warning: unreachable block in `if` or `while` expression
  --> $DIR/if-ret.rs:5:24
   |
LL | fn foo() { if (return) { } }
   |               -------- ^^^ unreachable block in `if` or `while` expression
   |               |
   |               any code following this expression is unreachable
   |
   = note: `#[warn(unreachable_code)]` (part of `#[warn(unused)]`) on by default

warning: 1 warning emitted