diff options
Diffstat (limited to 'third_party/rust/static_assertions/src/assert_impl.rs')
| -rw-r--r-- | third_party/rust/static_assertions/src/assert_impl.rs | 356 |
1 files changed, 356 insertions, 0 deletions
diff --git a/third_party/rust/static_assertions/src/assert_impl.rs b/third_party/rust/static_assertions/src/assert_impl.rs new file mode 100644 index 0000000000..480b6b6c61 --- /dev/null +++ b/third_party/rust/static_assertions/src/assert_impl.rs @@ -0,0 +1,356 @@ +/// Asserts that the type implements exactly one in a set of traits. +/// +/// Related: +/// - [`assert_impl_any!`] +/// - [`assert_impl_all!`] +/// - [`assert_not_impl_all!`] +/// - [`assert_not_impl_any!`] +/// +/// # Examples +/// +/// Given some type `Foo`, it is expected to implement either `Snap`, `Crackle`, +/// or `Pop`: +/// +/// ```compile_fail +/// # use static_assertions::assert_impl_one; fn main() {} +/// struct Foo; +/// +/// trait Snap {} +/// trait Crackle {} +/// trait Pop {} +/// +/// assert_impl_one!(Foo: Snap, Crackle, Pop); +/// ``` +/// +/// If _only_ `Crackle` is implemented, the assertion passes: +/// +/// ``` +/// # use static_assertions::assert_impl_one; fn main() {} +/// # struct Foo; +/// # trait Snap {} +/// # trait Crackle {} +/// # trait Pop {} +/// impl Crackle for Foo {} +/// +/// assert_impl_one!(Foo: Snap, Crackle, Pop); +/// ``` +/// +/// If `Snap` or `Pop` is _also_ implemented, the assertion fails: +/// +/// ```compile_fail +/// # use static_assertions::assert_impl_one; fn main() {} +/// # struct Foo; +/// # trait Snap {} +/// # trait Crackle {} +/// # trait Pop {} +/// # impl Crackle for Foo {} +/// impl Pop for Foo {} +/// +/// assert_impl_one!(Foo: Snap, Crackle, Pop); +/// ``` +/// +/// [`assert_impl_any!`]: macro.assert_impl_any.html +/// [`assert_impl_all!`]: macro.assert_impl_all.html +/// [`assert_not_impl_all!`]: macro.assert_not_impl_all.html +/// [`assert_not_impl_any!`]: macro.assert_not_impl_any.html +#[macro_export] +macro_rules! assert_impl_one { + ($x:ty: $($t:path),+ $(,)?) => { + const _: fn() = || { + // Generic trait that must be implemented for `$x` exactly once. + trait AmbiguousIfMoreThanOne<A> { + // Required for actually being able to reference the trait. + fn some_item() {} + } + + // Creates multiple scoped `Token` types for each trait `$t`, over + // which a specialized `AmbiguousIfMoreThanOne<Token>` is + // implemented for every type that implements `$t`. + $({ + #[allow(dead_code)] + struct Token; + + impl<T: ?Sized + $t> AmbiguousIfMoreThanOne<Token> for T {} + })+ + + // If there is only one specialized trait impl, type inference with + // `_` can be resolved and this can compile. Fails to compile if + // `$x` implements more than one `AmbiguousIfMoreThanOne<Token>` or + // does not implement any at all. + let _ = <$x as AmbiguousIfMoreThanOne<_>>::some_item; + }; + }; +} + +/// Asserts that the type implements _all_ of the given traits. +/// +/// See [`assert_not_impl_all!`] for achieving the opposite effect. +/// +/// # Examples +/// +/// This can be used to ensure types implement auto traits such as [`Send`] and +/// [`Sync`], as well as traits with [blanket `impl`s][blanket]. +/// +/// ``` +/// # #[macro_use] extern crate static_assertions; fn main() {} +/// assert_impl_all!(u32: Copy, Send); +/// assert_impl_all!(&str: Into<String>); +/// ``` +/// +/// The following example fails to compile because raw pointers do not implement +/// [`Send`] since they cannot be moved between threads safely: +/// +/// ```compile_fail +/// # #[macro_use] extern crate static_assertions; fn main() {} +/// assert_impl_all!(*const u8: Send); +/// ``` +/// +/// [`assert_not_impl_all!`]: macro.assert_not_impl_all.html +/// [`Send`]: https://doc.rust-lang.org/std/marker/trait.Send.html +/// [`Sync`]: https://doc.rust-lang.org/std/marker/trait.Sync.html +/// [blanket]: https://doc.rust-lang.org/book/ch10-02-traits.html#using-trait-bounds-to-conditionally-implement-methods +#[macro_export] +macro_rules! assert_impl_all { + ($type:ty: $($trait:path),+ $(,)?) => { + const _: fn() = || { + // Only callable when `$type` implements all traits in `$($trait)+`. + fn assert_impl_all<T: ?Sized $(+ $trait)+>() {} + assert_impl_all::<$type>(); + }; + }; +} + +/// Asserts that the type implements _any_ of the given traits. +/// +/// See [`assert_not_impl_any!