Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

3 files changed, 1946 insertions, 0 deletions

diff --git a/compiler/rustc_data_structures/src/owning_ref/LICENSE b/compiler/rustc_data_structures/src/owning_ref/LICENSE
new file mode 100644
index 000000000..dff72d1e4
--- /dev/null
+++ b/compiler/rustc_data_structures/src/owning_ref/LICENSE
@@ -0,0 +1,21 @@
+The MIT License (MIT)
+
+Copyright (c) 2015 Marvin Löbel
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/compiler/rustc_data_structures/src/owning_ref/mod.rs b/compiler/rustc_data_structures/src/owning_ref/mod.rs
new file mode 100644
index 000000000..ed5e56618
--- /dev/null
+++ b/compiler/rustc_data_structures/src/owning_ref/mod.rs
@@ -0,0 +1,1214 @@
+#![warn(missing_docs)]
+
+/*!
+# An owning reference.
+
+This crate provides the _owning reference_ types `OwningRef` and `OwningRefMut`
+that enables it to bundle a reference together with the owner of the data it points to.
+This allows moving and dropping of an `OwningRef` without needing to recreate the reference.
+
+This can sometimes be useful because Rust borrowing rules normally prevent
+moving a type that has been moved from. For example, this kind of code gets rejected:
+
+```compile_fail,E0515
+fn return_owned_and_referenced<'a>() -> (Vec<u8>, &'a [u8]) {
+    let v = vec![1, 2, 3, 4];
+    let s = &v[1..3];
+    (v, s)
+}
+```
+
+Even though, from a memory-layout point of view, this can be entirely safe
+if the new location of the vector still lives longer than the lifetime `'a`
+of the reference because the backing allocation of the vector does not change.
+
+This library enables this safe usage by keeping the owner and the reference
+bundled together in a wrapper type that ensure that lifetime constraint:
+
+```
+# use rustc_data_structures::owning_ref::OwningRef;
+# fn main() {
+fn return_owned_and_referenced() -> OwningRef<Vec<u8>, [u8]> {
+    let v = vec![1, 2, 3, 4];
+    let or = OwningRef::new(v);
+    let or = or.map(|v| &v[1..3]);
+    or
+}
+# }
+```
+
+It works by requiring owner types to dereference to stable memory locations
+and preventing mutable access to root containers, which in practice requires heap allocation
+as provided by `Box<T>`, `Rc<T>`, etc.
+
+Also provided are typedefs for common owner type combinations,
+which allow for less verbose type signatures.
+For example, `BoxRef<T>` instead of `OwningRef<Box<T>, T>`.
+
+The crate also provides the more advanced `OwningHandle` type,
+which allows more freedom in bundling a dependent handle object
+along with the data it depends on, at the cost of some unsafe needed in the API.
+See the documentation around `OwningHandle` for more details.
+
+# Examples
+
+## Basics
+
+```
+use rustc_data_structures::owning_ref::BoxRef;
+
+fn main() {
+    // Create an array owned by a Box.
+    let arr = Box::new([1, 2, 3, 4]) as Box<[i32]>;
+
+    // Transfer into a BoxRef.
+    let arr: BoxRef<[i32]> = BoxRef::new(arr);
+    assert_eq!(&*arr, &[1, 2, 3, 4]);
+
+    // We can slice the array without losing ownership or changing type.
+    let arr: BoxRef<[i32]> = arr.map(|arr| &arr[1..3]);
+    assert_eq!(&*arr, &[2, 3]);
+
+    // Also works for Arc, Rc, String and Vec!
+}
+```
+
+## Caching a reference to a struct field
+
+```
+use rustc_data_structures::owning_ref::BoxRef;
+
+fn main() {
+    struct Foo {
+        tag: u32,
+        x: u16,
+        y: u16,
+        z: u16,
+    }
+    let foo = Foo { tag: 1, x: 100, y: 200, z: 300 };
+
+    let or = BoxRef::new(Box::new(foo)).map(|foo| {
+        match foo.tag {
+            0 => &foo.x,
+            1 => &foo.y,
+            2 => &foo.z,
+            _ => panic!(),
+        }
+    });
+
+    assert_eq!(*or, 200);
+}
+```
+
+## Caching a reference to an entry in a vector
+
+```
+use rustc_data_structures::owning_ref::VecRef;
+
+fn main() {
+    let v = VecRef::new(vec![1, 2, 3, 4, 5]).map(|v| &v[3]);
+    assert_eq!(*v, 4);
+}
+```
+
+## Caching a subslice of a String
+
+```
+use rustc_data_structures::owning_ref::StringRef;
+
+fn main() {
+    let s = StringRef::new("hello world".to_owned())
+        .map(|s| s.split(' ').nth(1).unwrap());
+
+    assert_eq!(&*s, "world");
+}
+```
+
+## Reference counted slices that share ownership of the backing storage
+
+```
+use rustc_data_structures::owning_ref::RcRef;
+use std::rc::Rc;
+
+fn main() {
+    let rc: RcRef<[i32]> = RcRef::new(Rc::new([1, 2, 3, 4]) as Rc<[i32]>);
+    assert_eq!(&*rc, &[1, 2, 3, 4]);
+
+    let rc_a: RcRef<[i32]> = rc.clone().map(|s| &s[0..2]);
+    let rc_b = rc.clone().map(|s| &s[1..3]);
+    let rc_c = rc.clone().map(|s| &s[2..4]);
+    assert_eq!(&*rc_a, &[1, 2]);
+    assert_eq!(&*rc_b, &[2, 3]);
+    assert_eq!(&*rc_c, &[3, 4]);
+
+    let rc_c_a = rc_c.clone().map(|s| &s[1]);
+    assert_eq!(&*rc_c_a, &4);
+}
+```
+
+## Atomic reference counted slices that share ownership of the backing storage
+
+```
+use rustc_data_structures::owning_ref::ArcRef;
+use std::sync::Arc;
+
+fn main() {
+    use std::thread;
+
+    fn par_sum(rc: ArcRef<[i32]>) -> i32 {
+        if rc.len() == 0 {
+            return 0;
+        } else if rc.len() == 1 {
+            return rc[0];
+        }
+        let mid = rc.len() / 2;
+        let left = rc.clone().map(|s| &s[..mid]);
+        let right = rc.map(|s| &s[mid..]);
+
+        let left = thread::spawn(move || par_sum(left));
+        let right = thread::spawn(move || par_sum(right));
+
+        left.join().unwrap() + right.join().unwrap()
+    }
+
+    let rc: Arc<[i32]> = Arc::new([1, 2, 3, 4]);
+    let rc: ArcRef<[i32]> = rc.into();
+
+    assert_eq!(par_sum(rc), 10);
+}
+```
+
+## References into RAII locks
+
+```
+use rustc_data_structures::owning_ref::RefRef;
+use std::cell::{RefCell, Ref};
+
+fn main() {
+    let refcell = RefCell::new((1, 2, 3, 4));
+    // Also works with Mutex and RwLock
+
+    let refref = {
+        let refref = RefRef::new(refcell.borrow()).map(|x| &x.3);
+        assert_eq!(*refref, 4);
+
+        // We move the RAII lock and the reference to one of
+        // the subfields in the data it guards here:
+        refref
+    };
+
+    assert_eq!(*refref, 4);
+
+    drop(refref);
+
+    assert_eq!(*refcell.borrow(), (1, 2, 3, 4));
+}
+```
+
+## Mutable reference
+
+When the owned container implements `DerefMut`, it is also possible to make
+a _mutable owning reference_. (e.g., with `Box`, `RefMut`, `MutexGuard`)
+
+```
+use rustc_data_structures::owning_ref::RefMutRefMut;
+use std::cell::{RefCell, RefMut};
+
+fn main() {
+    let refcell = RefCell::new((1, 2, 3, 4));
+
+    let mut refmut_refmut = {
+        let mut refmut_refmut = RefMutRefMut::new(refcell.borrow_mut()).map_mut(|x| &mut x.3);
+        assert_eq!(*refmut_refmut, 4);
+        *refmut_refmut *= 2;
+
+        refmut_refmut
+    };
+
+    assert_eq!(*refmut_refmut, 8);
+    *refmut_refmut *= 2;
+
+    drop(refmut_refmut);
+
+    assert_eq!(*refcell.borrow(), (1, 2, 3, 16));
+}
+```
+*/
+
+pub use stable_deref_trait::{
+    CloneStableDeref as CloneStableAddress, StableDeref as StableAddress,
+};
+use std::mem;
+
+/// An owning reference.
+///
+/// This wraps an owner `O` and a reference `&T` pointing
+/// at something reachable from `O::Target` while keeping
+/// the ability to move `self` around.
+///
+/// The owner is usually a pointer that points at some base type.
+///
+/// For more details and examples, see the module and method docs.
+pub struct OwningRef<O, T: ?Sized> {
+    owner: O,
+    reference: *const T,
+}
+
+/// An mutable owning reference.
+///
+/// This wraps an owner `O` and a reference `&mut T` pointing
+/// at something reachable from `O::Target` while keeping
+/// the ability to move `self` around.
+///
+/// The owner is usually a pointer that points at some base type.
