Add String::display method

src/string.rs

@@ -78,6 +78,16 @@ impl String {
         StdString::from_utf8_lossy(&self.as_bytes()).into_owned()
     }
 
+    /// Returns an object that implements [`Display`] for safely printing a Lua [`String`] that may
+    /// contain non-Unicode data.
+    ///
+    /// This may perform lossy conversion.
+    ///
+    /// [`Display`]: fmt::Display
+    pub fn display(&self) -> impl fmt::Display + '_ {
+        Display(self)
+    }
+
     /// Get the bytes that make up this string.
     ///
     /// The returned slice will not contain the terminating nul byte, but will contain any nul
@@ -216,6 +226,15 @@ impl Serialize for String {
     }
 }
 
+struct Display<'a>(&'a String);
+
+impl fmt::Display for Display<'_> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let bytes = self.0.as_bytes();
+        <bstr::BStr as fmt::Display>::fmt(bstr::BStr::new(&bytes), f)
+    }
+}
+
 /// A borrowed string (`&str`) that holds a strong reference to the Lua state.
 pub struct BorrowedStr<'a>(&'a str, #[allow(unused)] Lua);
 

src/table.rs

@@ -800,7 +800,7 @@ impl Table {
             for (key, value) in pairs {
                 match key {
                     Value::String(key) if is_simple_key(&key.as_bytes()) => {
-                        write!(fmt, "{}{}", " ".repeat(ident + 2), key.to_string_lossy())?;
+                        write!(fmt, "{}{}", " ".repeat(ident + 2), key.display())?;
                         write!(fmt, " = ")?;
                     }
                     _ => {

tests/string.rs

@@ -114,3 +114,17 @@ fn test_string_pointer() -> Result<()> {
 
     Ok(())
 }
+
+#[test]
+fn test_string_display() -> Result<()> {
+    let lua = Lua::new();
+
+    let s = lua.create_string("hello")?;
+    assert_eq!(format!("{}", s.display()), "hello");
+
+    // With invalid utf8
+    let s = lua.create_string(b"hello\0world\xFF")?;
+    assert_eq!(format!("{}", s.display()), "hello\0world�");
+
+    Ok(())
+}