error[E0596]: cannot borrow `self` as mutable, as it is not declared as mutable
  --> $DIR/issue-31424.rs:7:9
   |
LL |         (&mut self).bar();
   |         ^^^^^^^^^^^ cannot borrow as mutable
   |
note: the binding is already a mutable borrow
  --> $DIR/issue-31424.rs:6:12
   |
LL |     fn foo(&mut self) {
   |            ^^^^^^^^^
help: try removing `&mut` here
  --> $DIR/issue-31424.rs:7:9
   |
LL |         (&mut self).bar();
   |         ^^^^^^^^^^^

warning: function cannot return without recursing
  --> $DIR/issue-31424.rs:13:5
   |
LL |     fn bar(self: &mut Self) {
   |     ^^^^^^^^^^^^^^^^^^^^^^^ cannot return without recursing
...
LL |         (&mut self).bar();
   |         ----------------- recursive call site
   |
   = note: `#[warn(unconditional_recursion)]` on by default
   = help: a `loop` may express intention better if this is on purpose

error[E0596]: cannot borrow `self` as mutable, as it is not declared as mutable
  --> $DIR/issue-31424.rs:16:9
   |
LL |         (&mut self).bar();
   |         ^^^^^^^^^^^ cannot borrow as mutable
   |
note: the binding is already a mutable borrow
  --> $DIR/issue-31424.rs:13:18
   |
LL |     fn bar(self: &mut Self) {
   |                  ^^^^^^^^^
help: try removing `&mut` here
  --> $DIR/issue-31424.rs:16:9
   |
LL |         (&mut self).bar();
   |         ^^^^^^^^^^^

error: aborting due to 2 previous errors; 1 warning emitted

For more information about this error, try `rustc --explain E0596`.