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Build-time assertion #257
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Build-time assertion #257
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,33 @@ | ||
| // SPDX-License-Identifier: GPL-2.0 | ||
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||
| //! Build-time error. | ||
| //! | ||
| //! This crate provides a function `build_error`, which will panic in | ||
| //! compile-time if executed in const context, and will cause a build error | ||
| //! if not executed at compile time and the optimizer does not optimise away the | ||
| //! call. | ||
| //! | ||
| //! It is used by `build_assert!` in the kernel crate, allowing checking of | ||
| //! conditions that could be checked statically, but could not be enforced in | ||
| //! Rust yet (e.g. perform some checks in const functions, but those | ||
| //! functions could still be called in the runtime). | ||
|
|
||
| #![no_std] | ||
| #![feature(const_panic, core_panic)] | ||
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||
| /// Panics if executed in const context, or triggers a build error if not. | ||
| #[inline(never)] | ||
| #[cold] | ||
| #[no_mangle] | ||
| #[track_caller] | ||
| pub const fn build_error(msg: &'static str) -> ! { | ||
| // Could also be `panic!(msg)` to avoid using unstable feature `core_panic`, | ||
| // but it is not allowed in Rust 2021, while `panic!("{}", msg)` could not | ||
| // yet be used in const context. | ||
| core::panicking::panic(msg); | ||
| } | ||
|
|
||
| #[cfg(CONFIG_RUST_BUILD_ASSERT_WARN)] | ||
| #[link_section = ".gnu.warning.build_error"] | ||
| #[used] | ||
| static BUILD_ERROR_WARNING: [u8; 45] = *b"call to build_error present after compilation"; |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,77 @@ | ||
| // SPDX-License-Identifier: GPL-2.0 | ||
|
|
||
| //! Build-time assert. | ||
|
|
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| /// Fails the build if the code path calling `build_error!` can possibly be executed. | ||
| /// | ||
| /// If the macro is executed in const context, `build_error!` will panic. | ||
| /// If the compiler or optimizer cannot guarantee that `build_error!` can never | ||
| /// be called, a build error will be triggered. | ||
| /// | ||
| /// # Examples | ||
| /// ```no_run | ||
| /// #[inline] | ||
| /// fn foo(a: usize) -> usize { | ||
| /// a.checked_add(1).unwrap_or_else(|| build_error!("overflow")) | ||
| /// } | ||
| /// ``` | ||
| #[macro_export] | ||
| macro_rules! build_error { | ||
| () => {{ | ||
| $crate::build_error("") | ||
| }}; | ||
| ($msg:expr) => {{ | ||
| $crate::build_error($msg) | ||
| }}; | ||
| } | ||
|
|
||
| /// Asserts that a boolean expression is `true` at compile time. | ||
| /// | ||
| /// If the condition is evaluated to `false` in const context, `build_assert!` | ||
| /// will panic. If the compiler or optimizer cannot guarantee the condition will | ||
| /// be evaluated to `true`, a build error will be triggered. | ||
| /// | ||
| /// [`static_assert!`] should be preferred to `build_assert!` whenever possible. | ||
| /// | ||
| /// # Examples | ||
| /// | ||
| /// These examples show that different types of [`assert!`] will trigger errors | ||
| /// at different stage of compilation. It is preferred to err as early as | ||
| /// possible, so [`static_assert!`] should be used whenever possible. | ||
| /// ```no_run | ||
| /// fn foo() { | ||
| /// static_assert!(1 > 1); // Compile-time error | ||
| /// build_assert!(1 > 1); // Build-time error | ||
| /// assert!(1 > 1); // Run-time error | ||
| /// } | ||
| /// ``` | ||
| /// | ||
| /// When the condition refers to generic parameters or parameters of an inline function, | ||
| /// [`static_assert!`] cannot be used. Use `build_assert!` in this scenario. | ||
| /// ```no_run | ||
| /// fn foo<const N: usize>() { | ||
| /// // `static_assert!(N > 1);` is not allowed | ||
| /// build_assert!(N > 1); // Build-time check | ||
| /// assert!(N > 1); // Run-time check | ||
| /// } | ||
| /// | ||
| /// #[inline] | ||
| /// fn bar(n: usize) { | ||
| /// // `static_assert!(n > 1);` is not allowed | ||
| /// build_assert!(n > 1); // Build-time check | ||
| /// assert!(n > 1); // Run-time check | ||
| /// } | ||
| /// ``` | ||
| #[macro_export] | ||
| macro_rules! build_assert { | ||
| ($cond:expr $(,)?) => {{ | ||
| if !$cond { | ||
| $crate::build_error(concat!("assertion failed: ", stringify!($cond))); | ||
| } | ||
| }}; | ||
| ($cond:expr, $msg:expr) => {{ | ||
| if !$cond { | ||
| $crate::build_error($msg); | ||
| } | ||
| }}; | ||
| } |
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Is this one related or is another cleanup?
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This is in a separate commit. I couldn't build on my machine without this change, but it is trivial enough that I think it might not worth a separate PR.