linux-kernel - Re: [PATCH 5/7] rust: str: take advantage of the `-> Result` support in KUnit `#[test]`'s

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Message-ID: <CANiq72kLz7nXOKR+f=pNCu=hEEs6XQV_oDr9-xB_sq7N+svQ3A@mail.gmail.com>
Date: Sun, 4 May 2025 23:54:33 +0200
From: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To: Tamir Duberstein <tamird@...il.com>, David Gow <davidgow@...gle.com>
Cc: Miguel Ojeda <ojeda@...nel.org>, Brendan Higgins <brendan.higgins@...ux.dev>, 
	Alex Gaynor <alex.gaynor@...il.com>, Rae Moar <rmoar@...gle.com>, 
	linux-kselftest@...r.kernel.org, kunit-dev@...glegroups.com, 
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>, 
	Danilo Krummrich <dakr@...nel.org>, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org, patches@...ts.linux.dev
Subject: Re: [PATCH 5/7] rust: str: take advantage of the `-> Result` support
 in KUnit `#[test]`'s

On Sun, May 4, 2025 at 8:23 PM Tamir Duberstein <tamird@...il.com> wrote:
>
> I see. Up to you, obviously, but ISTM that this degree of freedom is
> unnecessary, but perhaps there's a benefit I'm underappreciating?

Well, having this allows one to write code like the rest of the kernel
code, instead of, say, `.unwrap()`ing or `assert!`ing everywhere.

So easier to read, easier to copy-paste from normal code, and people
(especially those learning) wouldn't get accustomed to seeing
`.unwrap()`s etc. everywhere.

Having said that, C KUnit uses the macros for things that require
stopping the test, even if "unrelated" to the actual test, and it does
not look like normal code, of course. They do have `->init()` which
can return a failure, but not the test cases themselves.

David perhaps has some advice here. Perhaps test functions being
fallible (like returning `int`) were considered (or asserts for
"unrelated" things) for C at some point and discarded.

The custom `?` is quite tempting, to get the best of both worlds,
assuming we could make it work well.

> Even without this change, couldn't you apply
>
>      macro_rules! format {
>          ($($f:tt)*) => ({
> -            &*String::from_fmt(kernel::fmt!($($f)*))
> +            CString::try_from_fmt(kernel::fmt!($($f)*)).unwrap().to_str().unwrap()
>          })
>      }
>
> and achieve roughly the same reduction in line count in the test module?

Sure, the line would need to change again later, but that is fine too,
we can do a separate commit.

Cheers,
Miguel