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/

16 files changed, 1032 insertions, 29 deletions

diff --git a/src/etc/char_private.py b/src/etc/char_private.py
new file mode 100644
index 00000000000..3566d143529
--- /dev/null
+++ b/src/etc/char_private.py
@@ -0,0 +1,154 @@
+#!/usr/bin/env python
+#
+# Copyright 2011-2016 The Rust Project Developers. See the COPYRIGHT
+# file at the top-level directory of this distribution and at
+# http://rust-lang.org/COPYRIGHT.
+#
+# Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+# http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+# <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+# option. This file may not be copied, modified, or distributed
+# except according to those terms.
+
+# This script uses the following Unicode tables:
+# - Categories.txt
+
+import os
+import subprocess
+
+def to_ranges(iter):
+    current = None
+    for i in iter:
+        if current is None or i != current[1] or i in (0x10000, 0x20000):
+            if current is not None:
+                yield tuple(current)
+            current = [i, i + 1]
+        else:
+            current[1] += 1
+    if current is not None:
+        yield tuple(current)
+
+def get_escaped(dictionary):
+    for i in range(0x110000):
+        if dictionary.get(i, "Cn") in "Cc Cf Cs Co Cn Zl Zp Zs".split() and i != ord(' '):
+            yield i
+
+def get_file(f):
+    try:
+        return open(os.path.basename(f))
+    except FileNotFoundError:
+        subprocess.run(["curl", "-O", f], check=True)
+        return open(os.path.basename(f))
+
+def main():
+    file = get_file("http://www.unicode.org/notes/tn36/Categories.txt")
+
+    dictionary = {int(line.split()[0], 16): line.split()[1] for line in file}
+
+    CUTOFF=0x10000
+    singletons0 = []
+    singletons1 = []
+    normal0 = []
+    normal1 = []
+    extra = []
+
+    for a, b in to_ranges(get_escaped(dictionary)):
+        if a > 2 * CUTOFF:
+            extra.append((a, b - a))
+        elif a == b - 1:
+            if a & CUTOFF:
+                singletons1.append(a & ~CUTOFF)
+            else:
+                singletons0.append(a)
+        elif a == b - 2:
+            if a & CUTOFF:
+                singletons1.append(a & ~CUTOFF)
+                singletons1.append((a + 1) & ~CUTOFF)
+            else:
+                singletons0.append(a)
+                singletons0.append(a + 1)
+        else:
+            if a >= 2 * CUTOFF:
+                extra.append((a, b - a))
+            elif a & CUTOFF:
+                normal1.append((a & ~CUTOFF, b - a))
+            else:
+                normal0.append((a, b - a))
+
+    print("""\
+// Copyright 2012-2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// NOTE: The following code was generated by "src/etc/char_private.py",
+//       do not edit directly!
+
+use slice::SliceExt;
+
+fn check(x: u16, singletons: &[u16], normal: &[u16]) -> bool {
+    for &s in singletons {
+        if x == s {
+            return false;
+        } else if x < s {
+            break;
+        }
+    }
+    for w in normal.chunks(2) {
+        let start = w[0];
+        let len = w[1];
+        let difference = (x as i32) - (start as i32);
+        if 0 <= difference {
+            if difference < len as i32 {
+                return false;
+            }
+        } else {
+            break;
+        }
+    }
+    true
+}
+
+pub fn is_printable(x: char) -> bool {
+    let x = x as u32;
+    let lower = x as u16;
+    if x < 0x10000 {
+        check(lower, SINGLETONS0, NORMAL0)
+    } else if x < 0x20000 {
+        check(lower, SINGLETONS1, NORMAL1)
+    } else {\
+""")
+    for a, b in extra:
+        print("        if 0x{:x} <= x && x < 0x{:x} {{".format(a, a + b))
+        print("            return false;")
+        print("        }")
+    print("""\
+        true
+    }
+}\
+""")
+    print()
