error[E0391]: cycle detected when simplifying constant for the type system `Tr::A`
  --> $DIR/defaults-cyclic-fail.rs:5:5
   |
LL |     const A: u8 = Self::B;
   |     ^^^^^^^^^^^
   |
note: ...which requires const-evaluating + checking `Tr::A`...
  --> $DIR/defaults-cyclic-fail.rs:5:19
   |
LL |     const A: u8 = Self::B;
   |                   ^^^^^^^
note: ...which requires simplifying constant for the type system `Tr::B`...
  --> $DIR/defaults-cyclic-fail.rs:8:5
   |
LL |     const B: u8 = Self::A;
   |     ^^^^^^^^^^^
note: ...which requires const-evaluating + checking `Tr::B`...
  --> $DIR/defaults-cyclic-fail.rs:8:19
   |
LL |     const B: u8 = Self::A;
   |                   ^^^^^^^
   = note: ...which again requires simplifying constant for the type system `Tr::A`, completing the cycle
note: cycle used when optimizing promoted MIR for `main`
  --> $DIR/defaults-cyclic-fail.rs:16:16
   |
LL |     assert_eq!(<() as Tr>::A, 0);
   |                ^^^^^^^^^^^^^
   = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0391`.