Auto merge of #34485 - tbu-:pr_unicode_debug_str, r=alexcrichton

Escape fewer Unicode codepoints in `Debug` impl of `str`

Use the same procedure as Python to determine whether a character is
printable, described in [PEP 3138]. In particular, this means that the
following character classes are escaped:

- Cc (Other, Control)
- Cf (Other, Format)
- Cs (Other, Surrogate), even though they can't appear in Rust strings
- Co (Other, Private Use)
- Cn (Other, Not Assigned)
- Zl (Separator, Line)
- Zp (Separator, Paragraph)
- Zs (Separator, Space), except for the ASCII space `' '` `0x20`

This allows for user-friendly inspection of strings that are not
English (e.g. compare `"\u{e9}\u{e8}\u{ea}"` to `"éèê"`).

Fixes #34318.
CC #34422.

[PEP 3138]: https://www.python.org/dev/peps/pep-3138/

2 files changed, 9 insertions, 0 deletions

diff --git a/src/libcollections/lib.rs b/src/libcollections/lib.rs
index f027d074cb6..7fc6e54d69f 100644
--- a/src/libcollections/lib.rs
+++ b/src/libcollections/lib.rs
@@ -33,6 +33,7 @@
 #![feature(allow_internal_unstable)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
+#![cfg_attr(not(test), feature(char_escape_debug))]
 #![feature(core_intrinsics)]
 #![feature(dropck_parametricity)]
 #![feature(fmt_internals)]
diff --git a/src/libcollections/str.rs b/src/libcollections/str.rs
index 55308a46f0a..4c64019de09 100644
--- a/src/libcollections/str.rs
+++ b/src/libcollections/str.rs
@@ -1697,6 +1697,14 @@ impl str {
         return s;
     }
 
+    /// Escapes each char in `s` with `char::escape_debug`.
+    #[unstable(feature = "str_escape",
+               reason = "return type may change to be an iterator",
+               issue = "27791")]
+    pub fn escape_debug(&self) -> String {
+        self.chars().flat_map(|c| c.escape_debug()).collect()
+    }
+
     /// Escapes each char in `s` with `char::escape_default`.
     #[unstable(feature = "str_escape",
                reason = "return type may change to be an iterator",