Re: [PATCH 3/4] rust: macros: replace Self with the concrete type in #[pin_data]

[Martin Rodriguez Reboredo <yakoyoku@gmail.com>]

On 4/24/23 05:11, Benno Lossin 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@proton.me>
> Reported-by: Alice Ryhl <aliceryhl@google.com>
> ---
>  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
> 
> 

Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>