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rust: macros: add `decl_generics` to `parse_generics()` 

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>
This commit is contained in:
Benno Lossin 2024-03-09 15:53:25 +00:00 committed by Miguel Ojeda
parent a321f3ad0a
commit 9762dca54a
3 changed files with 96 additions and 31 deletions
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125
rust/macros/helpers.rs
View File

@ -1,6 +1,6 @@
// SPDX-License-Identifier: GPL-2.0
use proc_macro::{token_stream, Group, Punct, Spacing, TokenStream, TokenTree};
use proc_macro::{token_stream, Group, TokenStream, TokenTree};
pub(crate) fn try_ident(it: &mut token_stream::IntoIter) -> Option<String> {
if let Some(TokenTree::Ident(ident)) = it.next() {
@ -70,8 +70,41 @@ pub(crate) fn expect_end(it: &mut token_stream::IntoIter) {
}
}
/// Parsed generics.
///
/// See the field documentation for an explanation what each of the fields represents.
///
/// # Examples
///
/// ```rust,ignore
/// # let input = todo!();
/// 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() {
/// // ...
/// }
/// }
/// }
/// ```
pub(crate) struct Generics {
/// The generics with bounds and default values (e.g. `T: Clone, const N: usize = 0`).
///
/// Use this on type definitions e.g. `struct Foo<$decl_generics> ...` (or `union`/`enum`).
#[allow(dead_code)]
pub(crate) decl_generics: Vec<TokenTree>,
/// The generics with bounds (e.g. `T: Clone, const N: usize`).
///
/// Use this on `impl` blocks e.g. `impl<$impl_generics> Trait for ...`.
pub(crate) impl_generics: Vec<TokenTree>,
/// The generics without bounds and without default values (e.g. `T, N`).
///
/// Use this when you use the type that is declared with these generics e.g.
/// `Foo<$ty_generics>`.
pub(crate) ty_generics: Vec<TokenTree>,
}
@ -79,6 +112,8 @@ pub(crate) struct Generics {
///
/// The generics are not present in the rest, but a where clause might remain.
pub(crate) fn parse_generics(input: TokenStream) -> (Generics, Vec<TokenTree>) {
// The generics with bounds and default values.
let mut decl_generics = vec![];
// `impl_generics`, the declared generics with their bounds.
let mut impl_generics = vec![];
// Only the names of the generics, without any bounds.
@ -90,10 +125,17 @@ pub(crate) fn parse_generics(input: TokenStream) -> (Generics, Vec<TokenTree>) {
let mut toks = input.into_iter();
// If we are at the beginning of a generic parameter.
let mut at_start = true;
for tt in &mut toks {
let mut skip_until_comma = false;
while let Some(tt) = toks.next() {
if nesting == 1 && matches!(&tt, TokenTree::Punct(p) if p.as_char() == '>') {
// Found the end of the generics.
break;
} else if nesting >= 1 {
decl_generics.push(tt.clone());
}
match tt.clone() {
TokenTree::Punct(p) if p.as_char() == '<' => {
if nesting >= 1 {
if nesting >= 1 && !skip_until_comma {
// This is inside of the generics and part of some bound.
impl_generics.push(tt);
}
@ -105,49 +147,70 @@ pub(crate) fn parse_generics(input: TokenStream) -> (Generics, Vec<TokenTree>) {
break;
} else {
nesting -= 1;
if nesting >= 1 {
if nesting >= 1 && !skip_until_comma {
// We are still inside of the generics and part of some bound.
impl_generics.push(tt);
}
if nesting == 0 {
break;
}
}
}
tt => {
TokenTree::Punct(p) if skip_until_comma && p.as_char() == ',' => {
if nesting == 1 {
// Here depending on the token, it might be a generic variable name.
match &tt {
// Ignore const.
TokenTree::Ident(i) if i.to_string() == "const" => {}
TokenTree::Ident(_) if at_start => {
ty_generics.push(tt.clone());
// We also already push the `,` token, this makes it easier to append
// generics.
ty_generics.push(TokenTree::Punct(Punct::new(',', Spacing::Alone)));
at_start = false;
}
TokenTree::Punct(p) if p.as_char() == ',' => at_start = true,
// Lifetimes begin with `'`.
TokenTree::Punct(p) if p.as_char() == '\'' && at_start => {
ty_generics.push(tt.clone());
}
_ => {}
}
}
if nesting >= 1 {
impl_generics.push(tt.clone());
impl_generics.push(tt);
} else if nesting == 0 {
// If we haven't entered the generics yet, we still want to keep these tokens.
rest.push(tt);
skip_until_comma = false;
}
}
_ if !skip_until_comma => {
match nesting {
// If we haven't entered the generics yet, we still want to keep these tokens.
0 => rest.push(tt),
1 => {
// Here depending on the token, it might be a generic variable name.
match tt.clone() {
TokenTree::Ident(i) if at_start && i.to_string() == "const" => {
let Some(name) = toks.next() else {
// Parsing error.
break;
};
impl_generics.push(tt);
impl_generics.push(name.clone());
ty_generics.push(name.clone());
decl_generics.push(name);
at_start = false;
}
TokenTree::Ident(_) if at_start => {
impl_generics.push(tt.clone());
ty_generics.push(tt);
at_start = false;
}
TokenTree::Punct(p) if p.as_char() == ',' => {
impl_generics.push(tt.clone());
ty_generics.push(tt);
at_start = true;
}
// Lifetimes begin with `'`.
TokenTree::Punct(p) if p.as_char() == '\'' && at_start => {
impl_generics.push(tt.clone());
ty_generics.push(tt);
}
// Generics can have default values, we skip these.
TokenTree::Punct(p) if p.as_char() == '=' => {
skip_until_comma = true;
}
_ => impl_generics.push(tt),
}
}
_ => impl_generics.push(tt),
}
}
_ => {}
}
}
rest.extend(toks);
(
Generics {
impl_generics,
decl_generics,
ty_generics,
},
rest,

1
rust/macros/pin_data.rs
View File

@ -10,6 +10,7 @@ pub(crate) fn pin_data(args: TokenStream, input: TokenStream) -> TokenStream {
let (
Generics {
impl_generics,
decl_generics: _,
ty_generics,
},
rest,

1
rust/macros/zeroable.rs
View File

@ -7,6 +7,7 @@ pub(crate) fn derive(input: TokenStream) -> TokenStream {
let (
Generics {
impl_generics,
decl_generics: _,
ty_generics,
},
mut rest,