Rollup merge of rust-lang#62421 - JohnTitor:U007D-master, r=alexcrichton

Introduce `as_deref` to Option

This is re-submission for rust-lang#59628.
Renames `deref()` to `as_deref()` and adds `deref_mut()` impls and tests.

CC rust-lang#50264

r? @Kimundi
(I picked you as you're the previous reviewer.)

src/libcore/option.rs

@@ -136,7 +136,7 @@
 #![stable(feature = "rust1", since = "1.0.0")]
 
 use crate::iter::{FromIterator, FusedIterator, TrustedLen};
-use crate::{convert, fmt, hint, mem, ops::{self, Deref}};
+use crate::{convert, fmt, hint, mem, ops::{self, Deref, DerefMut}};
 use crate::pin::Pin;
 
 // Note that this is not a lang item per se, but it has a hidden dependency on
@@ -1104,17 +1104,28 @@ impl<T: Default> Option<T> {
 
 #[unstable(feature = "inner_deref", reason = "newly added", issue = "50264")]
 impl<T: Deref> Option<T> {
-    /// Converts from `&Option<T>` to `Option<&T::Target>`.
+    /// Converts from `Option<T>` (or `&Option<T>`) to `Option<&T::Target>`.
     ///
     /// Leaves the original Option in-place, creating a new one with a reference
     /// to the original one, additionally coercing the contents via [`Deref`].
     ///
     /// [`Deref`]: ../../std/ops/trait.Deref.html
-    pub fn deref(&self) -> Option<&T::Target> {
+    pub fn as_deref(&self) -> Option<&T::Target> {
         self.as_ref().map(|t| t.deref())
     }
 }
 
+#[unstable(feature = "inner_deref", reason = "newly added", issue = "50264")]
+impl<T: DerefMut> Option<T> {
+    /// Converts from `Option<T>` (or `&mut Option<T>`) to `Option<&mut T::Target>`.
+    ///
+    /// Leaves the original `Option` in-place, creating a new one containing a mutable reference to
+    /// the inner type's `Deref::Target` type.
+    pub fn as_deref_mut(&mut self) -> Option<&mut T::Target> {
+        self.as_mut().map(|t| t.deref_mut())
+    }
+}
+
 impl<T, E> Option<Result<T, E>> {
     /// Transposes an `Option` of a [`Result`] into a [`Result`] of an `Option`.
     ///

src/libcore/result.rs

@@ -232,7 +232,7 @@
 
 use crate::fmt;
 use crate::iter::{FromIterator, FusedIterator, TrustedLen};
-use crate::ops::{self, Deref};
+use crate::ops::{self, Deref, DerefMut};
 
 /// `Result` is a type that represents either success ([`Ok`]) or failure ([`Err`]).
 ///
@@ -981,42 +981,75 @@ impl<T: Default, E> Result<T, E> {
 
 #[unstable(feature = "inner_deref", reason = "newly added", issue = "50264")]
 impl<T: Deref, E> Result<T, E> {
-    /// Converts from `&Result<T, E>` to `Result<&T::Target, &E>`.
+    /// Converts from `Result<T, E>` (or `&Result<T, E>`) to `Result<&T::Target, &E>`.
     ///
-    /// Leaves the original Result in-place, creating a new one with a reference
-    /// to the original one, additionally coercing the `Ok` arm of the Result via
-    /// `Deref`.
-    pub fn deref_ok(&self) -> Result<&T::Target, &E> {
+    /// Leaves the original `Result` in-place, creating a new one containing a reference to the
+    /// `Ok` type's `Deref::Target` type.
+    pub fn as_deref_ok(&self) -> Result<&T::Target, &E> {
         self.as_ref().map(|t| t.deref())
     }
 }
 
 #[unstable(feature = "inner_deref", reason = "newly added", issue = "50264")]
 impl<T, E: Deref> Result<T, E> {
-    /// Converts from `&Result<T, E>` to `Result<&T, &E::Target>`.
+    /// Converts from `Result<T, E>` (or `&Result<T, E>`) to `Result<&T, &E::Target>`.
     ///
-    /// Leaves the original Result in-place, creating a new one with a reference
-    /// to the original one, additionally coercing the `Err` arm of the Result via
-    /// `Deref`.
-    pub fn deref_err(&self) -> Result<&T, &E::Target>
+    /// Leaves the original `Result` in-place, creating a new one containing a reference to the
+    /// `Err` type's `Deref::Target` type.
+    pub fn as_deref_err(&self) -> Result<&T, &E::Target>
     {
         self.as_ref().map_err(|e| e.deref())
     }
 }
 
