Delegate <CStr as Debug> to ByteStr

This allows UTF-8 characters to be printed without escapes, rather than
just ASCII.

Author: tamird

library/alloc/src/ffi/c_str.rs

@@ -714,6 +714,8 @@ impl ops::Deref for CString {
     }
 }
 
+/// Delegates to the [`CStr`] implementation of [`fmt::Debug`],
+/// showing invalid UTF-8 as hex escapes.
 #[stable(feature = "rust1", since = "1.0.0")]
 impl fmt::Debug for CString {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {

library/core/src/ffi/c_str.rs

@@ -162,10 +162,12 @@ impl fmt::Display for FromBytesUntilNulError {
     }
 }
 
+/// Shows the underlying bytes as a normal string, with invalid UTF-8
+/// presented as hex escape sequences.
 #[stable(feature = "cstr_debug", since = "1.3.0")]
 impl fmt::Debug for CStr {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "\"{}\"", self.to_bytes().escape_ascii())
+        fmt::Debug::fmt(crate::bstr::ByteStr::from_bytes(self.to_bytes()), f)
     }
 }
 

library/coretests/tests/ffi/cstr.rs

@@ -17,7 +17,7 @@ fn compares_as_u8s() {
 #[test]
 fn debug() {
     let s = c"abc\x01\x02\n\xE2\x80\xA6\xFF";
-    assert_eq!(format!("{s:?}"), r#""abc\x01\x02\n\xe2\x80\xa6\xff""#);
+    assert_eq!(format!("{s:?}"), "\"abc\\x01\\x02\\n…\\xff\"");
 }
 
 #[test]