+    print("const SINGLETONS0: &'static [u16] = &[")
+    for s in singletons0:
+        print("    0x{:x},".format(s))
+    print("];")
+    print("const SINGLETONS1: &'static [u16] = &[")
+    for s in singletons1:
+        print("    0x{:x},".format(s))
+    print("];")
+    print("const NORMAL0: &'static [u16] = &[")
+    for a, b in normal0:
+        print("    0x{:x}, 0x{:x},".format(a, b))
+    print("];")
+    print("const NORMAL1: &'static [u16] = &[")
+    for a, b in normal1:
+        print("    0x{:x}, 0x{:x},".format(a, b))
+    print("];")
+
+if __name__ == '__main__':
+    main()
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",
diff --git a/src/libcollectionstest/str.rs b/src/libcollectionstest/str.rs
index 07428f3f8b2..a61925cd3be 100644
--- a/src/libcollectionstest/str.rs
+++ b/src/libcollectionstest/str.rs
@@ -704,15 +704,31 @@ fn test_escape_unicode() {
 }
 
 #[test]
+fn test_escape_debug() {
+    assert_eq!("abc".escape_debug(), "abc");
+    assert_eq!("a c".escape_debug(), "a c");
+    assert_eq!("éèê".escape_debug(), "éèê");
+    assert_eq!("\r\n\t".escape_debug(), "\\r\\n\\t");
+    assert_eq!("'\"\\".escape_debug(), "\\'\\\"\\\\");
+    assert_eq!("\u{7f}\u{ff}".escape_debug(), "\\u{7f}\u{ff}");
+    assert_eq!("\u{100}\u{ffff}".escape_debug(), "\u{100}\\u{ffff}");
+    assert_eq!("\u{10000}\u{10ffff}".escape_debug(), "\u{10000}\\u{10ffff}");
+    assert_eq!("ab\u{200b}".escape_debug(), "ab\\u{200b}");
+    assert_eq!("\u{10d4ea}\r".escape_debug(), "\\u{10d4ea}\\r");
+}
+
+#[test]
 fn test_escape_default() {
     assert_eq!("abc".escape_default(), "abc");
     assert_eq!("a c".escape_default(), "a c");
+    assert_eq!("éèê".escape_default(), "\\u{e9}\\u{e8}\\u{ea}");
     assert_eq!("\r\n\t".escape_default(), "\\r\\n\\t");
     assert_eq!("'\"\\".escape_default(), "\\'\\\"\\\\");
+    assert_eq!("\u{7f}\u{ff}".escape_default(), "\\u{7f}\\u{ff}");
     assert_eq!("\u{100}\u{ffff}".escape_default(), "\\u{100}\\u{ffff}");
     assert_eq!("\u{10000}\u{10ffff}".escape_default(), "\\u{10000}\\u{10ffff}");
-    assert_eq!("ab\u{fb00}".escape_default(), "ab\\u{fb00}");
-    assert_eq!("\u{1d4ea}\r".escape_default(), "\\u{1d4ea}\\r");
+    assert_eq!("ab\u{200b}".escape_default(), "ab\\u{200b}");
+    assert_eq!("\u{10d4ea}\r".escape_default(), "\\u{10d4ea}\\r");
 }
 
 #[test]
diff --git a/src/libcore/char.rs b/src/libcore/char.rs
index 0e7f04c7758..a3440fe8aa6 100644
--- a/src/libcore/char.rs
+++ b/src/libcore/char.rs
@@ -17,6 +17,7 @@
 
 use prelude::v1::*;
 
+use char_private::is_printable;
 use mem::transmute;
 
 // UTF-8 ranges and tags for encoding characters
@@ -263,6 +264,8 @@ pub trait CharExt {
     fn escape_unicode(self) -> EscapeUnicode;
     #[stable(feature = "core", since = "1.6.0")]
     fn escape_default(self) -> EscapeDefault;
+    #[unstable(feature = "char_escape_debug", issue = "35068")]
+    fn escape_debug(self) -> EscapeDebug;
     #[stable(feature = "core", since = "1.6.0")]
     fn len_utf8(self) -> usize;
     #[stable(feature = "core", since = "1.6.0")]
@@ -327,6 +330,19 @@ impl CharExt for char {
     }
 
     #[inline]
+    fn escape_debug(self) -> EscapeDebug {
+        let init_state = match self {
+            '\t' => EscapeDefaultState::Backslash('t'),
+            '\r' => EscapeDefaultState::Backslash('r'),
+            '\n' => EscapeDefaultState::Backslash('n'),
+            '\\' | '\'' | '"' => EscapeDefaultState::Backslash(self),
+            c if is_printable(c) => EscapeDefaultState::Char(c),
+            c => EscapeDefaultState::Unicode(c.escape_unicode()),
+        };
+        EscapeDebug(EscapeDefault { state: init_state })
+    }
+
+    #[inline]
     fn len_utf8(self) -> usize {
         let code = self as u32;
         if code < MAX_ONE_B {
@@ -600,6 +616,27 @@ impl ExactSizeIterator for EscapeDefault {
     }
 }
 
+/// An iterator that yields the literal escape code of a `char`.
