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Update tracking bug for removal of YokeTraitHack #1134

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merged 3 commits into from
Oct 3, 2021
Merged

Update tracking bug for removal of YokeTraitHack #1134

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2271eb7
Update tracking bug for removal of YokeTraitHack
sffc Oct 1, 2021
1477d31
Use real Yoke types
sffc Oct 1, 2021
e9c739f
clippy
sffc Oct 1, 2021
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93 changes: 70 additions & 23 deletions utils/yoke/src/trait_hack.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,7 @@
//!
//! # Trait bounds in Yoke
//!
//! [Compiler bug #85636](https://github.com/rust-lang/rust/issues/85636) makes it tricky to add
//! [Compiler bug #89196](https://github.com/rust-lang/rust/issues/89196) makes it tricky to add
//! trait bounds involving `yoke` types.
//!
//! For example, you may want to write:
Expand All @@ -26,22 +26,62 @@
//!
//! # Examples
//!
//! Code that does not compile:
//! Code that does not compile ([playground](https://play.rust-lang.org/?version=beta&mode=debug&edition=2018&gist=ebbda5b15a398d648bdff9e439b27dc0)):
//!
//! ***[#1061](https://github.com/unicode-org/icu4x/issues/1061): The following example
//! compiles starting in Rust 1.56.
//! ```compile_fail
//! use yoke::*;
//!
//! ```ignore
//! use yoke::Yoke;
//! use yoke::Yokeable;
//! trait MiniDataMarker {
//! type Yokeable: for<'a> Yokeable<'a>;
//! }
//!
//! // Example trait and struct for illustration purposes:
//! trait MyTrait {}
//! struct MyStruct {}
//! impl MyTrait for MyStruct {}
//! unsafe impl<'a> Yokeable<'a> for MyStruct {
//! struct MiniDataPayload<M>
//! where
//! M: MiniDataMarker
//! {
//! pub yoke: Yoke<M::Yokeable, ()>,
//! }
//!
//! impl<M> Clone for MiniDataPayload<M>
//! where
//! M: MiniDataMarker,
//! for<'a> <M::Yokeable as Yokeable<'a>>::Output: Clone,
//! {
//! fn clone(&self) -> Self {
//! unimplemented!()
//! }
//! }
//!
//! trait MiniDataProvider<M>
//! where
//! M: MiniDataMarker
//! {
//! fn mini_load_payload(&self) -> MiniDataPayload<M>;
//! }
//!
//! struct MiniStructProvider<M>
//! where
//! M: MiniDataMarker,
//! {
//! pub payload: MiniDataPayload<M>,
//! }
//!
//! impl<M> MiniDataProvider<M> for MiniStructProvider<M>
//! where
//! M: MiniDataMarker,
//! for<'a> <M::Yokeable as Yokeable<'a>>::Output: Clone,
//! {
//! fn mini_load_payload(&self) -> MiniDataPayload<M> {
//! self.payload.clone()
//! }
//! }
//!
//! #[derive(Clone)]
//! struct SimpleStruct(pub u32);
//!
//! unsafe impl<'a> Yokeable<'a> for SimpleStruct {
//! // (not shown; see `Yokeable` for examples)
//! # type Output = MyStruct;
//! # type Output = SimpleStruct;
//! # fn transform(&'a self) -> &'a Self::Output {
//! # self
//! # }
Expand All @@ -63,17 +103,24 @@
//! # }
//! }
//!
//! impl<Y, C> MyTrait for Yoke<Y, C>
//! where
//! Y: for<'a> Yokeable<'a>,
//! for<'a> <Y as Yokeable<'a>>::Output: MyTrait,
//! {}
//!
//! fn example() {
//! let y = Yoke::<MyStruct, ()>::new_always_owned(MyStruct {});
//! // error[E0277]: the trait bound `for<'a> <MyStruct as Yokeable<'a>>::Output: MyTrait` is not satisfied
//! let _: &dyn MyTrait = &y;
//! impl MiniDataMarker for SimpleStruct {
//! type Yokeable = SimpleStruct;
//! }
//!
//! let provider = MiniStructProvider {
//! payload: MiniDataPayload {
//! yoke: Yoke::new_always_owned(SimpleStruct(42))
//! }
//! };
//!
//! // Broken:
//! // "method cannot be called on `MiniStructProvider<_>` due to unsatisfied trait bounds"
//! let payload: MiniDataPayload<SimpleStruct> = provider.mini_load_payload();
//!
//! // Working:
//! let payload = MiniDataProvider::<SimpleStruct>::mini_load_payload(&provider);
//!
//! assert_eq!(payload.yoke.get().0, 42);
//! ```
//!
//! Example for binding the trait to a reference:
Expand Down