Rename "nightly" feature

[danlehmann]

const_trait has been removed from upstream Rust, so on a new compiler nightly no longer builds (for example, From<> is no longer const). There is currently no alternative, so we just probably just remove this optional feature

[hecatia-elegua]

You know I'm using this functionality and probably also know that they've just temporarily removed it. Please don't.
If you must, put it in some far-off file or a more scary feature name?

[danlehmann]

Just to clarify why this is a problem: When using a current nightly compiler (I am testing nightly-2023-04-20), arbitrary-int using the "nightly" feature fails to build as it relies on:

error[E0635]: unknown feature `const_convert`
 --> /Users/daniel/.cargo/registry/src/index.crates.io-6f17d22bba15001f/arbitrary-int-1.2.5/src/lib.rs:2:42
  |
2 | #![cfg_attr(feature = "nightly", feature(const_convert, const_trait_impl))]
  |                                          ^^^^^^^^^^^^^

error: const `impl` for trait `From` which is not marked with `#[const_trait]`
   --> /Users/daniel/.cargo/registry/src/index.crates.io-6f17d22bba15001f/arbitrary-int-1.2.5/src/lib.rs:789:67
    |
789 |             impl<const BITS: usize, const BITS_FROM: usize> const From<UInt<$from, BITS_FROM>>
    |                                                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
...
865 | from_arbitrary_int_impl!(u8, [u16, u32, u64, u128]);
    | --------------------------------------------------- in this macro invocation
    |
    = note: marking a trait with `#[const_trait]` ensures all default method bodies are `const`
    = note: adding a non-const method body in the future would be a breaking change
    = note: this error originates in the macro `from_arbitrary_int_impl` (in Nightly builds, run with -Z macro-backtrace for more info)

[danlehmann]

Do you have a source for it being temporarily disabled? I was under the impression they are moving to keyword generics, which might be years out.

[hecatia-elegua]

rust-lang/rust#110395 (comment)

[danlehmann]

Thanks! Let's rename the feature then? We can add a comment saying that this is requires an old compiler

[danlehmann]

Out of curiosity, which part of your code relies on this? In bitbybit, I completely side-stepped Number by entirely relying on .value() and the knowledge of how many bits e.g. a u5 is (by looking at the name). I assume in your case that wouldn't work bitenums?

[hecatia-elegua]

One example is <Self as arbitrary_int::Number>::MAX.value(). I also use new in const context, not sure where rn and I need some sleep

[danlehmann]

@hecatia-elegua please see #27. Does this work for you?