+///
+/// This `struct` is created by the [`escape_debug()`] method on [`char`]. See its
+/// documentation for more.
+///
+/// [`escape_debug()`]: ../../std/primitive.char.html#method.escape_debug
+/// [`char`]: ../../std/primitive.char.html
+#[unstable(feature = "char_escape_debug", issue = "35068")]
+#[derive(Clone, Debug)]
+pub struct EscapeDebug(EscapeDefault);
+
+#[unstable(feature = "char_escape_debug", issue = "35068")]
+impl Iterator for EscapeDebug {
+    type Item = char;
+    fn next(&mut self) -> Option<char> { self.0.next() }
+    fn size_hint(&self) -> (usize, Option<usize>) { self.0.size_hint() }
+}
+
+#[unstable(feature = "char_escape_debug", issue = "35068")]
+impl ExactSizeIterator for EscapeDebug { }
+
 /// An iterator over `u8` entries represending the UTF-8 encoding of a `char`
 /// value.
 ///
diff --git a/src/libcore/char_private.rs b/src/libcore/char_private.rs
new file mode 100644
index 00000000000..1d8f95cd4b8
--- /dev/null
+++ b/src/libcore/char_private.rs
@@ -0,0 +1,695 @@
+// Copyright 2012-2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// NOTE: The following code was generated by "src/etc/char_private.py",
+//       do not edit directly!
+
+use slice::SliceExt;
+
+fn check(x: u16, singletons: &[u16], normal: &[u16]) -> bool {
+    for &s in singletons {
+        if x == s {
+            return false;
+        } else if x < s {
+            break;
+        }
+    }
+    for w in normal.chunks(2) {
+        let start = w[0];
+        let len = w[1];
+        let difference = (x as i32) - (start as i32);
+        if 0 <= difference {
+            if difference < len as i32 {
+                return false;
+            }
+        } else {
+            break;
+        }
+    }
+    true
+}
+
+pub fn is_printable(x: char) -> bool {
+    let x = x as u32;
+    let lower = x as u16;
+    if x < 0x10000 {
+        check(lower, SINGLETONS0, NORMAL0)
+    } else if x < 0x20000 {
+        check(lower, SINGLETONS1, NORMAL1)
+    } else {
+        if 0x20000 <= x && x < 0x2f800 {
+            return false;
+        }
+        if 0x2fa1e <= x && x < 0xe0100 {
+            return false;
+        }
+        if 0xe01f0 <= x && x < 0x110000 {
+            return false;
+        }
+        true
+    }
+}
+
+const SINGLETONS0: &'static [u16] = &[
+    0xad,
+    0x378,
+    0x379,
+    0x38b,
+    0x38d,
+    0x3a2,
+    0x557,
+    0x558,
+    0x560,
+    0x588,
+    0x590,
+    0x61c,
+    0x61d,
+    0x6dd,
+    0x70e,
+    0x70f,
+    0x74b,
+    0x74c,
+    0x82e,
+    0x82f,
+    0x83f,
