Add the Layout of the failed allocation to TryReserveError::AllocError

… and add a separately-unstable field to force non-exhaustive matching
(`#[non_exhaustive]` is no implemented yet on enum variants)
so that we have the option to later expose the allocator’s error value.

CC https://github.com/rust-lang/wg-allocators/issues/23

1 files changed, 14 insertions, 11 deletions

diff --git a/src/liballoc/collections/mod.rs b/src/liballoc/collections/mod.rs
index 48c3ed8a57d..f1f22fe48c5 100644
--- a/src/liballoc/collections/mod.rs
+++ b/src/liballoc/collections/mod.rs
@@ -41,25 +41,28 @@ pub use linked_list::LinkedList;
 #[doc(no_inline)]
 pub use vec_deque::VecDeque;
 
-use crate::alloc::{AllocErr, LayoutErr};
+use crate::alloc::{Layout, LayoutErr};
 
-/// Augments `AllocErr` with a CapacityOverflow variant.
+/// The error type for `try_reserve` methods.
 #[derive(Clone, PartialEq, Eq, Debug)]
 #[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
 pub enum TryReserveError {
     /// Error due to the computed capacity exceeding the collection's maximum
     /// (usually `isize::MAX` bytes).
     CapacityOverflow,
-    /// Error due to the allocator (see the `AllocErr` type's docs).
-    AllocErr,
-}
 
-#[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
-impl From<AllocErr> for TryReserveError {
-    #[inline]
-    fn from(AllocErr: AllocErr) -> Self {
-        TryReserveError::AllocErr
-    }
+    /// The memory allocator returned an error
+    AllocError {
+        /// The layout of allocation request that failed
+        layout: Layout,
+
+        #[doc(hidden)]
+        #[unstable(feature = "container_error_extra", issue = "0", reason = "\
+            Enable exposing the allocator’s custom error value \
+            if an associated type is added in the future: \
+            https://github.com/rust-lang/wg-allocators/issues/23")]
+        non_exhaustive: (),
+    },
 }
 
 #[unstable(feature = "try_reserve", reason = "new API", issue="48043")]