1 files changed, 46 insertions, 0 deletions
diff --git a/library/std/src/sys_common/bytestring.rs b/library/std/src/sys_common/bytestring.rs
new file mode 100644
index 00000000000..dccc3bc4a19
--- /dev/null
+++ b/library/std/src/sys_common/bytestring.rs
@@ -0,0 +1,46 @@
+#![allow(dead_code)]
+
+use crate::fmt::{Formatter, Result, Write};
+use core::str::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 crate::fmt::{Debug, Formatter, Result};
+
+    #[test]
+    fn smoke() {
+        struct Helper<'a>(&'a [u8]);
+
+        impl Debug for Helper<'_> {
+            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);
+    }
+}