+    0x85c,
+    0x85d,
+    0x8a1,
+    0x8ff,
+    0x978,
+    0x980,
+    0x984,
+    0x98d,
+    0x98e,
+    0x991,
+    0x992,
+    0x9a9,
+    0x9b1,
+    0x9ba,
+    0x9bb,
+    0x9c5,
+    0x9c6,
+    0x9c9,
+    0x9ca,
+    0x9de,
+    0x9e4,
+    0x9e5,
+    0xa04,
+    0xa11,
+    0xa12,
+    0xa29,
+    0xa31,
+    0xa34,
+    0xa37,
+    0xa3a,
+    0xa3b,
+    0xa3d,
+    0xa49,
+    0xa4a,
+    0xa5d,
+    0xa84,
+    0xa8e,
+    0xa92,
+    0xaa9,
+    0xab1,
+    0xab4,
+    0xaba,
+    0xabb,
+    0xac6,
+    0xaca,
+    0xace,
+    0xacf,
+    0xae4,
+    0xae5,
+    0xb04,
+    0xb0d,
+    0xb0e,
+    0xb11,
+    0xb12,
+    0xb29,
+    0xb31,
+    0xb34,
+    0xb3a,
+    0xb3b,
+    0xb45,
+    0xb46,
+    0xb49,
+    0xb4a,
+    0xb5e,
+    0xb64,
+    0xb65,
+    0xb84,
+    0xb91,
+    0xb9b,
+    0xb9d,
+    0xbc9,
+    0xbce,
+    0xbcf,
+    0xc04,
+    0xc0d,
+    0xc11,
+    0xc29,
+    0xc34,
+    0xc45,
+    0xc49,
+    0xc57,
+    0xc64,
+    0xc65,
+    0xc80,
+    0xc81,
+    0xc84,
+    0xc8d,
+    0xc91,
+    0xca9,
+    0xcb4,
+    0xcba,
+    0xcbb,
+    0xcc5,
+    0xcc9,
+    0xcdf,
+    0xce4,
+    0xce5,
+    0xcf0,
+    0xd04,
+    0xd0d,
+    0xd11,
+    0xd3b,
+    0xd3c,
+    0xd45,
+    0xd49,
+    0xd64,
+    0xd65,
+    0xd80,
+    0xd81,
+    0xd84,
+    0xdb2,
+    0xdbc,
+    0xdbe,
+    0xdbf,
+    0xdd5,
+    0xdd7,
+    0xe83,
+    0xe85,
+    0xe86,
+    0xe89,
+    0xe8b,
+    0xe8c,
+    0xe98,
+    0xea0,
+    0xea4,
+    0xea6,
+    0xea8,
+    0xea9,
+    0xeac,
+    0xeba,
+    0xebe,
+    0xebf,
+    0xec5,
+    0xec7,
+    0xece,
+    0xecf,
+    0xeda,
+    0xedb,
+    0xf48,
+    0xf98,
+    0xfbd,
+    0xfcd,
+    0x10c6,
+    0x10ce,
+    0x10cf,
+    0x1249,
+    0x124e,
+    0x124f,
+    0x1257,
+    0x1259,
+    0x125e,
+    0x125f,
+    0x1289,
+    0x128e,
+    0x128f,
+    0x12b1,
+    0x12b6,
+    0x12b7,
+    0x12bf,
+    0x12c1,
+    0x12c6,
+    0x12c7,
+    0x12d7,
+    0x1311,
+    0x1316,
+    0x1317,
+    0x135b,
+    0x135c,
+    0x1680,
+    0x170d,
+    0x176d,
+    0x1771,
+    0x17de,
+    0x17df,
+    0x180e,
+    0x180f,
+    0x196e,
+    0x196f,
+    0x1a1c,
+    0x1a1d,
+    0x1a5f,
+    0x1a7d,
+    0x1a7e,
+    0x1f16,
+    0x1f17,
+    0x1f1e,
+    0x1f1f,
+    0x1f46,
+    0x1f47,
+    0x1f4e,
+    0x1f4f,
+    0x1f58,
+    0x1f5a,
+    0x1f5c,
+    0x1f5e,
+    0x1f7e,
+    0x1f7f,
+    0x1fb5,
+    0x1fc5,
+    0x1fd4,
+    0x1fd5,
+    0x1fdc,
+    0x1ff0,
+    0x1ff1,
+    0x1ff5,
+    0x2072,
+    0x2073,
