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//! Compile-time assertions to ensure that invariants are met. //! //! _All_ assertions within this crate are performed at **compile-time**. This //! allows for finding errors quickly and early when it comes to ensuring //! certain features or aspects of a codebase. //! //! # Usage //! //! This crate is available [on crates.io][crate] and can be used by adding the //! following to your project's `Cargo.toml`: //! //! ```toml //! [dependencies] //! static_assertions = "0.2.5" //! ``` //! //! and this to your crate root: //! //! ``` //! #[macro_use] //! extern crate static_assertions; //! # fn main() {} //! ``` //! //! # Examples //! //! Very thorough examples are provided in the docs for each individual macro. //! Failure case examples are also documented. //! //! # Limitations //! //! Due to implementation details, some macros can only be used normally from //! within the context of a function. To use these macros in other contexts, a //! unique label must be provided. //! //! ```compile_fail //! # #[macro_use] extern crate static_assertions; //! # fn main() {} //! // error: expected item after attributes //! const_assert!(true == true); //! ``` //! //! This can be fixed via: //! //! ``` //! # #[macro_use] extern crate static_assertions; //! # fn main() {} //! const_assert!(label; true == true); //! ``` //! //! This issue can be followed [here][issue1]. Feedback and potential solutions //! are welcome! //! //! [issue1]: https://github.com/nvzqz/static-assertions-rs/issues/1 //! [crate]: https://crates.io/crates/static_assertions #![no_std] #![deny(unused_macros)] #[doc(hidden)] pub extern crate core as _core; /// Asserts that a given configuration is set. /// /// # Examples /// /// A project may not support a set of configurations and thus you may want to /// report why: /// /// ``` /// # #[macro_use] /// # extern crate static_assertions; /// // We should only be compiling for Unix or Linux /// # #[cfg(any(unix, linux))] /// assert_cfg!(any(unix, linux)); /// # fn main() {} /// ``` /// /// If users need to specify a database back-end: /// /// ``` /// # #[macro_use] /// # extern crate static_assertions; /// # #[cfg(target_pointer_width = "0")] // Impossible /// assert_cfg!("Must exclusively use MySQL or MongoDB as database back-end", /// all(not(all(feature = "mysql", feature = "mongodb")), /// any( feature = "mysql", feature = "mongodb"))); /// # fn main() {} /// ``` /// /// We can't be compiling for both Unix _and_ Windows simultaneously: /// /// ```compile_fail /// # #[macro_use] extern crate static_assertions; /// # fn main() { /// assert_cfg!("No, that's not how it works! ಠ_ಠ", all(unix, windows)); /// # } /// ``` #[macro_export] macro_rules! assert_cfg { () => {}; ($msg:expr, $($cfg:tt)*) => { #[cfg(not($($cfg)*))] compile_error!($msg); }; ($($cfg:tt)*) => { #[cfg(not($($cfg)*))] compile_error!(concat!("Cfg does not pass: ", stringify!($($cfg)*))); }; } /// Asserts that types are equal in size. /// /// When performing operations such as pointer casts or dealing with [`usize`] /// versus [`u64`] versus [`u32`], the size of your types matter. This is where /// this macro comes into play. /// /// # Alternatives /// /// There are also [`assert_eq_size_val`](macro.assert_eq_size_val.html) and /// [`assert_eq_size_ptr`](macro.assert_eq_size_ptr.html). Instead of specifying /// types to compare, values' sizes can be directly compared against each other. /// /// # Examples /// /// ``` /// # #[macro_use] /// # extern crate static_assertions; /// // Can be declared outside of a function if labeled /// assert_eq_size!(bytes; (u8, u8), u16); /// /// fn main() { /// // Supports unlimited arguments: /// assert_eq_size!([u8; 4], (u16, u16), u32); /// } /// ``` /// /// The following produces a compilation failure because `u32` has 4 times the /// size of `u8`: /// /// ```compile_fail /// # #[macro_use] extern crate static_assertions; /// # fn main() { /// assert_eq_size!