From 1f9ed172545687e5c04c77490a45896be6d2e459 Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Wed, 4 Sep 2024 22:43:45 +0200 Subject: rust: start using the `#[expect(...)]` attribute In Rust, it is possible to `allow` particular warnings (diagnostics, lints) locally, making the compiler ignore instances of a given warning within a given function, module, block, etc. It is similar to `#pragma GCC diagnostic push` + `ignored` + `pop` in C: #pragma GCC diagnostic push #pragma GCC diagnostic ignored "-Wunused-function" static void f(void) {} #pragma GCC diagnostic pop But way less verbose: #[allow(dead_code)] fn f() {} By that virtue, it makes it possible to comfortably enable more diagnostics by default (i.e. outside `W=` levels) that may have some false positives but that are otherwise quite useful to keep enabled to catch potential mistakes. The `#[expect(...)]` attribute [1] takes this further, and makes the compiler warn if the diagnostic was _not_ produced. For instance, the following will ensure that, when `f()` is called somewhere, we will have to remove the attribute: #[expect(dead_code)] fn f() {} If we do not, we get a warning from the compiler: warning: this lint expectation is unfulfilled --> x.rs:3:10 | 3 | #[expect(dead_code)] | ^^^^^^^^^ | = note: `#[warn(unfulfilled_lint_expectations)]` on by default This means that `expect`s do not get forgotten when they are not needed. See the next commit for more details, nuances on its usage and documentation on the feature. The attribute requires the `lint_reasons` [2] unstable feature, but it is becoming stable in 1.81.0 (to be released on 2024-09-05) and it has already been useful to clean things up in this patch series, finding cases where the `allow`s should not have been there. Thus, enable `lint_reasons` and convert some of our `allow`s to `expect`s where possible. This feature was also an example of the ongoing collaboration between Rust and the kernel -- we tested it in the kernel early on and found an issue that was quickly resolved [3]. Cc: Fridtjof Stoldt Cc: Urgau Link: https://rust-lang.github.io/rfcs/2383-lint-reasons.html#expect-lint-attribute [1] Link: https://github.com/rust-lang/rust/issues/54503 [2] Link: https://github.com/rust-lang/rust/issues/114557 [3] Reviewed-by: Alice Ryhl Reviewed-by: Trevor Gross Tested-by: Gary Guo Reviewed-by: Gary Guo Link: https://lore.kernel.org/r/20240904204347.168520-18-ojeda@kernel.org Signed-off-by: Miguel Ojeda --- rust/kernel/print.rs | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'rust/kernel/print.rs') diff --git a/rust/kernel/print.rs b/rust/kernel/print.rs index 45af17095a24..a28077a7cb30 100644 --- a/rust/kernel/print.rs +++ b/rust/kernel/print.rs @@ -14,7 +14,7 @@ use core::{ use crate::str::RawFormatter; // Called from `vsprintf` with format specifier `%pA`. -#[allow(clippy::missing_safety_doc)] +#[expect(clippy::missing_safety_doc)] #[no_mangle] unsafe extern "C" fn rust_fmt_argument( buf: *mut c_char, @@ -140,7 +140,7 @@ pub fn call_printk_cont(args: fmt::Arguments<'_>) { #[doc(hidden)] #[cfg(not(testlib))] #[macro_export] -#[allow(clippy::crate_in_macro_def)] +#[expect(clippy::crate_in_macro_def)] macro_rules! print_macro ( // The non-continuation cases (most of them, e.g. `INFO`). ($format_string:path, false, $($arg:tt)+) => ( -- cgit