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Date:   Sat, 24 Jun 2023 15:20:36 +0000
To:     Benno Lossin <benno.lossin@proton.me>
From:   =?utf-8?Q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>
Cc:     Miguel Ojeda <ojeda@kernel.org>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
        Alice Ryhl <aliceryhl@google.com>,
        Andreas Hindborg <nmi@metaspace.dk>,
        rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org,
        patches@lists.linux.dev, Asahi Lina <lina@asahilina.net>
Subject: Re: [PATCH 7/7] rust: init: add support for arbitrary paths in init macros
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On Saturday, June 24th, 2023 at 11:25, Benno Lossin <benno.lossin@proton.me=
> wrote:

> Previously only `ident` and generic types were supported in the
> `{try_}{pin_}init!` macros. This patch allows arbitrary path fragments,
> so for example `Foo::Bar` but also very complex paths such as
> `<Foo as Baz>::Bar::<0, i32>`.
>=20
> Internally this is accomplished by using `path` fragments. Due to some
> peculiar declarative macro limitations, we have to "forget" certain
> additional parsing information in the token trees. This is achieved by
> the new `retokenize` proc macro. It does not modify the input, but just
> strips this information. For example, if a declarative macro takes
> `$t:path` as its input, it cannot sensibly propagate this to a macro that
> takes `$($p:tt)*` as its input, since the `$t` token will only be
> considered one `tt` token for the second macro. If we first pipe the
> tokens through `retokenize`, then it parses as expected.
>=20
> Suggested-by: Asahi Lina <lina@asahilina.net>
> Signed-off-by: Benno Lossin <benno.lossin@proton.me>

