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

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Message-ID: <CAJ-ks9mEWshCkpq8=7=MKVDz8N-aUVSj0w-YdCsEvEhH3U7h_g@mail.gmail.com>
Date: Tue, 25 Mar 2025 09:39:09 -0400
From: Tamir Duberstein <tamird@...il.com>
To: Benno Lossin <benno.lossin@...ton.me>
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 7:18 AM Benno Lossin <benno.lossin@...ton.me> wrote:
>
> 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`.

We're in violent agreement. The change I've made is to use `tt`
everywhere, including where `ident` is currently used with `<>`.