linux-kernel - Re: [PATCH v1 1/2] rust: time: Rename Delta's methods as_micros_ceil and as

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Message-Id: <20250624.231428.764205178512881259.fujita.tomonori@gmail.com>
Date: Tue, 24 Jun 2025 23:14:28 +0900 (JST)
From: FUJITA Tomonori <fujita.tomonori@...il.com>
To: aliceryhl@...gle.com
Cc: fujita.tomonori@...il.com, miguel.ojeda.sandonis@...il.com,
 a.hindborg@...nel.org, alex.gaynor@...il.com, ojeda@...nel.org,
 anna-maria@...utronix.de, bjorn3_gh@...tonmail.com, boqun.feng@...il.com,
 dakr@...nel.org, frederic@...nel.org, gary@...yguo.net,
 jstultz@...gle.com, linux-kernel@...r.kernel.org, lossin@...nel.org,
 lyude@...hat.com, rust-for-linux@...r.kernel.org, sboyd@...nel.org,
 tglx@...utronix.de, tmgross@...ch.edu
Subject: Re: [PATCH v1 1/2] rust: time: Rename Delta's methods
 as_micros_ceil and as_millis

On Tue, 24 Jun 2025 14:54:24 +0100
Alice Ryhl <aliceryhl@...gle.com> wrote:

>> >> So would the function be defined like this?
>> >>
>> >> fn as_nanos(self) -> i64;
>> >>
>> >> If that's the case, then we've come full circle back to the original
>> >> problem; Clippy warns against using as_* names for trait methods that
>> >> take self as follows:
>> >>
>> >> warning: methods called `as_*` usually take `self` by reference or `self` by mutable reference
>> >>    --> /home/fujita/git/linux-rust/rust/kernel/time/hrtimer.rs:430:17
>> >>     |
>> >> 430 |     fn as_nanos(self) -> i64;
>> >>     |                 ^^^^
>> >>     |
>> >>     = help: consider choosing a less ambiguous name
>> >>     = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#wrong_self_convention
>> >>     = note: `-W clippy::wrong-self-convention` implied by `-W clippy::all`
>> >>     = help: to override `-W clippy::all` add `#[allow(clippy::wrong_self_convention)]`
>> >>
>> >> https://lore.kernel.org/rust-for-linux/20250610132823.3457263-2-fujita.tomonori@gmail.com/
>> >
>> > Are we missing a derive(Copy) for this type? Clippy does not emit that
>> > lint if the type is Copy:
>> > https://github.com/rust-lang/rust-clippy/issues/273
>>
>> I think that both Delta and Instant structs implement Copy.
>>
>> #[repr(transparent)]
>> #[derive(PartialEq, PartialOrd, Eq, Ord)]
>> pub struct Instant<C: ClockSource> {
>>     inner: bindings::ktime_t,
>>     _c: PhantomData<C>,
>> }
>>
>> impl<C: ClockSource> Clone for Instant<C> {
>>     fn clone(&self) -> Self {
>>         *self
>>     }
>> }
>>
>> impl<C: ClockSource> Copy for Instant<C> {}
>>
>> #[derive(Copy, Clone, PartialEq, PartialOrd, Eq, Ord, Debug)]
>> pub struct Delta {
>>     nanos: i64,
>> }
>>
>> The above warning is about the trait method.
> 
> Wait, it's a trait method!?

Yes. Clippy warns the following implementation:

pub trait HrTimerExpires {
    fn as_nanos(self) -> i64;
}

Clippy doesn't warn when the methods on Delta and Instant are written
similarly. So Clippy is happy about the followings:

pub trait HrTimerExpires {
    fn as_nanos(&self) -> i64;
}

impl HrTimerExpires for Delta {
    fn as_nanos(&self) -> i64 {
        Delta::as_nanos(*self)
    }
}