+    0x208f,
+    0x2700,
+    0x2c2f,
+    0x2c5f,
+    0x2d26,
+    0x2d2e,
+    0x2d2f,
+    0x2da7,
+    0x2daf,
+    0x2db7,
+    0x2dbf,
+    0x2dc7,
+    0x2dcf,
+    0x2dd7,
+    0x2ddf,
+    0x2e9a,
+    0x3040,
+    0x3097,
+    0x3098,
+    0x318f,
+    0x321f,
+    0x32ff,
+    0xa78f,
+    0xa9ce,
+    0xaa4e,
+    0xaa4f,
+    0xaa5a,
+    0xaa5b,
+    0xab07,
+    0xab08,
+    0xab0f,
+    0xab10,
+    0xab27,
+    0xabee,
+    0xabef,
+    0xfa6e,
+    0xfa6f,
+    0xfb37,
+    0xfb3d,
+    0xfb3f,
+    0xfb42,
+    0xfb45,
+    0xfd90,
+    0xfd91,
+    0xfdfe,
+    0xfdff,
+    0xfe53,
+    0xfe67,
+    0xfe75,
+    0xffc8,
+    0xffc9,
+    0xffd0,
+    0xffd1,
+    0xffd8,
+    0xffd9,
+    0xffe7,
+    0xfffe,
+    0xffff,
+];
+const SINGLETONS1: &'static [u16] = &[
+    0xc,
+    0x27,
+    0x3b,
+    0x3e,
+    0x4e,
+    0x4f,
+    0x31f,
+    0x39e,
+    0x49e,
+    0x49f,
+    0x806,
+    0x807,
+    0x809,
+    0x836,
+    0x83d,
+    0x83e,
+    0x856,
+    0xa04,
+    0xa14,
+    0xa18,
+    0xb56,
+    0xb57,
+    0x10bd,
+    0x1135,
+    0xd127,
+    0xd128,
+    0xd455,
+    0xd49d,
+    0xd4a0,
+    0xd4a1,
+    0xd4a3,
+    0xd4a4,
+    0xd4a7,
+    0xd4a8,
+    0xd4ad,
+    0xd4ba,
+    0xd4bc,
+    0xd4c4,
+    0xd506,
+    0xd50b,
+    0xd50c,
+    0xd515,
+    0xd51d,
+    0xd53a,
+    0xd53f,
+    0xd545,
+    0xd551,
+    0xd6a6,
+    0xd6a7,
+    0xd7cc,
+    0xd7cd,
+    0xee04,
+    0xee20,
+    0xee23,
+    0xee25,
+    0xee26,
+    0xee28,
+    0xee33,
+    0xee38,
+    0xee3a,
+    0xee48,
+    0xee4a,
+    0xee4c,
+    0xee50,
+    0xee53,
+    0xee55,
+    0xee56,
+    0xee58,
+    0xee5a,
+    0xee5c,
+    0xee5e,
+    0xee60,
+    0xee63,
+    0xee65,
+    0xee66,
+    0xee6b,
+    0xee73,
+    0xee78,
+    0xee7d,
+    0xee7f,
+    0xee8a,
+    0xeea4,
+    0xeeaa,
+    0xf0af,
+    0xf0b0,
+    0xf0bf,
+    0xf0c0,
+    0xf0d0,
+    0xf12f,
+    0xf336,
+    0xf3c5,
+    0xf43f,
+    0xf441,
+    0xf4f8,
+    0xf53e,
+    0xf53f,
+];
+const NORMAL0: &'static [u16] = &[
+    0x0, 0x20,
+    0x7f, 0x22,
+    0x37f, 0x5,
+    0x528, 0x9,
+    0x58b, 0x4,
+    0x5c8, 0x8,
+    0x5eb, 0x5,
+    0x5f5, 0x11,
+    0x7b2, 0xe,
+    0x7fb, 0x5,
+    0x85f, 0x41,
+    0x8ad, 0x37,
+    0x9b3, 0x3,
+    0x9cf, 0x8,
+    0x9d8, 0x4,
+    0x9fc, 0x5,
+    0xa0b, 0x4,
+    0xa43, 0x4,
+    0xa4e, 0x3,
+    0xa52, 0x7,
+    0xa5f, 0x7,
+    0xa76, 0xb,
+    0xad1, 0xf,
+    0xaf2, 0xf,
+    0xb4e, 0x8,
+    0xb58, 0x4,
+    0xb78, 0xa,
+    0xb8b, 0x3,
+    0xb96, 0x3,
