Auto merge of rust-lang#134666 - matthiaskrgr:rollup-whe0chp, r=matthiaskrgr

Rollup of 6 pull requests

Successful merges:

 - rust-lang#130289 (docs: Permissions.readonly() also ignores root user special permissions)
 - rust-lang#134583 (docs: `transmute<&mut T, &mut MaybeUninit<T>>` is unsound when exposed to safe code)
 - rust-lang#134611 (Align `{i686,x86_64}-win7-windows-msvc` to their parent targets)
 - rust-lang#134629 (compiletest: Allow using a specific debugger when running debuginfo tests)
 - rust-lang#134642 (Implement `PointerLike` for `isize`, `NonNull`, `Cell`, `UnsafeCell`, and `SyncUnsafeCell`.)
 - rust-lang#134660 (Fix spacing of markdown code block fences in compiler rustdoc)

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

Author: bors

core/src/cell.rs

@@ -252,7 +252,7 @@
 
 use crate::cmp::Ordering;
 use crate::fmt::{self, Debug, Display};
-use crate::marker::{PhantomData, Unsize};
+use crate::marker::{PhantomData, PointerLike, Unsize};
 use crate::mem;
 use crate::ops::{CoerceUnsized, Deref, DerefMut, DerefPure, DispatchFromDyn};
 use crate::pin::PinCoerceUnsized;
@@ -677,6 +677,9 @@ impl<T: CoerceUnsized<U>, U> CoerceUnsized<Cell<U>> for Cell<T> {}
 #[unstable(feature = "dispatch_from_dyn", issue = "none")]
 impl<T: DispatchFromDyn<U>, U> DispatchFromDyn<Cell<U>> for Cell<T> {}
 
+#[unstable(feature = "pointer_like_trait", issue = "none")]
+impl<T: PointerLike> PointerLike for Cell<T> {}
+
 impl<T> Cell<[T]> {
     /// Returns a `&[Cell<T>]` from a `&Cell<[T]>`
     ///
@@ -2258,6 +2261,9 @@ impl<T: CoerceUnsized<U>, U> CoerceUnsized<UnsafeCell<U>> for UnsafeCell<T> {}
 #[unstable(feature = "dispatch_from_dyn", issue = "none")]
 impl<T: DispatchFromDyn<U>, U> DispatchFromDyn<UnsafeCell<U>> for UnsafeCell<T> {}
 
+#[unstable(feature = "pointer_like_trait", issue = "none")]
+impl<T: PointerLike> PointerLike for UnsafeCell<T> {}
+
 /// [`UnsafeCell`], but [`Sync`].
 ///
 /// This is just an `UnsafeCell`, except it implements `Sync`
@@ -2364,6 +2370,9 @@ impl<T: CoerceUnsized<U>, U> CoerceUnsized<SyncUnsafeCell<U>> for SyncUnsafeCell
 //#[unstable(feature = "sync_unsafe_cell", issue = "95439")]
 impl<T: DispatchFromDyn<U>, U> DispatchFromDyn<SyncUnsafeCell<U>> for SyncUnsafeCell<T> {}
 
+#[unstable(feature = "pointer_like_trait", issue = "none")]
+impl<T: PointerLike> PointerLike for SyncUnsafeCell<T> {}
+
 #[allow(unused)]
 fn assert_coerce_unsized(
     a: UnsafeCell<&i32>,

core/src/marker.rs

@@ -1003,6 +1003,7 @@ pub trait PointerLike {}
 marker_impls! {
     #[unstable(feature = "pointer_like_trait", issue = "none")]
     PointerLike for
+        isize,
         usize,
         {T} &T,
         {T} &mut T,

core/src/mem/maybe_uninit.rs

@@ -232,6 +232,26 @@ use crate::{fmt, intrinsics, ptr, slice};
 /// remain `#[repr(transparent)]`. That said, `MaybeUninit<T>` will *always* guarantee that it has
 /// the same size, alignment, and ABI as `T`; it's just that the way `MaybeUninit` implements that
 /// guarantee may evolve.
+///
+/// Note that even though `T` and `MaybeUninit<T>` are ABI compatible it is still unsound to
+/// transmute `&mut T` to `&mut MaybeUninit<T>` and expose that to safe code because it would allow
+/// safe code to access uninitialized memory:
+///
+/// ```rust,no_run
+/// use core::mem::MaybeUninit;
+///
+/// fn unsound_transmute<T>(val: &mut T) -> &mut MaybeUninit<T> {
+///     unsafe { core::mem::transmute(val) }
+/// }
+///
+/// fn main() {
+///     let mut code = 0;
+///     let code = &mut code;
+///     let code2 = unsound_transmute(code);
+///     *code2 = MaybeUninit::uninit();
+///     std::process::exit(*code); // UB! Accessing uninitialized memory.
+/// }
+/// ```
 #[stable(feature = "maybe_uninit", since = "1.36.0")]
 // Lang item so we can wrap other types in it. This is useful for coroutines.
 #[lang = "maybe_uninit"]

core/src/ptr/non_null.rs

@@ -1555,6 +1555,10 @@ impl<T: ?Sized, U: ?Sized> DispatchFromDyn<NonNull<U>> for NonNull<T> where T: U
 #[stable(feature = "pin", since = "1.33.0")]
 unsafe impl<T: ?Sized> PinCoerceUnsized for NonNull<T> {}
 
+#[unstable(feature = "pointer_like_trait", issue = "none")]
+#[cfg(not(bootstrap))]
+impl<T> core::marker::PointerLike for NonNull<T> {}
+
 #[stable(feature = "nonnull", since = "1.25.0")]
 impl<T: ?Sized> fmt::Debug for NonNull<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {

std/src/fs.rs

@@ -1869,8 +1869,10 @@ impl Permissions {
     ///
     /// # Note
     ///
-    /// This function does not take Access Control Lists (ACLs) or Unix group
-    /// membership into account.
+    /// This function does not take Access Control Lists (ACLs), Unix group
+    /// membership and other nuances into account.
+    /// Therefore the return value of this function cannot be relied upon
+    /// to predict whether attempts to read or write the file will actually succeed.
     ///
     /// # Windows
     ///
@@ -1885,10 +1887,13 @@ impl Permissions {
     /// # Unix (including macOS)
     ///
     /// On Unix-based platforms this checks if *any* of the owner, group or others
-    /// write permission bits are set. It does not check if the current
-    /// user is in the file's assigned group. It also does not check ACLs.
-    /// Therefore the return value of this function cannot be relied upon
-    /// to predict whether attempts to read or write the file will actually succeed.
+    /// write permission bits are set. It does not consider anything else, including:
+    ///
+    /// * Whether the current user is in the file's assigned group.
+    /// * Permissions granted by ACL.
+    /// * That `root` user can write to files that do not have any write bits set.
+    /// * Writable files on a filesystem that is mounted read-only.
+    ///
     /// The [`PermissionsExt`] trait gives direct access to the permission bits but
     /// also does not read ACLs.
     ///