Auto merge of rust-lang#84956 - RalfJung:rollup-m70mx2n, r=RalfJung

Rollup of 11 pull requests

Successful merges:

 - rust-lang#83553 (Update `ptr` docs with regards to `ptr::addr_of!`)
 - rust-lang#84183 (Update RELEASES.md for 1.52.0)
 - rust-lang#84709 (Add doc alias for `chdir` to `std::env::set_current_dir`)
 - rust-lang#84803 (Reduce duplication in `impl_dep_tracking_hash` macros)
 - rust-lang#84808 (Account for unsatisfied bounds in E0599)
 - rust-lang#84843 (use else if in std library )
 - rust-lang#84865 (rustbuild: Pass a `threads` flag that works to windows-gnu lld)
 - rust-lang#84878 (Clarify documentation for `[T]::contains`)
 - rust-lang#84882 (platform-support: Center the contents of the `std` and `host` columns)
 - rust-lang#84903 (Remove `rustc_middle::mir::interpret::CheckInAllocMsg::NullPointerTest`)
 - rust-lang#84913 (Do not ICE on invalid const param)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

Author: bors

core/src/ptr/mod.rs

@@ -720,9 +720,6 @@ pub const unsafe fn read<T>(src: *const T) -> T {
 ///
 /// ## On `packed` structs
 ///
-/// It is currently impossible to create raw pointers to unaligned fields
-/// of a packed struct.
-///
 /// Attempting to create a raw pointer to an `unaligned` struct field with
 /// an expression such as `&packed.unaligned as *const FieldType` creates an
 /// intermediate unaligned reference before converting that to a raw pointer.
@@ -731,9 +728,13 @@ pub const unsafe fn read<T>(src: *const T) -> T {
 /// As a result, using `&packed.unaligned as *const FieldType` causes immediate
 /// *undefined behavior* in your program.
 ///
+/// Instead you must use the [`ptr::addr_of!`](addr_of) macro to
+/// create the pointer. You may use that returned pointer together with this
+/// function.
+///
 /// An example of what not to do and how this relates to `read_unaligned` is:
 ///
-/// ```no_run
+/// ```
 /// #[repr(packed, C)]
 /// struct Packed {
 ///     _padding: u8,
@@ -745,24 +746,15 @@ pub const unsafe fn read<T>(src: *const T) -> T {
 ///     unaligned: 0x01020304,
 /// };
 ///
-/// #[allow(unaligned_references)]
-/// let v = unsafe {
-///     // Here we attempt to take the address of a 32-bit integer which is not aligned.
-///     let unaligned =
-///         // A temporary unaligned reference is created here which results in
-///         // undefined behavior regardless of whether the reference is used or not.
-///         &packed.unaligned
-///         // Casting to a raw pointer doesn't help; the mistake already happened.
-///         as *const u32;
+/// // Take the address of a 32-bit integer which is not aligned.
+/// // In contrast to `&packed.unaligned as *const _`, this has no undefined behavior.
+/// let unaligned = std::ptr::addr_of!(packed.unaligned);
 ///
-///     let v = std::ptr::read_unaligned(unaligned);
-///
-///     v
-/// };
+/// let v = unsafe { std::ptr::read_unaligned(unaligned) };
+/// assert_eq!(v, 0x01020304);
 /// ```
 ///
 /// Accessing unaligned fields directly with e.g. `packed.unaligned` is safe however.
-// FIXME: Update docs based on outcome of RFC #2582 and friends.
 ///
 /// # Examples
 ///
@@ -916,9 +908,6 @@ pub const unsafe fn write<T>(dst: *mut T, src: T) {
 ///
 /// ## On `packed` structs
 ///
-/// It is currently impossible to create raw pointers to unaligned fields
-/// of a packed struct.
-///
 /// Attempting to create a raw pointer to an `unaligned` struct field with
 /// an expression such as `&packed.unaligned as *const FieldType` creates an
 /// intermediate unaligned reference before converting that to a raw pointer.
@@ -927,36 +916,32 @@ pub const unsafe fn write<T>(dst: *mut T, src: T) {
 /// As a result, using `&packed.unaligned as *const FieldType` causes immediate
 /// *undefined behavior* in your program.
 ///
-/// An example of what not to do and how this relates to `write_unaligned` is:
+/// Instead you must use the [`ptr::addr_of_mut!`](addr_of_mut)
+/// macro to create the pointer. You may use that returned pointer together with
+/// this function.
+///
+/// An example of how to do it and how this relates to `write_unaligned` is:
 ///
-/// ```no_run
+/// ```
 /// #[repr(packed, C)]
 /// struct Packed {
 ///     _padding: u8,
 ///     unaligned: u32,
 /// }
 ///
-/// let v = 0x01020304;
 /// let mut packed: Packed = unsafe { std::mem::zeroed() };
 ///
-/// #[allow(unaligned_references)]
-/// let v = unsafe {
-///     // Here we attempt to take the address of a 32-bit integer which is not aligned.
-///     let unaligned =
-///         // A temporary unaligned reference is created here which results in
-///         // undefined behavior regardless of whether the reference is used or not.
-///         &mut packed.unaligned
-///         // Casting to a raw pointer doesn't help; the mistake already happened.
-///         as *mut u32;
+/// // Take the address of a 32-bit integer which is not aligned.
+/// // In contrast to `&packed.unaligned as *mut _`, this has no undefined behavior.
+/// let unaligned = std::ptr::addr_of_mut!(packed.unaligned);
 ///
-///     std::ptr::write_unaligned(unaligned, v);
+/// unsafe { std::ptr::write_unaligned(unaligned, 42) };
 ///
-///     v
-/// };
+/// assert_eq!({packed.unaligned}, 42); // `{...}` forces copying the field instead of creating a reference.
 /// ```
 ///
-/// Accessing unaligned fields directly with e.g. `packed.unaligned` is safe however.
-// FIXME: Update docs based on outcome of RFC #2582 and friends.
+/// Accessing unaligned fields directly with e.g. `packed.unaligned` is safe however
+/// (as can be seen in the `assert_eq!` above).
 ///
 /// # Examples
 ///