 #[unstable(feature = "inner_deref", reason = "newly added", issue = "50264")]
 impl<T: Deref, E: Deref> Result<T, E> {
-    /// Converts from `&Result<T, E>` to `Result<&T::Target, &E::Target>`.
+    /// Converts from `Result<T, E>` (or `&Result<T, E>`) to `Result<&T::Target, &E::Target>`.
     ///
-    /// Leaves the original Result in-place, creating a new one with a reference
-    /// to the original one, additionally coercing both the `Ok` and `Err` arms
-    /// of the Result via `Deref`.
-    pub fn deref(&self) -> Result<&T::Target, &E::Target>
+    /// Leaves the original `Result` in-place, creating a new one containing a reference to both
+    /// the `Ok` and `Err` types' `Deref::Target` types.
+    pub fn as_deref(&self) -> Result<&T::Target, &E::Target>
     {
         self.as_ref().map(|t| t.deref()).map_err(|e| e.deref())
     }
 }
 
+#[unstable(feature = "inner_deref", reason = "newly added", issue = "50264")]
+impl<T: DerefMut, E> Result<T, E> {
+    /// Converts from `Result<T, E>` (or `&mut Result<T, E>`) to `Result<&mut T::Target, &mut E>`.
+    ///
+    /// Leaves the original `Result` in-place, creating a new one containing a mutable reference to
+    /// the `Ok` type's `Deref::Target` type.
+    pub fn as_deref_mut_ok(&mut self) -> Result<&mut T::Target, &mut E> {
+        self.as_mut().map(|t| t.deref_mut())
+    }
+}
+
+#[unstable(feature = "inner_deref", reason = "newly added", issue = "50264")]
+impl<T, E: DerefMut> Result<T, E> {
+    /// Converts from `Result<T, E>` (or `&mut Result<T, E>`) to `Result<&mut T, &mut E::Target>`.
+    ///
+    /// Leaves the original `Result` in-place, creating a new one containing a mutable reference to
+    /// the `Err` type's `Deref::Target` type.
+    pub fn as_deref_mut_err(&mut self) -> Result<&mut T, &mut E::Target>
+    {
+        self.as_mut().map_err(|e| e.deref_mut())
+    }
+}
+
+#[unstable(feature = "inner_deref", reason = "newly added", issue = "50264")]
+impl<T: DerefMut, E: DerefMut> Result<T, E> {
+    /// Converts from `Result<T, E>` (or `&mut Result<T, E>`) to
+    /// `Result<&mut T::Target, &mut E::Target>`.
+    ///
+    /// Leaves the original `Result` in-place, creating a new one containing a mutable reference to
+    /// both the `Ok` and `Err` types' `Deref::Target` types.
+    pub fn as_deref_mut(&mut self) -> Result<&mut T::Target, &mut E::Target>
+    {
+        self.as_mut().map(|t| t.deref_mut()).map_err(|e| e.deref_mut())
+    }
+}
+
 impl<T, E> Result<Option<T>, E> {
     /// Transposes a `Result` of an `Option` into an `Option` of a `Result`.
     ///

src/libcore/tests/option.rs

@@ -1,6 +1,8 @@
 use core::option::*;
 use core::mem;
 use core::clone::Clone;
+use core::array::FixedSizeArray;
+use core::ops::DerefMut;
 
 #[test]
 fn test_get_ptr() {
@@ -310,20 +312,38 @@ fn test_try() {
 }
 
 #[test]
-fn test_option_deref() {
+fn test_option_as_deref() {
     // Some: &Option<T: Deref>::Some(T) -> Option<&T::Deref::Target>::Some(&*T)
     let ref_option = &Some(&42);
-    assert_eq!(ref_option.deref(), Some(&42));
+    assert_eq!(ref_option.as_deref(), Some(&42));
 
     let ref_option = &Some(String::from("a result"));
-    assert_eq!(ref_option.deref(), Some("a result"));
+    assert_eq!(ref_option.as_deref(), Some("a result"));
 
     let ref_option = &Some(vec![1, 2, 3, 4, 5]);
-    assert_eq!(ref_option.deref(), Some(&[1, 2, 3, 4, 5][..]));
+    assert_eq!(ref_option.as_deref(), Some([1, 2, 3, 4, 5].as_slice()));
 
     // None: &Option<T: Deref>>::None -> None
     let ref_option: &Option<&i32> = &None;
-    assert_eq!(ref_option.deref(), None);
+    assert_eq!(ref_option.as_deref(), None);
+}
+
+#[test]
+fn test_option_as_deref_mut() {
+    // Some: &mut Option<T: Deref>::Some(T) -> Option<&mut T::Deref::Target>::Some(&mut *T)
+    let mut val = 42;
+    let ref_option = &mut Some(&mut val);
+    assert_eq!(ref_option.as_deref_mut(), Some(&mut 42));
+
+    let ref_option = &mut Some(String::from("a result"));
+    assert_eq!(ref_option.as_deref_mut(), Some(String::from("a result").deref_mut()));
+
+    let ref_option = &mut Some(vec![1, 2, 3, 4, 5]);
+    assert_eq!(ref_option.as_deref_mut(), Some([1, 2, 3, 4, 5].as_mut_slice()));
+
+    // None: &mut Option<T: Deref>>::None -> None
+    let ref_option: &mut Option<&mut i32> = &mut None;
+    assert_eq!(ref_option.as_deref_mut(), None);
 }
 
 #[test]