Stop calling visitors V

compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs

@@ -540,19 +540,23 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
         }
     }
 
+    /// Suggest `map[k] = v` => `map.insert(k, v)` and the like.
     fn suggest_map_index_mut_alternatives(&self, ty: Ty<'tcx>, err: &mut Diag<'tcx>, span: Span) {
         let Some(adt) = ty.ty_adt_def() else { return };
         let did = adt.did();
         if self.infcx.tcx.is_diagnostic_item(sym::HashMap, did)
             || self.infcx.tcx.is_diagnostic_item(sym::BTreeMap, did)
         {
-            struct V<'a, 'tcx> {
+            /// Walks through the HIR, looking for the corresponding span for this error.
+            /// When it finds it, see if it corresponds to assignment operator whose LHS
+            /// is an index expr.
+            struct SuggestIndexOperatorAlternativeVisitor<'a, 'tcx> {
                 assign_span: Span,
                 err: &'a mut Diag<'tcx>,
                 ty: Ty<'tcx>,
                 suggested: bool,
             }
-            impl<'a, 'tcx> Visitor<'tcx> for V<'a, 'tcx> {
+            impl<'a, 'tcx> Visitor<'tcx> for SuggestIndexOperatorAlternativeVisitor<'a, 'tcx> {
                 fn visit_stmt(&mut self, stmt: &'tcx hir::Stmt<'tcx>) {
                     hir::intravisit::walk_stmt(self, stmt);
                     let expr = match stmt.kind {
@@ -645,7 +649,12 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
             let Some(body_id) = hir_map.maybe_body_owned_by(local_def_id) else { return };
             let body = self.infcx.tcx.hir().body(body_id);
 
-            let mut v = V { assign_span: span, err, ty, suggested: false };
+            let mut v = SuggestIndexOperatorAlternativeVisitor {
+                assign_span: span,
+                err,
+                ty,
+                suggested: false,
+            };
             v.visit_body(body);
             if !v.suggested {
                 err.help(format!(