rust: macros: add macro to easily run KUnit tests

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>

rust/kernel/kunit.rs

@@ -6,6 +6,8 @@
 //!
 //! Reference: <https://www.kernel.org/doc/html/latest/dev-tools/kunit/index.html>
 
+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.
@@ -180,3 +182,12 @@ 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);
+    }
+}

rust/kernel/lib.rs

@@ -31,6 +31,8 @@
 #[cfg(not(CONFIG_RUST))]
 compile_error!("Missing kernel configuration for conditional compilation");
 
+extern crate self as kernel;
+
 #[cfg(not(test))]
 #[cfg(not(testlib))]
 mod allocator;

rust/macros/kunit.rs

@@ -0,0 +1,149 @@
+// 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")
+    }
+
+    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_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_case!(bar, kunit_rust_wrapper_bar);
+    //
+    // static mut KUNIT_CASE_NULL: kernel::bindings::kunit_case = kernel::kunit_case!();
+    //
+    // 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_case!({}, {});",
+            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_case!();"
+    )
+    .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]", "");
+    tokens.push(TokenTree::Group(Group::new(
+        Delimiter::Brace,
+        new_body.parse().unwrap(),
+    )));
+
+    tokens.into_iter().collect()
+}

rust/macros/lib.rs

@@ -4,6 +4,7 @@
 
 mod concat_idents;
 mod helpers;
+mod kunit;
 mod module;
 mod vtable;
 
@@ -189,3 +190,31 @@ pub fn vtable(attr: TokenStream, ts: TokenStream) -> TokenStream {
 pub fn concat_idents(ts: TokenStream) -> TokenStream {
     concat_idents::concat_idents(ts)
 }
+
+/// 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)
+}