Is it possible to write some edition-aware crate?

help
1

I had previously committed an ACP about derive PartialEq/PartialOrd in case Eq/Ord is

pub type True = ();
pub type False = [();0];
#[cfg(if edition >= 2024)] // how to achieve that
type Default = True;
#[cfg(not(if edition >= 2024))] // how to achieve that
type Default = False;
// since Default is False for old code, such line does nothing.
//add type Flag=Default in some traits.
impl<T> ... for ... where ...::Flag:True

IIRC, there's someone who wrote a program that support using different edition syntax(with macro) in one file(with macro support)
But I cannot find that piece of code.

Can I have some edition-aware code?

2

May I ask what you need such a configuration value for? Because crates are always compiled with the edition specified in their manifest file. So if a crate with a 2021 edition imports your 2018 edition crate as a dependency, your crate will still be built using the 2018 edition. This includes the code generated by macros.

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3

I once wrote an ACP about Ord/PartialOrd.
Currently, impl Ord directly without impl PartialOrd is a logic error. But impl/derive PartialOrd from Ord should be very easy.

It makes sense to automatically generate PartialOrd with Ord impl/derived. But it is a breaking change.

I want to check whether a Default type could be added in Ord trait, which is False in old edition and True in new edition, thus old crate won't use the impl<T:Ord<ImplPartialOrd=True>> PartialOrd for T and thus compatitable, new crate use it automatically thus there's no need to impl PartialOrd and Ord for the same struct.

4

I assume there are compiler built-ins for detecting the edition, unavailable to normal crates.

Might be worth asking this at internals

5

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