warning: unnecessary braces around assigned value
  --> $DIR/unused_parens_borrow.rs:20:13
   |
LL |     let _ = { a.b };
   |             ^^^^^^^ help: remove these braces
   |
note: the lint level is defined here
  --> $DIR/unused_parens_borrow.rs:2:9
   |
LL | #![warn(unused_braces)]
   |         ^^^^^^^^^^^^^