Re: [PATCH v3 2/3] rust: macros: add macro to easily run KUnit tests

[Boqun Feng <boqun.feng@gmail.com>]

On Wed, Oct 30, 2024 at 12:57:14PM +0800, David Gow wrote:
> From: José Expósito <jose.exposito89@gmail.com>
> Add a new procedural macro (`#[kunit_tests(kunit_test_suit_name)]`) to
> run KUnit tests using a user-space like syntax.
> 
> The macro, that should be used on modules, transforms every `#[test]`
> in a `kunit_case!` and adds a `kunit_unsafe_test_suite!` registering
> all of them.
> 
> The only difference with user-space tests is that instead of using
> `#[cfg(test)]`, `#[kunit_tests(kunit_test_suit_name)]` is used.
> 
> Note that `#[cfg(CONFIG_KUNIT)]` is added so the test module is not
> compiled when `CONFIG_KUNIT` is set to `n`.
> 
> Reviewed-by: David Gow <davidgow@google.com>
> Signed-off-by: José Expósito <jose.exposito89@gmail.com>
> [Updated to use new const fn.]
> Signed-off-by: David Gow <davidgow@google.com>
> ---
> 
> Changes since v2:
> https://lore.kernel.org/linux-kselftest/20241029092422.2884505-3-davidgow@google.com/
> - Include missing rust/macros/kunit.rs file from v2. (Thanks Boqun!)
> - The proc macro now emits an error if the suite name is too long.
> 
> Changes since v1:
> https://lore.kernel.org/lkml/20230720-rustbind-v1-2-c80db349e3b5@google.com/
> - Rebased on top of rust-next
> - Make use of the new const functions, rather than the kunit_case!()
>   macro.
> 
> ---
>  MAINTAINERS          |   1 +
>  rust/kernel/kunit.rs |  11 ++++
>  rust/macros/kunit.rs | 153 +++++++++++++++++++++++++++++++++++++++++++
>  rust/macros/lib.rs   |  29 ++++++++
>  4 files changed, 194 insertions(+)
>  create mode 100644 rust/macros/kunit.rs
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index b77f4495dcf4..b65035ede675 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -12433,6 +12433,7 @@ F:	Documentation/dev-tools/kunit/
>  F:	include/kunit/
>  F:	lib/kunit/
>  F:	rust/kernel/kunit.rs
> +F:	rust/macros/kunit.rs
>  F:	scripts/rustdoc_test_*
>  F:	tools/testing/kunit/
>  
> diff --git a/rust/kernel/kunit.rs b/rust/kernel/kunit.rs
> index 27bc4139d352..ac296467a552 100644
> --- a/rust/kernel/kunit.rs
> +++ b/rust/kernel/kunit.rs
> @@ -40,6 +40,8 @@ pub fn info(args: fmt::Arguments<'_>) {
>      }
>  }
>  
> +use macros::kunit_tests;
> +
>  /// Asserts that a boolean expression is `true` at runtime.
>  ///
>  /// Public but hidden since it should only be used from generated tests.
> @@ -269,3 +271,12 @@ macro_rules! kunit_unsafe_test_suite {
>          };
>      };
>  }
> +
> +#[kunit_tests(rust_kernel_kunit)]
> +mod tests {
> +    #[test]
> +    fn rust_test_kunit_kunit_tests() {
> +        let running = true;
> +        assert_eq!(running, true);
> +    }
> +}
> diff --git a/rust/macros/kunit.rs b/rust/macros/kunit.rs
> new file mode 100644
> index 000000000000..850d268cc96a
> --- /dev/null
> +++ b/rust/macros/kunit.rs
> @@ -0,0 +1,153 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! Procedural macro to run KUnit tests using a user-space like syntax.
> +//!
> +//! Copyright (c) 2023 José Expósito <jose.exposito89@gmail.com>
> +
> +use proc_macro::{Delimiter, Group, TokenStream, TokenTree};
> +use std::fmt::Write;
> +
> +pub(crate) fn kunit_tests(attr: TokenStream, ts: TokenStream) -> TokenStream {
> +    if attr.to_string().is_empty() {
> +        panic!("Missing test name in #[kunit_tests(test_name)] macro")
> +    }
> +
> +    if attr.to_string().as_bytes().len() > 255 {
> +        panic!("The test suite name `{}` exceeds the maximum length of 255 bytes.", attr)
> +    }
> +
> +    let mut tokens: Vec<_> = ts.into_iter().collect();
> +
> +    // Scan for the "mod" keyword.
> +    tokens
> +        .iter()
> +        .find_map(|token| match token {
> +            TokenTree::Ident(ident) => match ident.to_string().as_str() {
> +                "mod" => Some(true),
> +                _ => None,
> +            },
> +            _ => None,
> +        })
> +        .expect("#[kunit_tests(test_name)] attribute should only be applied to modules");
> +
> +    // Retrieve the main body. The main body should be the last token tree.
> +    let body = match tokens.pop() {
> +        Some(TokenTree::Group(group)) if group.delimiter() == Delimiter::Brace => group,
