Assorted feature gate updates / other adjustments to fix compilation …

…on the latest nightly compiler

demo/main_demo.rs

@@ -9,7 +9,6 @@
 // of a single program.
 #![feature(
   const_fn_floating_point_arithmetic,
-  const_fn_trait_bound,
   const_mut_refs,
   const_precise_live_drops,
   // Weirdly named feature, as it doesn't necessarily relate to `Cell` at all.

src/heap/heap_trait_impls.rs

@@ -32,7 +32,15 @@ impl<T: Copy, const N: usize> const Clone for StaticHeap<T, N> {
 
   #[inline(always)]
   fn clone_from(&mut self, source: &Self) {
-    self.data.clone_from(&source.data);
+    // Calling `clone_from` directly through `self.data` is not accepted by the compiler currently
+    // for some reason in the context of this impl being `const`.
+    unsafe {
+      self
+        .data
+        .as_mut_ptr()
+        .copy_from_nonoverlapping(source.data.as_ptr(), source.data.length);
+      self.data.set_len(source.data.length);
+    }
   }
 }
 

src/lib.rs

@@ -33,8 +33,6 @@
   const_assume,
   const_eval_select,
   const_fn_floating_point_arithmetic,
-  const_fn_fn_ptr_basics,
-  const_fn_trait_bound,
   const_intrinsic_copy,
   const_maybe_uninit_as_mut_ptr,
   const_maybe_uninit_assume_init,

src/string/string_trait_impls.rs

@@ -80,7 +80,15 @@ impl<const N: usize> const Clone for StaticString<N> {
 
   #[inline(always)]
   fn clone_from(&mut self, other: &Self) {
-    self.vec.clone_from(&other.vec);
+    // Calling `clone_from` directly through `self.vec` is not accepted by the compiler currently
+    // for some reason in the context of this impl being `const`.
+    unsafe {
+      self
+        .vec
+        .as_mut_ptr()
+        .copy_from_nonoverlapping(other.vec.as_ptr(), other.vec.length);
+      self.vec.set_len(other.vec.length);
+    }
   }
 }
 

test/test_staticvec.rs

@@ -3,7 +3,6 @@
   adt_const_params,
   box_syntax,
   const_fn_floating_point_arithmetic,
-  const_fn_trait_bound,
   const_trait_impl,
   exact_size_is_empty,
   generic_const_exprs,
@@ -602,7 +601,7 @@ fn extend_from_slice() {
   assert_eq!(vec, [1, 2, 3, 4]);
   let mut vec2 = StaticVec::<i32, 0>::new();
   vec2.extend_from_slice(&[2, 3, 4]);
-  assert_eq!(vec2, []);  
+  assert_eq!(vec2, []);
 }
 
 #[test]
@@ -617,10 +616,10 @@ fn filled_with() {
   assert_eq!(v[1], 2);
   assert_eq!(v[2], 3);
   assert_eq!(v[3], 4);
-  let v2 = StaticVec::<i32, 0>::filled_with(|| { 0 });
+  let v2 = StaticVec::<i32, 0>::filled_with(|| 0);
   assert_eq!(v2.len(), 0);
   assert_eq!(v2.capacity(), 0);
-  assert_eq!(v2.remaining_capacity(), 0);  
+  assert_eq!(v2.remaining_capacity(), 0);
 }
 
 #[test]