reporting, while maintaining the macro_backtrace.

src/libsyntax/ext/tt/quoted.rs

@@ -73,6 +73,7 @@ pub enum KleeneOp {
     ZeroOrMore,
     /// Kleene plus (`+`) for one or more repetitions
     OneOrMore,
+    /// Kleene optional (`?`) for zero or one reptitions
     ZeroOrOne,
 }