Rollup merge of #88976 - notriddle:notriddle/cow-from-cstr-docs, r=Mark-Simulacrum

Clean up and add doc comments for CStr

CC #51430

Author: Manishearth

Diff for: compiler/rustc_expand/src/mbe/quoted.rs

@@ -72,7 +72,7 @@ pub(super) fn parse(
                                             // this with just `span.edition()`. A
                                             // `SyntaxContext::root()` from the current crate will
                                             // have the edition of the current crate, and a
-                                            // `SyntaxxContext::root()` from a foreign crate will
+                                            // `SyntaxContext::root()` from a foreign crate will
                                             // have the edition of that crate (which we manually
                                             // retrieve via the `edition` parameter).
                                             if span.ctxt() == SyntaxContext::root() {

Diff for: library/std/src/ffi/c_str.rs

@@ -915,6 +915,7 @@ impl From<CString> for Box<CStr> {
 
 #[stable(feature = "cow_from_cstr", since = "1.28.0")]
 impl<'a> From<CString> for Cow<'a, CStr> {
+    /// Converts a [`CString`] into an owned [`Cow`] without copying or allocating.
     #[inline]
     fn from(s: CString) -> Cow<'a, CStr> {
         Cow::Owned(s)
@@ -923,6 +924,7 @@ impl<'a> From<CString> for Cow<'a, CStr> {
 
 #[stable(feature = "cow_from_cstr", since = "1.28.0")]
 impl<'a> From<&'a CStr> for Cow<'a, CStr> {
+    /// Converts a [`CStr`] into a borrowed [`Cow`] without copying or allocating.
     #[inline]
     fn from(s: &'a CStr) -> Cow<'a, CStr> {
         Cow::Borrowed(s)
@@ -931,6 +933,7 @@ impl<'a> From<&'a CStr> for Cow<'a, CStr> {
 
 #[stable(feature = "cow_from_cstr", since = "1.28.0")]
 impl<'a> From<&'a CString> for Cow<'a, CStr> {
+    /// Converts a `&`[`CString`] into a borrowed [`Cow`] without copying or allocating.
     #[inline]
     fn from(s: &'a CString) -> Cow<'a, CStr> {
         Cow::Borrowed(s.as_c_str())