Cannot use constants as enum values

[OpenByteDev]

Since the update from 0.5.7 to 0.5.8 using a constants as the value of an enum variant does not work anymore:

const CONST_ONE: u32 = 1;
#[derive(
    TryFromPrimitive, IntoPrimitive
)]
#[repr(u32)]
pub enum Enum {
    One = CONST_ONE,
}

Produces the following error:

error: Expected literal
  --> src\error.rs:58:11
   |
58 |     One = CONST_ONE,
   |           ^^^^^^^^^

[kevinaboos]

Confirmed, we're facing the same issue in Theseus OS. Previously we were on 0.5.7, and some of our CI passes randomly started failing within the last 2 hours due to num_enum 0.5.8 breaking this. (Ultimately our mistake for not freezing/locking the lockfile versions used for doc builds)

I think 0.5.8 likely needs to be yanked because it somehow broke semver compatibility guarantees.

[kevinaboos]

This is likely the culprit:

num_enum/num_enum_derive/src/lib.rs

Line 41 in 4cd978d

_ => die!(val_exp => "Expected literal"),

[AlexDBlack]

rdkafka also appears to be affected:
https://github.com/fede1024/rust-rdkafka/blob/master/rdkafka-sys/src/bindings.rs#L182

error: Expected literal
   --> /root/.cargo/registry/src/gh.neting.cc-1ecc6299db9ec823/rdkafka-sys-4.3.0+1.9.2/src/bindings.rs:182:32
    |
182 |     RD_KAFKA_RESP_ERR__BEGIN = -200,
    |                                ^^^^
error[E0277]: the trait bound `rd_kafka_resp_err_t: From<i32>` is not satisfied

We have CI builds failing just now with num_enum 0.5.8 that previously passed with 0.5.7.

Edit: manually pinning the version appears to be a workaround.

num_enum = "=0.5.7"
num_enum_derive = "=0.5.7"

[Dhghomon]

Yes, looks like this was the change that did it! I also started with a cryptic error in rdkafka which hasn't seen any changes for quite some time and eventually noticed the derive trait their error enum uses which led me to here.

Love the macro name there 😂

[illicitonion]

I've yanked 0.5.8 - thanks for the reports, and sorry for the breakage!