Remove unstable GATs implementation.

This change migrates to a stable GATs implementation for entity storage
(i.e., graphs) and removes the `unstable` Cargo feature and its
corresponding `build.rs`.

As part of this change, the input type parameter `G` used in many view
implementations has been removed anywhere the compiler required a
lifetime bound. The `GraphData` type parameter is not actually composed
into view types, but the compiler cannot determine this. As such, any
bounds on this type should be avoided. The parameter `G` may be
completely removed in a subsequent change, because while it sometimes
makes the code a bit easier to read, it may also cause confusion.

plexus/Cargo.toml

@@ -46,7 +46,6 @@ geometry-glam = ["theon/geometry-glam"]
 geometry-mint = ["theon/geometry-mint"]
 geometry-nalgebra = ["theon/geometry-nalgebra"]
 geometry-ultraviolet = ["theon/geometry-ultraviolet"]
-unstable = []
 
 [dependencies]
 approx = "^0.3.0"

plexus/src/entity/mod.rs

@@ -16,19 +16,7 @@ pub enum EntityError {
     Data,
 }
 
-#[cfg(not(all(nightly, feature = "unstable")))]
-pub trait Lifetime: 'static {}
-
-#[cfg(not(all(nightly, feature = "unstable")))]
-impl<T> Lifetime for T where T: 'static {}
-
-#[cfg(all(nightly, feature = "unstable"))]
-pub trait Lifetime {}
-
-#[cfg(all(nightly, feature = "unstable"))]
-impl<T> Lifetime for T {}
-
-pub trait Entity: Lifetime + Sized {
+pub trait Entity: Sized {
     type Key: Key;
     type Storage: Default + Dispatch<Self> + Storage<Self>;
 }

plexus/src/entity/storage/hash.rs

@@ -117,63 +117,32 @@ where
     }
 }
 
-#[cfg(not(all(nightly, feature = "unstable")))]
-impl<E> Dispatch<E> for HashStorage<E, (), Dynamic>
-where
-    E: Entity<Storage = Self>,
-    InnerKey<E::Key>: Eq + Hash,
-{
-    type Target = dyn 'static + DependentStorage<E>;
-}
-
-#[cfg(all(nightly, feature = "unstable"))]
 #[rustfmt::skip]
 impl<E> Dispatch<E> for HashStorage<E, (), Dynamic>
 where
     E: Entity<Storage = Self>,
     InnerKey<E::Key>: Eq + Hash,
 {
-    type Target<'a> where E: 'a = dyn 'a + DependentStorage<E>;
-}
-
-#[cfg(not(all(nightly, feature = "unstable")))]
-impl<E> Dispatch<E> for HashStorage<E, IncrementalKeyer, Dynamic>
-where
-    E: Entity<Storage = Self>,
-    E::Key: Key<Inner = u64>,
-{
-    type Target = dyn 'static + IndependentStorage<E>;
+    type Target<'a> = dyn 'a + DependentStorage<E> where E: 'a;
 }
 
-#[cfg(all(nightly, feature = "unstable"))]
 #[rustfmt::skip]
 impl<E> Dispatch<E> for HashStorage<E, IncrementalKeyer, Dynamic>
 where
     E: Entity<Storage = Self>,
     E::Key: Key<Inner = u64>,
 {
-    type Target<'a> where E: 'a = dyn 'a + IndependentStorage<E>;
-}
-
-#[cfg(not(all(nightly, feature = "unstable")))]
-impl<E, R> Dispatch<E> for HashStorage<E, R, Static>
-where
-    E: Entity<Storage = Self>,
-    InnerKey<E::Key>: Eq + Hash,
-    R: 'static + Default,
-{
-    type Target = Self;
+    type Target<'a> = dyn 'a + IndependentStorage<E> where E: 'a;
 }
 
-#[cfg(all(nightly, feature = "unstable"))]
 #[rustfmt::skip]
 impl<E, R> Dispatch<E> for HashStorage<E, R, Static>
 where
     E: Entity<Storage = Self>,
     InnerKey<E::Key>: Eq + Hash,
     R: 'static + Default,
 {
-    type Target<'a> where E: 'a = Self;
+    type Target<'a> = Self where E: 'a;
 }
 
 impl<E, R, P> Enumerate<E> for HashStorage<E, R, P>

plexus/src/entity/storage/mod.rs

@@ -10,9 +10,6 @@ pub mod prelude {
     pub use crate::entity::storage::{Enumerate, Get, Insert, InsertWithKey, Remove};
 }
 
