warning: unused return value of `foo` that must be used
  --> $DIR/must-use-block-expr.rs:13:9
   |
LL |         foo();
   |         ^^^^^
   |
note: the lint level is defined here
  --> $DIR/must-use-block-expr.rs:4:9
   |
LL | #![warn(unused_must_use)]
   |         ^^^^^^^^^^^^^^^
help: use `let _ = ...` to ignore the resulting value
   |
LL |         let _ = foo();
   |         +++++++

warning: unused return value of `foo` that must be used
  --> $DIR/must-use-block-expr.rs:20:9
   |
LL |         foo()
   |         ^^^^^
   |
help: use `let _ = ...` to ignore the resulting value
   |
LL |         let _ = foo();
   |         +++++++      +

warning: unused arithmetic operation that must be used
  --> $DIR/must-use-block-expr.rs:29:9
   |
LL |         1 + 2;
   |         ^^^^^ the arithmetic operation produces a value
   |
help: use `let _ = ...` to ignore the resulting value
   |
LL |         let _ = 1 + 2;
   |         +++++++

warning: unused arithmetic operation that must be used
  --> $DIR/must-use-block-expr.rs:33:9
   |
LL |         1 + 2
   |         ^^^^^ the arithmetic operation produces a value
   |
help: use `let _ = ...` to ignore the resulting value
   |
LL |         let _ = 1 + 2;
   |         +++++++      +

warning: 4 warnings emitted