On Sun Sep 20, 2026 at 2:20 PM CEST, Gary Guo wrote:
> On Fri Sep 18, 2026 at 7:03 PM BST, Alexandre Courbot wrote:
>> On Thu Sep 17, 2026 at 9:53 AM BST, Gary Guo wrote:
>>> On Tue Sep 15, 2026 at 8:39 AM BST, Alexandre Courbot wrote:
>>>> On Wed Sep 2, 2026 at 6:16 PM JST, Eliot Courtney wrote:
>>>>> Currently, using NonZero/Bounded constants is quite verbose. It's
>>>>> unfortunate because it disincentivizes using it in interface boundaries.
>>>>> Introduce a macro to make it nicer to use. The macro `cv!` (for constant
>>>>> value) takes a const integer expression and widens it to i128 (at build
>>>>> time only) before passing it as a const generic value to a new trait
>>>>> `FromConst`. The value is then converted and appears in the
>>>>> associated constant `FromConst::VALUE`. The trait is implemented by
>>>>> NonZero, Bounded, and Alignment and lets values of each be constructed
>>>>> from constants without a verbose turbofish syntax.
>>>>> For example, `const { NonZero::new(1).unwrap() }` can be written as
>>>>> `cv!(1)`.
>>>>>
>>>>> Suggested-by: Gary Guo <[email protected]>
>>>>> Signed-off-by: Eliot Courtney <[email protected]>
>>>>
>>>> I don't think we have any user but nova-core at the moment, and it
>>>> benefits from this in several series (patch 3 here, but also ID pool and
>>>> later r000). Miguel, is this ok if we take it (i.e. the next revision)
>>>> through drm-rust-next?
>>>
>>> How about a topic tag shared between Rust and drm-rust-next? We could also
>>> remove the old num casts API as part of topic tag and fix all existing
>>> users as
>>> part of merge.
>>
>> Not opposed to the idea but IIRC there was already some pushback to the
>> idea. There doesn't seem to be an urgency to remove the old num casts
>> API that justifies doing it now with a more complicated merge path.
>
> Sorry, what pushbacks? I thought that `cv!` is what everyone agrees on. I see
> no
> downside of this compared to the turbofish const conversion APIs.
>
> I am not opposed to delaying removal for the next cycle, but IMO the `cv!`
> macro
> should be present on Rust tree so it's visible and improvements can be made
> from
> there, so I think we should do a topic tag regardless whether the old API
> removal happens or not.
I think Alex refers to this thread [1]; there's was some more context to this
though.
[1] https://lore.kernel.org/all/[email protected]/