-#[cfg(not(all(nightly, feature = "unstable")))]
-pub type StorageTarget<E> = <<E as Entity>::Storage as Dispatch<E>>::Target;
-#[cfg(all(nightly, feature = "unstable"))]
 pub type StorageTarget<'a, E> = <<E as Entity>::Storage as Dispatch<E>>::Target<'a>;
 
 pub type InnerKey<K> = <K as Key>::Inner;
@@ -48,15 +45,6 @@ where
     }
 }
 
-#[cfg(not(all(nightly, feature = "unstable")))]
-pub trait Dispatch<E>
-where
-    E: Entity,
-{
-    type Target: ?Sized + Storage<E>;
-}
-
-#[cfg(all(nightly, feature = "unstable"))]
 #[rustfmt::skip]
 pub trait Dispatch<E>
 where

plexus/src/entity/view.rs

@@ -321,10 +321,12 @@ where
 
 impl<'a, E> Orphan<'a, E>
 where
-    E: 'a + Payload,
+    E: Payload,
+    E::Data: 'a,
 {
     pub fn bind<M>(storage: &'a mut M, key: E::Key) -> Option<Self>
     where
+        E: 'a,
         M: AsStorageMut<E>,
     {
         View::bind(storage, key).map(Orphan::from)
@@ -336,6 +338,7 @@ where
 
     pub fn bind_into<T, M>(storage: &'a mut M, key: E::Key) -> Option<T>
     where
+        E: 'a,
         T: From<Self>,
         M: AsStorageMut<E>,
     {
@@ -357,7 +360,8 @@ where
 
 impl<'a, E> AsRef<E::Key> for Orphan<'a, E>
 where
-    E: 'a + Payload,
+    E: Payload,
+    E::Data: 'a,
 {
     fn as_ref(&self) -> &E::Key {
         &self.key
@@ -366,7 +370,8 @@ where
 
 impl<'a, E> ClosedView for Orphan<'a, E>
 where
-    E: 'a + Payload,
+    E: Payload,
+    E::Data: 'a,
 {
     type Key = E::Key;
     type Entity = E;
@@ -379,6 +384,7 @@ where
 impl<'a, E, M> From<View<&'a mut M, E>> for Orphan<'a, E>
 where
     E: 'a + Payload,
+    E::Data: 'a,
     M: AsStorageMut<E>,
 {
     fn from(view: View<&'a mut M, E>) -> Self {
@@ -391,11 +397,17 @@ where
     }
 }
 
-impl<'a, E> Eq for Orphan<'a, E> where E: 'a + Payload {}
+impl<'a, E> Eq for Orphan<'a, E>
+where
+    E: Payload,
+    E::Data: 'a,
+{
+}
 
 impl<'a, E> Hash for Orphan<'a, E>
 where
-    E: 'a + Payload,
+    E: Payload,
+    E::Data: 'a,
 {
     fn hash<H>(&self, state: &mut H)
     where
@@ -407,7 +419,8 @@ where
 
 impl<'a, E> PartialEq for Orphan<'a, E>
 where
-    E: 'a + Payload,
+    E: Payload,
+    E::Data: 'a,
 {
     fn eq(&self, other: &Self) -> bool {
         self.key == other.key

plexus/src/graph/data.rs

@@ -1,5 +1,4 @@
 use crate::entity::borrow::Reborrow;
-use crate::entity::Lifetime;
 
 pub type Data<M> = <M as Parametric>::Data;
 
@@ -64,11 +63,11 @@ pub type Data<M> = <M as Parametric>::Data;
 ///
 /// [`AsPosition`]: crate::geometry::AsPosition
 /// [`MeshGraph`]: crate::graph::MeshGraph
-pub trait GraphData: Lifetime + Sized {
-    type Vertex: Clone + Lifetime;
-    type Arc: Clone + Default + Lifetime;
-    type Edge: Clone + Default + Lifetime;
-    type Face: Clone + Default + Lifetime;
+pub trait GraphData: Sized {
+    type Vertex: Clone;
+    type Arc: Clone + Default;
+    type Edge: Clone + Default;
+    type Face: Clone + Default;
 }
 
 impl GraphData for () {
@@ -80,7 +79,7 @@ impl GraphData for () {
 
 impl<T> GraphData for (T, T)
 where
-    T: Clone + Lifetime,
+    T: Clone,
 {
     type Vertex = Self;
     type Arc = ();
@@ -90,7 +89,7 @@ where
 
 impl<T> GraphData for (T, T, T)
 where
-    T: Clone + Lifetime,
+    T: Clone,
 {
     type Vertex = Self;
     type Arc = ();
@@ -100,7 +99,7 @@ where
 
 impl<T> GraphData for [T; 2]
 where
-    T: Clone + Lifetime,
+    T: Clone,
 {
     type Vertex = Self;
     type Arc = ();
@@ -110,7 +109,7 @@ where
 
 impl<T> GraphData for [T; 3]
 where
-    T: Clone + Lifetime,
+    T: Clone,
 {
     type Vertex = Self;
     type Arc = ();