linux-kernel - Re: [PATCH 3/5] rust: list: use consistent type parameter names

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Message-ID: <D8PA5CKNMCGA.UODS331S36EG@proton.me>
Date: Tue, 25 Mar 2025 10:37:29 +0000
From: Benno Lossin <benno.lossin@...ton.me>
To: Tamir Duberstein <tamird@...il.com>, Boqun Feng <boqun.feng@...il.com>
Cc: Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, Gary Guo <gary@...yguo.net>, Björn Roy Baron <bjorn3_gh@...tonmail.com>, Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki" <rafael@...nel.org>, rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH 3/5] rust: list: use consistent type parameter names

On Tue Mar 25, 2025 at 10:52 AM CET, Tamir Duberstein wrote:
> On Tue, Mar 25, 2025 at 12:02 AM Boqun Feng <boqun.feng@...il.com> wrote:
>> On Mon, Mar 24, 2025 at 05:56:57PM -0400, Tamir Duberstein wrote:
>> > On Mon, Mar 24, 2025 at 5:51 PM Tamir Duberstein <tamird@...il.com> wrote:
>> > > On Mon, Mar 24, 2025 at 5:42 PM Boqun Feng <boqun.feng@...il.com> wrote:
>> > > > On Mon, Mar 24, 2025 at 05:33:45PM -0400, Tamir Duberstein wrote:
>> > > > >              #[inline]
>> > > > > @@ -81,16 +81,16 @@ pub unsafe trait HasSelfPtr<T: ?Sized, const ID: u64 = 0>
>> > > > >  /// Implements the [`HasListLinks`] and [`HasSelfPtr`] traits for the given type.
>> > > > >  #[macro_export]
>> > > > >  macro_rules! impl_has_list_links_self_ptr {
>> > > > > -    ($(impl$({$($implarg:tt)*})?
>> > > > > +    ($(impl$({$($generics:tt)*})?
>> > > >
>> > > > While you're at it, can you also change this to be
>> > > >
>> > > >         ($(impl$(<$($generics:tt)*>)?
>> > > >
>> > > > ?
>> > > >
>> > > > I don't know why we chose <> for impl_has_list_links, but {} for
>> > > > impl_has_list_links_self_ptr ;-)
>> > >
>> > > This doesn't work in all cases:
>> > >
>> > > error: local ambiguity when calling macro `impl_has_work`: multiple
>> > > parsing options: built-in NTs tt ('generics') or 1 other option.
>> > >    --> ../rust/kernel/workqueue.rs:522:11
>> > >     |
>> > > 522 |     impl<T> HasWork<Self> for ClosureWork<T> { self.work }
>> > >
>> > > The reason that `impl_has_list_links` uses <> and all others use {} is
>> > > that `impl_has_list_links` is the only one that captures the generic
>> > > parameter as an `ident`, the rest use `tt`. So we could change
>>
>> Why impl_has_list_links uses generics at `ident` but rest use `tt`? I'm
>> a bit curious.
>
> I think it's because `ident` cannot deal with lifetimes or const
> generics - or at least I was not able to make it work with them.

If you use `ident`, you can use the normal `<>` as the delimiters of
generics. For `tt`, you have to use `{}` (or `()`/`[]`). 

---
Cheers,
Benno