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

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Message-ID: <CAJ-ks9n66_vVg3ww58VqfXV6+phng8Bhq9C=NNn854gXK0KAHg@mail.gmail.com>
Date: Tue, 25 Mar 2025 05:52:20 -0400
From: Tamir Duberstein <tamird@...il.com>
To: 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>, 
	Benno Lossin <benno.lossin@...ton.me>, 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 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:
> > > > > Refer to the type parameters of `impl_has_list_links{,_self_ptr}!` by
> > > > > the same name used in `impl_list_item!`.
> > > > >
> > > > > Signed-off-by: Tamir Duberstein <tamird@...il.com>
> > > > > ---
> > > > >  rust/kernel/list/impl_list_item_mod.rs | 10 +++++-----
> > > > >  1 file changed, 5 insertions(+), 5 deletions(-)
> > > > >
> > > > > diff --git a/rust/kernel/list/impl_list_item_mod.rs b/rust/kernel/list/impl_list_item_mod.rs
> > > > > index 5ed66fdce953..9d2102138c48 100644
> > > > > --- a/rust/kernel/list/impl_list_item_mod.rs
> > > > > +++ b/rust/kernel/list/impl_list_item_mod.rs
> > > > > @@ -41,7 +41,7 @@ unsafe fn raw_get_list_links(ptr: *mut Self) -> *mut ListLinks<ID> {
> > > > >  /// Implements the [`HasListLinks`] trait for the given type.
> > > > >  #[macro_export]
> > > > >  macro_rules! impl_has_list_links {
> > > > > -    ($(impl$(<$($implarg:ident),*>)?
> > > > > +    ($(impl$(<$($generics:ident),*>)?
> > > > >         HasListLinks$(<$id:tt>)?
> > > > >         for $self:ty
> > > > >         { self$(.$field:ident)* }
> > > > > @@ -51,7 +51,7 @@ macro_rules! impl_has_list_links {
> > > > >          //
> > > > >          // The behavior of `raw_get_list_links` is not changed since the `addr_of_mut!` macro is
> > > > >          // equivalent to the pointer offset operation in the trait definition.
> > > > > -        unsafe impl$(<$($implarg),*>)? $crate::list::HasListLinks$(<$id>)? for $self {
> > > > > +        unsafe impl$(<$($generics),*>)? $crate::list::HasListLinks$(<$id>)? for $self {
> > > > >              const OFFSET: usize = ::core::mem::offset_of!(Self, $($field).*) as usize;
> > > > >
> > > > >              #[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.