[Merged by Bors] - Avoid making Fetchs Clone
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| /// While calling this method on its own cannot cause UB it is marked `unsafe` as the caller must ensure | ||
| /// that the returned value is not used in any way that would cause two `QueryItem<Self>` for the same | ||
| /// `archetype_index` or `table_row` to be alive at the same time. | ||
| unsafe fn clone_fetch<'w>( |
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I feel like we probably want a safe read-only version of this too.
I'm not sure if it's immediately useful though.
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I don't think it really matters, none of the call sites seem to know that Self: ReadOnlyWorldQuery holds, it'd be trivial to write a safe function later if we need it so i'm not bothered about this
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Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
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# Objective - Do not implement `Copy` or `Clone` for `Fetch` types as this is kind of sus soundness wise (it feels like cloning an `IterMut` in safe code to me). Cloning a fetch seems important to think about soundness wise when doing it so I prefer this over adding a `Clone` bound to the assoc type definition (i.e. `type Fetch: Clone`) even though that would also solve the other listed things here. - Remove a bunch of `QueryFetch<'w, Q>: Clone` bounds from our API as now all fetches can be "cloned" for use in `iter_combinations`. This should also help avoid the type inference regression ptrification introduced where `for<'a> QueryFetch<'a, Q>: Trait` bounds misbehave since we no longer need any of those kind of higher ranked bounds (although in practice we had none anyway). - Stop being able to "forget" to implement clone for fetches, we've had a lot of issues where either `derive(Clone)` was used instead of a manual impl (so we ended up with too tight bounds on the impl) or flat out forgot to implement Clone at all. With this change all fetches are able to be cloned for `iter_combinations` so this will no longer be possible to mess up. On an unrelated note, while making this PR I realised we probably want safety invariants on `archetype/table_fetch` that nothing aliases the table_row/archetype_index according to the access we set. --- ## Changelog `Clone` and `Copy` were removed from all `Fetch` types. ## Migration Guide - Call `WorldQuery::clone_fetch` instead of `fetch.clone()`. Make sure to add safety comments :)
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Fetchs CloneFetchs Clone
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# Objective - Do not implement `Copy` or `Clone` for `Fetch` types as this is kind of sus soundness wise (it feels like cloning an `IterMut` in safe code to me). Cloning a fetch seems important to think about soundness wise when doing it so I prefer this over adding a `Clone` bound to the assoc type definition (i.e. `type Fetch: Clone`) even though that would also solve the other listed things here. - Remove a bunch of `QueryFetch<'w, Q>: Clone` bounds from our API as now all fetches can be "cloned" for use in `iter_combinations`. This should also help avoid the type inference regression ptrification introduced where `for<'a> QueryFetch<'a, Q>: Trait` bounds misbehave since we no longer need any of those kind of higher ranked bounds (although in practice we had none anyway). - Stop being able to "forget" to implement clone for fetches, we've had a lot of issues where either `derive(Clone)` was used instead of a manual impl (so we ended up with too tight bounds on the impl) or flat out forgot to implement Clone at all. With this change all fetches are able to be cloned for `iter_combinations` so this will no longer be possible to mess up. On an unrelated note, while making this PR I realised we probably want safety invariants on `archetype/table_fetch` that nothing aliases the table_row/archetype_index according to the access we set. --- ## Changelog `Clone` and `Copy` were removed from all `Fetch` types. ## Migration Guide - Call `WorldQuery::clone_fetch` instead of `fetch.clone()`. Make sure to add safety comments :)