+///
+/// For more details and examples, see the module and method docs.
+pub struct OwningRefMut<O, T: ?Sized> {
+    owner: O,
+    reference: *mut T,
+}
+
+/// Helper trait for an erased concrete type an owner dereferences to.
+/// This is used in form of a trait object for keeping
+/// something around to (virtually) call the destructor.
+pub trait Erased {}
+impl<T> Erased for T {}
+
+/// Helper trait for erasing the concrete type of what an owner dereferences to,
+/// for example `Box<T> -> Box<Erased>`. This would be unneeded with
+/// higher kinded types support in the language.
+#[allow(unused_lifetimes)]
+pub unsafe trait IntoErased<'a> {
+    /// Owner with the dereference type substituted to `Erased`.
+    type Erased;
+    /// Performs the type erasure.
+    fn into_erased(self) -> Self::Erased;
+}
+
+/// Helper trait for erasing the concrete type of what an owner dereferences to,
+/// for example `Box<T> -> Box<Erased + Send>`. This would be unneeded with
+/// higher kinded types support in the language.
+#[allow(unused_lifetimes)]
+pub unsafe trait IntoErasedSend<'a> {
+    /// Owner with the dereference type substituted to `Erased + Send`.
+    type Erased: Send;
+    /// Performs the type erasure.
+    fn into_erased_send(self) -> Self::Erased;
+}
+
+/// Helper trait for erasing the concrete type of what an owner dereferences to,
+/// for example `Box<T> -> Box<Erased + Send + Sync>`. This would be unneeded with
+/// higher kinded types support in the language.
+#[allow(unused_lifetimes)]
+pub unsafe trait IntoErasedSendSync<'a> {
+    /// Owner with the dereference type substituted to `Erased + Send + Sync`.
+    type Erased: Send + Sync;
+    /// Performs the type erasure.
+    fn into_erased_send_sync(self) -> Self::Erased;
+}
+
+/////////////////////////////////////////////////////////////////////////////
+// OwningRef
+/////////////////////////////////////////////////////////////////////////////
+
+impl<O, T: ?Sized> OwningRef<O, T> {
+    /// Creates a new owning reference from an owner
+    /// initialized to the direct dereference of it.
+    ///
+    /// # Example
+    /// ```
+    /// use rustc_data_structures::owning_ref::OwningRef;
+    ///
+    /// fn main() {
+    ///     let owning_ref = OwningRef::new(Box::new(42));
+    ///     assert_eq!(*owning_ref, 42);
+    /// }
+    /// ```
+    pub fn new(o: O) -> Self
+    where
+        O: StableAddress,
+        O: Deref<Target = T>,
+    {
+        OwningRef { reference: &*o, owner: o }
+    }
+
+    /// Like `new`, but doesn’t require `O` to implement the `StableAddress` trait.
+    /// Instead, the caller is responsible to make the same promises as implementing the trait.
+    ///
+    /// This is useful for cases where coherence rules prevents implementing the trait
+    /// without adding a dependency to this crate in a third-party library.
+    pub unsafe fn new_assert_stable_address(o: O) -> Self
+    where
+        O: Deref<Target = T>,
+    {
+        OwningRef { reference: &*o, owner: o }
+    }
+
+    /// Converts `self` into a new owning reference that points at something reachable
+    /// from the previous one.
+    ///
+    /// This can be a reference to a field of `U`, something reachable from a field of
+    /// `U`, or even something unrelated with a `'static` lifetime.
+    ///
+    /// # Example
+    /// ```
+    /// use rustc_data_structures::owning_ref::OwningRef;
+    ///
+    /// fn main() {
+    ///     let owning_ref = OwningRef::new(Box::new([1, 2, 3, 4]));
+    ///
+    ///     // create an owning reference that points at the
+    ///     // third element of the array.
+    ///     let owning_ref = owning_ref.map(|array| &array[2]);
+    ///     assert_eq!(*owning_ref, 3);
+    /// }
+    /// ```
+    pub fn map<F, U: ?Sized>(self, f: F) -> OwningRef<O, U>
+    where
+        O: StableAddress,
+        F: FnOnce(&T) -> &U,
+    {
+        OwningRef { reference: f(&self), owner: self.owner }
+    }
+
+    /// Tries to convert `self` into a new owning reference that points
+    /// at something reachable from the previous one.
+    ///
+    /// This can be a reference to a field of `U`, something reachable from a field of
+    /// `U`, or even something unrelated with a `'static` lifetime.
+    ///
+    /// # Example
+    /// ```
+    /// use rustc_data_structures::owning_ref::OwningRef;
+    ///
+    /// fn main() {
+    ///     let owning_ref = OwningRef::new(Box::new([1, 2, 3, 4]));
+    ///
+    ///     // create an owning reference that points at the
+    ///     // third element of the array.
+    ///     let owning_ref = owning_ref.try_map(|array| {
+    ///         if array[2] == 3 { Ok(&array[2]) } else { Err(()) }
+    ///     });
+    ///     assert_eq!(*owning_ref.unwrap(), 3);
+    /// }
+    /// ```
+    pub fn try_map<F, U: ?Sized, E>(self, f: F) -> Result<OwningRef<O, U>, E>
+    where
+        O: StableAddress,
+        F: FnOnce(&T) -> Result<&U, E>,
+    {
+        Ok(OwningRef { reference: f(&self)?, owner: self.owner })
+    }
+
+    /// Converts `self` into a new owning reference with a different owner type.
+    ///
+    /// The new owner type needs to still contain the original owner in some way
+    /// so that the reference into it remains valid. This function is marked unsafe
+    /// because the user needs to manually uphold this guarantee.
+    pub unsafe fn map_owner<F, P>(self, f: F) -> OwningRef<P, T>
+    where
+        O: StableAddress,
+        P: StableAddress,
+        F: FnOnce(O) -> P,
+    {
+        OwningRef { reference: self.reference, owner: f(self.owner) }
+    }
+
+    /// Converts `self` into a new owning reference where the owner is wrapped
+    /// in an additional `Box<O>`.
+    ///
+    /// This can be used to safely erase the owner of any `OwningRef<O, T>`
+    /// to an `OwningRef<Box<Erased>, T>`.
+    pub fn map_owner_box(self) -> OwningRef<Box<O>, T> {
+        OwningRef { reference: self.reference, owner: Box::new(self.owner) }
+    }
+
+    /// Erases the concrete base type of the owner with a trait object.
+    ///
+    /// This allows mixing of owned references with different owner base types.
+    ///
+    /// # Example
+    /// ```
+    /// use rustc_data_structures::owning_ref::{OwningRef, Erased};
+    ///
+    /// fn main() {
+    ///     // N.B., using the concrete types here for explicitness.
+    ///     // For less verbose code type aliases like `BoxRef` are provided.
+    ///
+    ///     let owning_ref_a: OwningRef<Box<[i32; 4]>, [i32; 4]>
+    ///         = OwningRef::new(Box::new([1, 2, 3, 4]));
+    ///
+    ///     let owning_ref_b: OwningRef<Box<Vec<(i32, bool)>>, Vec<(i32, bool)>>
+    ///         = OwningRef::new(Box::new(vec![(0, false), (1, true)]));
+    ///
+    ///     let owning_ref_a: OwningRef<Box<[i32; 4]>, i32>
+    ///         = owning_ref_a.map(|a| &a[0]);
+    ///
+    ///     let owning_ref_b: OwningRef<Box<Vec<(i32, bool)>>, i32>
+    ///         = owning_ref_b.map(|a| &a[1].0);
+    ///
+    ///     let owning_refs: [OwningRef<Box<dyn Erased>, i32>; 2]
+    ///         = [owning_ref_a.erase_owner(), owning_ref_b.erase_owner()];
+    ///
+    ///     assert_eq!(*owning_refs[0], 1);
+    ///     assert_eq!(*owning_refs[1], 1);
+    /// }
+    /// ```
+    pub fn erase_owner<'a>(self) -> OwningRef<O::Erased, T>
+    where
+        O: IntoErased<'a>,
+    {
+        OwningRef { reference: self.reference, owner: self.owner.into_erased() }
+    }
+
+    /// Erases the concrete base type of the owner with a trait object which implements `Send`.
+    ///
+    /// This allows mixing of owned references with different owner base types.
+    pub fn erase_send_owner<'a>(self) -> OwningRef<O::Erased, T>
+    where
+        O: IntoErasedSend<'a>,
+    {
+        OwningRef { reference: self.reference, owner: self.owner.into_erased_send() }
+    }
+
+    /// Erases the concrete base type of the owner with a trait object
+    /// which implements `Send` and `Sync`.
+    ///
+    /// This allows mixing of owned references with different owner base types.
+    pub fn erase_send_sync_owner<'a>(self) -> OwningRef<O::Erased, T>
+    where
+        O: IntoErasedSendSync<'a>,
+    {
+        OwningRef { reference: self.reference, owner: self.owner.into_erased_send_sync() }
+    }
+
+    // UNIMPLEMENTED: wrap_owner
+
+    // FIXME: Naming convention?
+    /// A getter for the underlying owner.
