error[E0502]: cannot borrow `vec` as immutable because it is also borrowed as mutable
  --> $DIR/suggest-local-var-for-vector.rs:3:9
   |
LL |     vec[vec.len() - 1] = 123;
   |     ----^^^-----------
   |     |  ||
   |     |  |immutable borrow occurs here
   |     |  mutable borrow later used here
   |     mutable borrow occurs here
   |
help: try adding a local storing this...
  --> $DIR/suggest-local-var-for-vector.rs:3:9
   |
LL |     vec[vec.len() - 1] = 123;
   |         ^^^^^^^^^
help: ...and then using that local here
  --> $DIR/suggest-local-var-for-vector.rs:3:8
   |
LL |     vec[vec.len() - 1] = 123;
   |        ^^^^^^^^^^^^^^^

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0502`.