Moved get_component(_unchecked_mut) from Query to QueryState

[bushrat011899]

Objective

• Fixes Add QueryState::(get_)component(_mut) #9683

Solution

• Moved get_component from Query to QueryState.
• Moved get_component_unchecked_mut from Query to QueryState.
• Moved QueryComponentError from bevy_ecs::system to bevy_ecs::query. Minor Breaking Change.
• Narrowed scope of unsafe blocks in Query methods.

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Migration Guide

• use bevy_ecs::system::QueryComponentError; -> use bevy_ecs::query::QueryComponentError;

Notes

I am not very familiar with unsafe Rust nor its use within Bevy, so I may have committed a Rust faux pas during the migration.

[Shatur]

Does it makes sense to move component and component_mut too?

[bushrat011899]

Does it makes sense to move component and component_mut too?

It might do, I started with get_component and get_component_unchecked_mut because they were the last two methods that had sizeable implementations. There are several other functions which may want to be reworked as well:

• par_iter: This doesn't require any additional information beyond get_component_unchecked_mut.
• par_iter_mut: See par_iter.
• many: Currently calls Query::get_many; should instead call QueryState::get_many_read_only_manual.
• many_mut: See many.
• get_component_mut: See many.
• single: See many.
• single_mut: See many.
• contains: See par_iter.

Additionally, neither Query nor QueryState have the following methods, but probably should for completeness:

• component
• component_mut

If we also migrate the above to QueryState, then all of Query's methods simply forward to QueryState. Is that a desirable state for Query and QueryState to be in?

[Shatur]

Additionally, neither Query nor QueryState have the following methods, but probably should for completeness:

Query have these methods since #9659. This is why I asking.

[bushrat011899]

Additionally, neither Query nor QueryState have the following methods, but probably should for completeness:

Query have these methods since #9659. This is why I asking.

I missed that merge from my branch, apologies! Below would be the complete list of candidates to migrate over:

• par_iter: This doesn't require any additional information beyond get_component_unchecked_mut.
• par_iter_mut: See par_iter.
• many: Currently calls Query::get_many; should instead call QueryState::get_many_read_only_manual.
• many_mut: See many.
• get_component_mut: See many.
• single: See many.
• single_mut: See many.
• contains: See par_iter.
• component: See many.
• component_mut: See many.

I'm going to update my PR with the requested changes from @tguichaoua, then I'll migrate the above over just to demonstrate what that change would look like.

[alice-i-cecile]

If we also migrate the above to QueryState, then all of Query's methods simply forward to QueryState. Is that a desirable state for Query and QueryState to be in?

Yes; I much prefer that! Unless there's a very good (and commented) reason not to, these APIs should be mirrors of each other. Due to the fact that every Query stores a QueryState, method forwarding like this is the best way to achieve that.