+    pub fn owner(&self) -> &O {
+        &self.owner
+    }
+
+    // FIXME: Naming convention?
+    /// Discards the reference and retrieves the owner.
+    pub fn into_inner(self) -> O {
+        self.owner
+    }
+}
+
+impl<O, T: ?Sized> OwningRefMut<O, T> {
+    /// Creates a new owning reference from an owner
+    /// initialized to the direct dereference of it.
+    ///
+    /// # Example
+    /// ```
+    /// use rustc_data_structures::owning_ref::OwningRefMut;
+    ///
+    /// fn main() {
+    ///     let owning_ref_mut = OwningRefMut::new(Box::new(42));
+    ///     assert_eq!(*owning_ref_mut, 42);
+    /// }
+    /// ```
+    pub fn new(mut o: O) -> Self
+    where
+        O: StableAddress,
+        O: DerefMut<Target = T>,
+    {
+        OwningRefMut { reference: &mut *o, owner: o }
+    }
+
+    /// Like `new`, but doesn’t require `O` to implement the `StableAddress` trait.
+    /// Instead, the caller is responsible to make the same promises as implementing the trait.
+    ///
+    /// This is useful for cases where coherence rules prevents implementing the trait
+    /// without adding a dependency to this crate in a third-party library.
+    pub unsafe fn new_assert_stable_address(mut o: O) -> Self
+    where
+        O: DerefMut<Target = T>,
+    {
+        OwningRefMut { reference: &mut *o, owner: o }
+    }
+
+    /// Converts `self` into a new _shared_ owning reference that points at
+    /// something reachable from the previous one.
+    ///
+    /// This can be a reference to a field of `U`, something reachable from a field of
+    /// `U`, or even something unrelated with a `'static` lifetime.
+    ///
+    /// # Example
+    /// ```
+    /// use rustc_data_structures::owning_ref::OwningRefMut;
+    ///
+    /// fn main() {
+    ///     let owning_ref_mut = OwningRefMut::new(Box::new([1, 2, 3, 4]));
+    ///
+    ///     // create an owning reference that points at the
+    ///     // third element of the array.
+    ///     let owning_ref = owning_ref_mut.map(|array| &array[2]);
+    ///     assert_eq!(*owning_ref, 3);
+    /// }
+    /// ```
+    pub fn map<F, U: ?Sized>(mut self, f: F) -> OwningRef<O, U>
+    where
+        O: StableAddress,
+        F: FnOnce(&mut T) -> &U,
+    {
+        OwningRef { reference: f(&mut self), owner: self.owner }
+    }
+
+    /// Converts `self` into a new _mutable_ owning reference that points at
+    /// something reachable from the previous one.
+    ///
+    /// This can be a reference to a field of `U`, something reachable from a field of
+    /// `U`, or even something unrelated with a `'static` lifetime.
+    ///
+    /// # Example
+    /// ```
+    /// use rustc_data_structures::owning_ref::OwningRefMut;
+    ///
+    /// fn main() {
+    ///     let owning_ref_mut = OwningRefMut::new(Box::new([1, 2, 3, 4]));
+    ///
+    ///     // create an owning reference that points at the
+    ///     // third element of the array.
+    ///     let owning_ref_mut = owning_ref_mut.map_mut(|array| &mut array[2]);
+    ///     assert_eq!(*owning_ref_mut, 3);
+    /// }
+    /// ```
+    pub fn map_mut<F, U: ?Sized>(mut self, f: F) -> OwningRefMut<O, U>
+    where
+        O: StableAddress,
+        F: FnOnce(&mut T) -> &mut U,
+    {
+        OwningRefMut { reference: f(&mut self), owner: self.owner }
+    }
+
+    /// Tries to convert `self` into a new _shared_ owning reference that points
+    /// at something reachable from the previous one.
+    ///
+    /// This can be a reference to a field of `U`, something reachable from a field of
+    /// `U`, or even something unrelated with a `'static` lifetime.
+    ///
+    /// # Example
+    /// ```
+    /// use rustc_data_structures::owning_ref::OwningRefMut;
+    ///
+    /// fn main() {
+    ///     let owning_ref_mut = OwningRefMut::new(Box::new([1, 2, 3, 4]));
+    ///
+    ///     // create an owning reference that points at the
+    ///     // third element of the array.
+    ///     let owning_ref = owning_ref_mut.try_map(|array| {
+    ///         if array[2] == 3 { Ok(&array[2]) } else { Err(()) }
+    ///     });
+    ///     assert_eq!(*owning_ref.unwrap(), 3);
+    /// }
+    /// ```
+    pub fn try_map<F, U: ?Sized, E>(mut self, f: F) -> Result<OwningRef<O, U>, E>
+    where
+        O: StableAddress,
+        F: FnOnce(&mut T) -> Result<&U, E>,
+    {
+        Ok(OwningRef { reference: f(&mut self)?, owner: self.owner })
+    }
+
+    /// Tries to convert `self` into a new _mutable_ owning reference that points
+    /// at something reachable from the previous one.
+    ///
+    /// This can be a reference to a field of `U`, something reachable from a field of
+    /// `U`, or even something unrelated with a `'static` lifetime.
+    ///
+    /// # Example
+    /// ```
+    /// use rustc_data_structures::owning_ref::OwningRefMut;
+    ///
+    /// fn main() {
+    ///     let owning_ref_mut = OwningRefMut::new(Box::new([1, 2, 3, 4]));
+    ///
+    ///     // create an owning reference that points at the
+    ///     // third element of the array.
+    ///     let owning_ref_mut = owning_ref_mut.try_map_mut(|array| {
+    ///         if array[2] == 3 { Ok(&mut array[2]) } else { Err(()) }
+    ///     });
+    ///     assert_eq!(*owning_ref_mut.unwrap(), 3);
+    /// }
+    /// ```
+    pub fn try_map_mut<F, U: ?Sized, E>(mut self, f: F) -> Result<OwningRefMut<O, U>, E>
+    where
+        O: StableAddress,
+        F: FnOnce(&mut T) -> Result<&mut U, E>,
+    {
+        Ok(OwningRefMut { reference: f(&mut self)?, owner: self.owner })
+    }
+
+    /// Converts `self` into a new owning reference with a different owner type.
+    ///
+    /// The new owner type needs to still contain the original owner in some way
+    /// so that the reference into it remains valid. This function is marked unsafe
+    /// because the user needs to manually uphold this guarantee.
+    pub unsafe fn map_owner<F, P>(self, f: F) -> OwningRefMut<P, T>
+    where
+        O: StableAddress,
+        P: StableAddress,
+        F: FnOnce(O) -> P,
+    {
+        OwningRefMut { reference: self.reference, owner: f(self.owner) }
+    }
+
+    /// Converts `self` into a new owning reference where the owner is wrapped
+    /// in an additional `Box<O>`.
+    ///
+    /// This can be used to safely erase the owner of any `OwningRefMut<O, T>`
+    /// to an `OwningRefMut<Box<Erased>, T>`.
+    pub fn map_owner_box(self) -> OwningRefMut<Box<O>, T> {
+        OwningRefMut { reference: self.reference, owner: Box::new(self.owner) }
+    }
+
+    /// Erases the concrete base type of the owner with a trait object.
+    ///
+    /// This allows mixing of owned references with different owner base types.
+    ///
+    /// # Example
+    /// ```
+    /// use rustc_data_structures::owning_ref::{OwningRefMut, Erased};
+    ///
+    /// fn main() {
+    ///     // N.B., using the concrete types here for explicitness.
+    ///     // For less verbose code type aliases like `BoxRef` are provided.
+    ///
+    ///     let owning_ref_mut_a: OwningRefMut<Box<[i32; 4]>, [i32; 4]>
+    ///         = OwningRefMut::new(Box::new([1, 2, 3, 4]));
+    ///
+    ///     let owning_ref_mut_b: OwningRefMut<Box<Vec<(i32, bool)>>, Vec<(i32, bool)>>
+    ///         = OwningRefMut::new(Box::new(vec![(0, false), (1, true)]));
+    ///
+    ///     let owning_ref_mut_a: OwningRefMut<Box<[i32; 4]>, i32>
+    ///         = owning_ref_mut_a.map_mut(|a| &mut a[0]);
+    ///
+    ///     let owning_ref_mut_b: OwningRefMut<Box<Vec<(i32, bool)>>, i32>
+    ///         = owning_ref_mut_b.map_mut(|a| &mut a[1].0);
+    ///
+    ///     let owning_refs_mut: [OwningRefMut<Box<dyn Erased>, i32>; 2]
+    ///         = [owning_ref_mut_a.erase_owner(), owning_ref_mut_b.erase_owner()];
+    ///
+    ///     assert_eq!(*owning_refs_mut[0], 1);
+    ///     assert_eq!(*owning_refs_mut[1], 1);
+    /// }
+    /// ```
+    pub fn erase_owner<'a>(self) -> OwningRefMut<O::Erased, T>
+    where
+        O: IntoErased<'a>,
+    {
+        OwningRefMut { reference: self.reference, owner: self.owner.into_erased() }
+    }
+
+    // UNIMPLEMENTED: wrap_owner
+
+    // FIXME: Naming convention?
