linux-kernel - Re: [PATCH] rust: init: change the generated name of guard variables

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Message-ID: <20240417160636.0e649b68@eugeo>
Date: Wed, 17 Apr 2024 16:06:36 +0100
From: Gary Guo <gary@...yguo.net>
To: Benno Lossin <benno.lossin@...ton.me>
Cc: Boqun Feng <boqun.feng@...il.com>, Miguel Ojeda <ojeda@...nel.org>, Alex
 Gaynor <alex.gaynor@...il.com>, Wedson Almeida Filho <wedsonaf@...il.com>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>, Andreas Hindborg
 <a.hindborg@...sung.com>, Alice Ryhl <aliceryhl@...gle.com>, Martin
 Rodriguez Reboredo <yakoyoku@...il.com>, rust-for-linux@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rust: init: change the generated name of guard
 variables

On Wed, 03 Apr 2024 22:09:49 +0000
Benno Lossin <benno.lossin@...ton.me> wrote:

> On 03.04.24 23:20, Boqun Feng wrote:
> > On Wed, Apr 03, 2024 at 07:43:37PM +0000, Benno Lossin wrote:  
> >> The initializers created by the `[try_][pin_]init!` macros utilize the
> >> guard pattern to drop already initialized fields, when initialization
> >> fails mid-way. These guards are generated to have the same name as the
> >> field that they handle. To prevent namespacing issues when the field  
> > 
> > Do you have an example of this kind of issues?  
> 
> https://lore.kernel.org/rust-for-linux/1e8a2a1f-abbf-44ba-8344-705a9cbb1627@proton.me/
> 

Here's the simplified example:

```
macro_rules! f {
    () => {
        let a = 1;
        let _: u32 = a;
    }
}

const a: u64 = 1;

fn main() {
    f!();
}
```

The `a` in `f` have a different hygiene so normally it is scoped to the
macro expansion and wouldn't escape. Interestingly a constant is still
preferred despite the hygiene so constants escaped into the macro,
leading to the error.

Would your change regress error message when `pin_init!` is used
wrongly? Personally I would say this kind of error is niche enough
(given the casing of constants and variables differ) that we probably
don't really need to care. So if error message would be affected then
we'd better off not making the change.

Best,
Gary