Regression "pattern _ not covered" in objc-encode-0.0.2, Rust 1.16

[brson]

brian@ip-10-145-43-250:~/dev/rust-objc-encode⟫ git remote -v
origin  https://github.com/SSheldon/rust-objc-encode (fetch)
origin  https://github.com/SSheldon/rust-objc-encode (push)
brian@ip-10-145-43-250:~/dev/rust-objc-encode⟫ git log -1
commit 1e377bf4481835767a5e31aa5480aa8ac91b56de
Author: Steven Sheldon <steven@sasheldon.com>
Date:   Sun Feb 19 16:43:21 2017 -0800

    Bumped to version 0.0.2

error[E0004]: non-exhaustive patterns: `_` not covered
  --> src/encoding/never.rs:16:15
   |
16 |         match self { }
   |               ^^^^ pattern `_` not covered

error[E0004]: non-exhaustive patterns: `_` not covered
  --> src/encoding/never.rs:22:15
   |
22 |         match self { }
   |               ^^^^ pattern `_` not covered

error[E0004]: non-exhaustive patterns: `_` not covered
  --> src/encoding/never.rs:26:15
   |
26 |         match self { }
   |               ^^^^ pattern `_` not covered

error[E0004]: non-exhaustive patterns: `_` not covered
  --> src/encoding/never.rs:32:15
   |
32 |         match self { }
   |               ^^^^ pattern `_` not covered

error: aborting due to 4 previous errors

error: build failed

The type is defined as

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum Never { }

cc @SSheldon

[brson]

Actually, on beta.3 the error is

error[E0004]: non-exhaustive patterns: type &encoding::never::Never is non-empty
  --> src/encoding/never.rs:16:15
   |
16 |         match self { }
   |               ^^^^
   |
help: Please ensure that all possible cases are being handled; possibly adding wildcards or more match arms.
  --> src/encoding/never.rs:16:15
   |
16 |         match self { }
   |               ^^^^

error[E0004]: non-exhaustive patterns: type &encoding::never::Never is non-empty
  --> src/encoding/never.rs:22:15
   |
22 |         match self { }
   |               ^^^^
   |
help: Please ensure that all possible cases are being handled; possibly adding wildcards or more match arms.
  --> src/encoding/never.rs:22:15
   |
22 |         match self { }
   |               ^^^^

error[E0004]: non-exhaustive patterns: type &encoding::never::Never is non-empty
  --> src/encoding/never.rs:26:15
   |
26 |         match self { }
   |               ^^^^
   |
help: Please ensure that all possible cases are being handled; possibly adding wildcards or more match arms.
  --> src/encoding/never.rs:26:15
   |
26 |         match self { }
   |               ^^^^

error[E0004]: non-exhaustive patterns: type &encoding::never::Never is non-empty
  --> src/encoding/never.rs:32:15
   |
32 |         match self { }
   |               ^^^^
   |
help: Please ensure that all possible cases are being handled; possibly adding wildcards or more match arms.
  --> src/encoding/never.rs:32:15
   |
32 |         match self { }
   |               ^^^^

error: aborting due to 4 previous errors

error: build failed

[SSheldon]

Also commented on #38972 about this, wasn't sure if it was covered by that issue or not though: #38972 (comment)

As far as I know, this should also impact the Void crate, which is used by more stuff

[SSheldon]

Ah actually, nevermind, the difference is that the void crate matches a value, where I was matching a reference. The repro case I gave in #38972 is:

enum Void { }

fn use_void(v: &Void) -> u32 {
    match v { }
}

fn main() { }

[arielb1]

The regression on matching &Void is intentional - matching on &Void being allowed was a pirate feature in 1.14.0 1.15.0.

[SSheldon]

So the repro case I gave would only ever have compiled on 1.15? It was feature-gated in 1.14 and is disallowed again in 1.16?

[arielb1]

@SSheldon

It was not even feature gated in 1.14 - it just didn't work. The feature was introduced in PR #36449 in 1.15.0 without proper consideration.

[SSheldon]

Ah welp, guess I was just writing the wrong code at the right time. Nothing is using objc-encode yet so I can just change it.

[brson]

Seems like this is expected behavior. Thanks @arielb1 and @SSheldon.