undo an optimization 😭

MIRI is buggy so we can't use fn pointers for comparisons

crates/bevy_utils/src/label.rs

@@ -81,6 +81,7 @@ macro_rules! define_label {
  $(#[$id_attr])*
  #[derive(Clone, Copy)]
  pub struct $id_name {
+ ty: ::std::any::TypeId,
  data: u64,
  f: fn(u64, &mut ::std::fmt::Formatter) -> ::std::fmt::Result,
  }
@@ -98,7 +99,7 @@ macro_rules! define_label {
  #[inline]
  fn as_label(&self) -> $id_name {
  let data = self.data();
- $id_name { data, f: Self::fmt }
+ $id_name { data, ty: ::std::any::TypeId::of::<Self>(), f: Self::fmt }
  }
  /// Returns a number used to distinguish different labels of the same type.
  fn data(&self) -> u64;
@@ -128,26 +129,23 @@ macro_rules! define_label {
  impl PartialEq for $id_name {
  #[inline]
  fn eq(&self, rhs: &Self) -> bool {
- (self.f as usize) == (rhs.f as usize) && self.data() == rhs.data()
+ self.ty == rhs.ty && self.data() == rhs.data()
  }
  }
  impl Eq for $id_name {}
 
 
  impl std::hash::Hash for $id_name {
  fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
- (self.f as usize).hash(state);
+ self.ty.hash(state);
  self.data().hash(state);
  }
  }
 
  impl $id_name {
  /// Returns true if this label was constructed from an instance of type `L`.
  pub fn is<L: $label_name>(self) -> bool {
- // FIXME: This is potentially incorrect, due to the
- // compiler unifying identical functions. We'll likely
- // have to store some kind of hash of the TypeId.
- (self.f as usize) == (<L as $label_name>::fmt as usize)
+ self.ty == ::std::any::TypeId::of::<L>()
  }
  /// Attempts to downcast this label to type `L`.
  ///