error[E0391]: unsupported cyclic reference between types/traits detected
  --> $DIR/issue-23305.rs:15:12
   |
15 | impl ToNbt<Self> {}
   |            ^^^^ cyclic reference
   |
note: the cycle begins when processing `<impl at $DIR/issue-23305.rs:15:1: 15:20>`...
  --> $DIR/issue-23305.rs:15:1
   |
15 | impl ToNbt<Self> {}
   | ^^^^^^^^^^^^^^^^^^^
   = note: ...which then again requires processing `<impl at $DIR/issue-23305.rs:15:1: 15:20>`, completing the cycle.

error: aborting due to previous error