Add a useful assertion.

rust-lang · Mar 11, 2022 · 9f0798b · 9f0798b
1 parent 4d4baf7
commit 9f0798b
Showing 1 changed file with 2 additions and 0 deletions.
diff --git a/compiler/rustc_expand/src/mbe/macro_parser.rs b/compiler/rustc_expand/src/mbe/macro_parser.rs
@@ -521,6 +521,8 @@ fn inner_parse_loop<'root, 'tt>(
             // then we could be at the end of a sequence or at the beginning of the next
             // repetition.
             if let Some(repetition) = &item.repetition {
+                debug_assert!(matches!(item.top_elts, Tt(TokenTree::Sequence(..))));
+
                 // At this point, regardless of whether there is a separator, we should add all
                 // matches from the complete repetition of the sequence to the shared, top-level
                 // `matches` list (actually, `up.matches`, which could itself not be the top-level,