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

2 files changed, 6 insertions, 2 deletions

diff --git a/src/libstd/collections/hash/map.rs b/src/libstd/collections/hash/map.rs
index db637a108cb..a0538986a22 100644
--- a/src/libstd/collections/hash/map.rs
+++ b/src/libstd/collections/hash/map.rs
@@ -2545,7 +2545,10 @@ fn map_entry<'a, K: 'a, V: 'a>(raw: base::RustcEntry<'a, K, V>) -> Entry<'a, K,
 fn map_collection_alloc_err(err: hashbrown::CollectionAllocErr) -> TryReserveError {
     match err {
         hashbrown::CollectionAllocErr::CapacityOverflow => TryReserveError::CapacityOverflow,
-        hashbrown::CollectionAllocErr::AllocErr { .. } => TryReserveError::AllocErr,
+        hashbrown::CollectionAllocErr::AllocErr { layout } => TryReserveError::AllocError {
+            layout,
+            non_exhaustive: (),
+        },
     }
 }
 
@@ -3405,7 +3408,7 @@ mod test_map {
             panic!("usize::MAX should trigger an overflow!");
         }
 
-        if let Err(AllocErr) = empty_bytes.try_reserve(MAX_USIZE / 8) {
+        if let Err(AllocError { .. }) = empty_bytes.try_reserve(MAX_USIZE / 8) {
         } else {
             panic!("usize::MAX / 8 should trigger an OOM!")
         }
diff --git a/src/libstd/lib.rs b/src/libstd/lib.rs
index 1f48315d3f8..760d92f1d7b 100644
--- a/src/libstd/lib.rs
+++ b/src/libstd/lib.rs
@@ -251,6 +251,7 @@
 #![feature(concat_idents)]
 #![feature(const_cstr_unchecked)]
 #![feature(const_raw_ptr_deref)]
+#![feature(container_error_extra)]
 #![feature(core_intrinsics)]
 #![feature(custom_test_frameworks)]
 #![feature(doc_alias)]