review comments

src/test/ui/impl-trait/equality.stderr

@@ -12,6 +12,7 @@ LL |     0_u32
    |
    = note: to return `impl Trait`, all returned values must be of the same type
    = help: you can instead return a trait object using `Box<dyn Foo>`
+   = help: alternatively, create a new `enum` with a variant for each returned type
    = note: for information on `impl Trait`, see <https://doc.rust-lang.org/book/ch10-02-traits.html#returning-types-that-implement-traits>
    = note: for information on trait objects, see <https://doc.rust-lang.org/book/ch17-02-trait-objects.html#using-trait-objects-that-allow-for-values-of-different-types>