+    /// A getter for the underlying owner.
+    pub fn owner(&self) -> &O {
+        &self.owner
+    }
+
+    // FIXME: Naming convention?
+    /// Discards the reference and retrieves the owner.
+    pub fn into_inner(self) -> O {
+        self.owner
+    }
+}
+
+/////////////////////////////////////////////////////////////////////////////
+// OwningHandle
+/////////////////////////////////////////////////////////////////////////////
+
+use std::ops::{Deref, DerefMut};
+
+/// `OwningHandle` is a complement to `OwningRef`. Where `OwningRef` allows
+/// consumers to pass around an owned object and a dependent reference,
+/// `OwningHandle` contains an owned object and a dependent _object_.
+///
+/// `OwningHandle` can encapsulate a `RefMut` along with its associated
+/// `RefCell`, or an `RwLockReadGuard` along with its associated `RwLock`.
+/// However, the API is completely generic and there are no restrictions on
+/// what types of owning and dependent objects may be used.
+///
+/// `OwningHandle` is created by passing an owner object (which dereferences
+/// to a stable address) along with a callback which receives a pointer to
+/// that stable location. The callback may then dereference the pointer and
+/// mint a dependent object, with the guarantee that the returned object will
+/// not outlive the referent of the pointer.
+///
+/// Since the callback needs to dereference a raw pointer, it requires `unsafe`
+/// code. To avoid forcing this unsafety on most callers, the `ToHandle` trait is
+/// implemented for common data structures. Types that implement `ToHandle` can
+/// be wrapped into an `OwningHandle` without passing a callback.
+pub struct OwningHandle<O, H>
+where
+    O: StableAddress,
+    H: Deref,
+{
+    handle: H,
+    _owner: O,
+}
+
+impl<O, H> Deref for OwningHandle<O, H>
+where
+    O: StableAddress,
+    H: Deref,
+{
+    type Target = H::Target;
+    fn deref(&self) -> &H::Target {
+        self.handle.deref()
+    }
+}
+
+unsafe impl<O, H> StableAddress for OwningHandle<O, H>
+where
+    O: StableAddress,
+    H: StableAddress,
+{
+}
+
+impl<O, H> DerefMut for OwningHandle<O, H>
+where
+    O: StableAddress,
+    H: DerefMut,
+{
+    fn deref_mut(&mut self) -> &mut H::Target {
+        self.handle.deref_mut()
+    }
+}
+
+/// Trait to implement the conversion of owner to handle for common types.
+pub trait ToHandle {
+    /// The type of handle to be encapsulated by the OwningHandle.
+    type Handle: Deref;
+
+    /// Given an appropriately-long-lived pointer to ourselves, create a
+    /// handle to be encapsulated by the `OwningHandle`.
+    unsafe fn to_handle(x: *const Self) -> Self::Handle;
+}
+
+/// Trait to implement the conversion of owner to mutable handle for common types.
+pub trait ToHandleMut {
+    /// The type of handle to be encapsulated by the OwningHandle.
+    type HandleMut: DerefMut;
+
+    /// Given an appropriately-long-lived pointer to ourselves, create a
+    /// mutable handle to be encapsulated by the `OwningHandle`.
+    unsafe fn to_handle_mut(x: *const Self) -> Self::HandleMut;
+}
+
+impl<O, H> OwningHandle<O, H>
+where
+    O: StableAddress<Target: ToHandle<Handle = H>>,
+    H: Deref,
+{
+    /// Creates a new `OwningHandle` for a type that implements `ToHandle`. For types
+    /// that don't implement `ToHandle`, callers may invoke `new_with_fn`, which accepts
+    /// a callback to perform the conversion.
+    pub fn new(o: O) -> Self {
+        OwningHandle::new_with_fn(o, |x| unsafe { O::Target::to_handle(x) })
+    }
+}
+
+impl<O, H> OwningHandle<O, H>
+where
+    O: StableAddress<Target: ToHandleMut<HandleMut = H>>,
+    H: DerefMut,
+{
+    /// Creates a new mutable `OwningHandle` for a type that implements `ToHandleMut`.
+    pub fn new_mut(o: O) -> Self {
+        OwningHandle::new_with_fn(o, |x| unsafe { O::Target::to_handle_mut(x) })
+    }
+}
+
+impl<O, H> OwningHandle<O, H>
+where
+    O: StableAddress,
+    H: Deref,
+{
+    /// Creates a new OwningHandle. The provided callback will be invoked with
+    /// a pointer to the object owned by `o`, and the returned value is stored
+    /// as the object to which this `OwningHandle` will forward `Deref` and
+    /// `DerefMut`.
+    pub fn new_with_fn<F>(o: O, f: F) -> Self
+    where
+        F: FnOnce(*const O::Target) -> H,
+    {
+        let h: H;
+        {
+            h = f(o.deref() as *const O::Target);
+        }
+
+        OwningHandle { handle: h, _owner: o }
+    }
+
+    /// Creates a new OwningHandle. The provided callback will be invoked with
+    /// a pointer to the object owned by `o`, and the returned value is stored
+    /// as the object to which this `OwningHandle` will forward `Deref` and
+    /// `DerefMut`.
+    pub fn try_new<F, E>(o: O, f: F) -> Result<Self, E>
+    where
+        F: FnOnce(*const O::Target) -> Result<H, E>,
+    {
+        let h: H;
+        {
+            h = f(o.deref() as *const O::Target)?;
+        }
+
+        Ok(OwningHandle { handle: h, _owner: o })
+    }
+}
+
+/////////////////////////////////////////////////////////////////////////////
+// std traits
+/////////////////////////////////////////////////////////////////////////////
+
+use std::borrow::Borrow;
+use std::cmp::{Eq, Ord, Ordering, PartialEq, PartialOrd};
+use std::convert::From;
+use std::fmt::{self, Debug};
+use std::hash::{Hash, Hasher};
+use std::marker::{Send, Sync};
+
+impl<O, T: ?Sized> Deref for OwningRef<O, T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        unsafe { &*self.reference }
+    }
+}
+
+impl<O, T: ?Sized> Deref for OwningRefMut<O, T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        unsafe { &*self.reference }
+    }
+}
+
+impl<O, T: ?Sized> DerefMut for OwningRefMut<O, T> {
+    fn deref_mut(&mut self) -> &mut T {
+        unsafe { &mut *self.reference }
+    }
+}
+
+unsafe impl<O, T: ?Sized> StableAddress for OwningRef<O, T> {}
+
+impl<O, T: ?Sized> AsRef<T> for OwningRef<O, T> {
+    fn as_ref(&self) -> &T {
+        &*self
+    }
+}
+
+impl<O, T: ?Sized> AsRef<T> for OwningRefMut<O, T> {
+    fn as_ref(&self) -> &T {
+        &*self
+    }
+}
+
+impl<O, T: ?Sized> AsMut<T> for OwningRefMut<O, T> {
+    fn as_mut(&mut self) -> &mut T {
+        &mut *self
+    }
+}
+
+impl<O, T: ?Sized> Borrow<T> for OwningRef<O, T> {
+    fn borrow(&self) -> &T {
+        &*self
+    }
+}
+
+impl<O, T: ?Sized> From<O> for OwningRef<O, T>
+where
+    O: StableAddress,
+    O: Deref<Target = T>,
+{
+    fn from(owner: O) -> Self {
+        OwningRef::new(owner)
+    }
+}
+
+impl<O, T: ?Sized> From<O> for OwningRefMut<O, T>
+where
+    O: StableAddress,
+    O: DerefMut<Target = T>,
+{
+    fn from(owner: O) -> Self {
+        OwningRefMut::new(owner)
+    }
+}
+
+impl<O, T: ?Sized> From<OwningRefMut<O, T>> for OwningRef<O, T>
+where
+    O: StableAddress,
+    O: DerefMut<Target = T>,
+{
+    fn from(other: OwningRefMut<O, T>) -> Self {
+        OwningRef { owner: other.owner, reference: other.reference }
+    }
+}
+
+// ^ FIXME: Is an Into impl for calling into_inner() possible as well?
