Update ecs query docs (#12595)

# Objective

I'm reading through the ecs query code for the first time, and updating
the docs:
- fixed some typos
- added some docs about things I was confused about (in particular what
the difference between `matches_component_set` and
`update_component_access` was)

crates/bevy_ecs/src/query/filter.rs

@@ -79,6 +79,12 @@ pub trait QueryFilter: WorldQuery {
     /// many elements are being iterated (such as `Iterator::collect()`).
     const IS_ARCHETYPAL: bool;
 
+    /// Returns true if the provided [`Entity`] and [`TableRow`] should be included in the query results.
+    /// If false, the entity will be skipped.
+    ///
+    /// Note that this is called after already restricting the matched [`Table`]s and [`Archetype`]s to the
+    /// ones that are compatible with the Filter's access.
+    ///
     /// # Safety
     ///
     /// Must always be called _after_ [`WorldQuery::set_table`] or [`WorldQuery::set_archetype`]. `entity` and
@@ -357,7 +363,7 @@ impl<T: WorldQuery> Clone for OrFetch<'_, T> {
     }
 }
 
-macro_rules! impl_query_filter_tuple {
+macro_rules! impl_or_query_filter {
     ($(($filter: ident, $state: ident)),*) => {
         #[allow(unused_variables)]
         #[allow(non_snake_case)]
@@ -506,7 +512,7 @@ macro_rules! impl_tuple_query_filter {
 }
 
 all_tuples!(impl_tuple_query_filter, 0, 15, F);
-all_tuples!(impl_query_filter_tuple, 0, 15, F, S);
+all_tuples!(impl_or_query_filter, 0, 15, F, S);
 
 /// A filter on a component that only retains results added after the system last ran.
 ///
@@ -524,7 +530,7 @@ all_tuples!(impl_query_filter_tuple, 0, 15, F, S);
 /// # Time complexity
 ///
 /// `Added` is not [`ArchetypeFilter`], which practically means that
-/// if query (with `T` component filter) matches million entities,
+/// if the query (with `T` component filter) matches a million entities,
 /// `Added<T>` filter will iterate over all of them even if none of them were just added.
 ///
 /// For example, these two systems are roughly equivalent in terms of performance:

crates/bevy_ecs/src/query/iter.rs

@@ -42,7 +42,7 @@ impl<'w, 's, D: QueryData, F: QueryFilter> QueryIter<'w, 's, D, F> {
     }
 
     /// Executes the equivalent of [`Iterator::for_each`] over a contiguous segment
-    /// from an table.
+    /// from a table.
     ///
     /// # Safety
     ///  - all `rows` must be in `[0, table.entity_count)`.
@@ -656,7 +656,7 @@ struct QueryIterationCursor<'w, 's, D: QueryData, F: QueryFilter> {
     archetype_entities: &'w [ArchetypeEntity],
     fetch: D::Fetch<'w>,
     filter: F::Fetch<'w>,
-    // length of the table table or length of the archetype, depending on whether both `D`'s and `F`'s fetches are dense
+    // length of the table or length of the archetype, depending on whether both `D`'s and `F`'s fetches are dense
     current_len: usize,
     // either table row or archetype index, depending on whether both `D`'s and `F`'s fetches are dense
     current_row: usize,
@@ -743,7 +743,7 @@ impl<'w, 's, D: QueryData, F: QueryFilter> QueryIterationCursor<'w, 's, D, F> {
 
     /// How many values will this cursor return at most?
     ///
-    /// Note that if `D::IS_ARCHETYPAL && F::IS_ARCHETYPAL`, the return value
+    /// Note that if `F::IS_ARCHETYPAL`, the return value
     /// will be **the exact count of remaining values**.
     fn max_remaining(&self, tables: &'w Tables, archetypes: &'w Archetypes) -> usize {
         let remaining_matched: usize = if Self::IS_DENSE {
@@ -788,7 +788,7 @@ impl<'w, 's, D: QueryData, F: QueryFilter> QueryIterationCursor<'w, 's, D, F> {
                 }
 
