TheRawMeatball 73c78c3667 Use lifetimed, type erased pointers in bevy_ecs (#3001) ... # Objective `bevy_ecs` has large amounts of unsafe code which is hard to get right and makes it difficult to audit for soundness. ## Solution Introduce lifetimed, type-erased pointers: `Ptr<'a>` `PtrMut<'a>` `OwningPtr<'a>'` and `ThinSlicePtr<'a, T>` which are newtypes around a raw pointer with a lifetime and conceptually representing strong invariants about the pointee and validity of the pointer. The process of converting bevy_ecs to use these has already caught multiple cases of unsound behavior. ## Changelog TL;DR for release notes: `bevy_ecs` now uses lifetimed, type-erased pointers internally, significantly improving safety and legibility without sacrificing performance. This should have approximately no end user impact, unless you were meddling with the (unfortunately public) internals of `bevy_ecs`. - `Fetch`, `FilterFetch` and `ReadOnlyFetch` trait no longer have a `'state` lifetime - this was unneeded - `ReadOnly/Fetch` associated types on `WorldQuery` are now on a new `WorldQueryGats<'world>` trait - was required to work around lack of Generic Associated Types (we wish to express `type Fetch<'a>: Fetch<'a>`) - `derive(WorldQuery)` no longer requires `'w` lifetime on struct - this was unneeded, and improves the end user experience - `EntityMut::get_unchecked_mut` returns `&'_ mut T` not `&'w mut T` - allows easier use of unsafe API with less footguns, and can be worked around via lifetime transmutery as a user - `Bundle::from_components` now takes a `ctx` parameter to pass to the `FnMut` closure - required because closure return types can't borrow from captures - `Fetch::init` takes `&'world World`, `Fetch::set_archetype` takes `&'world Archetype` and `&'world Tables`, `Fetch::set_table` takes `&'world Table` - allows types implementing `Fetch` to store borrows into world - `WorldQuery` trait now has a `shrink` fn to shorten the lifetime in `Fetch::<'a>::Item` - this works around lack of subtyping of assoc types, rust doesnt allow you to turn `<T as Fetch<'static>>::Item'` into `<T as Fetch<'a>>::Item'` - `QueryCombinationsIter` requires this - Most types implementing `Fetch` now have a lifetime `'w` - allows the fetches to store borrows of world data instead of using raw pointers ## Migration guide - `EntityMut::get_unchecked_mut` returns a more restricted lifetime, there is no general way to migrate this as it depends on your code - `Bundle::from_components` implementations must pass the `ctx` arg to `func` - `Bundle::from_components` callers have to use a fn arg instead of closure captures for borrowing from world - Remove lifetime args on `derive(WorldQuery)` structs as it is nonsensical - `<Q as WorldQuery>::ReadOnly/Fetch` should be changed to either `RO/QueryFetch<'world>` or `<Q as WorldQueryGats<'world>>::ReadOnly/Fetch` - `<F as Fetch<'w, 's>>` should be changed to `<F as Fetch<'w>>` - Change the fn sigs of `Fetch::init/set_archetype/set_table` to match respective trait fn sigs - Implement the required `fn shrink` on any `WorldQuery` implementations - Move assoc types `Fetch` and `ReadOnlyFetch` on `WorldQuery` impls to `WorldQueryGats` impls - Pass an appropriate `'world` lifetime to whatever fetch struct you are for some reason using ### Type inference regression in some cases rustc may give spurrious errors when attempting to infer the `F` parameter on a query/querystate this can be fixed by manually specifying the type, i.e. `QueryState:🆕:<_, ()>(world)`. The error is rather confusing: ```rust= error[E0271]: type mismatch resolving `<() as Fetch<'_>>::Item == bool` --> crates/bevy_pbr/src/render/light.rs:1413:30 | 1413 | main_view_query: QueryState::new(world), | ^^^^^^^^^^^^^^^ expected `bool`, found `()` | = note: required because of the requirements on the impl of `for<'x> FilterFetch<'x>` for `<() as WorldQueryGats<'x>>::Fetch` note: required by a bound in `bevy_ecs::query::QueryState::<Q, F>::new` --> crates/bevy_ecs/src/query/state.rs:49:32 | 49 | for<'x> QueryFetch<'x, F>: FilterFetch<'x>, | ^^^^^^^^^^^^^^^ required by this bound in `bevy_ecs::query::QueryState::<Q, F>::new` ``` --- Made with help from @BoxyUwU and @alice-i-cecile Co-authored-by: Boxy <supbscripter@gmail.com>		2022-04-27 23:44:06 +00:00
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src	Use lifetimed, type erased pointers in bevy_ecs (#3001)	2022-04-27 23:44:06 +00:00
Cargo.toml	Bump Bevy to 0.8.0-dev (#4505)	2022-04-17 23:04:52 +00:00