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Date: Tue, 23 May 2023 17:12:51 +0100
From: Gary Guo <gary@...yguo.net>
To: Benno Lossin <benno.lossin@...ton.me>
Cc: Miguel Ojeda <ojeda@...nel.org>,
Alex Gaynor <alex.gaynor@...il.com>,
Wedson Almeida Filho <wedsonaf@...il.com>,
Boqun Feng <boqun.feng@...il.com>,
Björn Roy Baron <bjorn3_gh@...tonmail.com>,
rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
patches@...ts.linux.dev, Alice Ryhl <aliceryhl@...gle.com>
Subject: Re: [PATCH 3/4] rust: macros: replace Self with the concrete type
in #[pin_data]
On Mon, 24 Apr 2023 08:11:43 +0000
Benno Lossin <benno.lossin@...ton.me> wrote:
> When using `#[pin_data]` on a struct that used `Self` in the field
> types, a type error would be emitted when trying to use `pin_init!`.
> Since an internal type would be referenced by `Self` instead of the
> defined struct.
> This patch fixes this issue by replacing all occurrences of `Self` in
> the `#[pin_data]` macro with the concrete type circumventing the issue.
> Since rust allows type definitions inside of blocks, which are
> expressions, the macro also checks for these and emits a compile error
> when it finds `trait`, `enum`, `union`, `struct` or `impl`. These
> keywords allow creating new `Self` contexts, which conflicts with the
> current implementation of replacing every `Self` ident. If these were
> allowed, some `Self` idents would be replaced incorrectly.
>
> Signed-off-by: Benno Lossin <benno.lossin@...ton.me>
> Reported-by: Alice Ryhl <aliceryhl@...gle.com>
Reviewed-by: Gary Guo <gary@...yguo.net>
> ---
> rust/macros/pin_data.rs | 108 ++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 104 insertions(+), 4 deletions(-)
>
> diff --git a/rust/macros/pin_data.rs b/rust/macros/pin_data.rs
> index c593b05d9e8c..6d58cfda9872 100644
> --- a/rust/macros/pin_data.rs
> +++ b/rust/macros/pin_data.rs
> @@ -1,7 +1,7 @@
> // SPDX-License-Identifier: Apache-2.0 OR MIT
>
> use crate::helpers::{parse_generics, Generics};
> -use proc_macro::TokenStream;
> +use proc_macro::{Group, Punct, Spacing, TokenStream, TokenTree};
>
> pub(crate) fn pin_data(args: TokenStream, input: TokenStream) -> TokenStream {
> // This proc-macro only does some pre-parsing and then delegates the actual parsing to
> @@ -12,16 +12,116 @@ pub(crate) fn pin_data(args: TokenStream, input: TokenStream) -> TokenStream {
> impl_generics,
> ty_generics,
> },
> - mut rest,
> + rest,
> ) = parse_generics(input);
> + // The struct definition might contain the `Self` type. Since `__pin_data!` will define a new
> + // type with the same generics and bounds, this poses a problem, since `Self` will refer to the
> + // new type as opposed to this struct definition. Therefore we have to replace `Self` with the
> + // concrete name.
> +
> + // Errors that occur when replacing `Self` with `struct_name`.
> + let mut errs = TokenStream::new();
> + // The name of the struct with ty_generics.
> + let struct_name = rest
> + .iter()
> + .skip_while(|tt| !matches!(tt, TokenTree::Ident(i) if i.to_string() == "struct"))
> + .nth(1)
> + .and_then(|tt| match tt {
> + TokenTree::Ident(_) => {
> + let tt = tt.clone();
> + let mut res = vec![tt];
> + if !ty_generics.is_empty() {
> + // We add this, so it is maximally compatible with e.g. `Self::CONST` which
> + // will be replaced by `StructName::<$generics>::CONST`.
> + res.push(TokenTree::Punct(Punct::new(':', Spacing::Joint)));
> + res.push(TokenTree::Punct(Punct::new(':', Spacing::Alone)));
> + res.push(TokenTree::Punct(Punct::new('<', Spacing::Alone)));
> + res.extend(ty_generics.iter().cloned());
> + res.push(TokenTree::Punct(Punct::new('>', Spacing::Alone)));
> + }
> + Some(res)
> + }
> + _ => None,
> + })
> + .unwrap_or_else(|| {
> + // If we did not find the name of the struct then we will use `Self` as the replacement
> + // and add a compile error to ensure it does not compile.
> + errs.extend(
> + "::core::compile_error!(\"Could not locate type name.\");"
> + .parse::<TokenStream>()
> + .unwrap(),
> + );
> + "Self".parse::<TokenStream>().unwrap().into_iter().collect()
> + });
> + let impl_generics = impl_generics
> + .into_iter()
> + .flat_map(|tt| replace_self_and_deny_type_defs(&struct_name, tt, &mut errs))
> + .collect::<Vec<_>>();
> + let mut rest = rest
> + .into_iter()
> + .flat_map(|tt| {
> + // We ignore top level `struct` tokens, since they would emit a compile error.
> + if matches!(&tt, TokenTree::Ident(i) if i.to_string() == "struct") {
> + vec![tt]
> + } else {
> + replace_self_and_deny_type_defs(&struct_name, tt, &mut errs)
> + }
> + })
> + .collect::<Vec<_>>();
> // This should be the body of the struct `{...}`.
> let last = rest.pop();
> - quote!(::kernel::__pin_data! {
> + let mut quoted = quote!(::kernel::__pin_data! {
> parse_input:
> @args(#args),
> @sig(#(#rest)*),
> @impl_generics(#(#impl_generics)*),
> @ty_generics(#(#ty_generics)*),
> @body(#last),
> - })
> + });
> + quoted.extend(errs);
> + quoted
> +}
> +
> +/// Replaces `Self` with `struct_name` and errors on `enum`, `trait`, `struct` `union` and `impl`
> +/// keywords.
> +///
> +/// The error is appended to `errs` to allow normal parsing to continue.
> +fn replace_self_and_deny_type_defs(
> + struct_name: &Vec<TokenTree>,
> + tt: TokenTree,
> + errs: &mut TokenStream,
> +) -> Vec<TokenTree> {
> + match tt {
> + TokenTree::Ident(ref i)
> + if i.to_string() == "enum"
> + || i.to_string() == "trait"
> + || i.to_string() == "struct"
> + || i.to_string() == "union"
> + || i.to_string() == "impl" =>
> + {
> + errs.extend(
> + format!(
> + "::core::compile_error!(\"Cannot use `{i}` inside of struct definition with \
> + `#[pin_data]`.\");"
> + )
> + .parse::<TokenStream>()
> + .unwrap()
> + .into_iter()
> + .map(|mut tok| {
> + tok.set_span(tt.span());
> + tok
> + }),
> + );
> + vec![tt]
> + }
> + TokenTree::Ident(i) if i.to_string() == "Self" => struct_name.clone(),
> + TokenTree::Literal(_) | TokenTree::Punct(_) | TokenTree::Ident(_) => vec![tt],
> + TokenTree::Group(g) => vec![TokenTree::Group(Group::new(
> + g.delimiter(),
> + g.stream()
> + .into_iter()
> + .flat_map(|tt| replace_self_and_deny_type_defs(struct_name, tt, errs))
> + .collect(),
> + ))],
> + }
> }
> --
> 2.40.0
>
>
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