Use escaped byte string representation for CString Debug

Faithfully represent the contents of the CString and CStr in their Debug
impl, by treating them as byte strings with our default escaping to
ascii representation.

Add impl Debug for Cstr.

Fixes #26964.

diff --git a/src/libstd/ffi/c_str.rs b/src/libstd/ffi/c_str.rs
index f13c10156f579acd7b01801ba1f29a0d415d5584..c9fe6e7e0b123d8e35267eb25347f09f9805c927 100644 (file)
--- a/src/libstd/ffi/c_str.rs
+++ b/src/libstd/ffi/c_str.rs
@@ -8,13 +8,14 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+use ascii;
 use borrow::{Cow, ToOwned, Borrow};
 use boxed::Box;
 use clone::Clone;
 use convert::{Into, From};
 use cmp::{PartialEq, Eq, PartialOrd, Ord, Ordering};
 use error::Error;
-use fmt;
+use fmt::{self, Write};
 use io;
 use iter::Iterator;
 use libc;
@@ -268,7 +269,18 @@ fn deref(&self) -> &CStr {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl fmt::Debug for CString {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        fmt::Debug::fmt(&String::from_utf8_lossy(self.as_bytes()), f)
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+#[stable(feature = "cstr_debug", since = "1.3.0")]
+impl fmt::Debug for CStr {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        try!(write!(f, "\""));
+        for byte in self.to_bytes().iter().flat_map(|&b| ascii::escape_default(b)) {
+            try!(f.write_char(byte as char));
+        }
+        write!(f, "\"")
     }
 }
 
@@ -501,8 +513,8 @@ fn build_with_zero3() {
 
     #[test]
     fn formatted() {
-        let s = CString::new(&b"12"[..]).unwrap();
-        assert_eq!(format!("{:?}", s), "\"12\"");
+        let s = CString::new(&b"abc\x01\x02\n\xE2\x80\xA6\xFF"[..]).unwrap();
+        assert_eq!(format!("{:?}", s), r#""abc\x01\x02\n\xe2\x80\xa6\xff""#);
     }
 
     #[test]