linux-kernel - Re: [PATCH v2] rust: macros: vtable: fix `HAS_*` redefinition (`gen_const

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Date:   Sun, 6 Aug 2023 17:02:01 +0100
From:   Gary Guo <gary@...yguo.net>
To:     "Qingsong Chen" <changxian.cqs@...group.com>
Cc:     linux-kernel@...r.kernel.org,
        "田洪亮" <tate.thl@...group.com>,
        "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>,
        "Benno Lossin" <benno.lossin@...ton.me>,
        "Sergio González Collado" <sergio.collado@...il.com>,
        <rust-for-linux@...r.kernel.org>
Subject: Re: [PATCH v2] rust: macros: vtable: fix `HAS_*` redefinition
 (`gen_const_name`)

On Thu, 03 Aug 2023 22:09:23 +0800
"Qingsong Chen" <changxian.cqs@...group.com> wrote:

> If we define the same function name twice in a trait (using `#[cfg]`),
> the `vtable` macro will redefine its `gen_const_name`, e.g. this will
> define `HAS_BAR` twice:
> 
> ```rust
>     #[vtable]
>     pub trait Foo {
>         #[cfg(CONFIG_X)]
>         fn bar();
> 
>         #[cfg(not(CONFIG_X))]
>         fn bar(x: usize);
>     }
> ```
> 
> Changelog:
> ----------
> v1 -> v2:
> - Use `BTreeSet` and existing `consts` as suggested by Alice and Gary.
> - Reword commit messages as suggested by Miguel.
> ====================
> 
> Fixes: b44becc5ee80 ("rust: macros: add `#[vtable]` proc macro")
> Signed-off-by: Qingsong Chen <changxian.cqs@...group.com>
> ---
>  rust/macros/vtable.rs | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/rust/macros/vtable.rs b/rust/macros/vtable.rs
> index 34d5e7fb5768..8a1baedcc280 100644
> --- a/rust/macros/vtable.rs
> +++ b/rust/macros/vtable.rs
> @@ -1,7 +1,7 @@
>  // SPDX-License-Identifier: GPL-2.0
>  
>  use proc_macro::{Delimiter, Group, TokenStream, TokenTree};
> -use std::collections::HashSet;
> +use std::collections::BTreeSet;
>  use std::fmt::Write;
>  
>  pub(crate) fn vtable(_attr: TokenStream, ts: TokenStream) -> TokenStream {
> @@ -28,7 +28,7 @@ pub(crate) fn vtable(_attr: TokenStream, ts: TokenStream) -> TokenStream {
>  
>      let mut body_it = body.stream().into_iter();
>      let mut functions = Vec::new();
> -    let mut consts = HashSet::new();
> +    let mut consts = BTreeSet::new();

I don't think this is actually necessary because `consts` is never
iterated on.

>      while let Some(token) = body_it.next() {
>          match token {
>              TokenTree::Ident(ident) if ident.to_string() == "fn" => {
> @@ -74,6 +74,7 @@ pub(crate) fn vtable(_attr: TokenStream, ts: TokenStream) -> TokenStream {
>                  const {gen_const_name}: bool = false;",
>              )
>              .unwrap();
> +            consts.insert(gen_const_name);
>          }
>      } else {
>          const_items = "const USE_VTABLE_ATTR: () = ();".to_owned();