`] for achieving the opposite effect. +/// +/// # Examples +/// +/// `u8` cannot be converted from `u16`, but it can be converted into `u16`: +/// +/// ``` +/// # #[macro_use] extern crate static_assertions; fn main() {} +/// assert_impl_any!(u8: From<u16>, Into<u16>); +/// ``` +/// +/// The unit type cannot be converted from `u8` or `u16`, but it does implement +/// [`Send`]: +/// +/// ``` +/// # #[macro_use] extern crate static_assertions; fn main() {} +/// assert_impl_any!((): From<u8>, From<u16>, Send); +/// ``` +/// +/// The following example fails to compile because raw pointers do not implement +/// [`Send`] or [`Sync`] since they cannot be moved or shared between threads +/// safely: +/// +/// ```compile_fail +/// # #[macro_use] extern crate static_assertions; fn main() {} +/// assert_impl_any!(*const u8: Send, Sync); +/// ``` +/// +/// [`assert_not_impl_any!`]: macro.assert_not_impl_any.html +/// [`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_any { + ($x:ty: $($t:path),+ $(,)?) => { + const _: fn() = || { + use $crate::_core::marker::PhantomData; + use $crate::_core::ops::Deref; + + // Fallback to use as the first iterative assignment to `previous`. + let previous = AssertImplAnyFallback; + struct AssertImplAnyFallback; + + // Ensures that blanket traits can't impersonate the method. This + // prevents a false positive attack where---if a blanket trait is in + // scope that has `_static_assertions_impl_any`---the macro will + // compile when it shouldn't. + // + // See https://github.com/nvzqz/static-assertions-rs/issues/19 for + // more info. + struct ActualAssertImplAnyToken; + trait AssertImplAnyToken {} + impl AssertImplAnyToken for ActualAssertImplAnyToken {} + fn assert_impl_any_token<T: AssertImplAnyToken>(_: T) {} + + $(let previous = { + struct Wrapper<T, N>(PhantomData<T>, N); + + // If the method for this wrapper can't be called then the + // compiler will insert a deref and try again. This forwards the + // compiler's next attempt to the previous wrapper. + impl<T, N> Deref for Wrapper<T, N> { + type Target = N; + + fn deref(&self) -> &Self::Target { + &self.1 + } + } + + // This impl is bounded on the `$t` trait, so the method can + // only be called if `$x` implements `$t`. This is why a new + // `Wrapper` is defined for each `previous`. + impl<T: $t, N> Wrapper<T, N> { + fn _static_assertions_impl_any(&self) -> ActualAssertImplAnyToken { + ActualAssertImplAnyToken + } + } + + Wrapper::<$x, _>(PhantomData, previous) + };)+ + + // Attempt to find the method that can actually be called. The found + // method must return a type that implements the sealed `Token` + // trait, this ensures that blanket trait methods can't cause this + // macro to compile. + assert_impl_any_token(previous._static_assertions_impl_any()); + }; + }; +} + +/// Asserts that the type does **not** implement _all_ of the given traits. +/// +/// This can be used to ensure types do not implement auto traits such as +/// [`Send`] and [`Sync`], as well as traits with [blanket `impl`s][blanket]. +/// +/// Note that the combination of all provided traits is required to not be +/// implemented. If you want to check that none of multiple traits are +/// implemented you should invoke [`assert_not_impl_any!`] instead. +/// +/// # Examples +/// +/// Although `u32` implements `From<u16>`, it does not implement `Into<usize>`: +/// +/// ``` +/// # #[macro_use] extern crate static_assertions; fn main() {} +/// assert_not_impl_all!(u32: From<u16>, Into<usize>); +/// ``` +/// +/// The following example fails to compile since `u32` can be converted into +/// `u64`. +/// +/// ```compile_fail +/// # #[macro_use] extern crate static_assertions; fn main() {} +/// assert_not_impl_all!