+    0xba0, 0x3,
+    0xba5, 0x3,
+    0xbab, 0x3,
+    0xbba, 0x4,
+    0xbc3, 0x3,
+    0xbd1, 0x6,
+    0xbd8, 0xe,
+    0xbfb, 0x6,
+    0xc3a, 0x3,
+    0xc4e, 0x7,
+    0xc5a, 0x6,
+    0xc70, 0x8,
+    0xcce, 0x7,
+    0xcd7, 0x7,
+    0xcf3, 0xf,
+    0xd4f, 0x8,
+    0xd58, 0x8,
+    0xd76, 0x3,
+    0xd97, 0x3,
+    0xdc7, 0x3,
+    0xdcb, 0x4,
+    0xde0, 0x12,
+    0xdf5, 0xc,
+    0xe3b, 0x4,
+    0xe5c, 0x25,
+    0xe8e, 0x6,
+    0xee0, 0x20,
+    0xf6d, 0x4,
+    0xfdb, 0x25,
+    0x10c8, 0x5,
+    0x137d, 0x3,
+    0x139a, 0x6,
+    0x13f5, 0xb,
+    0x169d, 0x3,
+    0x16f1, 0xf,
+    0x1715, 0xb,
+    0x1737, 0x9,
+    0x1754, 0xc,
+    0x1774, 0xc,
+    0x17ea, 0x6,
+    0x17fa, 0x6,
+    0x181a, 0x6,
+    0x1878, 0x8,
+    0x18ab, 0x5,
+    0x18f6, 0xa,
+    0x191d, 0x3,
+    0x192c, 0x4,
+    0x193c, 0x4,
+    0x1941, 0x3,
+    0x1975, 0xb,
+    0x19ac, 0x4,
+    0x19ca, 0x6,
+    0x19db, 0x3,
+    0x1a8a, 0x6,
+    0x1a9a, 0x6,
+    0x1aae, 0x52,
+    0x1b4c, 0x4,
+    0x1b7d, 0x3,
+    0x1bf4, 0x8,
+    0x1c38, 0x3,
+    0x1c4a, 0x3,
+    0x1c80, 0x40,
+    0x1cc8, 0x8,
+    0x1cf7, 0x9,
+    0x1de7, 0x15,
+    0x1fff, 0x11,
+    0x2028, 0x8,
+    0x205f, 0x11,
+    0x209d, 0x3,
+    0x20ba, 0x16,
+    0x20f1, 0xf,
+    0x218a, 0x6,
+    0x23f4, 0xc,
+    0x2427, 0x19,
+    0x244b, 0x15,
+    0x2b4d, 0x3,
+    0x2b5a, 0xa6,
+    0x2cf4, 0x5,
+    0x2d28, 0x5,
+    0x2d68, 0x7,
+    0x2d71, 0xe,
+    0x2d97, 0x9,
+    0x2e3c, 0x44,
+    0x2ef4, 0xc,
+    0x2fd6, 0x1a,
+    0x2ffc, 0x5,
+    0x3100, 0x5,
+    0x312e, 0x3,
+    0x31bb, 0x5,
+    0x31e4, 0xc,
+    0x3400, 0x19c0,
+    0x4e00, 0x5200,
+    0xa48d, 0x3,
+    0xa4c7, 0x9,
+    0xa62c, 0x14,
+    0xa698, 0x7,
+    0xa6f8, 0x8,
+    0xa794, 0xc,
+    0xa7ab, 0x4d,
+    0xa82c, 0x4,
+    0xa83a, 0x6,
+    0xa878, 0x8,
+    0xa8c5, 0x9,
+    0xa8da, 0x6,
+    0xa8fc, 0x4,
+    0xa954, 0xb,
+    0xa97d, 0x3,
+    0xa9da, 0x4,
+    0xa9e0, 0x20,
+    0xaa37, 0x9,
+    0xaa7c, 0x4,
+    0xaac3, 0x18,
+    0xaaf7, 0xa,
+    0xab17, 0x9,
+    0xab2f, 0x91,
+    0xabfa, 0x2bb6,
+    0xd7c7, 0x4,
+    0xd7fc, 0x2104,
+    0xfada, 0x26,
+    0xfb07, 0xc,
+    0xfb18, 0x5,
+    0xfbc2, 0x11,
+    0xfd40, 0x10,
+    0xfdc8, 0x28,
+    0xfe1a, 0x6,
+    0xfe27, 0x9,
+    0xfe6c, 0x4,
+    0xfefd, 0x4,
+    0xffbf, 0x3,
+    0xffdd, 0x3,
+    0xffef, 0xd,
+];
+const NORMAL1: &'static [u16] = &[
+    0x5e, 0x22,
+    0xfb, 0x5,
+    0x103, 0x4,
+    0x134, 0x3,
+    0x18b, 0x5,
+    0x19c, 0x34,
+    0x1fe, 0x82,
+    0x29d, 0x3,
+    0x2d1, 0x2f,
