bevy_reflect: Use active_types instead of active_fields where appropriate (#19922)

# Objective

Follow on fixes for #19876, using `active_types` instead of
`active_fields` where appropriate.

Helps a tiny bit with #19873.

## Solution

- Describe the solution used to achieve the objective above.

## Testing

I checked the output of `cargo expand` and ran `cargo run -p ci`.

Author: nnethercote

crates/bevy_reflect/derive/src/derive_data.rs

@@ -605,13 +605,11 @@ impl<'a> ReflectStruct<'a> {
     }
 
     /// Get a collection of types which are exposed to the reflection API
-    pub fn active_types(&self) -> Vec<Type> {
-        // Collect via `IndexSet` to eliminate duplicate types.
+    pub fn active_types(&self) -> IndexSet<Type> {
+        // Collect into an `IndexSet` to eliminate duplicate types.
         self.active_fields()
             .map(|field| field.reflected_type().clone())
             .collect::<IndexSet<_>>()
-            .into_iter()
-            .collect::<Vec<_>>()
     }
 
     /// Get an iterator of fields which are exposed to the reflection API.
@@ -634,7 +632,7 @@ impl<'a> ReflectStruct<'a> {
     }
 
     pub fn where_clause_options(&self) -> WhereClauseOptions {
-        WhereClauseOptions::new_with_fields(self.meta(), self.active_types().into_boxed_slice())
+        WhereClauseOptions::new_with_types(self.meta(), self.active_types())
     }
 
     /// Generates a `TokenStream` for `TypeInfo::Struct` or `TypeInfo::TupleStruct` construction.
@@ -841,13 +839,11 @@ impl<'a> ReflectEnum<'a> {
     }
 
     /// Get a collection of types which are exposed to the reflection API
-    pub fn active_types(&self) -> Vec<Type> {
-        // Collect via `IndexSet` to eliminate duplicate types.
+    pub fn active_types(&self) -> IndexSet<Type> {
+        // Collect into an `IndexSet` to eliminate duplicate types.
         self.active_fields()
             .map(|field| field.reflected_type().clone())
             .collect::<IndexSet<_>>()
-            .into_iter()
-            .collect::<Vec<_>>()
     }
 
     /// Get an iterator of fields which are exposed to the reflection API
@@ -856,7 +852,7 @@ impl<'a> ReflectEnum<'a> {
     }
 
     pub fn where_clause_options(&self) -> WhereClauseOptions {
-        WhereClauseOptions::new_with_fields(self.meta(), self.active_types().into_boxed_slice())
+        WhereClauseOptions::new_with_types(self.meta(), self.active_types())
     }
 
     /// Returns the `GetTypeRegistration` impl as a `TokenStream`.
@@ -869,7 +865,7 @@ impl<'a> ReflectEnum<'a> {
         crate::registration::impl_get_type_registration(
             where_clause_options,
             None,
-            Some(self.active_fields().map(StructField::reflected_type)),
+            Some(self.active_types().iter()),
         )
     }
 

crates/bevy_reflect/derive/src/where_clause_options.rs

@@ -1,28 +1,26 @@
 use crate::derive_data::ReflectMeta;
 use bevy_macro_utils::fq_std::{FQAny, FQSend, FQSync};
+use indexmap::IndexSet;
 use proc_macro2::{TokenStream, TokenTree};
 use quote::{quote, ToTokens};
 use syn::{punctuated::Punctuated, Ident, Token, Type, WhereClause};
 
 /// Options defining how to extend the `where` clause for reflection.
 pub(crate) struct WhereClauseOptions<'a, 'b> {
     meta: &'a ReflectMeta<'b>,
-    active_fields: Box<[Type]>,
+    active_types: IndexSet<Type>,
 }
 
 impl<'a, 'b> WhereClauseOptions<'a, 'b> {
     pub fn new(meta: &'a ReflectMeta<'b>) -> Self {
         Self {
             meta,
-            active_fields: Box::new([]),
+            active_types: IndexSet::new(),
         }
     }
 
-    pub fn new_with_fields(meta: &'a ReflectMeta<'b>, active_fields: Box<[Type]>) -> Self {
-        Self {
-            meta,
-            active_fields,
-        }
+    pub fn new_with_types(meta: &'a ReflectMeta<'b>, active_types: IndexSet<Type>) -> Self {
+        Self { meta, active_types }
     }
 
     pub fn meta(&self) -> &'a ReflectMeta<'b> {
@@ -207,7 +205,7 @@ impl<'a, 'b> WhereClauseOptions<'a, 'b> {
                 false
             }
 
-            Some(self.active_fields.iter().filter_map(move |ty| {
+            Some(self.active_types.iter().filter_map(move |ty| {
                 // Field type bounds are only required if `ty` is generic. How to determine that?
                 // Search `ty`s token stream for identifiers that match the identifiers from the
                 // function's type params. E.g. if `T` and `U` are the type param identifiers and