(u32, u8); /// # } /// ``` /// /// [`usize`]: https://doc.rust-lang.org/std/primitive.usize.html /// [`u64`]: https://doc.rust-lang.org/std/primitive.u64.html /// [`u32`]: https://doc.rust-lang.org/std/primitive.u32.html #[macro_export] macro_rules! assert_eq_size { ($x:ty, $($xs:ty),+ $(,)*) => { $(let _ = $crate::_core::mem::transmute::<$x, $xs>;)+ }; ($label:ident; $($xs:tt)+) => { #[allow(dead_code, non_snake_case)] fn $label() { assert_eq_size!($($xs)+); } }; } /// Asserts that values pointed to are equal in size. /// /// This especially is useful for when coercing pointers between different types /// and ensuring the underlying values are the same size. /// /// # Examples /// /// ``` /// # #[macro_use] /// # extern crate static_assertions; /// fn operation(x: &(u32, u32), y: &[u16; 4]) { /// assert_eq_size_ptr!(x, y); /// } /// # fn main() {} /// ``` /// /// Byte arrays of different lengths have different sizes: /// /// ```compile_fail /// # #[macro_use] extern crate static_assertions; /// # fn main() { /// static BYTES: &[u8; 4] = &[ /// /* ... */ /// # 0; 4 /// ]; /// /// static TABLE: &[u8; 16] = &[ /// /* ... */ /// # 0; 16 /// ]; /// /// assert_eq_size_ptr!(BYTES, TABLE); /// # } /// ``` #[macro_export] macro_rules! assert_eq_size_ptr { ($x:expr, $($xs:expr),+ $(,)*) => { #[allow(unknown_lints, unsafe_code, forget_copy, useless_transmute)] || unsafe { use $crate::_core::{mem, ptr}; let mut copy = ptr::read($x); $(ptr::write(&mut copy, mem::transmute(ptr::read($xs)));)+ mem::forget(copy); }; } } /// Asserts that values are equal in size. /// /// This macro doesn't consume its arguments and thus works for /// non-[`Clone`]able values. /// /// # Examples /// /// ``` /// # #[macro_use] /// # extern crate static_assertions; /// # fn main() { /// struct Byte(u8); /// /// let x = 10u8; /// let y = Byte(42); // Works for non-cloneable types /// /// assert_eq_size_val!(x, y); /// assert_eq_size_val!(x, y, 0u8); /// # } /// ``` /// /// Even though both values are 0, they are of types with different sizes: /// /// ```compile_fail /// # #[macro_use] extern crate static_assertions; /// # fn main() { /// assert_eq_size_val!(0u8, 0u32); /// # } /// ``` /// /// [`Clone`]: https://doc.rust-lang.org/std/clone/trait.Clone.html #[macro_export] macro_rules! assert_eq_size_val { ($x:expr, $($xs:expr),+ $(,)*) => { assert_eq_size_ptr!(&$x, $(&$xs),+); } } /// Asserts that constant expressions evaluate to `true`. /// /// There also exists [`const_assert_eq`](macro.const_assert_eq.html) for /// validating whether a sequence of expressions are equal to one another. /// /// # Examples /// /// Constant expressions can be ensured to have certain properties via this /// macro If the expression evaluates to `false`, the file will fail to compile. /// This is synonymous to [`static_assert` in C++][static_assert]. /// /// As a [limitation](index.html#limitations), a unique label is required if /// the macro is used outside of a function. /// /// ``` /// # #[macro_use] /// # extern crate static_assertions; /// const FIVE: usize = 5; /// /// const_assert!(twenty_five; FIVE * FIVE == 25); /// /// fn main() { /// const_assert!(2 + 2 == 4); /// const_assert!(FIVE - FIVE == 0); /// } /// ``` /// /// Some expressions are blatantly false: /// /// ```compile_fail /// # #[macro_use] extern crate static_assertions; /// # fn main() { /// const_assert!(1 >= 2); /// # } /// ``` /// /// [static_assert]: http://en.cppreference.com/w/cpp/language/static_assert #[macro_export] macro_rules! const_assert { ($($xs:expr),+ $(,)*) => { #[allow(unknown_lints, eq_op)] let _ = [(); 0 - !($($xs)&&+) as usize]; }; ($label:ident; $($xs:tt)+) => { #[allow(dead_code, non_snake_case)] fn $label() { const_assert!($($xs)+); } }; } /// Asserts that constants are equal in value. /// /// # Examples /// /// Works as a shorthand for `const_assert!