(u32: Into<u64>); +/// ``` +/// +/// The following compiles because [`Cell`] is not both [`Sync`] _and_ [`Send`]: +/// +/// ``` +/// # #[macro_use] extern crate static_assertions; fn main() {} +/// use std::cell::Cell; +/// +/// assert_not_impl_all!(Cell<u32>: Sync, Send); +/// ``` +/// +/// But it is [`Send`], so this fails to compile: +/// +/// ```compile_fail +/// # #[macro_use] extern crate static_assertions; fn main() {} +/// # std::cell::Cell; +/// assert_not_impl_all!(Cell<u32>: Send); +/// ``` +/// +/// [`Send`]: https://doc.rust-lang.org/std/marker/trait.Send.html +/// [`Sync`]: https://doc.rust-lang.org/std/marker/trait.Sync.html +/// [`assert_not_impl_any!`]: macro.assert_not_impl_any.html +/// [`Cell`]: https://doc.rust-lang.org/std/cell/struct.Cell.html +/// [blanket]: https://doc.rust-lang.org/book/ch10-02-traits.html#using-trait-bounds-to-conditionally-implement-methods +#[macro_export] +macro_rules! assert_not_impl_all { + ($x:ty: $($t:path),+ $(,)?) => { + const _: fn() = || { + // Generic trait with a blanket impl over `()` for all types. + trait AmbiguousIfImpl<A> { + // Required for actually being able to reference the trait. + fn some_item() {} + } + + impl<T: ?Sized> AmbiguousIfImpl<()> for T {} + + // Used for the specialized impl when *all* traits in + // `$($t)+` are implemented. + #[allow(dead_code)] + struct Invalid; + + impl<T: ?Sized $(+ $t)+> AmbiguousIfImpl<Invalid> for T {} + + // If there is only one specialized trait impl, type inference with + // `_` can be resolved and this can compile. Fails to compile if + // `$x` implements `AmbiguousIfImpl<Invalid>`. + let _ = <$x as AmbiguousIfImpl<_>>::some_item; + }; + }; +} + +/// Asserts that the type does **not** implement _any_ of the given traits. +/// +/// This can be used to ensure types do not implement auto traits such as +/// [`Send`] and [`Sync`], as well as traits with [blanket `impl`s][blanket]. +/// +/// This macro causes a compilation failure if any of the provided individual +/// traits are implemented for the type. If you want to check that a combination +/// of traits is not implemented you should invoke [`assert_not_impl_all!`] +/// instead. For single traits both macros behave the same. +/// +/// # Examples +/// +/// If `u32` were to implement `Into` conversions for `usize` _and_ for `u8`, +/// the following would fail to compile: +/// +/// ``` +/// # #[macro_use] extern crate static_assertions; fn main() {} +/// assert_not_impl_any!(u32: Into<usize>, Into<u8>); +/// ``` +/// +/// This is also good for simple one-off cases: +/// +/// ``` +/// # #[macro_use] extern crate static_assertions; fn main() {} +/// assert_not_impl_any!(&'static mut u8: Copy); +/// ``` +/// +/// The following example fails to compile since `u32` can be converted into +/// `u64` even though it can not be converted into a `u16`: +/// +/// ```compile_fail +/// # #[macro_use] extern crate static_assertions; fn main() {} +/// assert_not_impl_any!(u32: Into<u64>, Into<u16>); +/// ``` +/// +/// [`Send`]: https://doc.rust-lang.org/std/marker/trait.Send.html +/// [`Sync`]: https://doc.rust-lang.org/std/marker/trait.Sync.html +/// [`assert_not_impl_all!`]: macro.assert_not_impl_all.html +/// [blanket]: https://doc.rust-lang.org/book/ch10-02-traits.html#using-trait-bounds-to-conditionally-implement-methods +#[macro_export] +macro_rules! assert_not_impl_any { + ($x:ty: $($t:path),+ $(,)?) => { + const _: fn() = || { + // Generic trait with a blanket impl over `()` for all types. + trait AmbiguousIfImpl<A> { + // Required for actually being able to reference the trait. + fn some_item() {} + } + + impl<T: ?Sized> AmbiguousIfImpl<()> for T {} + + // Creates multiple scoped `Invalid` types for each trait `$t`, over + // which a specialized `AmbiguousIfImpl<Invalid>` is implemented for + // every type that implements `$t`. + $({ + #[allow(dead_code)] + struct Invalid; + + impl<T: ?Sized + $t> AmbiguousIfImpl<Invalid> for T {} + })+ + + // If there is only one specialized trait impl, type inference with + // `_` can be resolved and this can compile. Fails to compile if + // `$x` implements any `AmbiguousIfImpl<Invalid>`. + let _ = <$x as AmbiguousIfImpl<_>>::some_item; + }; + }; +} |