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

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Message-ID: <D8PB0LN62GOX.3P4K4V96OLVQ9@proton.me>
Date: Tue, 25 Mar 2025 11:18:17 +0000
From: Benno Lossin <benno.lossin@...ton.me>
To: Tamir Duberstein <tamird@...il.com>
Cc: Boqun Feng <boqun.feng@...il.com>, 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 11:42 AM CET, Tamir Duberstein wrote:
> On Tue, Mar 25, 2025 at 6:37 AM Benno Lossin <benno.lossin@...ton.me> wrote:
>> 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 `()`/`[]`).
>
> Yes I know. But with `ident` you cannot capture lifetimes or const generics.

Why is that required for this macro? I think we could use `tt`.

---
Cheers,
Benno