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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 12:19:13 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 12:19:13 +0000 |
commit | 218caa410aa38c29984be31a5229b9fa717560ee (patch) | |
tree | c54bd55eeb6e4c508940a30e94c0032fbd45d677 /vendor/static_assertions/src/assert_obj_safe.rs | |
parent | Releasing progress-linux version 1.67.1+dfsg1-1~progress7.99u1. (diff) | |
download | rustc-218caa410aa38c29984be31a5229b9fa717560ee.tar.xz rustc-218caa410aa38c29984be31a5229b9fa717560ee.zip |
Merging upstream version 1.68.2+dfsg1.
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'vendor/static_assertions/src/assert_obj_safe.rs')
-rw-r--r-- | vendor/static_assertions/src/assert_obj_safe.rs | 76 |
1 files changed, 76 insertions, 0 deletions
diff --git a/vendor/static_assertions/src/assert_obj_safe.rs b/vendor/static_assertions/src/assert_obj_safe.rs new file mode 100644 index 000000000..ecbba9647 --- /dev/null +++ b/vendor/static_assertions/src/assert_obj_safe.rs @@ -0,0 +1,76 @@ +// FIXME: Link below is required to render in index +/// Asserts that the traits support dynamic dispatch +/// ([object-safety](https://doc.rust-lang.org/book/ch17-02-trait-objects.html#object-safety-is-required-for-trait-objects)). +/// +/// 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 +/// +/// When exposing a public API, it's important that traits that could previously +/// use dynamic dispatch can still do so in future compatible crate versions. +/// +/// ``` +/// # #[macro_use] extern crate static_assertions; fn main() {} +/// trait MySafeTrait { +/// fn foo(&self) -> u32; +/// } +/// +/// assert_obj_safe!(std::fmt::Write, MySafeTrait); +/// ``` +/// +/// Works with traits that are not in the calling module: +/// +/// ``` +/// # #[macro_use] extern crate static_assertions; fn main() {} +/// mod inner { +/// pub trait BasicTrait { +/// fn bar(&self); +/// } +/// assert_obj_safe!(BasicTrait); +/// } +/// +/// assert_obj_safe!(inner::BasicTrait); +/// ``` +/// +/// The following example fails to compile because raw pointers cannot be sent +/// between threads safely: +/// +/// ```compile_fail +/// # #[macro_use] extern crate static_assertions; fn main() {} +/// assert_impl!(*const u8, Send); +/// ``` +/// +/// The following example fails to compile because generics without +/// `where Self: Sized` are not allowed in [object-safe][object] trait methods: +/// +/// ```compile_fail +/// # #[macro_use] extern crate static_assertions; fn main() {} +/// trait MyUnsafeTrait { +/// fn baz<T>(&self) -> T; +/// } +/// +/// assert_obj_safe!(MyUnsafeTrait); +/// ``` +/// +/// When we fix that, the previous code will compile: +/// +/// ``` +/// # #[macro_use] extern crate static_assertions; fn main() {} +/// trait MyUnsafeTrait { +/// fn baz<T>(&self) -> T where Self: Sized; +/// } +/// +/// assert_obj_safe!(MyUnsafeTrait); +/// ``` +/// +/// [object]: https://doc.rust-lang.org/book/ch17-02-trait-objects.html#object-safety-is-required-for-trait-objects +#[macro_export] +macro_rules! assert_obj_safe { + ($($xs:path),+ $(,)?) => { + $(const _: Option<&$xs> = None;)+ + }; +} |