error[E0391]: unsupported cyclic reference between types/traits detected
  --> $DIR/issue-12511.rs:14:1
   |
14 | trait t2 : t1 {
   | ^^^^^^^^^^^^^ cyclic reference
   |
note: the cycle begins when computing the supertraits of `t1`...
  --> $DIR/issue-12511.rs:11:1
   |
11 | trait t1 : t2 {
   | ^^^^^^^^^^^^^
note: ...which then requires computing the supertraits of `t2`...
  --> $DIR/issue-12511.rs:11:1
   |
11 | trait t1 : t2 {
   | ^^^^^^^^^^^^^
   = note: ...which then again requires computing the supertraits of `t1`, completing the cycle.

error: aborting due to previous error