                 // SAFETY: set_table was called prior.
-                // `current_row` is a table row in range of the current table, because if it was not, then the if above would have been executed.
+                // `current_row` is a table row in range of the current table, because if it was not, then the above would have been executed.
                 let entity = unsafe { self.table_entities.get_unchecked(self.current_row) };
                 let row = TableRow::from_usize(self.current_row);
                 if !F::filter_fetch(&mut self.filter, *entity, row) {
@@ -799,7 +799,7 @@ impl<'w, 's, D: QueryData, F: QueryFilter> QueryIterationCursor<'w, 's, D, F> {
                 // SAFETY:
                 // - set_table was called prior.
                 // - `current_row` must be a table row in range of the current table,
-                //   because if it was not, then the if above would have been executed.
+                //   because if it was not, then the above would have been executed.
                 // - fetch is only called once for each `entity`.
                 let item = unsafe { D::fetch(&mut self.fetch, *entity, row) };
 

crates/bevy_ecs/src/query/state.rs

@@ -22,6 +22,17 @@ use super::{
 };
 
 /// Provides scoped access to a [`World`] state according to a given [`QueryData`] and [`QueryFilter`].
+///
+/// This data is cached between system runs, and is used to:
+/// - store metadata about which [`Table`] or [`Archetype`] are matched by the query. "Matched" means
+/// that the query will iterate over the data in the matched table/archetype.
+/// - cache the [`State`] needed to compute the [`Fetch`] struct used to retrieve data
+/// from a specific [`Table`] or [`Archetype`]
+/// - build iterators that can iterate over the query results
+///
+/// [`State`]: crate::query::world_query::WorldQuery::State
+/// [`Fetch`]: crate::query::world_query::WorldQuery::Fetch
+/// [`Table`]: crate::storage::Table
 #[repr(C)]
 // SAFETY NOTE:
 // Do not add any new fields that use the `D` or `F` generic parameters as this may
@@ -29,8 +40,12 @@ use super::{
 pub struct QueryState<D: QueryData, F: QueryFilter = ()> {
     world_id: WorldId,
     pub(crate) archetype_generation: ArchetypeGeneration,
+    /// Metadata about the [`Table`](crate::storage::Table)s matched by this query.
     pub(crate) matched_tables: FixedBitSet,
+    /// Metadata about the [`Archetype`]s matched by this query.
     pub(crate) matched_archetypes: FixedBitSet,
+    /// [`FilteredAccess`] computed by combining the `D` and `F` access. Used to check which other queries
+    /// this query can run in parallel with.
     pub(crate) component_access: FilteredAccess<ComponentId>,
     // NOTE: we maintain both a TableId bitset and a vec because iterating the vec is faster
     pub(crate) matched_table_ids: Vec<TableId>,
@@ -330,6 +345,11 @@ impl<D: QueryData, F: QueryFilter> QueryState<D, F> {
         }
     }
 
+    /// Process the given [`Archetype`] to update internal metadata about the [`Table`](crate::storage::Table)s
+    /// and [`Archetype`]s that are matched by this query.
+    ///
+    /// Returns `true` if the given `archetype` matches the query. Otherwise, returns `false`.
+    /// If there is no match, then there is no need to update the query's [`FilteredAccess`].
     fn new_archetype_internal(&mut self, archetype: &Archetype) -> bool {
         if D::matches_component_set(&self.fetch_state, &|id| archetype.contains(id))
             && F::matches_component_set(&self.filter_state, &|id| archetype.contains(id))

crates/bevy_ecs/src/query/world_query.rs

@@ -120,6 +120,8 @@ pub unsafe trait WorldQuery {
     ) -> Self::Item<'w>;
 
     /// Adds any component accesses used by this [`WorldQuery`] to `access`.
+    ///
+    /// Used to check which queries are disjoint and can run in parallel
     // This does not have a default body of `{}` because 99% of cases need to add accesses
     // and forgetting to do so would be unsound.
     fn update_component_access(state: &Self::State, access: &mut FilteredAccess<ComponentId>);
@@ -132,6 +134,9 @@ pub unsafe trait WorldQuery {
     fn get_state(world: &World) -> Option<Self::State>;
 
     /// Returns `true` if this query matches a set of components. Otherwise, returns `false`.
+    ///
+    /// Used to check which [`Archetype`]s can be skipped by the query
+    /// (if none of the [`Component`](crate::component::Component)s match)
     fn matches_component_set(
         state: &Self::State,
         set_contains_id: &impl Fn(ComponentId) -> bool,

crates/bevy_ecs/src/system/query.rs

@@ -552,7 +552,7 @@ impl<'w, 's, D: QueryData, F: QueryFilter> Query<'w, 's, D, F> {
     /// Returns an [`Iterator`] over the read-only query items generated from an [`Entity`] list.
     ///
     /// Items are returned in the order of the list of entities, and may not be unique if the input
-    /// doesnn't guarantee uniqueness. Entities that don't match the query are skipped.
+    /// doesn't guarantee uniqueness. Entities that don't match the query are skipped.
     ///
     /// # Example
     ///