Reviewed-by: Bj=C3=B6rn Roy Baron <bjorn3_gh@protonmail.com>

> ---
>  rust/kernel/init/__internal.rs |  2 ++
>  rust/kernel/init/macros.rs     | 42 +++++++++++++++++++---------------
>  rust/macros/lib.rs             | 17 +++++++++++++-
>  3 files changed, 41 insertions(+), 20 deletions(-)
>=20
> diff --git a/rust/kernel/init/__internal.rs b/rust/kernel/init/__internal=
.rs
> index 7abd1fb65e41..e36a706a4a1b 100644
> --- a/rust/kernel/init/__internal.rs
> +++ b/rust/kernel/init/__internal.rs
> @@ -9,6 +9,8 @@
>=20
>  use super::*;
>=20
> +pub use ::macros::retokenize;
> +
>  /// See the [nomicon] for what subtyping is. See also [this table].
>  ///
>  /// [nomicon]: https://doc.rust-lang.org/nomicon/subtyping.html
> diff --git a/rust/kernel/init/macros.rs b/rust/kernel/init/macros.rs
> index 5dcb2e513f26..6a82be675808 100644
> --- a/rust/kernel/init/macros.rs
> +++ b/rust/kernel/init/macros.rs
> @@ -998,7 +998,7 @@ impl<$($impl_generics)*> $pin_data<$($ty_generics)*>
>  macro_rules! __init_internal {
>      (
>          @this($($this:ident)?),
> -        @typ($t:ident $(::<$($generics:ty),*>)?),
> +        @typ($t:path),
>          @fields($($fields:tt)*),
>          @error($err:ty),
>          // Either `PinData` or `InitData`, `$use_data` should only be pr=
esent in the `PinData`
> @@ -1012,7 +1012,7 @@ macro_rules! __init_internal {
>      ) =3D> {
>          $crate::__init_internal!(with_update_parsed:
>              @this($($this)?),
> -            @typ($t $(::<$($generics),*>)? ),
> +            @typ($t),
>              @fields($($fields)*),
>              @error($err),
>              @data($data, $($use_data)?),
> @@ -1023,7 +1023,7 @@ macro_rules! __init_internal {
>      };
>      (
>          @this($($this:ident)?),
> -        @typ($t:ident $(::<$($generics:ty),*>)?),
> +        @typ($t:path),
>          @fields($($fields:tt)*),
>          @error($err:ty),
>          // Either `PinData` or `InitData`, `$use_data` should only be pr=
esent in the `PinData`
> @@ -1037,7 +1037,7 @@ macro_rules! __init_internal {
>      ) =3D> {
>          $crate::__init_internal!(with_update_parsed:
>              @this($($this)?),
> -            @typ($t $(::<$($generics),*>)? ),
> +            @typ($t),
>              @fields($($fields)*),
>              @error($err),
>              @data($data, $($use_data)?),
> @@ -1048,7 +1048,7 @@ macro_rules! __init_internal {
>      };
>      (
>          @this($($this:ident)?),
> -        @typ($t:ident $(::<$($generics:ty),*>)?),
> +        @typ($t:path),
>          @fields($($fields:tt)*),
>          @error($err:ty),
>          // Either `PinData` or `InitData`, `$use_data` should only be pr=
esent in the `PinData`
> @@ -1062,7 +1062,7 @@ macro_rules! __init_internal {
>      ) =3D> {
>          $crate::__init_internal!(
>              @this($($this)?),
> -            @typ($t $(::<$($generics),*>)? ),
> +            @typ($t),
>              @fields($($fields)*),
>              @error($err),
>              @data($data, $($use_data)?),
> @@ -1073,7 +1073,7 @@ macro_rules! __init_internal {
>      };
>      (with_update_parsed:
>          @this($($this:ident)?),
> -        @typ($t:ident $(::<$($generics:ty),*>)?),
> +        @typ($t:path),
>          @fields($($fields:tt)*),
>          @error($err:ty),
>          // Either `PinData` or `InitData`, `$use_data` should only be pr=
esent in the `PinData`
> @@ -1092,7 +1092,7 @@ macro_rules! __init_internal {
>          // Get the data about fields from the supplied type.
>          let data =3D unsafe {
>              use $crate::init::__internal::$has_data;
> -            $t$(::<$($generics),*>)?::$get_data()
> +            $crate::init::__internal::retokenize!($t::$get_data())
>          };
>          // Ensure that `data` really is of type `$data` and help with ty=
pe inference:
>          let init =3D $crate::init::__internal::$data::make_closure::<_, =
__InitOk, $err>(
> @@ -1247,7 +1247,7 @@ fn is_zeroable<T: Zeroable>(ptr: *mut T) {}
>      };
>      (make_initializer:
>          @slot($slot:ident),
> -        @type_name($t:ident),
> +        @type_name($t:path),
>          @munch_fields(..Zeroable::zeroed() $(,)?),
>          @acc($($acc:tt)*),
>      ) =3D> {
> @@ -1263,15 +1263,17 @@ fn is_zeroable<T: Zeroable>(ptr: *mut T) {}
>              // not get executed, so it has no effect.
>              ::core::ptr::write($slot, zeroed);
>              zeroed =3D ::core::mem::zeroed();
> -            ::core::ptr::write($slot, $t {
> -                $($acc)*
> -                ..zeroed
> -            });
> +            $crate::init::__internal::retokenize!(
> +                ::core::ptr::write($slot, $t {
> +                    $($acc)*
> +                    ..zeroed
> +                });
> +            );
>          }
>      };
>      (make_initializer:
>          @slot($slot:ident),
> -        @type_name($t:ident),
> +        @type_name($t:path),
>          @munch_fields($(,)?),
>          @acc($($acc:tt)*),
>      ) =3D> {
> @@ -1279,14 +1281,16 @@ fn is_zeroable<T: Zeroable>(ptr: *mut T) {}
>          // Since we are in the `if false` branch, this will never get ex=
ecuted. We abuse `slot` to
>          // get the correct type inference here:
>          unsafe {
> -            ::core::ptr::write($slot, $t {
> -                $($acc)*
> -            });
> +            $crate::init::__internal::retokenize!(
> +                ::core::ptr::write($slot, $t {
> +                    $($acc)*
> +                });
> +            );
>          }
>      };
>      (make_initializer:
>          @slot($slot:ident),
> -        @type_name($t:ident),
> +        @type_name($t:path),
>          @munch_fields($field:ident <- $val:expr, $($rest:tt)*),
>          @acc($($acc:tt)*),
>      ) =3D> {
> @@ -1299,7 +1303,7 @@ fn is_zeroable<T: Zeroable>(ptr: *mut T) {}
>      };
>      (make_initializer:
>          @slot($slot:ident),
> -        @type_name($t:ident),
> +        @type_name($t:path),
>          @munch_fields($field:ident $(: $val:expr)?, $($rest:tt)*),
>          @acc($($acc:tt)*),
>      ) =3D> {
> diff --git a/rust/macros/lib.rs b/rust/macros/lib.rs
> index 9f056a5c780a..d329ab622fd4 100644
> --- a/rust/macros/lib.rs
> +++ b/rust/macros/lib.rs
> @@ -12,7 +12,7 @@
>  mod vtable;
>  mod zeroable;
>=20
> -use proc_macro::TokenStream;
> +use proc_macro::{Group, TokenStream, TokenTree};
>=20
>  /// Declares a kernel module.
>  ///
> @@ -266,3 +266,18 @@ pub fn pinned_drop(args: TokenStream, input: TokenSt=
ream) -> TokenStream {
>  pub fn derive_zeroable(input: TokenStream) -> TokenStream {
>      zeroable::derive(input)
>  }
> +
> +/// Does not modify the given TokenStream, but removes any declarative m=
acro information.
> +#[proc_macro]
> +pub fn retokenize(input: TokenStream) -> TokenStream {
> +    fn id(tt: TokenTree) -> TokenTree {
> +        match tt {
> +            TokenTree::Group(g) =3D> TokenTree::Group(Group::new(
> +                g.delimiter(),
> +                g.stream().into_iter().map(id).collect(),
> +            )),
> +            x =3D> x,
> +        }
> +    }
> +    input.into_iter().map(id).collect()
> +}
> --
> 2.41.0