Make `#[system_param(ignore)]` and `#[world_query(ignore)]` unnecessary #8030

JoJoJet · 2023-03-10T21:02:08Z

Objective

When using PhantomData fields with the #[derive(SystemParam)] or #[derive(WorldQuery)] macros, the user is required to add the #[system_param(ignore)] attribute so that the macro knows to treat that field specially. This is undesirable, since it makes the macro more fragile and less consistent.

Solution

Implement SystemParam and WorldQuery for PhantomData. This makes the ignore attributes unnecessary.

Some internal changes make the derive macro compatible with types that have invariant lifetimes, which fixes #8192. From what I can tell, this fix requires PhantomData to implement SystemParam in order to ensure that all of a type's generic parameters are always constrained.

Changelog

Implemented SystemParam and WorldQuery for PhantomData<T>.
Fixed a miscompilation caused when invariant lifetimes were used with the SystemParam macro.

…m-data

alice-i-cecile · 2023-03-10T21:12:58Z

This also prevents you from using any other weirder types in here. But I've never seen a case for that, and can't imagine one, so I think that's net good.

crates/bevy_ecs/src/query/fetch.rs

alice-i-cecile · 2023-03-10T21:22:49Z

crates/bevy_ecs/src/system/system_param.rs

+// SAFETY: No world access.
+unsafe impl<T: ?Sized> SystemParam for PhantomData<T> {
+    type State = ();
+    type Item<'world, 'state> = Self;


I think this is better than just returning () because it's easier to debug.

It's also necessary, since SystemParams have to be reflexive :)

…m-data

james7132

Not totally sure that using PhantomData is a 1:1 replacement for world_query(ignore) and system_param(ignore) for all T: Default, though removing that functionality seems like a good idea to me to encourage users to use Local<T> instead.

crates/bevy_ecs/macros/src/lib.rs

crates/bevy_ecs/src/query/fetch.rs

JoJoJet · 2023-03-28T19:45:38Z

I figured out how to do this without removing the ignore attributes, so this PR is now non-breaking. I will remove the attributes in a follow-up PR.

crates/bevy_ecs/macros/src/lib.rs

# Objective Follow-up to #8030. Now that `SystemParam` and `WorldQuery` are implemented for `PhantomData`, the `ignore` attributes are now unnecessary. --- ## Changelog - Removed the attributes `#[system_param(ignore)]` and `#[world_query(ignore)]`. ## Migration Guide The attributes `#[system_param(ignore)]` and `#[world_query]` ignore have been removed. If you were using either of these with `PhantomData` fields, you can simply remove the attribute: ```rust #[derive(SystemParam)] struct MyParam<'w, 's, Marker> { ... // Before: #[system_param(ignore) _marker: PhantomData<Marker>, // After: _marker: PhantomData<Marker>, } #[derive(WorldQuery)] struct MyQuery<Marker> { ... // Before: #[world_query(ignore) _marker: PhantomData<Marker>, // After: _marker: PhantomData<Marker>, } ``` If you were using this for another type that implements `Default`, consider wrapping that type in `Local<>` (this only works for `SystemParam`): ```rust #[derive(SystemParam)] struct MyParam<'w, 's> { // Before: #[system_param(ignore)] value: MyDefaultType, // This will be initialized using `Default` each time `MyParam` is created. // After: value: Local<MyDefaultType>, // This will be initialized using `Default` the first time `MyParam` is created. } ``` If you are implementing either trait and need to preserve the exact behavior of the old `ignore` attributes, consider manually implementing `SystemParam` or `WorldQuery` for a wrapper struct that uses the `Default` trait: ```rust // Before: #[derive(WorldQuery) struct MyQuery { #[world_query(ignore)] str: String, } // After: #[derive(WorldQuery) struct MyQuery { str: DefaultQuery<String>, } pub struct DefaultQuery<T: Default>(pub T); unsafe impl<T: Default> WorldQuery for DefaultQuery<T> { type Item<'w> = Self; ... unsafe fn fetch<'w>(...) -> Self::Item<'w> { Self(T::default()) } } ```

…ry (bevyengine#8030) When using `PhantomData` fields with the `#[derive(SystemParam)]` or `#[derive(WorldQuery)]` macros, the user is required to add the `#[system_param(ignore)]` attribute so that the macro knows to treat that field specially. This is undesirable, since it makes the macro more fragile and less consistent. Implement `SystemParam` and `WorldQuery` for `PhantomData`. This makes the `ignore` attributes unnecessary. Some internal changes make the derive macro compatible with types that have invariant lifetimes, which fixes bevyengine#8192. From what I can tell, this fix requires `PhantomData` to implement `SystemParam` in order to ensure that all of a type's generic parameters are always constrained. --- + Implemented `SystemParam` and `WorldQuery` for `PhantomData<T>`. + Fixed a miscompilation caused when invariant lifetimes were used with the `SystemParam` macro.

…ry (#8030) When using `PhantomData` fields with the `#[derive(SystemParam)]` or `#[derive(WorldQuery)]` macros, the user is required to add the `#[system_param(ignore)]` attribute so that the macro knows to treat that field specially. This is undesirable, since it makes the macro more fragile and less consistent. Implement `SystemParam` and `WorldQuery` for `PhantomData`. This makes the `ignore` attributes unnecessary. Some internal changes make the derive macro compatible with types that have invariant lifetimes, which fixes #8192. From what I can tell, this fix requires `PhantomData` to implement `SystemParam` in order to ensure that all of a type's generic parameters are always constrained. --- + Implemented `SystemParam` and `WorldQuery` for `PhantomData<T>`. + Fixed a miscompilation caused when invariant lifetimes were used with the `SystemParam` macro.

