Add lossless debug implementation for unix OsStrs

src/libstd/sys/redox/os_str.rs

@@ -18,6 +18,7 @@ use mem;
 use rc::Rc;
 use sync::Arc;
 use sys_common::{AsInner, IntoInner};
+use sys_common::bytestring::debug_fmt_bytestring;
 use std_unicode::lossy::Utf8Lossy;
 
 #[derive(Clone, Hash)]
@@ -31,7 +32,7 @@ pub struct Slice {
 
 impl fmt::Debug for Slice {
     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
-        fmt::Debug::fmt(&Utf8Lossy::from_bytes(&self.inner), formatter)
+        debug_fmt_bytestring(&self.inner, formatter)
     }
 }
 

src/libstd/sys/unix/os_str.rs

@@ -18,6 +18,7 @@ use mem;
 use rc::Rc;
 use sync::Arc;
 use sys_common::{AsInner, IntoInner};
+use sys_common::bytestring::debug_fmt_bytestring;
 use std_unicode::lossy::Utf8Lossy;
 
 #[derive(Clone, Hash)]
@@ -31,7 +32,7 @@ pub struct Slice {
 
 impl fmt::Debug for Slice {
     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
-        fmt::Debug::fmt(&Utf8Lossy::from_bytes(&self.inner), formatter)
+        debug_fmt_bytestring(&self.inner, formatter)
     }
 }
 

src/libstd/sys/wasm/os_str.rs

@@ -18,6 +18,7 @@ use mem;
 use rc::Rc;
 use sync::Arc;
 use sys_common::{AsInner, IntoInner};
+use sys_common::bytestring::debug_fmt_bytestring;
 use std_unicode::lossy::Utf8Lossy;
 
 #[derive(Clone, Hash)]
@@ -31,7 +32,7 @@ pub struct Slice {
 
 impl fmt::Debug for Slice {
     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
-        fmt::Debug::fmt(&Utf8Lossy::from_bytes(&self.inner), formatter)
+        debug_fmt_bytestring(&self.inner, formatter)
     }
 }
 

src/libstd/sys_common/bytestring.rs

@@ -0,0 +1,56 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![allow(dead_code)]
+
+use fmt::{Formatter, Result, Write};
+use std_unicode::lossy::{Utf8Lossy, Utf8LossyChunk};
+
+pub fn debug_fmt_bytestring(slice: &[u8], f: &mut Formatter) -> Result {
+    // Writes out a valid unicode string with the correct escape sequences
+    fn write_str_escaped(f: &mut Formatter, s: &str) -> Result {
+        for c in s.chars().flat_map(|c| c.escape_debug()) {
+            f.write_char(c)?
+        }
+        Ok(())
+    }
+
+    f.write_str("\"")?;
+    for Utf8LossyChunk { valid, broken } in Utf8Lossy::from_bytes(slice).chunks() {
+        write_str_escaped(f, valid)?;
+        for b in broken {
+            write!(f, "\\x{:02X}", b)?;
+        }
+    }
+    f.write_str("\"")
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use fmt::{Formatter, Result, Debug};
+
+    #[test]
+    fn smoke() {
+        struct Helper<'a>(&'a [u8]);
+
+        impl<'a> Debug for Helper<'a> {
+            fn fmt(&self, f: &mut Formatter) -> Result {
+                debug_fmt_bytestring(self.0, f)
+            }
+        }
+
+        let input =      b"\xF0hello,\tworld";
+        let expected = r#""\xF0hello,\tworld""#;
+        let output = format!("{:?}", Helper(input));
+
+        assert!(output == expected);
+    }
+}

src/libstd/sys_common/mod.rs

@@ -43,6 +43,7 @@ pub mod thread_info;
 pub mod thread_local;
 pub mod util;
 pub mod wtf8;
+pub mod bytestring;
 
 cfg_if! {
     if #[cfg(any(target_os = "redox", target_os = "l4re"))] {