> +        _ => panic!("cannot locate main body of module"),
> +    };
> +
> +    // Get the functions set as tests. Search for `[test]` -> `fn`.
> +    let mut body_it = body.stream().into_iter();
> +    let mut tests = Vec::new();
> +    while let Some(token) = body_it.next() {
> +        match token {
> +            TokenTree::Group(ident) if ident.to_string() == "[test]" => match body_it.next() {
> +                Some(TokenTree::Ident(ident)) if ident.to_string() == "fn" => {
> +                    let test_name = match body_it.next() {
> +                        Some(TokenTree::Ident(ident)) => ident.to_string(),
> +                        _ => continue,
> +                    };
> +                    tests.push(test_name);
> +                }
> +                _ => continue,
> +            },
> +            _ => (),
> +        }
> +    }
> +
> +    // Add `#[cfg(CONFIG_KUNIT)]` before the module declaration.
> +    let config_kunit = "#[cfg(CONFIG_KUNIT)]".to_owned().parse().unwrap();
> +    tokens.insert(
> +        0,
> +        TokenTree::Group(Group::new(Delimiter::None, config_kunit)),
> +    );
> +
> +    // Generate the test KUnit test suite and a test case for each `#[test]`.
> +    // The code generated for the following test module:
> +    //
> +    // ```
> +    // #[kunit_tests(kunit_test_suit_name)]
> +    // mod tests {
> +    //     #[test]
> +    //     fn foo() {
> +    //         assert_eq!(1, 1);
> +    //     }
> +    //
> +    //     #[test]
> +    //     fn bar() {
> +    //         assert_eq!(2, 2);
> +    //     }
> +    // ```
> +    //
> +    // Looks like:
> +    //
> +    // ```
> +    // unsafe extern "C" fn kunit_rust_wrapper_foo(_test: *mut kernel::bindings::kunit) {
> +    //     foo();
> +    // }
> +    // static mut KUNIT_CASE_FOO: kernel::bindings::kunit_case =
> +    //     kernel::kunit::kunit_case(foo, kunit_rust_wrapper_foo);
> +    //
> +    // unsafe extern "C" fn kunit_rust_wrapper_bar(_test: * mut kernel::bindings::kunit) {
> +    //     bar();
> +    // }
> +    // static mut KUNIT_CASE_BAR: kernel::bindings::kunit_case =
> +    //     kernel::kunit::kunit_case(bar, kunit_rust_wrapper_bar);
> +    //
> +    // static mut KUNIT_CASE_NULL: kernel::bindings::kunit_case = kernel::kunit::kunit_case_null();
> +    //
> +    // static mut TEST_CASES : &mut[kernel::bindings::kunit_case] = unsafe {
> +    //     &mut [KUNIT_CASE_FOO, KUNIT_CASE_BAR, KUNIT_CASE_NULL]
> +    // };
> +    //
> +    // kernel::kunit_unsafe_test_suite!(kunit_test_suit_name, TEST_CASES);
> +    // ```
> +    let mut kunit_macros = "".to_owned();
> +    let mut test_cases = "".to_owned();
> +    for test in tests {
> +        let kunit_wrapper_fn_name = format!("kunit_rust_wrapper_{}", test);
> +        let kunit_case_name = format!("KUNIT_CASE_{}", test.to_uppercase());
> +        let kunit_wrapper = format!(
> +            "unsafe extern \"C\" fn {}(_test: *mut kernel::bindings::kunit) {{ {}(); }}",
> +            kunit_wrapper_fn_name, test
> +        );
> +        let kunit_case = format!(
> +            "static mut {}: kernel::bindings::kunit_case = kernel::kunit::kunit_case(kernel::c_str!(\"{}\"), {});",
> +            kunit_case_name, test, kunit_wrapper_fn_name
> +        );
> +        writeln!(kunit_macros, "{kunit_wrapper}").unwrap();
> +        writeln!(kunit_macros, "{kunit_case}").unwrap();
> +        writeln!(test_cases, "{kunit_case_name},").unwrap();
> +    }
> +
> +    writeln!(
> +        kunit_macros,
> +        "static mut KUNIT_CASE_NULL: kernel::bindings::kunit_case = kernel::kunit::kunit_case_null();"
> +    )
> +    .unwrap();
> +
> +    writeln!(
> +        kunit_macros,
> +        "static mut TEST_CASES : &mut[kernel::bindings::kunit_case] = unsafe {{ &mut[{test_cases} KUNIT_CASE_NULL] }};"
> +    )
> +    .unwrap();
> +
> +    writeln!(
> +        kunit_macros,
> +        "kernel::kunit_unsafe_test_suite!({attr}, TEST_CASES);"
> +    )
> +    .unwrap();
> +
> +    let new_body: TokenStream = vec![body.stream(), kunit_macros.parse().unwrap()]
> +        .into_iter()
> +        .collect();
> +
> +    // Remove the `#[test]` macros.
> +    let new_body = new_body.to_string().replace("#[test]", "");

