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compiler/rustc_borrowck/src/diagnostics/mod.rs

@@ -687,6 +687,9 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
             return;
         };
 
+        // Look for the where-bound which introduces the placeholder.
+        // As we're using the HIR, we need to handle both `for<'a> T: Trait<'a>`
+        // and `T: for<'a> Trait`<'a>.
         for pred in generics.predicates {
             let WherePredicateKind::BoundPredicate(WhereBoundPredicate {
                 bound_generic_params,

compiler/rustc_borrowck/src/diagnostics/region_errors.rs

@@ -236,7 +236,9 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
             .collect::<Vec<_>>();
         debug!(?gat_id_and_generics);
 
-        // find higher-ranked trait bounds bounded to the generic associated types
+        // Look for the where-bound which introduces the placeholder.
+        // As we're using the HIR, we need to handle both `for<'a> T: Trait<'a>`
+        // and `T: for<'a> Trait`<'a>.
         let mut hrtb_bounds = vec![];
         gat_id_and_generics.iter().flatten().for_each(|&(gat_hir_id, generics)| {
             for pred in generics.predicates {