linux-kernel - Re: [PATCH v2 1/2] rust: macros: Add derive Display for enums

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Message-ID: <90fac786f019f06765edb7c362e96f1a19801f26.camel@mailbox.org>
Date: Tue, 06 Jan 2026 06:56:05 +0100
From: Maurice Hieronymus <mhi@...lbox.org>
To: Danilo Krummrich <dakr@...nel.org>
Cc: Gary Guo <gary@...yguo.net>, Benno Lossin <lossin@...nel.org>, 
	aliceryhl@...gle.com, acourbot@...dia.com, airlied@...il.com,
 simona@...ll.ch, 	nouveau@...ts.freedesktop.org,
 dri-devel@...ts.freedesktop.org, 	linux-kernel@...r.kernel.org,
 ojeda@...nel.org, boqun.feng@...il.com, 	bjorn3_gh@...tonmail.com,
 a.hindborg@...nel.org, tmgross@...ch.edu, 	rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v2 1/2] rust: macros: Add derive Display for enums

On Mon, 2026-01-05 at 23:03 +0100, Danilo Krummrich wrote:
> On Mon Jan 5, 2026 at 10:11 PM CET, Maurice Hieronymus wrote:
> > Before I start implementing, I want to reach common ground.
> > 
> > In my opinion a derive macro which implements Display would be
> > perfectly fine, as long as the name suggests what it does. So for
> > example #[derive(DisplayEnumVariant)]. This would communicate the
> > intent clearly to the user.
> > 
> > Benno, would you be okay with that? If not, Gary and Danilo, are
> > you
> > fine with the proposed trait implementation (e.g. the variant_name
> > function)?
> 
> Actually, it might even be reasonable to have both. In the Nova
> driver we have
> the case that we want to print the enum variant exactly as it is
> defined in the
> code and a lowercase version of the enum variant.
> 
> > Are there any common use-cases where one wants to change the case
> > of
> > the enum variants? If not, I would not implement an argument and
> > rather
> > name the macro accordingly, so the intent is clear.
> 
> As mentioned above, we do have a case in Nova where we also want a
> lowercase
> representation to construct a firmware path with.

So there would be the need to have two derive macros:

1. #[derive(DisplayEnumVariant)]
Implements Display for all enum variants as they are (original case).

2. #[derive(ImplementVariantName(Case::Lowercase))]
Implements the mentioned trait. Case could be an Enum where one could
choose between Case::Lowercase and Case::Original.

Something along those lines?