warning: the feature `const_generics` is incomplete and may cause the compiler to crash
  --> $DIR/issue-62187-encountered-polymorphic-const.rs:3:12
   |
LL | #![feature(const_generics)]
   |            ^^^^^^^^^^^^^^
   |
   = note: `#[warn(incomplete_features)]` on by default

warning: unused variable: `foo`
  --> $DIR/issue-62187-encountered-polymorphic-const.rs:15:9
   |
LL |     let foo = <[u8; 2]>::BIT_LEN;
   |         ^^^ help: consider prefixing with an underscore: `_foo`
   |
   = note: `#[warn(unused_variables)]` on by default