`OsString` `Debug` implementation prints escaped single quotes

[tamird]

fn main() {
    let string = "'";
    assert_eq!(
        format!("{:?}", string),
        format!("{:?}", std::ffi::OsString::from(string))
    );
}

produces

thread 'main' panicked at 'assertion failed: `(left == right)`
  left: `"\"'\""`,
 right: `"\"\\'\""`', src/main.rs:3:5

(playground)

#83046 reported the behavior of <str as Debug>::fmt escaping single quotes, and it was changed in #83079. Should we do the same for OsString?

I ran into this in #114132. It seems easy to fix for unix:

diff --git a/library/core/src/str/lossy.rs b/library/core/src/str/lossy.rs
index 59f873d1268..7e5ae364361 100644
--- a/library/core/src/str/lossy.rs
+++ b/library/core/src/str/lossy.rs
@@ -1,3 +1,4 @@
+use crate::char::EscapeDebugExtArgs;
 use crate::fmt;
 use crate::fmt::Formatter;
 use crate::fmt::Write;
@@ -85,7 +86,11 @@ fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
                 let valid = chunk.valid();
                 let mut from = 0;
                 for (i, c) in valid.char_indices() {
-                    let esc = c.escape_debug();
+                    let esc = c.escape_debug_ext(EscapeDebugExtArgs {
+                        escape_grapheme_extended: true,
+                        escape_single_quote: false,
+                        escape_double_quote: true,
+                    });
                     // If char needs escaping, flush backlog so far and write, else skip
                     if esc.len() != 1 {
                         f.write_str(&valid[from..i])?;

But on windows OsString is implemented using Wtf8, which is in std rather than core, which means it can't call char::escape_debug_ext:

rust/library/std/src/sys_common/wtf8.rs

Line 532 in 139b49b

for c in s.chars().flat_map(|c| c.escape_debug()) {

[tamird]

Tagging some of the folks involved in #83046 and #83079 for guidance @marcianx @osa1 @m-ou-se.

[tamird]

Looks like Wtf8 is in core now. Sent #148798.

@rustbot claim