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614724e780
Users were using the hidden exported `kernel::build_error` function
instead of the intended `kernel::build_error!` macro, e.g. see the
previous commit.
To force to use the macro, move it into the `build_assert` module,
thus making it a compilation error and avoiding a collision in the same
"namespace". Using the function now would require typing the module name
(which is hidden), not just a single character.
Now attempting to use the function will trigger this error with the
right suggestion by the compiler:
error[E0423]: expected function, found macro `kernel::build_error`
--> samples/rust/rust_minimal.rs:29:9
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29 | kernel::build_error();
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help: use `!` to invoke the macro
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29 | kernel::build_error!();
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An alternative would be using an alias, but it would be more complex
and moving it into the module seems right since it belongs there and
reduces the amount of code at the crate root.
Keep the `#[doc(hidden)]` inside `build_assert` in case the module is
not hidden in the future.
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20241123222849.350287-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
87 lines
2.6 KiB
Rust
87 lines
2.6 KiB
Rust
// SPDX-License-Identifier: GPL-2.0
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//! Build-time assert.
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#[doc(hidden)]
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pub use build_error::build_error;
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/// Fails the build if the code path calling `build_error!` can possibly be executed.
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///
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/// If the macro is executed in const context, `build_error!` will panic.
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/// If the compiler or optimizer cannot guarantee that `build_error!` can never
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/// be called, a build error will be triggered.
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///
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/// # Examples
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///
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/// ```
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/// # use kernel::build_error;
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/// #[inline]
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/// fn foo(a: usize) -> usize {
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/// a.checked_add(1).unwrap_or_else(|| build_error!("overflow"))
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/// }
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///
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/// assert_eq!(foo(usize::MAX - 1), usize::MAX); // OK.
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/// // foo(usize::MAX); // Fails to compile.
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/// ```
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#[macro_export]
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macro_rules! build_error {
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() => {{
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$crate::build_assert::build_error("")
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}};
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($msg:expr) => {{
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$crate::build_assert::build_error($msg)
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}};
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}
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/// Asserts that a boolean expression is `true` at compile time.
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///
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/// If the condition is evaluated to `false` in const context, `build_assert!`
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/// will panic. If the compiler or optimizer cannot guarantee the condition will
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/// be evaluated to `true`, a build error will be triggered.
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///
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/// [`static_assert!`] should be preferred to `build_assert!` whenever possible.
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///
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/// # Examples
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///
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/// These examples show that different types of [`assert!`] will trigger errors
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/// at different stage of compilation. It is preferred to err as early as
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/// possible, so [`static_assert!`] should be used whenever possible.
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/// ```ignore
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/// fn foo() {
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/// static_assert!(1 > 1); // Compile-time error
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/// build_assert!(1 > 1); // Build-time error
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/// assert!(1 > 1); // Run-time error
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/// }
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/// ```
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///
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/// When the condition refers to generic parameters or parameters of an inline function,
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/// [`static_assert!`] cannot be used. Use `build_assert!` in this scenario.
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/// ```
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/// fn foo<const N: usize>() {
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/// // `static_assert!(N > 1);` is not allowed
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/// build_assert!(N > 1); // Build-time check
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/// assert!(N > 1); // Run-time check
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/// }
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///
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/// #[inline]
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/// fn bar(n: usize) {
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/// // `static_assert!(n > 1);` is not allowed
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/// build_assert!(n > 1); // Build-time check
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/// assert!(n > 1); // Run-time check
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/// }
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/// ```
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///
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/// [`static_assert!`]: crate::static_assert!
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#[macro_export]
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macro_rules! build_assert {
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($cond:expr $(,)?) => {{
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if !$cond {
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$crate::build_assert::build_error(concat!("assertion failed: ", stringify!($cond)));
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}
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}};
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($cond:expr, $msg:expr) => {{
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if !$cond {
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$crate::build_assert::build_error($msg);
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}
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}};
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}
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