error[E0015]: calls in constants are limited to constant functions, tuple structs and tuple variants
 --> $DIR/generic_const_fail.rs:8:51
  |
8 | const _PATH: KeyPath<Container<String>, String> = keypath!(Container<String>.names[0]);
  |                                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)