Rollup merge of #85001 - CDirkx:bytestring, r=JohnTitor

Merge `sys_common::bytestring` back into `os_str_bytes`

`bytestring` contains code for correctly debug formatting a byte slice (`[u8]`). This functionality is and has historically only been used to provide the debug formatting of byte-based os-strings (on unix etc.).

Having this functionality in the separate `bytestring` module was useful in the past to reduce duplication, as [when it was added](#46798) `os_str_bytes` was still split into `sys::{unix, redox, wasi, etc.}::os_str`. However, now that is no longer the case, there is not much reason for the `bytestring` functionality to be separate from `os_str_bytes`; I don't think it is very likely that another part of std will need to handle formatting byte strings that are not os-strings in the future (everything should be `utf8`). This is why this PR merges the functionality of `bytestring` directly into the debug implementation in `os_str_bytes`.

library/std/src/sys_common/mod.rs

@@ -21,7 +21,6 @@
 mod tests;
 
 pub mod backtrace;
-pub mod bytestring;
 pub mod condvar;
 pub mod fs;
 pub mod io;

library/std/src/sys_common/os_str_bytes.rs

@@ -2,16 +2,18 @@
 //! systems: just a `Vec<u8>`/`[u8]`.
 
 use crate::borrow::Cow;
-
 use crate::fmt;
+use crate::fmt::Write;
 use crate::mem;
 use crate::rc::Rc;
 use crate::str;
 use crate::sync::Arc;
-use crate::sys_common::bytestring::debug_fmt_bytestring;
 use crate::sys_common::{AsInner, IntoInner};
 
-use core::str::lossy::Utf8Lossy;
+use core::str::lossy::{Utf8Lossy, Utf8LossyChunk};
+
+#[cfg(test)]
+mod tests;
 
 #[derive(Hash)]
 #[repr(transparent)]
@@ -26,7 +28,19 @@ pub struct Slice {
 
 impl fmt::Debug for Slice {
     fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
-        debug_fmt_bytestring(&self.inner, formatter)
+        // Writes out a valid unicode string with the correct escape sequences
+
+        formatter.write_str("\"")?;
+        for Utf8LossyChunk { valid, broken } in Utf8Lossy::from_bytes(&self.inner).chunks() {
+            for c in valid.chars().flat_map(|c| c.escape_debug()) {
+                formatter.write_char(c)?
+            }
+
+            for b in broken {
+                write!(formatter, "\\x{:02X}", b)?;
+            }
+        }
+        formatter.write_str("\"")
     }
 }
 

library/std/src/sys_common/os_str_bytes/tests.rs

@@ -0,0 +1,10 @@
+use super::*;
+
+#[test]
+fn slice_debug_output() {
+    let input = Slice::from_u8_slice(b"\xF0hello,\tworld");
+    let expected = r#""\xF0hello,\tworld""#;
+    let output = format!("{:?}", input);
+
+    assert_eq!(output, expected);
+}