error[E0391]: cycle detected when computing the supertraits of `T1`
  --> $DIR/issue-12511.rs:1:12
   |
LL | trait T1 : T2 {
   |            ^^
   |
note: ...which requires computing the supertraits of `T2`...
  --> $DIR/issue-12511.rs:5:12
   |
LL | trait T2 : T1 {
   |            ^^
   = note: ...which again requires computing the supertraits of `T1`, completing the cycle

error: aborting due to previous error

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