Rollup merge of #88226 - steffahn:an_rc, r=michaelwoerister

Fix typo “a Rc” → “an Rc” (and a few more)

After stumbling about it in the dev-guide, I’ve devided to eliminate all mentions of “a Rc”, replacing it with “an Rc”. E.g.
```plain
$ rg "(^|[^'])\ba\b[^\w=:]*\bRc"
compiler/rustc_data_structures/src/owning_ref/mod.rs
1149:/// Typedef of a owning reference that uses a `Rc` as the owner.

library/std/src/ffi/os_str.rs
919:    /// Converts a [`OsString`] into a [`Rc`]`<OsStr>` without copying or allocating.

library/std/src/ffi/c_str.rs
961:    /// Converts a [`CString`] into a [`Rc`]`<CStr>` without copying or allocating.

src/doc/rustc-dev-guide/src/query.md
61:are cheaply cloneable; insert a `Rc` if necessary).

src/doc/book/src/ch15-06-reference-cycles.md
72:decreases the reference count of the `a` `Rc<List>` instance from 2 to 1 as

library/alloc/src/rc.rs
1746:    /// Converts a generic type `T` into a `Rc<T>`
```
_(the match in the book is a false positive)_
Since the dev-guide is a submodule, it’s getting a separate PR: rust-lang/rustc-dev-guide#1191

I’ve also gone ahead and done the same search for `RwLock` and hit a few cases in the `OwningRef` adaption. Then, I couldn’t keep the countless cases of “a owning …” or “a owner” unaddressed, which concludes this PR.

`@rustbot` label C-cleanup

compiler/rustc_data_structures/src/owning_ref/mod.rs

@@ -5,7 +5,7 @@
 
 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 a `OwningRef` without needing to recreate the reference.
+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:
@@ -1146,7 +1146,7 @@ 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 a `Rc` as the owner.
+/// 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>;
@@ -1157,9 +1157,9 @@ pub type RefRef<'a, T, U = T> = OwningRef<Ref<'a, T>, U>;
 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 a `RwLockReadGuard` as the owner.
+/// 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 a `RwLockWriteGuard` as the owner.
+/// 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.
@@ -1173,7 +1173,7 @@ pub type StringRefMut = OwningRefMut<String, str>;
 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 a `RwLockWriteGuard` as the owner.
+/// 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> {

library/alloc/src/rc.rs

@@ -1745,7 +1745,7 @@ impl<T: ?Sized> fmt::Pointer for Rc<T> {
 #[cfg(not(no_global_oom_handling))]
 #[stable(feature = "from_for_ptrs", since = "1.6.0")]
 impl<T> From<T> for Rc<T> {
-    /// Converts a generic type `T` into a `Rc<T>`
+    /// Converts a generic type `T` into an `Rc<T>`
     ///
     /// The conversion allocates on the heap and moves `t`
     /// from the stack into it.

library/std/src/ffi/c_str.rs

@@ -958,7 +958,7 @@ impl From<&CStr> for Arc<CStr> {
 
 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
 impl From<CString> for Rc<CStr> {
-    /// Converts a [`CString`] into a [`Rc`]`<CStr>` without copying or allocating.
+    /// Converts a [`CString`] into an [`Rc`]`<CStr>` without copying or allocating.
     #[inline]
     fn from(s: CString) -> Rc<CStr> {
         let rc: Rc<[u8]> = Rc::from(s.into_inner());

library/std/src/ffi/os_str.rs

@@ -916,7 +916,7 @@ impl From<&OsStr> for Arc<OsStr> {
 
 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
 impl From<OsString> for Rc<OsStr> {
-    /// Converts an [`OsString`] into a [`Rc`]`<OsStr>` without copying or allocating.
+    /// Converts an [`OsString`] into an [`Rc`]`<OsStr>` without copying or allocating.
     #[inline]
     fn from(s: OsString) -> Rc<OsStr> {
         let rc = s.inner.into_rc();

src/test/ui/drop/dropck_legal_cycles.rs

@@ -368,7 +368,7 @@ pub fn main() {
     // We can use refcells if we're single-threaded (as this test is).
     // If one were to generalize these constructions to a
     // multi-threaded context, then it might seem like we could choose
-    // between either a RwLock or a Mutex to hold the owned arcs on
+    // between either an RwLock or a Mutex to hold the owned arcs on
     // each node.
     //
     // Part of the point of this test is to actually confirm that the