error[E0391]: cycle detected when const-evaluating + checking `a`
  --> $DIR/infinite-recursion-const-fn.rs:3:1
   |
LL | const fn a() -> usize {
   | ^^^^^^^^^^^^^^^^^^^^^
   |
note: ...which requires const-evaluating + checking `b`...
  --> $DIR/infinite-recursion-const-fn.rs:7:1
   |
LL | const fn b() -> usize {
   | ^^^^^^^^^^^^^^^^^^^^^
   = note: ...which again requires const-evaluating + checking `a`, completing the cycle
note: cycle used when const-evaluating + checking `ARR::{constant#0}`
  --> $DIR/infinite-recursion-const-fn.rs:10:18
   |
LL | const ARR: [i32; a()] = [5; 6];
   |                  ^^^

error: aborting due to previous error

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