Yeah, I want to see how you do it this time ;-) So if you do a
`.to_string()` on a `TokenStream`, you lose all the span [1] information
("span information" is a term invited by me, hope I get it right ;-))
e.g. if there is a compile error in the test code, the compiler cannot
report the exact line of the error, it can only report there is an
error.

Last time I find how to preserve the Span:

	https://lore.kernel.org/rust-for-linux/ZMba0_XXZuTgWyWY@boqun-archlinux/

Hope it helps!

[1]: https://doc.rust-lang.org/proc_macro/struct.Span.html

Regards,
Boqun

> +    tokens.push(TokenTree::Group(Group::new(
> +        Delimiter::Brace,
> +        new_body.parse().unwrap(),
> +    )));
> +
> +    tokens.into_iter().collect()
> +}
> diff --git a/rust/macros/lib.rs b/rust/macros/lib.rs
> index 939ae00b723a..098925b99982 100644
> --- a/rust/macros/lib.rs
> +++ b/rust/macros/lib.rs
> @@ -10,6 +10,7 @@
>  mod quote;
>  mod concat_idents;
>  mod helpers;
> +mod kunit;
>  mod module;
>  mod paste;
>  mod pin_data;
> @@ -430,3 +431,31 @@ pub fn paste(input: TokenStream) -> TokenStream {
>  pub fn derive_zeroable(input: TokenStream) -> TokenStream {
>      zeroable::derive(input)
>  }
> +
> +/// Registers a KUnit test suite and its test cases using a user-space like syntax.
> +///
> +/// This macro should be used on modules. If `CONFIG_KUNIT` (in `.config`) is `n`, the target module
> +/// is ignored.
> +///
> +/// # Examples
> +///
> +/// ```ignore
> +/// # use macros::kunit_tests;
> +///
> +/// #[kunit_tests(kunit_test_suit_name)]
> +/// mod tests {
> +///     #[test]
> +///     fn foo() {
> +///         assert_eq!(1, 1);
> +///     }
> +///
> +///     #[test]
> +///     fn bar() {
> +///         assert_eq!(2, 2);
> +///     }
> +/// }
> +/// ```
> +#[proc_macro_attribute]
> +pub fn kunit_tests(attr: TokenStream, ts: TokenStream) -> TokenStream {
> +    kunit::kunit_tests(attr, ts)
> +}
> -- 
> 2.47.0.163.g1226f6d8fa-goog
>