error[E0119]: conflicting implementations of trait `Foo` for type `i32`
  --> $DIR/ice-124857-combine-effect-const-infer-vars.rs:10:1
   |
LL | impl const Foo for i32 {}
   | ---------------------- first implementation here
LL |
LL | impl<T> const Foo for T where T: ~const Foo {}
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `i32`

error: aborting due to 1 previous error

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