src/test/ui/rfc-2361-dbg-macro/dbg-macro-expected-behavior.rs

   1 // run-pass
   2 // check-run-results
   3
   4 // Tests ensuring that `dbg!(expr)` has the expected run-time behavior.
   5 // as well as some compile time properties we expect.
   6
   7 #[derive(Copy, Clone, Debug)]
   8 struct Unit;
   9
  10 #[derive(Copy, Clone, Debug, PartialEq)]
  11 struct Point<T> {
  12     x: T,
  13     y: T,
  14 }
  15
  16 #[derive(Debug, PartialEq)]
  17 struct NoCopy(usize);
  18
  19 fn main() {
  20     let a: Unit = dbg!(Unit);
  21     let _: Unit = dbg!(a);
  22     // We can move `a` because it's Copy.
  23     drop(a);
  24
  25     // `Point<T>` will be faithfully formatted according to `{:#?}`.
  26     let a = Point { x: 42, y: 24 };
  27     let b: Point<u8> = dbg!(Point { x: 42, y: 24 }); // test stringify!(..)
  28     let c: Point<u8> = dbg!(b);
  29     // Identity conversion:
  30     assert_eq!(a, b);
  31     assert_eq!(a, c);
  32     // We can move `b` because it's Copy.
  33     drop(b);
  34
  35     // Without parameters works as expected.
  36     let _: () = dbg!();
  37
  38     // Test that we can borrow and that successive applications is still identity.
  39     let a = NoCopy(1337);
  40     let b: &NoCopy = dbg!(dbg!(&a));
  41     assert_eq!(&a, b);
  42
  43     // Test involving lifetimes of temporaries:
  44     fn f<'a>(x: &'a u8) -> &'a u8 { x }
  45     let a: &u8 = dbg!(f(&42));
  46     assert_eq!(a, &42);
  47
  48     // Test side effects:
  49     let mut foo = 41;
  50     assert_eq!(7331, dbg!({
  51         foo += 1;
  52         eprintln!("before");
  53         7331
  54     }));
  55     assert_eq!(foo, 42);
  56
  57     // Test trailing comma:
  58     assert_eq!(("Yeah",), dbg!(("Yeah",)));
  59
  60     // Test multiple arguments:
  61     assert_eq!((1u8, 2u32), dbg!(1,
  62                                  2));
  63
  64     // Test multiple arguments + trailing comma:
  65     assert_eq!((1u8, 2u32, "Yeah"), dbg!(1u8, 2u32,
  66                                          "Yeah",));
  67 }