error: unreachable block in `if` expression
  --> $DIR/expr_if.rs:7:17
   |
LL |       if {return} {
   |  _________________^
LL | |         println!("Hello, world!");
LL | |     }
   | |_____^
   |
note: lint level defined here
  --> $DIR/expr_if.rs:4:9
   |
LL | #![deny(unreachable_code)]
   |         ^^^^^^^^^^^^^^^^

error: unreachable statement
  --> $DIR/expr_if.rs:27:5
   |
LL |     println!("But I am.");
   |     ^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

error: aborting due to 2 previous errors