…ry (bevyengine#8030) When using `PhantomData` fields with the `#[derive(SystemParam)]` or `#[derive(WorldQuery)]` macros, the user is required to add the `#[system_param(ignore)]` attribute so that the macro knows to treat that field specially. This is undesirable, since it makes the macro more fragile and less consistent. Implement `SystemParam` and `WorldQuery` for `PhantomData`. This makes the `ignore` attributes unnecessary. Some internal changes make the derive macro compatible with types that have invariant lifetimes, which fixes bevyengine#8192. From what I can tell, this fix requires `PhantomData` to implement `SystemParam` in order to ensure that all of a type's generic parameters are always constrained. --- + Implemented `SystemParam` and `WorldQuery` for `PhantomData<T>`. + Fixed a miscompilation caused when invariant lifetimes were used with the `SystemParam` macro.

JoJoJet added 14 commits March 9, 2023 22:16

impl SystemParam for PhantomData

c766e7c

ensure state types don't collide for SystemParam

8994d13

add a dedicated method for generating identifiers with no collision

92d7921

add a comment describing the collision algorithm

1c6d01f

use explicit lifetimes in the SystemParam derive

a25fb60

remove #system_param(ignore)

65f332e

clean up state struct lifetimes

43507a6

Merge remote-tracking branch 'upstream/main' into system-param-phanto…

6df2d0a

…m-data

remove unused attributes

4e5797c

use a descriptive name for a macro variable

6eac07a

implement WorldQuery for PhantomData

653fc46

add a compile test

e18e7af

remove #[world_query(ignore)]

715f8ec

make world_query(ignore) an error

f60909b

JoJoJet added A-ECS Entities, components, systems, and events C-Usability A simple quality-of-life change that makes Bevy easier to use C-Breaking-Change A breaking change to Bevy's public API that needs to be noted in a migration guide labels Mar 10, 2023

alice-i-cecile reviewed Mar 10, 2023

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crates/bevy_ecs/src/query/fetch.rs Show resolved Hide resolved

add comments to IS_DENSE and IS_ARCHETYPAL

4ee9978

alice-i-cecile reviewed Mar 10, 2023

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alice-i-cecile approved these changes Mar 10, 2023

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JoJoJet added 5 commits March 10, 2023 17:11

update a comment

3a55ca1

disallow #[system_param] attributes

c4005ac

Merge remote-tracking branch 'upstream/main' into system-param-phanto…

136033c

…m-data

remove an unused const

eaddf9a

undo an overlapping change

b2f4309

alice-i-cecile requested a review from james7132 March 13, 2023 03:33

james7132 requested changes Mar 13, 2023

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crates/bevy_ecs/macros/src/lib.rs Outdated Show resolved Hide resolved

crates/bevy_ecs/macros/src/lib.rs Outdated Show resolved Hide resolved

crates/bevy_ecs/src/query/fetch.rs Outdated Show resolved Hide resolved

add an example demonstrating PhantomData queries

0ab464c

add a test case for invariant lifetimes

93624c3

JoJoJet added the C-Bug An unexpected or incorrect behavior label Mar 24, 2023

JoJoJet added 5 commits March 28, 2023 14:51

re-add #[system_param(ignore)]

eb3e17d

re-add #[world_query(ignore)]

f3572b1

restore some docs

bcfee71

cargo fmt

10edef0

re-order an example

f8469c5

JoJoJet removed the C-Breaking-Change A breaking change to Bevy's public API that needs to be noted in a migration guide label Mar 28, 2023

alice-i-cecile added this to the 0.10.1 milestone Mar 28, 2023

JoJoJet added 2 commits March 28, 2023 15:47

allow unlimited ignored fields

2579709

reduce churn

6a3cfce

JoJoJet commented Mar 29, 2023

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JoJoJet added 2 commits March 28, 2023 20:05

Update crates/bevy_ecs/macros/src/lib.rs

8ff0178

deduplicate regression tests

464e095

james7132 approved these changes Mar 30, 2023

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james7132 added the S-Ready-For-Final-Review This PR has been approved by the community. It's ready for a maintainer to consider merging it label Mar 30, 2023

alice-i-cecile added this pull request to the merge queue Mar 30, 2023

github-merge-queue bot removed this pull request from the merge queue due to failed status checks Mar 30, 2023

alice-i-cecile added this pull request to the merge queue Mar 30, 2023

Merged via the queue into bevyengine:main with commit d9113cc Mar 30, 2023

JoJoJet mentioned this pull request Mar 30, 2023

Remove #[system_param(ignore)] and #[world_query(ignore)] #8265

Merged

JoJoJet deleted the system-param-phantom-data branch March 30, 2023 15:56

This was referenced Jun 28, 2023

News: Release 0.11 (wrong branch ... see #657) bevyengine/bevy-website#656

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Make `#[system_param(ignore)]` and `#[world_query(ignore)]` unnecessary #8030

Make `#[system_param(ignore)]` and `#[world_query(ignore)]` unnecessary #8030

JoJoJet commented Mar 10, 2023 •

edited

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alice-i-cecile commented Mar 10, 2023

alice-i-cecile Mar 10, 2023

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JoJoJet commented Mar 28, 2023

Make #[system_param(ignore)] and #[world_query(ignore)] unnecessary #8030

Make #[system_param(ignore)] and #[world_query(ignore)] unnecessary #8030

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JoJoJet commented Mar 10, 2023 • edited Loading

Objective

Solution

Changelog

alice-i-cecile commented Mar 10, 2023

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JoJoJet commented Mar 28, 2023

Make `#[system_param(ignore)]` and `#[world_query(ignore)]` unnecessary #8030

Make `#[system_param(ignore)]` and `#[world_query(ignore)]` unnecessary #8030

JoJoJet commented Mar 10, 2023 •

edited

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