error[E0119]: conflicting implementations of trait `Foo` for type `(_,)`
  --> $DIR/overlap-const-with-nonconst.rs:23:1
   |
LL | / impl<T> const Foo for T
LL | | where
LL | |     T: ~const Bar,
   | |__________________- first implementation here
...
LL |   impl<T> Foo for (T,) {
   |   ^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `(_,)`

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0119`.