CoAlloc: meta_num_slots... macros- WIP

Author: peter-lyons-kehl

library/alloc/src/raw_vec.rs

@@ -7,6 +7,7 @@ use core::mem::{self, ManuallyDrop, MaybeUninit, SizedTypeProperties};
 use core::ops::Drop;
 use core::ptr::{self, NonNull, Unique};
 use core::slice;
+use core::alloc::CoAllocMetaBase;
 
 #[cfg(not(no_global_oom_handling))]
 use crate::alloc::handle_alloc_error;
@@ -136,12 +137,11 @@ where
     /// the returned `RawVec`.
     pub const fn new_in(alloc: A) -> Self {
         // `cap: 0` means "unallocated". zero-sized types are ignored.
-        #[allow(unreachable_code)] // @FIXME CoAlloc
         Self {
             ptr: Unique::dangling(),
             cap: 0,
             alloc,
-            metas: [loop {}; // @FIXME CoAlloc
+            metas: [A::CoAllocMeta::new_plain(); // @FIXME CoAlloc
                 alloc::co_alloc_metadata_num_slots_with_preference::<A>(COOP_PREF)],
         }
     }
@@ -221,7 +221,7 @@ where
                 ptr: unsafe { Unique::new_unchecked(ptr.cast().as_ptr()) },
                 cap: capacity,
                 alloc,
-                metas: [loop {}; // @FIXME CoAlloc
+                metas: [A::CoAllocMeta::new_plain(); // @FIXME CoAlloc
                     alloc::co_alloc_metadata_num_slots_with_preference::<A>(COOP_PREF)],
             }
         }
@@ -244,7 +244,7 @@ where
             ptr: unsafe { Unique::new_unchecked(ptr) },
             cap: capacity,
             alloc,
-            metas: [loop {}; //@FIXME CoAlloc
+            metas: [A::CoAllocMeta::new_plain(); //@FIXME CoAlloc
                 alloc::co_alloc_metadata_num_slots_with_preference::<A>(COOP_PREF)],
         }
     }

library/core/src/alloc/global.rs

@@ -1,11 +1,12 @@
 use crate::alloc::Layout;
+use crate::alloc::{CoAllocMetaBase, CoAllocMetaPlain};
 use crate::cmp;
 use crate::ptr;
 
 #[unstable(feature = "global_co_alloc_meta", issue = "none")]
-#[allow(missing_debug_implementations)]
+#[derive(Debug)]
 /// Used for parameters and results (to/from `GlobalCoAllocator`'s functions, where applicable).
-pub struct RawAndMeta<M: Clone + Copy> {
+pub struct RawAndMeta<M: CoAllocMetaBase> {
     pub ptr: *mut u8,
     pub meta: M,
 }
@@ -129,10 +130,12 @@ pub struct RawAndMeta<M: Clone + Copy> {
 ///   having side effects.
 #[stable(feature = "global_alloc", since = "1.28.0")]
 pub unsafe trait GlobalAlloc {
+    /// NOT for public use. The default value MAY be REMOVED or CHANGED.
+    /// 
     /// @FIXME Validate (preferrable at compile time, otherwise as a test) that this type's
     /// alignment <= `usize` alignment.
     #[unstable(feature = "global_co_alloc_meta", issue = "none")]
-    type CoAllocMeta: Clone + Copy = ();
+    type CoAllocMeta: CoAllocMetaBase = CoAllocMetaPlain;
 
     /// Allocate memory as described by the given `layout`.
     ///

library/core/src/alloc/mod.rs

@@ -50,19 +50,17 @@ impl fmt::Display for AllocError {
 
 /// (Non-Null) Pointer and coallocation metadata.
 #[unstable(feature = "global_co_alloc_meta", issue = "none")]
-#[allow(missing_debug_implementations)]
-#[derive(Clone, Copy)]
-pub struct PtrAndMeta<M: Clone + Copy> {
+#[derive(Clone, Copy, Debug)]
+pub struct PtrAndMeta<M: CoAllocMetaBase> {
     pub ptr: NonNull<u8>,
     pub meta: M,
 }
 
 /// (NonNull) Slice and coallocation metadata.
 #[unstable(feature = "global_co_alloc_meta", issue = "none")]
-#[allow(missing_debug_implementations)]
-#[derive(Clone, Copy)]
+#[derive(Clone, Copy, Debug)]
 /// Used for results (from `CoAllocator`'s functions, where applicable).
-pub struct SliceAndMeta<M: Clone + Copy> {
+pub struct SliceAndMeta<M: CoAllocMetaBase> {
     pub slice: NonNull<[u8]>,
     pub meta: M,
 }
@@ -78,7 +76,6 @@ macro_rules! SHORT_TERM_VEC_PREFERS_COOP {
 
 /// `Result` of `SliceAndMeta` or `AllocError`.
 #[unstable(feature = "global_co_alloc_meta", issue = "none")]
-#[allow(missing_debug_implementations)]
 pub type SliceAndMetaResult<M> = Result<SliceAndMeta<M>, AllocError>;
 
 // @FIXME REMOVE
@@ -158,9 +155,11 @@ pub unsafe trait Allocator {
     // It applies to the global (default) allocator only. And/or System allocator?! @FIXME
     const CO_ALLOCATES_WITH_META: bool = false;
 
+    /// NOT for public use. The default value MAY be REMOVED or CHANGED.
+    /// 
     /// @FIXME Validate (preferrable at compile time, otherwise as a test) that this type's
     /// alignment <= `usize` alignment.
-    type CoAllocMeta: Clone + Copy = ();
+    type CoAllocMeta: CoAllocMetaBase = CoAllocMetaPlain;
 
     /// Attempts to allocate a block of memory.
     ///
@@ -588,3 +587,24 @@ where
         unsafe { (**self).shrink(ptr, old_layout, new_layout) }
     }
 }
+
+#[unstable(feature = "global_co_alloc_meta", issue = "none")]
+pub trait CoAllocMetaBase: Clone + Copy {
+    /// NOT for public use. This MAY BE REMOVED or CHANGED.
+    /// 
+    /// For EXPERIMENTATION only.
+    fn new_plain() -> Self;
+}
+
+#[unstable(feature = "global_co_alloc_meta", issue = "none")]
+#[derive(Clone, Copy, Debug)]
+pub struct CoAllocMetaPlain {}
+
+static CO_ALLOC_META_PLAIN: CoAllocMetaPlain = CoAllocMetaPlain {};
+
+#[unstable(feature = "global_co_alloc_meta", issue = "none")]
+impl CoAllocMetaBase for CoAllocMetaPlain {
+    fn new_plain() -> Self {
+        CO_ALLOC_META_PLAIN
+    }
+}