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# Objective - Do not implement `Copy` or `Clone` for `Fetch` types as this is kind of sus soundness wise (it feels like cloning an `IterMut` in safe code to me). Cloning a fetch seems important to think about soundness wise when doing it so I prefer this over adding a `Clone` bound to the assoc type definition (i.e. `type Fetch: Clone`) even though that would also solve the other listed things here. - Remove a bunch of `QueryFetch<'w, Q>: Clone` bounds from our API as now all fetches can be "cloned" for use in `iter_combinations`. This should also help avoid the type inference regression ptrification introduced where `for<'a> QueryFetch<'a, Q>: Trait` bounds misbehave since we no longer need any of those kind of higher ranked bounds (although in practice we had none anyway). - Stop being able to "forget" to implement clone for fetches, we've had a lot of issues where either `derive(Clone)` was used instead of a manual impl (so we ended up with too tight bounds on the impl) or flat out forgot to implement Clone at all. With this change all fetches are able to be cloned for `iter_combinations` so this will no longer be possible to mess up. On an unrelated note, while making this PR I realised we probably want safety invariants on `archetype/table_fetch` that nothing aliases the table_row/archetype_index according to the access we set. --- ## Changelog `Clone` and `Copy` were removed from all `Fetch` types. ## Migration Guide - Call `WorldQuery::clone_fetch` instead of `fetch.clone()`. Make sure to add safety comments :)
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…8246) # Objective Cloning a `WorldQuery` type's "fetch" struct was made unsafe in #5593, by adding the `unsafe fn clone_fetch` to `WorldQuery`. However, as that method's documentation explains, it is not the right place to put the safety invariant: > While calling this method on its own cannot cause UB it is marked `unsafe` as the caller must ensure that the returned value is not used in any way that would cause two `QueryItem<Self>` for the same `archetype_index` or `table_row` to be alive at the same time. You can clone a fetch struct all you want and it will never cause undefined behavior -- in order for something to go wrong, you need to improperly call `WorldQuery::fetch` with it (which is marked unsafe). Additionally, making it unsafe to clone a fetch struct does not even prevent undefined behavior, since there are other ways to incorrectly use a fetch struct. For example, you could just call fetch more than once for the same entity, which is not currently forbidden by any documented invariants. ## Solution Document a safety invariant on `WorldQuery::fetch` that requires the caller to not create aliased `WorldQueryItem`s for mutable types. Remove the `clone_fetch` function, and add the bound `Fetch: Clone` instead. --- ## Changelog - Removed the associated function `WorldQuery::clone_fetch`, and added a `Clone` bound to `WorldQuery::Fetch`. ## Migration Guide ### `fetch` invariants The function `WorldQuery::fetch` has had the following safety invariant added: > If this type does not implement `ReadOnlyWorldQuery`, then the caller must ensure that it is impossible for more than one `Self::Item` to exist for the same entity at any given time. This invariant was always required for soundness, but was previously undocumented. If you called this function manually anywhere, you should check to make sure that this invariant is not violated. ### Removed `clone_fetch` The function `WorldQuery::clone_fetch` has been removed. The associated type `WorldQuery::Fetch` now has the bound `Clone`. Before: ```rust struct MyFetch<'w> { ... } unsafe impl WorldQuery for MyQuery { ... type Fetch<'w> = MyFetch<'w> unsafe fn clone_fetch<'w>(fetch: &Self::Fetch<'w>) -> Self::Fetch<'w> { MyFetch { field1: fetch.field1, field2: fetch.field2.clone(), ... } } } ``` After: ```rust #[derive(Clone)] struct MyFetch<'w> { ... } unsafe impl WorldQuery for MyQuery { ... type Fetch<'w> = MyFetch<'w>; } ``` --------- Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
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Objective
CopyorCloneforFetchtypes as this is kind of sus soundness wise (it feels like cloning anIterMutin safe code to me). Cloning a fetch seems important to think about soundness wise when doing it so I prefer this over adding aClonebound to the assoc type definition (i.e.type Fetch: Clone) even though that would also solve the other listed things here.QueryFetch<'w, Q>: Clonebounds from our API as now all fetches can be "cloned" for use initer_combinations. This should also help avoid the type inference regression ptrification introduced wherefor<'a> QueryFetch<'a, Q>: Traitbounds misbehave since we no longer need any of those kind of higher ranked bounds (although in practice we had none anyway).derive(Clone)was used instead of a manual impl (so we ended up with too tight bounds on the impl) or flat out forgot to implement Clone at all. With this change all fetches are able to be cloned foriter_combinationsso this will no longer be possible to mess up.On an unrelated note, while making this PR I realised we probably want safety invariants on
archetype/table_fetchthat nothing aliases the table_row/archetype_index according to the access we set.Changelog
CloneandCopywere removed from allFetchtypes.Migration Guide
WorldQuery::clone_fetchinstead offetch.clone(). Make sure to add safety comments :)