error[E0499]: cannot borrow `active` as mutable more than once at a time
  --> tests/ui/dca_dbuf_bank_guard_double.rs:27:15
   |
22 |     let g1 = active.bank_guard(&mut ctx, Bank::M0);
   |              ------ first mutable borrow occurs here
...
27 |     let _g2 = active.bank_guard(&mut ctx, Bank::M1);
   |               ^^^^^^ second mutable borrow occurs here
28 |     let _ = g1.bank();
   |             -- first borrow later used here
