Check equivalence of indices in more cases

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -2116,7 +2116,13 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     None
                 }
             }) else {
-                note_default_suggestion();
+                let hir::Node::Expr(parent) = tcx.parent_hir_node(index1.hir_id) else { return };
+                let hir::ExprKind::Index(_, idx1, _) = parent.kind else { return };
+                let hir::Node::Expr(parent) = tcx.parent_hir_node(index2.hir_id) else { return };
+                let hir::ExprKind::Index(_, idx2, _) = parent.kind else { return };
+                if !idx1.equals(idx2) {
+                    err.help("use `.split_at_mut(position)` to obtain two mutable non-overlapping sub-slices");
+                }
                 return;
             };
 

tests/ui/suggestions/suggest-split-at-mut.stderr

@@ -8,8 +8,7 @@ LL |     let b = &mut foo[3];
 LL |     *a = 5;
    |     ------ first borrow later used here
    |
-   = help: consider using `.split_at_mut(position)` or similar method to obtain two mutable non-overlapping sub-slices
-   = help: consider using `.swap(index_1, index_2)` to swap elements at the specified indices
+   = help: use `.split_at_mut(position)` to obtain two mutable non-overlapping sub-slices
 
 error[E0499]: cannot borrow `foo` as mutable more than once at a time
   --> $DIR/suggest-split-at-mut.rs:13:18
@@ -59,8 +58,7 @@ LL |     *b = 6;
 LL |     println!("{:?} {:?}", a, b);
    |                           - immutable borrow later used here
    |
-   = help: consider using `.split_at_mut(position)` or similar method to obtain two mutable non-overlapping sub-slices
-   = help: consider using `.swap(index_1, index_2)` to swap elements at the specified indices
+   = help: use `.split_at_mut(position)` to obtain two mutable non-overlapping sub-slices
 
 error[E0502]: cannot borrow `foo[_]` as immutable because it is also borrowed as mutable
   --> $DIR/suggest-split-at-mut.rs:46:13
@@ -72,8 +70,7 @@ LL |     let b = &foo[2];
 LL |     *a = 5;
    |     ------ mutable borrow later used here
    |
-   = help: consider using `.split_at_mut(position)` or similar method to obtain two mutable non-overlapping sub-slices
-   = help: consider using `.swap(index_1, index_2)` to swap elements at the specified indices
+   = help: use `.split_at_mut(position)` to obtain two mutable non-overlapping sub-slices
 
 error[E0502]: cannot borrow `foo` as immutable because it is also borrowed as mutable
   --> $DIR/suggest-split-at-mut.rs:54:14