Tracking uninhabited types in matches

[Victor-Savu]

I think there has been a regression for the treatment of uninhabited types at some point:

#![feature(never_type)]

fn foo() ->  Result<(), !> {
    return Ok(());
}

fn main() {
    match foo() {
        Ok(_) => println!("yay!")
    }
}

now fails with:

error[E0004]: non-exhaustive patterns: `Err(_)` not covered
 --> src/main.rs:7:11
  |
7 |     match foo() {
  |           ^^^^^ pattern `Err(_)` not covered

I will bisect and report back when I find the commit which caused the regression.

Last known to work on:

• nightly-2018-03-15

Was already failing on:

• nightly-2018-04-01

[Victor-Savu]

Turns out the "problem" was introduced in #47630 which attempted to stabilize never_type and leave only this particular case under the exhaustive_patterns feature gate. When that PR was subsequently reverted in #49691, the split in feature gates was not reverted, so now the code above needs both features:

#![feature(never_type)]
#![feature(exhaustive_patterns)]

fn foo() ->  Result<(), !> {
    return Ok(());
}

fn main() {
    match foo() {
        Ok(_) => println!("yay!")
    }
}

I think this issue is not really relevant anymore, but I am afraid that this could be confusing. I look forward to the stabilization of both features, when all of this will go away :)