[WIP] light + improve

Author: petrochenkov

compiler/rustc_expand/src/mbe/transcribe.rs

@@ -347,7 +347,23 @@ fn maybe_use_metavar_location(
     metavar_span: Span,
     orig_tt: &TokenTree,
 ) -> TokenTree {
-    let insert = |mspans: &mut FxHashMap<_, _>, s, ms| mspans.try_insert(s, ms).is_ok();
+    let undelimited_seq = matches!(
+        stack.last(),
+        Some(Frame::Sequence {
+            tts: [_],
+            sep: None,
+            kleene_op: KleeneOp::ZeroOrMore | KleeneOp::OneOrMore,
+            ..
+        })
+    );
+    if undelimited_seq {
+        return orig_tt.clone();
+    }
+
+    let insert = |mspans: &mut FxHashMap<_, _>, s, ms| match mspans.try_insert(s, ms) {
+        Ok(_) => true,
+        Err(err) => *err.entry.get() == ms,
+    };
     let no_collision = match orig_tt {
         TokenTree::Token(token, ..) => {
             with_metavar_spans(|mspans| insert(mspans, token.span, metavar_span))
@@ -358,18 +374,7 @@ fn maybe_use_metavar_location(
                 && insert(mspans, dspan.entire(), metavar_span)
         }),
     };
-    let undelimited_seq = || {
-        matches!(
-            stack.last(),
-            Some(Frame::Sequence {
-                tts: [_],
-                sep: None,
-                kleene_op: KleeneOp::ZeroOrMore | KleeneOp::OneOrMore,
-                ..
-            })
-        )
-    };
-    if no_collision || undelimited_seq() || cx.source_map().is_imported(metavar_span) {
+    if no_collision || cx.source_map().is_imported(metavar_span) {
         return orig_tt.clone();
     }
 

tests/ui/impl-trait/impl-trait-in-macro.stderr

@@ -2,7 +2,7 @@ error[E0308]: mismatched types
   --> $DIR/impl-trait-in-macro.rs:9:9
    |
 LL |     ($($tr:tt)*) => { impl $($tr)* };
-   |                       ----------
+   |                       ----
    |                       |
    |                       expected type parameter
    |                       found type parameter