+
+impl<O, T: ?Sized> Debug for OwningRef<O, T>
+where
+    O: Debug,
+    T: Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "OwningRef {{ owner: {:?}, reference: {:?} }}", self.owner(), &**self)
+    }
+}
+
+impl<O, T: ?Sized> Debug for OwningRefMut<O, T>
+where
+    O: Debug,
+    T: Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "OwningRefMut {{ owner: {:?}, reference: {:?} }}", self.owner(), &**self)
+    }
+}
+
+impl<O, T: ?Sized> Clone for OwningRef<O, T>
+where
+    O: CloneStableAddress,
+{
+    fn clone(&self) -> Self {
+        OwningRef { owner: self.owner.clone(), reference: self.reference }
+    }
+}
+
+unsafe impl<O, T: ?Sized> CloneStableAddress for OwningRef<O, T> where O: CloneStableAddress {}
+
+unsafe impl<O, T: ?Sized> Send for OwningRef<O, T>
+where
+    O: Send,
+    for<'a> &'a T: Send,
+{
+}
+unsafe impl<O, T: ?Sized> Sync for OwningRef<O, T>
+where
+    O: Sync,
+    for<'a> &'a T: Sync,
+{
+}
+
+unsafe impl<O, T: ?Sized> Send for OwningRefMut<O, T>
+where
+    O: Send,
+    for<'a> &'a mut T: Send,
+{
+}
+unsafe impl<O, T: ?Sized> Sync for OwningRefMut<O, T>
+where
+    O: Sync,
+    for<'a> &'a mut T: Sync,
+{
+}
+
+impl Debug for dyn Erased {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "<Erased>",)
+    }
+}
+
+impl<O, T: ?Sized> PartialEq for OwningRef<O, T>
+where
+    T: PartialEq,
+{
+    fn eq(&self, other: &Self) -> bool {
+        (&*self as &T).eq(&*other as &T)
+    }
+}
+
+impl<O, T: ?Sized> Eq for OwningRef<O, T> where T: Eq {}
+
+impl<O, T: ?Sized> PartialOrd for OwningRef<O, T>
+where
+    T: PartialOrd,
+{
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        (&*self as &T).partial_cmp(&*other as &T)
+    }
+}
+
+impl<O, T: ?Sized> Ord for OwningRef<O, T>
+where
+    T: Ord,
+{
+    fn cmp(&self, other: &Self) -> Ordering {
+        (&*self as &T).cmp(&*other as &T)
+    }
+}
+
+impl<O, T: ?Sized> Hash for OwningRef<O, T>
+where
+    T: Hash,
+{
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        (&*self as &T).hash(state);
+    }
+}
+
+impl<O, T: ?Sized> PartialEq for OwningRefMut<O, T>
+where
+    T: PartialEq,
+{
+    fn eq(&self, other: &Self) -> bool {
+        (&*self as &T).eq(&*other as &T)
+    }
+}
+
+impl<O, T: ?Sized> Eq for OwningRefMut<O, T> where T: Eq {}
+
+impl<O, T: ?Sized> PartialOrd for OwningRefMut<O, T>
+where
+    T: PartialOrd,
+{
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        (&*self as &T).partial_cmp(&*other as &T)
+    }
+}
+
+impl<O, T: ?Sized> Ord for OwningRefMut<O, T>
+where
+    T: Ord,
+{
+    fn cmp(&self, other: &Self) -> Ordering {
+        (&*self as &T).cmp(&*other as &T)
+    }
+}
+
+impl<O, T: ?Sized> Hash for OwningRefMut<O, T>
+where
+    T: Hash,
+{
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        (&*self as &T).hash(state);
+    }
+}
+
+/////////////////////////////////////////////////////////////////////////////
+// std types integration and convenience type defs
+/////////////////////////////////////////////////////////////////////////////
+
+use std::boxed::Box;
+use std::cell::{Ref, RefCell, RefMut};
+use std::rc::Rc;
+use std::sync::Arc;
+use std::sync::{MutexGuard, RwLockReadGuard, RwLockWriteGuard};
+
+impl<T: 'static> ToHandle for RefCell<T> {
+    type Handle = Ref<'static, T>;
+    unsafe fn to_handle(x: *const Self) -> Self::Handle {
+        (*x).borrow()
+    }
+}
+
+impl<T: 'static> ToHandleMut for RefCell<T> {
+    type HandleMut = RefMut<'static, T>;
+    unsafe fn to_handle_mut(x: *const Self) -> Self::HandleMut {
+        (*x).borrow_mut()
+    }
+}
+
+// N.B., implementing ToHandle{,Mut} for Mutex and RwLock requires a decision
+// about which handle creation to use (i.e., read() vs try_read()) as well as
+// what to do with error results.
+
+/// Typedef of an owning reference that uses a `Box` as the owner.
+pub type BoxRef<T, U = T> = OwningRef<Box<T>, U>;
+/// Typedef of an owning reference that uses a `Vec` as the owner.
+pub type VecRef<T, U = T> = OwningRef<Vec<T>, U>;
+/// Typedef of an owning reference that uses a `String` as the owner.
+pub type StringRef = OwningRef<String, str>;
+
+/// Typedef of an owning reference that uses an `Rc` as the owner.
+pub type RcRef<T, U = T> = OwningRef<Rc<T>, U>;
+/// Typedef of an owning reference that uses an `Arc` as the owner.
+pub type ArcRef<T, U = T> = OwningRef<Arc<T>, U>;
+
+/// Typedef of an owning reference that uses a `Ref` as the owner.
+pub type RefRef<'a, T, U = T> = OwningRef<Ref<'a, T>, U>;
+/// Typedef of an owning reference that uses a `RefMut` as the owner.
+pub type RefMutRef<'a, T, U = T> = OwningRef<RefMut<'a, T>, U>;
+/// Typedef of an owning reference that uses a `MutexGuard` as the owner.
+pub type MutexGuardRef<'a, T, U = T> = OwningRef<MutexGuard<'a, T>, U>;
+/// Typedef of an owning reference that uses an `RwLockReadGuard` as the owner.
+pub type RwLockReadGuardRef<'a, T, U = T> = OwningRef<RwLockReadGuard<'a, T>, U>;
+/// Typedef of an owning reference that uses an `RwLockWriteGuard` as the owner.
+pub type RwLockWriteGuardRef<'a, T, U = T> = OwningRef<RwLockWriteGuard<'a, T>, U>;
+
+/// Typedef of a mutable owning reference that uses a `Box` as the owner.
+pub type BoxRefMut<T, U = T> = OwningRefMut<Box<T>, U>;
+/// Typedef of a mutable owning reference that uses a `Vec` as the owner.
+pub type VecRefMut<T, U = T> = OwningRefMut<Vec<T>, U>;
+/// Typedef of a mutable owning reference that uses a `String` as the owner.
+pub type StringRefMut = OwningRefMut<String, str>;
+
+/// Typedef of a mutable owning reference that uses a `RefMut` as the owner.
+pub type RefMutRefMut<'a, T, U = T> = OwningRefMut<RefMut<'a, T>, U>;
+/// Typedef of a mutable owning reference that uses a `MutexGuard` as the owner.
+pub type MutexGuardRefMut<'a, T, U = T> = OwningRefMut<MutexGuard<'a, T>, U>;
+/// Typedef of a mutable owning reference that uses an `RwLockWriteGuard` as the owner.
+pub type RwLockWriteGuardRefMut<'a, T, U = T> = OwningRef<RwLockWriteGuard<'a, T>, U>;
+
+unsafe impl<'a, T: 'a> IntoErased<'a> for Box<T> {
+    type Erased = Box<dyn Erased + 'a>;
+    fn into_erased(self) -> Self::Erased {
+        self
+    }
+}
+unsafe impl<'a, T: 'a> IntoErased<'a> for Rc<T> {
+    type Erased = Rc<dyn Erased + 'a>;
+    fn into_erased(self) -> Self::Erased {
+        self
+    }
+}
+unsafe impl<'a, T: 'a> IntoErased<'a> for Arc<T> {
+    type Erased = Arc<dyn Erased + 'a>;
+    fn into_erased(self) -> Self::Erased {
+        self
+    }
+}
+
+unsafe impl<'a, T: Send + 'a> IntoErasedSend<'a> for Box<T> {
+    type Erased = Box<dyn Erased + Send + 'a>;
+    fn into_erased_send(self) -> Self::Erased {
+        self
+    }
+}
+
+unsafe impl<'a, T: Send + 'a> IntoErasedSendSync<'a> for Box<T> {
+    type Erased = Box<dyn Erased + Sync + Send + 'a>;
+    fn into_erased_send_sync(self) -> Self::Erased {
+        let result: Box<dyn Erased + Send + 'a> = self;
+        // This is safe since Erased can always implement Sync
+        // Only the destructor is available and it takes &mut self
+        unsafe { mem::transmute(result) }
+    }
+}
+
+unsafe impl<'a, T: Send + Sync + 'a> IntoErasedSendSync<'a> for Arc<T> {
+    type Erased = Arc<dyn Erased + Send + Sync + 'a>;
+    fn into_erased_send_sync(self) -> Self::Erased {
+        self
+    }
+}
+
+/// Typedef of an owning reference that uses an erased `Box` as the owner.
+pub type ErasedBoxRef<U> = OwningRef<Box<dyn Erased>, U>;
+/// Typedef of an owning reference that uses an erased `Rc` as the owner.
+pub type ErasedRcRef<U> = OwningRef<Rc<dyn Erased>, U>;
+/// Typedef of an owning reference that uses an erased `Arc` as the owner.
+pub type ErasedArcRef<U> = OwningRef<Arc<dyn Erased>, U>;
+
+/// Typedef of a mutable owning reference that uses an erased `Box` as the owner.
+pub type ErasedBoxRefMut<U> = OwningRefMut<Box<dyn Erased>, U>;
+
+#[cfg(test)]
+mod tests;
diff --git a/compiler/rustc_data_structures/src/owning_ref/tests.rs b/compiler/rustc_data_structures/src/owning_ref/tests.rs
new file mode 100644
index 000000000..320c03d51
--- /dev/null
+++ b/compiler/rustc_data_structures/src/owning_ref/tests.rs
@@ -0,0 +1,711 @@
+// FIXME: owning_ref is not sound under stacked borrows. Preferably, get rid of it.