(a == b)`: /// /// ``` /// # #[macro_use] /// # extern crate static_assertions; /// const TWO: usize = 2; /// const_assert_eq!(two; TWO * TWO, TWO + TWO, 4); /// /// fn main() { /// const NUM: usize = 32; /// const_assert_eq!(NUM + NUM, 64); /// } /// ``` /// /// Just because 2 × 2 = 2 + 2 doesn't mean it holds true for other numbers: /// /// ```compile_fail /// # #[macro_use] extern crate static_assertions; /// # fn main() { /// const_assert_eq!(4 + 4, 4 * 4); /// # } /// ``` #[macro_export] macro_rules! const_assert_eq { ($x:expr, $($xs:expr),+ $(,)*) => { const_assert!($($x == $xs),+); }; ($label:ident; $x:expr, $($xs:expr),+ $(,)*) => { const_assert!($label; $($x == $xs),+); }; } /// Asserts that the traits are object-safe. /// /// This is useful for when changes are made to a trait that accidentally /// prevent it from being used as an object. Such a case would be adding a /// generic method and forgetting to add `where Self: Sized` after it. If left /// unnoticed, that mistake will affect crate users and break both forward and /// backward compatibility. /// /// # Examples /// /// ``` /// # #[macro_use] /// # extern crate static_assertions; /// assert_obj_safe!(basic; Send, Sync, AsRef<str>); /// /// mod inner { /// // Works with traits that are not in the calling module /// pub trait BasicTrait { /// fn foo(&self); /// } /// } /// /// trait MySafeTrait { /// fn bar(&self) -> u32; /// } /// /// fn main() { /// assert_obj_safe!(MySafeTrait); /// assert_obj_safe!(inner::BasicTrait); /// } /// ``` /// /// Generics without `where Self: Sized` are not allowed in object-safe traits: /// /// ```compile_fail /// # #[macro_use] extern crate static_assertions; /// trait MyUnsafeTrait { /// fn baz<T>(&self) -> T; /// } /// /// # fn main() { /// assert_obj_safe!(MyUnsafeTrait); /// # } /// ``` #[macro_export] macro_rules! assert_obj_safe { ($($xs:ty),+ $(,)*) => { $(let _: &$xs;)+ }; ($label:ident; $($xs:tt)+) => { #[allow(dead_code, non_snake_case)] fn $label() { assert_obj_safe!($($xs)+); } }; } /// Asserts that the type has the given fields. /// /// # Examples /// /// This may be used when types have odd fields as a result of `#[cfg]`. /// /// ``` /// # #[macro_use] extern crate static_assertions; /// # fn main() { /// struct Ty { /// #[cfg(windows)] /// value: u8, /// #[cfg(not(windows))] /// value: usize, /// } /// /// /* ... */ /// /// // Always have `value` regardless of OS /// assert_fields!(Ty, value); /// # } /// ``` /// /// Range does not have a field named `middle`: /// /// ```compile_fail /// # #[macro_use] extern crate static_assertions; /// # fn main() { /// use std::ops::Range; /// /// assert_fields!(Range<u32>, middle); /// # } /// ``` #[macro_export] macro_rules! assert_fields { ($t:path, $($f:ident),+) => { #[allow(unknown_lints, unneeded_field_pattern)] { $(let $t { $f: _, .. };)+ } }; ($label:ident; $($xs:tt)+) => { #[allow(dead_code, non_snake_case)] fn $label() { assert_fields!($($xs)+); } }; } /// Asserts that the type implements the given traits. /// /// # Examples /// /// Can be used to ensure types implement [`Send`], [`Sync`], and other traits: /// /// ``` /// # #[macro_use] extern crate static_assertions; /// # fn main() {} /// assert_impl!(str; String, Send, Sync, From<&'static str>); /// assert_impl!(vec; &'static [u8], Into<Vec<u8>>); /// ``` /// /// Raw pointers cannot be sent between threads safely: /// /// ```compile_fail /// # #[macro_use] extern crate static_assertions; /// # fn main() { /// assert_impl!(*const u8, Send); /// # } /// ``` /// /// [`Send`]: https://doc.rust-lang.org/std/marker/trait.Send.html /// [`Sync`]: https://doc.rust-lang.org/std/marker/trait.Sync.html #[macro_export] macro_rules! assert_impl { ($x:ty, $($t:path),+ $(,)*) => { { fn assert_impl<T>() where T: ?Sized $(+ $t)+ {} assert_impl::<$x>(); } }; ($label:ident; $($xs:tt)+) => { #[allow(dead_code, non_snake_case)] fn $label() { assert_impl!($($xs)+); } }; }