core/src/slice/mod.rs

@@ -1948,8 +1948,9 @@ impl<T> [T] {
     /// assert!(!v.contains(&50));
     /// ```
     ///
-    /// If you do not have an `&T`, but just an `&U` such that `T: Borrow<U>`
-    /// (e.g. `String: Borrow<str>`), you can use `iter().any`:
+    /// If you do not have a `&T`, but some other value that you can compare
+    /// with one (for example, `String` implements `PartialEq<str>`), you can
+    /// use `iter().any`:
     ///
     /// ```
     /// let v = [String::from("hello"), String::from("world")]; // slice of `String`

core/src/time.rs

@@ -518,13 +518,11 @@ impl Duration {
         if let Some(mut secs) = self.secs.checked_sub(rhs.secs) {
             let nanos = if self.nanos >= rhs.nanos {
                 self.nanos - rhs.nanos
+            } else if let Some(sub_secs) = secs.checked_sub(1) {
+                secs = sub_secs;
+                self.nanos + NANOS_PER_SEC - rhs.nanos
             } else {
-                if let Some(sub_secs) = secs.checked_sub(1) {
-                    secs = sub_secs;
-                    self.nanos + NANOS_PER_SEC - rhs.nanos
-                } else {
-                    return None;
-                }
+                return None;
             };
             debug_assert!(nanos < NANOS_PER_SEC);
             Some(Duration { secs, nanos })

std/src/env.rs

@@ -61,6 +61,7 @@ pub fn current_dir() -> io::Result<PathBuf> {
 /// assert!(env::set_current_dir(&root).is_ok());
 /// println!("Successfully changed working directory to {}!", root.display());
 /// ```
+#[doc(alias = "chdir")]
 #[stable(feature = "env", since = "1.0.0")]
 pub fn set_current_dir<P: AsRef<Path>>(path: P) -> io::Result<()> {
     os_imp::chdir(path.as_ref())

std/src/primitive_docs.rs

@@ -445,7 +445,27 @@ mod prim_unit {}
 /// Note that here the call to [`drop`] is for clarity - it indicates
 /// that we are done with the given value and it should be destroyed.
 ///
-/// ## 3. Get it from C.
+/// ## 3. Create it using `ptr::addr_of!`
+///
+/// Instead of coercing a reference to a raw pointer, you can use the macros
+/// [`ptr::addr_of!`] (for `*const T`) and [`ptr::addr_of_mut!`] (for `*mut T`).
+/// These macros allow you to create raw pointers to fields to which you cannot
+/// create a reference (without causing undefined behaviour), such as an
+/// unaligned field. This might be necessary if packed structs or uninitialized
+/// memory is involved.
+///
+/// ```
+/// #[derive(Debug, Default, Copy, Clone)]
+/// #[repr(C, packed)]
+/// struct S {
+///     aligned: u8,
+///     unaligned: u32,
+/// }
+/// let s = S::default();
+/// let p = std::ptr::addr_of!(s.unaligned); // not allowed with coercion
+/// ```
+///
+/// ## 4. Get it from C.
 ///
 /// ```
 /// # #![feature(rustc_private)]