linux-kernel - Re: [PATCH 2/3] rust: kernel: move `build_error` hidden function to prevent mistakes

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Message-ID: <CAH5fLggK_uL0izyDogqdxqp+UEiDbMW555zgS6jk=gw3n07f6A@mail.gmail.com>
Date: Mon, 25 Nov 2024 10:14:09 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: Miguel Ojeda <ojeda@...nel.org>
Cc: Alex Gaynor <alex.gaynor@...il.com>, FUJITA Tomonori <fujita.tomonori@...il.com>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Boqun Feng <boqun.feng@...il.com>, 
	Gary Guo <gary@...yguo.net>, Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <benno.lossin@...ton.me>, Trevor Gross <tmgross@...ch.edu>, 
	rust-for-linux@...r.kernel.org, netdev@...r.kernel.org, 
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org, 
	patches@...ts.linux.dev
Subject: Re: [PATCH 2/3] rust: kernel: move `build_error` hidden function to
 prevent mistakes

On Sat, Nov 23, 2024 at 11:29 PM Miguel Ojeda <ojeda@...nel.org> wrote:
>
> Users were using the hidden exported `kernel::build_error` function
> instead of the intended `kernel::build_error!` macro, e.g. see the
> previous commit.
>
> To force to use the macro, move it into the `build_assert` module,
> thus making it a compilation error and avoiding a collision in the same
> "namespace". Using the function now would require typing the module name
> (which is hidden), not just a single character.
>
> Now attempting to use the function will trigger this error with the
> right suggestion by the compiler:
>
>       error[E0423]: expected function, found macro `kernel::build_error`
>       --> samples/rust/rust_minimal.rs:29:9
>          |
>       29 |         kernel::build_error();
>          |         ^^^^^^^^^^^^^^^^^^^ not a function
>          |
>       help: use `!` to invoke the macro
>          |
>       29 |         kernel::build_error!();
>          |                            +
>
> An alternative would be using an alias, but it would be more complex
> and moving it into the module seems right since it belongs there and
> reduces the amount of code at the crate root.
>
> Keep the `#[doc(hidden)]` inside `build_assert` in case the module is
> not hidden in the future.
>
> Signed-off-by: Miguel Ojeda <ojeda@...nel.org>

Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>

> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> index bf8d7f841f94..73e33a41ea04 100644
> --- a/rust/kernel/lib.rs
> +++ b/rust/kernel/lib.rs
> @@ -32,7 +32,8 @@
>  pub mod alloc;
>  #[cfg(CONFIG_BLOCK)]
>  pub mod block;
> -mod build_assert;
> +#[doc(hidden)]
> +pub mod build_assert;

You could also put #![doc(hidden)] at the top of build_assert.rs to
simplify the lib.rs list. Not sure what is best.

Alice