rust: tests: add Kconfig for KUnit test

There are 6 individual Rust KUnit test suites (plus the doctests one). All
the tests are compiled unconditionally now, which adds ~200 kB to the
kernel image for me on x86_64. As Rust matures, this bloating will
inevitably grow.

Add Kconfig.test which includes a RUST_KUNIT_TESTS menu, and all
individual tests under it.

As usual, new tests are all enabled if KUNIT_ALL_TESTS=y.

Suggested-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Yury Norov <ynorov@nvidia.com>
Reviewed-by: David Gow <david@davidgow.net>
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260417031531.315281-3-ynorov@nvidia.com
[ Fixed capitalization. Used singular for "API" for consistency.
  Reworded to clarify these are suites and that there exists
  the doctests one (which is the biggest at the moment by
  far). - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

init/Kconfig

@@ -2213,6 +2213,8 @@ config RUST
 
 	  If unsure, say N.
 
+source "rust/kernel/Kconfig.test"
+
 config RUSTC_VERSION_TEXT
 	string
 	depends on RUST

rust/kernel/Kconfig.test

@@ -0,0 +1,76 @@
+# SPDX-License-Identifier: GPL-2.0-only
+menuconfig RUST_KUNIT_TESTS
+	bool "Rust KUnit tests"
+	depends on KUNIT && RUST
+	default KUNIT_ALL_TESTS
+	help
+	  This menu collects all options for Rust KUnit tests.
+	  See Documentation/rust/testing.rst for how to protect
+	  unit tests with these options.
+
+	  Say Y here to enable Rust KUnit tests.
+
+	  If unsure, say N.
+
+if RUST_KUNIT_TESTS
+config RUST_ALLOCATOR_KUNIT_TEST
+	bool "KUnit tests for Rust allocator API" if !KUNIT_ALL_TESTS
+	default KUNIT_ALL_TESTS
+	help
+	  This option enables KUnit tests for the Rust allocator API.
+	  These are only for development and testing, not for regular
+	  kernel use cases.
+
+	  If unsure, say N.
+
+config RUST_KVEC_KUNIT_TEST
+	bool "KUnit tests for Rust KVec API" if !KUNIT_ALL_TESTS
+	default KUNIT_ALL_TESTS
+	help
+	  This option enables KUnit tests for the Rust KVec API.
+	  These are only for development and testing, not for
+	  regular kernel use cases.
+
+	  If unsure, say N.
+
+config RUST_BITMAP_KUNIT_TEST
+	bool "KUnit tests for Rust bitmap API" if !KUNIT_ALL_TESTS
+	default KUNIT_ALL_TESTS
+	help
+	  This option enables KUnit tests for the Rust bitmap API.
+	  These are only for development and testing, not for regular
+	  kernel use cases.
+
+	  If unsure, say N.
+
+config RUST_KUNIT_SELFTEST
+	bool "KUnit selftests for Rust" if !KUNIT_ALL_TESTS
+	default KUNIT_ALL_TESTS
+	help
+	  This option enables KUnit selftests. These are only
+	  for development and testing, not for regular kernel
+	  use cases.
+
+	  If unsure, say N.
+
+config RUST_STR_KUNIT_TEST
+	bool "KUnit tests for Rust strings API" if !KUNIT_ALL_TESTS
+	default KUNIT_ALL_TESTS
+	help
+	  This option enables KUnit tests for the Rust strings API.
+	  These are only for development and testing, not for regular
+	  kernel use cases.
+
+	  If unsure, say N.
+
+config RUST_ATOMICS_KUNIT_TEST
+	bool "KUnit tests for Rust atomics API" if !KUNIT_ALL_TESTS
+	default KUNIT_ALL_TESTS
+	help
+	  This option enables KUnit tests for the Rust atomics API.
+	  These are only for development and testing, not for regular
+	  kernel use cases.
+
+	  If unsure, say N.
+
+endif

rust/kernel/alloc/allocator.rs

@@ -265,6 +265,7 @@ unsafe fn realloc(
     }
 }
 
+#[cfg(CONFIG_RUST_ALLOCATOR_KUNIT_TEST)]
 #[macros::kunit_tests(rust_allocator)]
 mod tests {
     use super::*;

rust/kernel/alloc/kvec.rs

@@ -1508,6 +1508,7 @@ fn drop(&mut self) {
     }
 }
 
+#[cfg(CONFIG_RUST_KVEC_KUNIT_TEST)]
 #[macros::kunit_tests(rust_kvec)]
 mod tests {
     use super::*;

rust/kernel/bitmap.rs

@@ -499,6 +499,7 @@ pub fn next_zero_bit(&self, start: usize) -> Option<usize> {
     }
 }
 
+#[cfg(CONFIG_RUST_BITMAP_KUNIT_TEST)]
 #[macros::kunit_tests(rust_kernel_bitmap)]
 mod tests {
     use super::*;

rust/kernel/kunit.rs

@@ -329,6 +329,7 @@ pub fn in_kunit_test() -> bool {
     !unsafe { bindings::kunit_get_current_test() }.is_null()
 }
 
+#[cfg(CONFIG_RUST_KUNIT_SELFTEST)]
 #[kunit_tests(rust_kernel_kunit)]
 mod tests {
     use super::*;

rust/kernel/str.rs

@@ -415,6 +415,7 @@ macro_rules! c_str {
     }};
 }
 
+#[cfg(CONFIG_RUST_STR_KUNIT_TEST)]
 #[kunit_tests(rust_kernel_str)]
 mod tests {
     use super::*;

rust/kernel/sync/atomic/predefine.rs

@@ -154,6 +154,7 @@ fn rhs_into_delta(rhs: usize) -> isize_atomic_repr {
     }
 }
 
+#[cfg(CONFIG_RUST_ATOMICS_KUNIT_TEST)]
 #[macros::kunit_tests(rust_atomics)]
 mod tests {
     use super::super::*;