Delete owning_ref from rustc_data_structures

`owning_ref` has soundness problems when used with `Box<T>`, and the
previous commit replaced its usages with a better abstraction.
This means that we can now get rid of it.

Author: Noratrieb

compiler/rustc_data_structures/src/lib.rs

@@ -26,6 +26,7 @@
 #![feature(test)]
 #![feature(thread_id_value)]
 #![feature(vec_into_raw_parts)]
+#![feature(ptr_sub_ptr)]
 #![allow(rustc::default_hash_types)]
 #![allow(rustc::potential_query_instability)]
 
@@ -76,7 +77,6 @@ pub mod jobserver;
 pub mod macros;
 pub mod map_in_place;
 pub mod obligation_forest;
-pub mod owning_ref;
 pub mod sip128;
 pub mod small_c_str;
 pub mod small_str;
@@ -103,6 +103,7 @@ pub mod vec_map;
 pub mod work_queue;
 pub use atomic_ref::AtomicRef;
 pub mod frozen;
+pub mod owned_slice;
 pub mod sso;
 pub mod steal;
 pub mod tagged_ptr;

compiler/rustc_data_structures/src/memmap.rs

@@ -2,9 +2,10 @@ use std::fs::File;
 use std::io;
 use std::ops::Deref;
 
-use crate::owning_ref::StableAddress;
+// FIXME(nilstrieb): This was created to implement owning_ref::StableAddress.
+// Since owning_ref has been deleted, this can be removed as well.
 
-/// A trivial wrapper for [`memmap2::Mmap`] that implements [`StableAddress`].
+/// A trivial wrapper for [`memmap2::Mmap`] that implements owning_ref::StableAddress.
 #[cfg(not(target_arch = "wasm32"))]
 pub struct Mmap(memmap2::Mmap);
 
@@ -39,9 +40,3 @@ impl Deref for Mmap {
         &*self.0
     }
 }
-
-// SAFETY: On architectures other than WASM, mmap is used as backing storage. The address of this
-// memory map is stable. On WASM, `Vec<u8>` is used as backing storage. The `Mmap` type doesn't
-// export any function that can cause the `Vec` to be re-allocated. As such the address of the
-// bytes inside this `Vec` is stable.
-unsafe impl StableAddress for Mmap {}