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rust: macros: allow generic parameter default values in #[pin_data]
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Add support for generic parameters defaults in `#[pin_data]` by using
the newly introduced `decl_generics` instead of the `impl_generics`.

Before this would not compile:

    #[pin_data]
    struct Foo<const N: usize = 0> {
        // ...
    }

because it would be expanded to this:

    struct Foo<const N: usize = 0> {
        // ...
    }

    const _: () = {
        struct __ThePinData<const N: usize = 0> {
            __phantom: ::core::marker::PhantomData<fn(Foo<N>) -> Foo<N>>,
        }
        impl<const N: usize = 0> ::core::clone::Clone for __ThePinData<N> {
            fn clone(&self) -> Self {
                *self
            }
        }

        // [...] rest of expansion omitted
    };

The problem is with the `impl<const N: usize = 0>`, since that is
invalid Rust syntax. It should not mention the default value at all,
since default values only make sense on type definitions.

The new `impl_generics` do not contain the default values, thus
generating correct Rust code.

This is used by the next commit that puts `#[pin_data]` on
`kernel::workqueue::Work`.

Signed-off-by: Benno Lossin <[email protected]>
Reviewed-by: Martin Rodriguez Reboredo <[email protected]>
Reviewed-by: Gary Guo <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
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@fbq
Benno Lossin authored and fbq committed Dec 28, 2023
1 parent ba17aad commit 1fd25cc
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Showing 2 changed files with 20 additions and 2 deletions.
19 changes: 18 additions & 1 deletion rust/kernel/init/macros.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -538,6 +538,7 @@ macro_rules! __pin_data {
),
@impl_generics($($impl_generics:tt)*),
@ty_generics($($ty_generics:tt)*),
@decl_generics($($decl_generics:tt)*),
@body({ $($fields:tt)* }),
) => {
// We now use token munching to iterate through all of the fields. While doing this we
Expand All @@ -560,6 +561,9 @@ macro_rules! __pin_data {
@impl_generics($($impl_generics)*),
// The 'ty generics', the generics that will need to be specified on the impl blocks.
@ty_generics($($ty_generics)*),
// The 'decl generics', the generics that need to be specified on the struct
// definition.
@decl_generics($($decl_generics)*),
// The where clause of any impl block and the declaration.
@where($($($whr)*)?),
// The remaining fields tokens that need to be processed.
Expand All @@ -585,6 +589,7 @@ macro_rules! __pin_data {
@name($name:ident),
@impl_generics($($impl_generics:tt)*),
@ty_generics($($ty_generics:tt)*),
@decl_generics($($decl_generics:tt)*),
@where($($whr:tt)*),
// We found a PhantomPinned field, this should generally be pinned!
@fields_munch($field:ident : $($($(::)?core::)?marker::)?PhantomPinned, $($rest:tt)*),
Expand All @@ -607,6 +612,7 @@ macro_rules! __pin_data {
@name($name),
@impl_generics($($impl_generics)*),
@ty_generics($($ty_generics)*),
@decl_generics($($decl_generics)*),
@where($($whr)*),
@fields_munch($($rest)*),
@pinned($($pinned)* $($accum)* $field: ::core::marker::PhantomPinned,),
Expand All @@ -623,6 +629,7 @@ macro_rules! __pin_data {
@name($name:ident),
@impl_generics($($impl_generics:tt)*),
@ty_generics($($ty_generics:tt)*),
@decl_generics($($decl_generics:tt)*),
@where($($whr:tt)*),
// We reached the field declaration.
@fields_munch($field:ident : $type:ty, $($rest:tt)*),
Expand All @@ -640,6 +647,7 @@ macro_rules! __pin_data {
@name($name),
@impl_generics($($impl_generics)*),
@ty_generics($($ty_generics)*),
