Need a lifetime hint for E0409 "variable is bound inconsistently"

[cuviper]

From https://users.rust-lang.org/t/how-to-match-t-and-t-in-the-same-arm/83835

Given the following code: playground

enum Foo<'a, T> {
    A,
    B(T),
    C(&'a T),
}

fn main() {
    let foo = Foo::<'static, ()>::A;
    
    match foo {
        Foo::A => {},
        Foo::B(ref t) | Foo::C(t) => todo!(),
    }
}

The current output is:

error[E0409]: variable `t` is bound inconsistently across alternatives separated by `|`
  --> src/main.rs:12:32
   |
12 |         Foo::B(ref t) | Foo::C(t) => todo!(),
   |                    -           ^ bound in different ways
   |                    |
   |                    first binding

The cause of the error is a lifetime difference, where B(ref t) binds &'_ T (for some local lifetime) and C(t) binds &'static T. It would be nice to have a hint about this, possibly suggesting a fix into C(&ref t) to reborrow that reference.

(Even better if the language/compiler could make that happen automatically!)

[cuviper]

Actually, now that I've re-read the E0409 help, is it actually insisting on having ref in all the same places, regardless of lifetime? Then I'm not sure what the hint should be, but it was confusing to the user -- "isn't t bound to an &T in both cases?" I suppose the error could be more explicit, "this one has ref and this one doesn't."

[estebank]

The requirement for all cases to be ref happens too early and ignores what the actual types are (and I believe, the restriction should be lifted as long as the actual types match on each binding, but that falls under t-lang's purview). In the meantime the actual suggestion should be for Foo:C(&ref t), sadly.