Don't enable allocator-api2/nightly feature

See #564 for rationale. Tentatively fixes said issue and #483, though
the root cause is up to the `allocator-api2` crate to fix.
Direct use of `allocator-api2` in tests had to be replaced with the
indirection used elsewhere in the crate.

Cargo.toml

@@ -47,7 +47,7 @@ default = ["default-hasher", "inline-more", "allocator-api2", "equivalent", "raw
 
 # Enables use of nightly features. This is only guaranteed to work on the latest
 # version of nightly Rust.
-nightly = ["allocator-api2?/nightly", "bumpalo/allocator_api"]
+nightly = ["bumpalo/allocator_api"]
 
 # Enables the RustcEntry API used to provide the standard library's Entry API.
 rustc-internal-api = []

src/map.rs

@@ -4690,9 +4690,9 @@ mod test_map {
     use super::Entry::{Occupied, Vacant};
     use super::EntryRef;
     use super::HashMap;
+    use crate::raw::{AllocError, Allocator, Global};
     use alloc::string::{String, ToString};
     use alloc::sync::Arc;
-    use allocator_api2::alloc::{AllocError, Allocator, Global};
     use core::alloc::Layout;
     use core::ptr::NonNull;
     use core::sync::atomic::{AtomicI8, Ordering};

src/raw/alloc.rs

@@ -1,4 +1,5 @@
 pub(crate) use self::inner::{do_alloc, Allocator, Global};
+#[cfg(test)] pub(crate) use self::inner::AllocError;
 
 // Nightly-case.
 // Use unstable `allocator_api` feature.
@@ -8,6 +9,7 @@ pub(crate) use self::inner::{do_alloc, Allocator, Global};
 mod inner {
     use crate::alloc::alloc::Layout;
     pub use crate::alloc::alloc::{Allocator, Global};
+    #[cfg(test)] pub use crate::alloc::alloc::AllocError;
     use core::ptr::NonNull;
 
     #[allow(clippy::map_err_ignore)]
@@ -29,6 +31,7 @@ mod inner {
 mod inner {
     use crate::alloc::alloc::Layout;
     pub use allocator_api2::alloc::{Allocator, Global};
+    #[cfg(test)] pub use allocator_api2::alloc::AllocError;
     use core::ptr::NonNull;
 
     #[allow(clippy::map_err_ignore)]

src/raw/mod.rs

@@ -13,6 +13,7 @@ use core::{hint, ptr};
 
 mod alloc;
 pub(crate) use self::alloc::{do_alloc, Allocator, Global};
+#[cfg(test)] pub(crate) use self::alloc::AllocError;
 
 #[inline]
 unsafe fn offset_from<T>(to: *const T, from: *const T) -> usize {
@@ -4240,7 +4241,7 @@ mod test_map {
     fn test_catch_panic_clone_from() {
         use ::alloc::sync::Arc;
         use ::alloc::vec::Vec;
-        use allocator_api2::alloc::{AllocError, Allocator, Global};
+        use super::{AllocError, Allocator, Global};
         use core::sync::atomic::{AtomicI8, Ordering};
         use std::thread;