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The generic parameters on a type definition can specify default values.
Currently `parse_generics()` cannot handle this though. For example when
parsing the following generics:
<T: Clone, const N: usize = 0>
The `impl_generics` will be set to `T: Clone, const N: usize = 0` and
`ty_generics` will be set to `T, N`. Now using the `impl_generics` on an
impl block:
impl<$($impl_generics)*> Foo {}
will result in invalid Rust code, because default values are only
available on type definitions.
Therefore add parsing support for generic parameter default values using
a new kind of generics called `decl_generics` and change the old
behavior of `impl_generics` to not contain the generic parameter default
values.
Now `Generics` has three fields:
- `impl_generics`: the generics with bounds
(e.g. `T: Clone, const N: usize`)
- `decl_generics`: the generics with bounds and default values
(e.g. `T: Clone, const N: usize = 0`)
- `ty_generics`: contains the generics without bounds and without
default values (e.g. `T, N`)
`impl_generics` is designed to be used on `impl<$impl_generics>`,
`decl_generics` for the type definition, so `struct Foo<$decl_generics>`
and `ty_generics` whenever you use the type, so `Foo<$ty_generics>`.
Here is an example that uses all three different types of generics:
let (Generics { decl_generics, impl_generics, ty_generics }, rest) = parse_generics(input);
quote! {
struct Foo<$($decl_generics)*> {
// ...
}
impl<$impl_generics> Foo<$ty_generics> {
fn foo() {
// ...
}
}
}
The next commit contains a fix to the `#[pin_data]` macro making it
compatible with generic parameter default values by relying on this new
behavior.
Signed-off-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20240309155243.482334-1-benno.lossin@proton.me
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
73 lines
2.6 KiB
Rust
73 lines
2.6 KiB
Rust
// SPDX-License-Identifier: GPL-2.0
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use crate::helpers::{parse_generics, Generics};
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use proc_macro::{TokenStream, TokenTree};
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pub(crate) fn derive(input: TokenStream) -> TokenStream {
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let (
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Generics {
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impl_generics,
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decl_generics: _,
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ty_generics,
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},
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mut rest,
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) = parse_generics(input);
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// This should be the body of the struct `{...}`.
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let last = rest.pop();
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// Now we insert `Zeroable` as a bound for every generic parameter in `impl_generics`.
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let mut new_impl_generics = Vec::with_capacity(impl_generics.len());
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// Are we inside of a generic where we want to add `Zeroable`?
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let mut in_generic = !impl_generics.is_empty();
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// Have we already inserted `Zeroable`?
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let mut inserted = false;
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// Level of `<>` nestings.
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let mut nested = 0;
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for tt in impl_generics {
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match &tt {
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// If we find a `,`, then we have finished a generic/constant/lifetime parameter.
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TokenTree::Punct(p) if nested == 0 && p.as_char() == ',' => {
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if in_generic && !inserted {
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new_impl_generics.extend(quote! { : ::kernel::init::Zeroable });
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}
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in_generic = true;
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inserted = false;
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new_impl_generics.push(tt);
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}
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// If we find `'`, then we are entering a lifetime.
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TokenTree::Punct(p) if nested == 0 && p.as_char() == '\'' => {
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in_generic = false;
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new_impl_generics.push(tt);
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}
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TokenTree::Punct(p) if nested == 0 && p.as_char() == ':' => {
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new_impl_generics.push(tt);
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if in_generic {
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new_impl_generics.extend(quote! { ::kernel::init::Zeroable + });
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inserted = true;
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}
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}
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TokenTree::Punct(p) if p.as_char() == '<' => {
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nested += 1;
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new_impl_generics.push(tt);
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}
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TokenTree::Punct(p) if p.as_char() == '>' => {
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assert!(nested > 0);
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nested -= 1;
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new_impl_generics.push(tt);
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}
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_ => new_impl_generics.push(tt),
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}
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}
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assert_eq!(nested, 0);
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if in_generic && !inserted {
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new_impl_generics.extend(quote! { : ::kernel::init::Zeroable });
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}
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quote! {
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::kernel::__derive_zeroable!(
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parse_input:
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@sig(#(#rest)*),
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@impl_generics(#(#new_impl_generics)*),
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@ty_generics(#(#ty_generics)*),
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@body(#last),
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);
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}
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}
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