Re: [PATCH v2 1/3] rust: kunit: add KUnit case and suite macros

[Alice Ryhl <aliceryhl@google.com>]

On Wed, Oct 30, 2024 at 5:59 AM David Gow <davidgow@google.com> wrote:
>
> On Tue, 29 Oct 2024 at 20:08, Alice Ryhl <aliceryhl@google.com> wrote:
> >
> > On Tue, Oct 29, 2024 at 10:24 AM David Gow <davidgow@google.com> wrote:
> > >
> > > From: José Expósito <jose.exposito89@gmail.com>
> > >
> > > Add a couple of Rust const functions and macros to allow to develop
> > > KUnit tests without relying on generated C code:
> > >
> > >  - The `kunit_unsafe_test_suite!` Rust macro is similar to the
> > >    `kunit_test_suite` C macro. It requires a NULL-terminated array of
> > >    test cases (see below).
> > >  - The `kunit_case` Rust function is similar to the `KUNIT_CASE` C macro.
> > >    It generates as case from the name and function.
> > >  - The `kunit_case_null` Rust function generates a NULL test case, which
> > >    is to be used as delimiter in `kunit_test_suite!`.
> > >
> > > While these functions and macros can be used on their own, a future
> > > patch will introduce another macro to create KUnit tests using a
> > > user-space like syntax.
> > >
> > > Signed-off-by: José Expósito <jose.exposito89@gmail.com>
> > > Co-developed-by: Matt Gilbride <mattgilbride@google.com>
> > > Signed-off-by: Matt Gilbride <mattgilbride@google.com>
> > > Co-developed-by: David Gow <davidgow@google.com>
> > > Signed-off-by: David Gow <davidgow@google.com>
> > > ---
> > >
> > > Changes since v1:
> > > https://lore.kernel.org/lkml/20230720-rustbind-v1-1-c80db349e3b5@google.com/
> > > - Rebase on top of rust-next
> > > - As a result, KUnit attributes are new set. These are hardcoded to the
> > >   defaults of "normal" speed and no module name.
> > > - Split the kunit_case!() macro into two const functions, kunit_case()
> > >   and kunit_case_null() (for the NULL terminator).
> > >
> > > ---
> > >  rust/kernel/kunit.rs | 108 +++++++++++++++++++++++++++++++++++++++++++
> > >  rust/kernel/lib.rs   |   1 +
> > >  2 files changed, 109 insertions(+)
> > >
> > > diff --git a/rust/kernel/kunit.rs b/rust/kernel/kunit.rs
> > > index 824da0e9738a..fc2d259db458 100644
> > > --- a/rust/kernel/kunit.rs
> > > +++ b/rust/kernel/kunit.rs
> > > @@ -161,3 +161,111 @@ macro_rules! kunit_assert_eq {
> > >          $crate::kunit_assert!($name, $file, $diff, $left == $right);
> > >      }};
> > >  }
> > > +
> > > +/// Represents an individual test case.
> > > +///
> > > +/// The test case should have the signature
> > > +/// `unsafe extern "C" fn test_case(test: *mut crate::bindings::kunit)`.
> > > +///
> > > +/// The `kunit_unsafe_test_suite!` macro expects a NULL-terminated list of test cases.
> > > +/// Use `kunit_case_null` to generate such a delimeter.
> > > +const fn kunit_case(name: &kernel::str::CStr, run_case: unsafe extern "C" fn(*mut kernel::bindings::kunit)) -> kernel::bindings::kunit_case {
> >
> > This should probably say `name: &'static CStr` to require that the
> > name lives forever.
>
> Fixed in v3, thanks.
>
> > > +/// Registers a KUnit test suite.
> > > +///
> > > +/// # Safety
> > > +///
> > > +/// `test_cases` must be a NULL terminated array of test cases.
> > > +///
> > > +/// # Examples
> > > +///
> > > +/// ```ignore
> > > +/// unsafe extern "C" fn test_fn(_test: *mut crate::bindings::kunit) {
> > > +///     let actual = 1 + 1;
> > > +///     let expected = 2;
> > > +///     assert_eq!(actual, expected);
> > > +/// }
> > > +///
> > > +/// static mut KUNIT_TEST_CASE: crate::bindings::kunit_case = crate::kunit_case(name, test_fn);
> > > +/// static mut KUNIT_NULL_CASE: crate::bindings::kunit_case = crate::kunit_case_null();
> > > +/// static mut KUNIT_TEST_CASES: &mut[crate::bindings::kunit_case] = unsafe {
> > > +///     &mut[KUNIT_TEST_CASE, KUNIT_NULL_CASE]
> > > +/// };
> > > +/// crate::kunit_unsafe_test_suite!(suite_name, KUNIT_TEST_CASES);
> > > +/// ```
> > > +#[macro_export]
> > > +macro_rules! kunit_unsafe_test_suite {
> > > +    ($name:ident, $test_cases:ident) => {
> > > +        const _: () = {
> > > +            static KUNIT_TEST_SUITE_NAME: [i8; 256] = {
> > > +                let name_u8 = core::stringify!($name).as_bytes();
> > > +                let mut ret = [0; 256];
> > > +
> > > +                let mut i = 0;
> > > +                while i < name_u8.len() {
> > > +                    ret[i] = name_u8[i] as i8;
> > > +                    i += 1;
> > > +                }
> >
> > I assume the name must be zero-terminated? If so, you probably need to
> > enforce that somehow, e.g. by failing if `name_u8` is longer than 255
> > bytes.
>
> Nice catch. I'm not sure how to nicely throw a compile time error in
> this function, so I'm truncating it here and doing a compile error in
> the macro in patch #2. This isn't ideal, but seems to work.

You should be able to just panic! if it happens.

Also, I believe it should be i < 255 instead of 256?

Alice