+#[cfg(not(miri))]
+mod owning_ref {
+    use super::super::OwningRef;
+    use super::super::{BoxRef, Erased, ErasedBoxRef, RcRef};
+    use std::cmp::{Ord, Ordering, PartialEq, PartialOrd};
+    use std::collections::hash_map::DefaultHasher;
+    use std::collections::HashMap;
+    use std::hash::{Hash, Hasher};
+    use std::rc::Rc;
+
+    #[derive(Debug, PartialEq)]
+    struct Example(u32, String, [u8; 3]);
+    fn example() -> Example {
+        Example(42, "hello world".to_string(), [1, 2, 3])
+    }
+
+    #[test]
+    fn new_deref() {
+        let or: OwningRef<Box<()>, ()> = OwningRef::new(Box::new(()));
+        assert_eq!(&*or, &());
+    }
+
+    #[test]
+    fn into() {
+        let or: OwningRef<Box<()>, ()> = Box::new(()).into();
+        assert_eq!(&*or, &());
+    }
+
+    #[test]
+    fn map_offset_ref() {
+        let or: BoxRef<Example> = Box::new(example()).into();
+        let or: BoxRef<_, u32> = or.map(|x| &x.0);
+        assert_eq!(&*or, &42);
+
+        let or: BoxRef<Example> = Box::new(example()).into();
+        let or: BoxRef<_, u8> = or.map(|x| &x.2[1]);
+        assert_eq!(&*or, &2);
+    }
+
+    #[test]
+    fn map_heap_ref() {
+        let or: BoxRef<Example> = Box::new(example()).into();
+        let or: BoxRef<_, str> = or.map(|x| &x.1[..5]);
+        assert_eq!(&*or, "hello");
+    }
+
+    #[test]
+    fn map_static_ref() {
+        let or: BoxRef<()> = Box::new(()).into();
+        let or: BoxRef<_, str> = or.map(|_| "hello");
+        assert_eq!(&*or, "hello");
+    }
+
+    #[test]
+    fn map_chained() {
+        let or: BoxRef<String> = Box::new(example().1).into();
+        let or: BoxRef<_, str> = or.map(|x| &x[1..5]);
+        let or: BoxRef<_, str> = or.map(|x| &x[..2]);
+        assert_eq!(&*or, "el");
+    }
+
+    #[test]
+    fn map_chained_inference() {
+        let or = BoxRef::new(Box::new(example().1)).map(|x| &x[..5]).map(|x| &x[1..3]);
+        assert_eq!(&*or, "el");
+    }
+
+    #[test]
+    fn owner() {
+        let or: BoxRef<String> = Box::new(example().1).into();
+        let or = or.map(|x| &x[..5]);
+        assert_eq!(&*or, "hello");
+        assert_eq!(&**or.owner(), "hello world");
+    }
+
+    #[test]
+    fn into_inner() {
+        let or: BoxRef<String> = Box::new(example().1).into();
+        let or = or.map(|x| &x[..5]);
+        assert_eq!(&*or, "hello");
+        let s = *or.into_inner();
+        assert_eq!(&s, "hello world");
+    }
+
+    #[test]
+    fn fmt_debug() {
+        let or: BoxRef<String> = Box::new(example().1).into();
+        let or = or.map(|x| &x[..5]);
+        let s = format!("{:?}", or);
+        assert_eq!(&s, "OwningRef { owner: \"hello world\", reference: \"hello\" }");
+    }
+
+    #[test]
+    fn erased_owner() {
+        let o1: BoxRef<Example, str> = BoxRef::new(Box::new(example())).map(|x| &x.1[..]);
+
+        let o2: BoxRef<String, str> = BoxRef::new(Box::new(example().1)).map(|x| &x[..]);
+
+        let os: Vec<ErasedBoxRef<str>> = vec![o1.erase_owner(), o2.erase_owner()];
+        assert!(os.iter().all(|e| &e[..] == "hello world"));
+    }
+
+    #[test]
+    fn raii_locks() {
+        use super::super::{MutexGuardRef, RwLockReadGuardRef, RwLockWriteGuardRef};
+        use super::super::{RefMutRef, RefRef};
+        use std::cell::RefCell;
+        use std::sync::{Mutex, RwLock};
+
+        {
+            let a = RefCell::new(1);
+            let a = {
+                let a = RefRef::new(a.borrow());
+                assert_eq!(*a, 1);
+                a
+            };
+            assert_eq!(*a, 1);
+            drop(a);
+        }
+        {
+            let a = RefCell::new(1);
+            let a = {
+                let a = RefMutRef::new(a.borrow_mut());
+                assert_eq!(*a, 1);
+                a
+            };
+            assert_eq!(*a, 1);
+            drop(a);
+        }
+        {
+            let a = Mutex::new(1);
+            let a = {
+                let a = MutexGuardRef::new(a.lock().unwrap());
+                assert_eq!(*a, 1);
+                a
+            };
+            assert_eq!(*a, 1);
+            drop(a);
+        }
+        {
+            let a = RwLock::new(1);
+            let a = {
+                let a = RwLockReadGuardRef::new(a.read().unwrap());
+                assert_eq!(*a, 1);
+                a
+            };
+            assert_eq!(*a, 1);
+            drop(a);
+        }
+        {
+            let a = RwLock::new(1);
+            let a = {
+                let a = RwLockWriteGuardRef::new(a.write().unwrap());
+                assert_eq!(*a, 1);
+                a
+            };
+            assert_eq!(*a, 1);
+            drop(a);
+        }
+    }
+
+    #[test]
+    fn eq() {
+        let or1: BoxRef<[u8]> = BoxRef::new(vec![1, 2, 3].into_boxed_slice());
+        let or2: BoxRef<[u8]> = BoxRef::new(vec![1, 2, 3].into_boxed_slice());
+        assert_eq!(or1.eq(&or2), true);
+    }
+
+    #[test]
+    fn cmp() {
+        let or1: BoxRef<[u8]> = BoxRef::new(vec![1, 2, 3].into_boxed_slice());
+        let or2: BoxRef<[u8]> = BoxRef::new(vec![4, 5, 6].into_boxed_slice());
+        assert_eq!(or1.cmp(&or2), Ordering::Less);
+    }
+
+    #[test]
+    fn partial_cmp() {
+        let or1: BoxRef<[u8]> = BoxRef::new(vec![4, 5, 6].into_boxed_slice());
+        let or2: BoxRef<[u8]> = BoxRef::new(vec![1, 2, 3].into_boxed_slice());
+        assert_eq!(or1.partial_cmp(&or2), Some(Ordering::Greater));
+    }
+
+    #[test]
+    fn hash() {
+        let mut h1 = DefaultHasher::new();
+        let mut h2 = DefaultHasher::new();
+
+        let or1: BoxRef<[u8]> = BoxRef::new(vec![1, 2, 3].into_boxed_slice());
+        let or2: BoxRef<[u8]> = BoxRef::new(vec![1, 2, 3].into_boxed_slice());
+
+        or1.hash(&mut h1);
+        or2.hash(&mut h2);
+
+        assert_eq!(h1.finish(), h2.finish());
+    }
+
+    #[test]
+    fn borrow() {
+        let mut hash = HashMap::new();
+        let key = RcRef::<String>::new(Rc::new("foo-bar".to_string())).map(|s| &s[..]);
+
+        hash.insert(key.clone().map(|s| &s[..3]), 42);
+        hash.insert(key.clone().map(|s| &s[4..]), 23);
+
+        assert_eq!(hash.get("foo"), Some(&42));
+        assert_eq!(hash.get("bar"), Some(&23));
+    }
+
+    #[test]
+    fn total_erase() {
+        let a: OwningRef<Vec<u8>, [u8]> = OwningRef::new(vec![]).map(|x| &x[..]);
+        let b: OwningRef<Box<[u8]>, [u8]> =
+            OwningRef::new(vec![].into_boxed_slice()).map(|x| &x[..]);
+
+        let c: OwningRef<Rc<Vec<u8>>, [u8]> = unsafe { a.map_owner(Rc::new) };
+        let d: OwningRef<Rc<Box<[u8]>>, [u8]> = unsafe { b.map_owner(Rc::new) };
+
+        let e: OwningRef<Rc<dyn Erased>, [u8]> = c.erase_owner();
+        let f: OwningRef<Rc<dyn Erased>, [u8]> = d.erase_owner();
+
+        let _g = e.clone();
+        let _h = f.clone();
+    }
+
+    #[test]
+    fn total_erase_box() {
+        let a: OwningRef<Vec<u8>, [u8]> = OwningRef::new(vec![]).map(|x| &x[..]);
+        let b: OwningRef<Box<[u8]>, [u8]> =
+            OwningRef::new(vec![].into_boxed_slice()).map(|x| &x[..]);
+
+        let c: OwningRef<Box<Vec<u8>>, [u8]> = a.map_owner_box();
+        let d: OwningRef<Box<Box<[u8]>>, [u8]> = b.map_owner_box();
+
+        let _e: OwningRef<Box<dyn Erased>, [u8]> = c.erase_owner();