@decl_generics($($decl_generics)*),
@where($($whr)*),
@fields_munch($($rest)*),
@pinned($($pinned)* $($accum)* $field: $type,),
Expand All @@ -656,6 +664,7 @@ macro_rules! __pin_data {
@name($name:ident),
@impl_generics($($impl_generics:tt)*),
@ty_generics($($ty_generics:tt)*),
@decl_generics($($decl_generics:tt)*),
@where($($whr:tt)*),
// We reached the field declaration.
@fields_munch($field:ident : $type:ty, $($rest:tt)*),
Expand All @@ -673,6 +682,7 @@ macro_rules! __pin_data {
@name($name),
@impl_generics($($impl_generics)*),
@ty_generics($($ty_generics)*),
@decl_generics($($decl_generics)*),
@where($($whr)*),
@fields_munch($($rest)*),
@pinned($($pinned)*),
Expand All @@ -689,6 +699,7 @@ macro_rules! __pin_data {
@name($name:ident),
@impl_generics($($impl_generics:tt)*),
@ty_generics($($ty_generics:tt)*),
@decl_generics($($decl_generics:tt)*),
@where($($whr:tt)*),
// We found the `#[pin]` attr.
@fields_munch(#[pin] $($rest:tt)*),
Expand All @@ -705,6 +716,7 @@ macro_rules! __pin_data {
@name($name),
@impl_generics($($impl_generics)*),
@ty_generics($($ty_generics)*),
@decl_generics($($decl_generics)*),
@where($($whr)*),
@fields_munch($($rest)*),
// We do not include `#[pin]` in the list of attributes, since it is not actually an
Expand All @@ -724,6 +736,7 @@ macro_rules! __pin_data {
@name($name:ident),
@impl_generics($($impl_generics:tt)*),
@ty_generics($($ty_generics:tt)*),
@decl_generics($($decl_generics:tt)*),
@where($($whr:tt)*),
// We reached the field declaration with visibility, for simplicity we only munch the
// visibility and put it into `$accum`.
Expand All @@ -741,6 +754,7 @@ macro_rules! __pin_data {
@name($name),
@impl_generics($($impl_generics)*),
@ty_generics($($ty_generics)*),
@decl_generics($($decl_generics)*),
@where($($whr)*),
@fields_munch($field $($rest)*),
@pinned($($pinned)*),
Expand All @@ -757,6 +771,7 @@ macro_rules! __pin_data {
@name($name:ident),
@impl_generics($($impl_generics:tt)*),
@ty_generics($($ty_generics:tt)*),
@decl_generics($($decl_generics:tt)*),
@where($($whr:tt)*),
// Some other attribute, just put it into `$accum`.
@fields_munch(#[$($attr:tt)*] $($rest:tt)*),
Expand All @@ -773,6 +788,7 @@ macro_rules! __pin_data {
@name($name),
@impl_generics($($impl_generics)*),
@ty_generics($($ty_generics)*),
@decl_generics($($decl_generics)*),
@where($($whr)*),
@fields_munch($($rest)*),
@pinned($($pinned)*),
Expand All @@ -789,6 +805,7 @@ macro_rules! __pin_data {
@name($name:ident),
@impl_generics($($impl_generics:tt)*),
@ty_generics($($ty_generics:tt)*),
@decl_generics($($decl_generics:tt)*),
@where($($whr:tt)*),
// We reached the end of the fields, plus an optional additional comma, since we added one
// before and the user is also allowed to put a trailing comma.
Expand All @@ -802,7 +819,7 @@ macro_rules! __pin_data {
) => {
// Declare the struct with all fields in the correct order.
$($struct_attrs)*
$vis struct $name <$($impl_generics)*>
$vis struct $name <$($decl_generics)*>
where $($whr)*
{
$($fields)*
Expand Down
3 changes: 2 additions & 1 deletion rust/macros/pin_data.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,7 @@ pub(crate) fn pin_data(args: TokenStream, input: TokenStream) -> TokenStream {
let (
Generics {
impl_generics,
decl_generics: _,
decl_generics,
ty_generics,
},
rest,
Expand Down Expand Up @@ -77,6 +77,7 @@ pub(crate) fn pin_data(args: TokenStream, input: TokenStream) -> TokenStream {
@sig(#(#rest)*),
@impl_generics(#(#impl_generics)*),
@ty_generics(#(#ty_generics)*),
@decl_generics(#(#decl_generics)*),
@body(#last),
});
quoted.extend(errs);
Expand Down

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