error[E0080]: could not evaluate constant expression
  --> $DIR/infinite-recursion-const-fn.rs:16:1
   |
LL | const fn a() -> usize { b() }
   |                         ---
   |                         |
   |                         reached the configured maximum number of stack frames
   |                         inside call to `b`
LL | const fn b() -> usize { a() }
   |                         ---
   |                         |
   |                         inside call to `a`
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LL | const ARR: [i32; a()] = [5; 6]; //~ ERROR could not evaluate constant expression
   | ^^^^^^^^^^^^^^^^^---^^^^^^^^^^^
   |                  |
   |                  inside call to `a`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0080`.