+        let _f: OwningRef<Box<dyn Erased>, [u8]> = d.erase_owner();
+    }
+
+    #[test]
+    fn try_map1() {
+        use std::any::Any;
+
+        let x = Box::new(123_i32);
+        let y: Box<dyn Any> = x;
+
+        assert!(OwningRef::new(y).try_map(|x| x.downcast_ref::<i32>().ok_or(())).is_ok());
+    }
+
+    #[test]
+    fn try_map2() {
+        use std::any::Any;
+
+        let x = Box::new(123_i32);
+        let y: Box<dyn Any> = x;
+
+        assert!(!OwningRef::new(y).try_map(|x| x.downcast_ref::<i32>().ok_or(())).is_err());
+    }
+}
+
+mod owning_handle {
+    use super::super::OwningHandle;
+    use super::super::RcRef;
+    use std::cell::RefCell;
+    use std::rc::Rc;
+    use std::sync::Arc;
+    use std::sync::RwLock;
+
+    #[test]
+    fn owning_handle() {
+        use std::cell::RefCell;
+        let cell = Rc::new(RefCell::new(2));
+        let cell_ref = RcRef::new(cell);
+        let mut handle =
+            OwningHandle::new_with_fn(cell_ref, |x| unsafe { x.as_ref() }.unwrap().borrow_mut());
+        assert_eq!(*handle, 2);
+        *handle = 3;
+        assert_eq!(*handle, 3);
+    }
+
+    #[test]
+    fn try_owning_handle_ok() {
+        use std::cell::RefCell;
+        let cell = Rc::new(RefCell::new(2));
+        let cell_ref = RcRef::new(cell);
+        let mut handle = OwningHandle::try_new::<_, ()>(cell_ref, |x| {
+            Ok(unsafe { x.as_ref() }.unwrap().borrow_mut())
+        })
+        .unwrap();
+        assert_eq!(*handle, 2);
+        *handle = 3;
+        assert_eq!(*handle, 3);
+    }
+
+    #[test]
+    fn try_owning_handle_err() {
+        use std::cell::RefCell;
+        let cell = Rc::new(RefCell::new(2));
+        let cell_ref = RcRef::new(cell);
+        let handle = OwningHandle::try_new::<_, ()>(cell_ref, |x| {
+            if false {
+                return Ok(unsafe { x.as_ref() }.unwrap().borrow_mut());
+            }
+            Err(())
+        });
+        assert!(handle.is_err());
+    }
+
+    #[test]
+    fn nested() {
+        use std::cell::RefCell;
+        use std::sync::{Arc, RwLock};
+
+        let result = {
+            let complex = Rc::new(RefCell::new(Arc::new(RwLock::new("someString"))));
+            let curr = RcRef::new(complex);
+            let curr =
+                OwningHandle::new_with_fn(curr, |x| unsafe { x.as_ref() }.unwrap().borrow_mut());
+            let mut curr = OwningHandle::new_with_fn(curr, |x| {
+                unsafe { x.as_ref() }.unwrap().try_write().unwrap()
+            });
+            assert_eq!(*curr, "someString");
+            *curr = "someOtherString";
+            curr
+        };
+        assert_eq!(*result, "someOtherString");
+    }
+
+    #[test]
+    fn owning_handle_safe() {
+        use std::cell::RefCell;
+        let cell = Rc::new(RefCell::new(2));
+        let cell_ref = RcRef::new(cell);
+        let handle = OwningHandle::new(cell_ref);
+        assert_eq!(*handle, 2);
+    }
+
+    #[test]
+    fn owning_handle_mut_safe() {
+        use std::cell::RefCell;
+        let cell = Rc::new(RefCell::new(2));
+        let cell_ref = RcRef::new(cell);
+        let mut handle = OwningHandle::new_mut(cell_ref);
+        assert_eq!(*handle, 2);
+        *handle = 3;
+        assert_eq!(*handle, 3);
+    }
+
+    #[test]
+    fn owning_handle_safe_2() {
+        let result = {
+            let complex = Rc::new(RefCell::new(Arc::new(RwLock::new("someString"))));
+            let curr = RcRef::new(complex);
+            let curr =
+                OwningHandle::new_with_fn(curr, |x| unsafe { x.as_ref() }.unwrap().borrow_mut());
+            let mut curr = OwningHandle::new_with_fn(curr, |x| {
+                unsafe { x.as_ref() }.unwrap().try_write().unwrap()
+            });
+            assert_eq!(*curr, "someString");
+            *curr = "someOtherString";
+            curr
+        };
+        assert_eq!(*result, "someOtherString");
+    }
+}
+
+// FIXME: owning_ref is not sound under stacked borrows. Preferably, get rid of it.
+#[cfg(not(miri))]
+mod owning_ref_mut {
+    use super::super::BoxRef;
+    use super::super::{BoxRefMut, Erased, ErasedBoxRefMut, OwningRefMut};
+    use std::cmp::{Ord, Ordering, PartialEq, PartialOrd};
+    use std::collections::hash_map::DefaultHasher;
+    use std::collections::HashMap;
+    use std::hash::{Hash, Hasher};
+
+    #[derive(Debug, PartialEq)]
+    struct Example(u32, String, [u8; 3]);
+    fn example() -> Example {
+        Example(42, "hello world".to_string(), [1, 2, 3])
+    }
+
+    #[test]
+    fn new_deref() {
+        let or: OwningRefMut<Box<()>, ()> = OwningRefMut::new(Box::new(()));
+        assert_eq!(&*or, &());
+    }
+
+    #[test]
+    fn new_deref_mut() {
+        let mut or: OwningRefMut<Box<()>, ()> = OwningRefMut::new(Box::new(()));
+        assert_eq!(&mut *or, &mut ());
+    }
+
+    #[test]
+    fn mutate() {
+        let mut or: OwningRefMut<Box<usize>, usize> = OwningRefMut::new(Box::new(0));
+        assert_eq!(&*or, &0);
+        *or = 1;
+        assert_eq!(&*or, &1);
+    }
+
+    #[test]
+    fn into() {
+        let or: OwningRefMut<Box<()>, ()> = Box::new(()).into();
+        assert_eq!(&*or, &());
+    }
+
+    #[test]
+    fn map_offset_ref() {
+        let or: BoxRefMut<Example> = Box::new(example()).into();
+        let or: BoxRef<_, u32> = or.map(|x| &mut x.0);
+        assert_eq!(&*or, &42);
+
+        let or: BoxRefMut<Example> = Box::new(example()).into();
+        let or: BoxRef<_, u8> = or.map(|x| &mut x.2[1]);
+        assert_eq!(&*or, &2);
+    }
+
+    #[test]
+    fn map_heap_ref() {
+        let or: BoxRefMut<Example> = Box::new(example()).into();
+        let or: BoxRef<_, str> = or.map(|x| &mut x.1[..5]);
+        assert_eq!(&*or, "hello");
+    }
+
+    #[test]
+    fn map_static_ref() {
+        let or: BoxRefMut<()> = Box::new(()).into();
+        let or: BoxRef<_, str> = or.map(|_| "hello");
+        assert_eq!(&*or, "hello");
+    }
+
+    #[test]
+    fn map_mut_offset_ref() {
+        let or: BoxRefMut<Example> = Box::new(example()).into();
+        let or: BoxRefMut<_, u32> = or.map_mut(|x| &mut x.0);
+        assert_eq!(&*or, &42);
+
+        let or: BoxRefMut<Example> = Box::new(example()).into();
+        let or: BoxRefMut<_, u8> = or.map_mut(|x| &mut x.2[1]);
+        assert_eq!(&*or, &2);
+    }
+
+    #[test]
+    fn map_mut_heap_ref() {
+        let or: BoxRefMut<Example> = Box::new(example()).into();
+        let or: BoxRefMut<_, str> = or.map_mut(|x| &mut x.1[..5]);
+        assert_eq!(&*or, "hello");
+    }
+
+    #[test]
+    fn map_mut_static_ref() {
+        static mut MUT_S: [u8; 5] = *b"hello";
+
+        let mut_s: &'static mut [u8] = unsafe { &mut MUT_S };
+
+        let or: BoxRefMut<()> = Box::new(()).into();
+        let or: BoxRefMut<_, [u8]> = or.map_mut(move |_| mut_s);
+        assert_eq!(&*or, b"hello");
+    }
+
+    #[test]
+    fn map_mut_chained() {
+        let or: BoxRefMut<String> = Box::new(example().1).into();
+        let or: BoxRefMut<_, str> = or.map_mut(|x| &mut x[1..5]);
+        let or: BoxRefMut<_, str> = or.map_mut(|x| &mut x[..2]);
+        assert_eq!(&*or, "el");
+    }
+
+    #[test]
+    fn map_chained_inference() {
+        let or = BoxRefMut::new(Box::new(example().1))
+            .map_mut(|x| &mut x[..5])
+            .map_mut(|x| &mut x[1..3]);
+        assert_eq!(&*or, "el");
+    }
+
+    #[test]
+    fn try_map_mut() {
+        let or: BoxRefMut<String> = Box::new(example().1).into();
+        let or: Result<BoxRefMut<_, str>, ()> = or.try_map_mut(|x| Ok(&mut x[1..5]));
+        assert_eq!(&*or.unwrap(), "ello");
+
+        let or: BoxRefMut<String> = Box::new(example().1).into();
+        let or: Result<BoxRefMut<_, str>, ()> = or.try_map_mut(|_| Err(()));
+        assert!(or.is_err());
+    }
+
+    #[test]
+    fn owner() {
+        let or: BoxRefMut<String> = Box::new(example().1).into();
+        let or = or.map_mut(|x| &mut x[..5]);
+        assert_eq!(&*or, "hello");
+        assert_eq!(&**or.owner(), "hello world");
+    }
+
+    #[test]
+    fn into_inner() {
+        let or: BoxRefMut<String> = Box::new(example().1).into();
+        let or = or.map_mut(|x| &mut x[..5]);
+        assert_eq!(&*or, "hello");
+        let s = *or.into_inner();
+        assert_eq!(&s, "hello world");
+    }
+
+    #[test]
+    fn fmt_debug() {
+        let or: BoxRefMut<String> = Box::new(example().1).into();
+        let or = or.map_mut(|x| &mut x[..5]);
+        let s = format!("{:?}", or);
+        assert_eq!(&s, "OwningRefMut { owner: \"hello world\", reference: \"hello\" }");
+    }
+
+    #[test]
+    fn erased_owner() {
+        let o1: BoxRefMut<Example, str> =
+            BoxRefMut::new(Box::new(example())).map_mut(|x| &mut x.1[..]);
+
+        let o2: BoxRefMut<String, str> =
+            BoxRefMut::new(Box::new(example().1)).map_mut(|x| &mut x[..]);
+
+        let os: Vec<ErasedBoxRefMut<str>> = vec![o1.erase_owner(), o2.erase_owner()];
+        assert!(os.iter().all(|e| &e[..] == "hello world"));
+    }
+
+    #[test]
+    fn raii_locks() {
+        use super::super::RefMutRefMut;
+        use super::super::{MutexGuardRefMut, RwLockWriteGuardRefMut};
+        use std::cell::RefCell;
+        use std::sync::{Mutex, RwLock};
+
+        {
+            let a = RefCell::new(1);
+            let a = {
+                let a = RefMutRefMut::new(a.borrow_mut());
+                assert_eq!(*a, 1);
+                a
+            };
+            assert_eq!(*a, 1);
+            drop(a);
+        }
+        {
+            let a = Mutex::new(1);
+            let a = {
+                let a = MutexGuardRefMut::new(a.lock().unwrap());
+                assert_eq!(*a, 1);
+                a
+            };
+            assert_eq!(*a, 1);
+            drop(a);
+        }
+        {
+            let a = RwLock::new(1);
+            let a = {
+                let a = RwLockWriteGuardRefMut::new(a.write().unwrap());
+                assert_eq!(*a, 1);
+                a
+            };
+            assert_eq!(*a, 1);
+            drop(a);
+        }
+    }
+
+    #[test]
+    fn eq() {
+        let or1: BoxRefMut<[u8]> = BoxRefMut::new(vec![1, 2, 3].into_boxed_slice());
+        let or2: BoxRefMut<[u8]> = BoxRefMut::new(vec![1, 2, 3].into_boxed_slice());
+        assert_eq!(or1.eq(&or2), true);
+    }
+
+    #[test]
+    fn cmp() {
+        let or1: BoxRefMut<[u8]> = BoxRefMut::new(vec![1, 2, 3].into_boxed_slice());
+        let or2: BoxRefMut<[u8]> = BoxRefMut::new(vec![4, 5, 6].into_boxed_slice());
+        assert_eq!(or1.cmp(&or2), Ordering::Less);
+    }
+
+    #[test]
+    fn partial_cmp() {
+        let or1: BoxRefMut<[u8]> = BoxRefMut::new(vec![4, 5, 6].into_boxed_slice());
+        let or2: BoxRefMut<[u8]> = BoxRefMut::new(vec![1, 2, 3].into_boxed_slice());
+        assert_eq!(or1.partial_cmp(&or2), Some(Ordering::Greater));
+    }
+
+    #[test]
+    fn hash() {
+        let mut h1 = DefaultHasher::new();
+        let mut h2 = DefaultHasher::new();
+
+        let or1: BoxRefMut<[u8]> = BoxRefMut::new(vec![1, 2, 3].into_boxed_slice());
+        let or2: BoxRefMut<[u8]> = BoxRefMut::new(vec![1, 2, 3].into_boxed_slice());
+
+        or1.hash(&mut h1);
+        or2.hash(&mut h2);
+
+        assert_eq!(h1.finish(), h2.finish());
+    }
+
+    #[test]
+    fn borrow() {
+        let mut hash = HashMap::new();
+        let key1 = BoxRefMut::<String>::new(Box::new("foo".to_string())).map(|s| &s[..]);
+        let key2 = BoxRefMut::<String>::new(Box::new("bar".to_string())).map(|s| &s[..]);
+
+        hash.insert(key1, 42);
+        hash.insert(key2, 23);
+
+        assert_eq!(hash.get("foo"), Some(&42));
+        assert_eq!(hash.get("bar"), Some(&23));
+    }
+
+    #[test]
+    fn total_erase() {
+        let a: OwningRefMut<Vec<u8>, [u8]> = OwningRefMut::new(vec![]).map_mut(|x| &mut x[..]);
+        let b: OwningRefMut<Box<[u8]>, [u8]> =
+            OwningRefMut::new(vec![].into_boxed_slice()).map_mut(|x| &mut x[..]);
+
+        let c: OwningRefMut<Box<Vec<u8>>, [u8]> = unsafe { a.map_owner(Box::new) };
+        let d: OwningRefMut<Box<Box<[u8]>>, [u8]> = unsafe { b.map_owner(Box::new) };
+
+        let _e: OwningRefMut<Box<dyn Erased>, [u8]> = c.erase_owner();
+        let _f: OwningRefMut<Box<dyn Erased>, [u8]> = d.erase_owner();
+    }
+
+    #[test]
+    fn total_erase_box() {
+        let a: OwningRefMut<Vec<u8>, [u8]> = OwningRefMut::new(vec![]).map_mut(|x| &mut x[..]);
+        let b: OwningRefMut<Box<[u8]>, [u8]> =
+            OwningRefMut::new(vec![].into_boxed_slice()).map_mut(|x| &mut x[..]);
+
+        let c: OwningRefMut<Box<Vec<u8>>, [u8]> = a.map_owner_box();
+        let d: OwningRefMut<Box<Box<[u8]>>, [u8]> = b.map_owner_box();
+
+        let _e: OwningRefMut<Box<dyn Erased>, [u8]> = c.erase_owner();
+        let _f: OwningRefMut<Box<dyn Erased>, [u8]> = d.erase_owner();
+    }
+
+    #[test]
+    fn try_map1() {
+        use std::any::Any;
+
+        let x = Box::new(123_i32);
+        let y: Box<dyn Any> = x;
+
+        assert!(OwningRefMut::new(y).try_map_mut(|x| x.downcast_mut::<i32>().ok_or(())).is_ok());
+    }
+
+    #[test]
+    fn try_map2() {
+        use std::any::Any;
+
+        let x = Box::new(123_i32);
+        let y: Box<dyn Any> = x;
+
+        assert!(!OwningRefMut::new(y).try_map_mut(|x| x.downcast_mut::<i32>().ok_or(())).is_err());
+    }
+
+    #[test]
+    fn try_map3() {
+        use std::any::Any;
+
+        let x = Box::new(123_i32);
+        let y: Box<dyn Any> = x;
+
+        assert!(OwningRefMut::new(y).try_map(|x| x.downcast_ref::<i32>().ok_or(())).is_ok());
+    }
+
+    #[test]
+    fn try_map4() {
+        use std::any::Any;
+
+        let x = Box::new(123_i32);
+        let y: Box<dyn Any> = x;
+
+        assert!(!OwningRefMut::new(y).try_map(|x| x.downcast_ref::<i32>().ok_or(())).is_err());
+    }
+
+    #[test]
+    fn into_owning_ref() {
+        use super::super::BoxRef;
+
+        let or: BoxRefMut<()> = Box::new(()).into();
+        let or: BoxRef<()> = or.into();
+        assert_eq!(&*or, &());
+    }
+
+    struct Foo {
+        u: u32,
+    }
+    struct Bar {
+        f: Foo,
+    }
+
+    #[test]
+    fn ref_mut() {
+        use std::cell::RefCell;
+
+        let a = RefCell::new(Bar { f: Foo { u: 42 } });
+        let mut b = OwningRefMut::new(a.borrow_mut());
+        assert_eq!(b.f.u, 42);
+        b.f.u = 43;
+        let mut c = b.map_mut(|x| &mut x.f);
+        assert_eq!(c.u, 43);
+        c.u = 44;
+        let mut d = c.map_mut(|x| &mut x.u);
+        assert_eq!(*d, 44);
+        *d = 45;
+        assert_eq!(*d, 45);
+    }
+}