+    0x324, 0xc,
+    0x34b, 0x35,
+    0x3c4, 0x4,
+    0x3d6, 0x2a,
+    0x4aa, 0x356,
+    0x839, 0x3,
+    0x860, 0xa0,
+    0x91c, 0x3,
+    0x93a, 0x5,
+    0x940, 0x40,
+    0x9b8, 0x6,
+    0x9c0, 0x40,
+    0xa07, 0x5,
+    0xa34, 0x4,
+    0xa3b, 0x4,
+    0xa48, 0x8,
+    0xa59, 0x7,
+    0xa80, 0x80,
+    0xb36, 0x3,
+    0xb73, 0x5,
+    0xb80, 0x80,
+    0xc49, 0x217,
+    0xe7f, 0x181,
+    0x104e, 0x4,
+    0x1070, 0x10,
+    0x10c2, 0xe,
+    0x10e9, 0x7,
+    0x10fa, 0x6,
+    0x1144, 0x3c,
+    0x11c9, 0x7,
+    0x11da, 0x4a6,
+    0x16b8, 0x8,
+    0x16ca, 0x936,
+    0x236f, 0x91,
+    0x2463, 0xd,
+    0x2474, 0xb8c,
+    0x342f, 0x33d1,
+    0x6a39, 0x4c7,
+    0x6f45, 0xb,
+    0x6f7f, 0x10,
+    0x6fa0, 0x4060,
+    0xb002, 0x1ffe,
+    0xd0f6, 0xa,
+    0xd173, 0x8,
+    0xd1de, 0x22,
+    0xd246, 0xba,
+    0xd357, 0x9,
+    0xd372, 0x8e,
+    0xd547, 0x3,
+    0xd800, 0x1600,
+    0xee3c, 0x6,
+    0xee43, 0x4,
+    0xee9c, 0x5,
+    0xeebc, 0x34,
+    0xeef2, 0x10e,
+    0xf02c, 0x4,
+    0xf094, 0xc,
+    0xf0e0, 0x20,
+    0xf10b, 0x5,
+    0xf16c, 0x4,
+    0xf19b, 0x4b,
+    0xf203, 0xd,
+    0xf23b, 0x5,
+    0xf249, 0x7,
+    0xf252, 0xae,
+    0xf321, 0xf,
+    0xf37d, 0x3,
+    0xf394, 0xc,
+    0xf3cb, 0x15,
+    0xf3f1, 0xf,
+    0xf4fd, 0x3,
+    0xf544, 0xc,
+    0xf568, 0x93,
+    0xf641, 0x4,
+    0xf650, 0x30,
+    0xf6c6, 0x3a,
+    0xf774, 0x88c,
+];
diff --git a/src/libcore/fmt/mod.rs b/src/libcore/fmt/mod.rs
index e5eb8f21382..173c55e35d5 100644
--- a/src/libcore/fmt/mod.rs
+++ b/src/libcore/fmt/mod.rs
@@ -1383,7 +1383,7 @@ impl Debug for str {
         f.write_char('"')?;
         let mut from = 0;
         for (i, c) in self.char_indices() {
-            let esc = c.escape_default();
+            let esc = c.escape_debug();
             // If char needs escaping, flush backlog so far and write, else skip
             if esc.len() != 1 {
                 f.write_str(&self[from..i])?;
@@ -1409,7 +1409,7 @@ impl Display for str {
 impl Debug for char {
     fn fmt(&self, f: &mut Formatter) -> Result {
         f.write_char('\'')?;
-        for c in self.escape_default() {
+        for c in self.escape_debug() {
             f.write_char(c)?
         }
         f.write_char('\'')
diff --git a/src/libcore/lib.rs b/src/libcore/lib.rs
index 0ad1f671f15..fabb3900ec6 100644
--- a/src/libcore/lib.rs
+++ b/src/libcore/lib.rs
@@ -103,17 +103,17 @@ mod int_macros;
 #[macro_use]
 mod uint_macros;
 
-#[path = "num/isize.rs"]  pub mod isize;
-#[path = "num/i8.rs"]   pub mod i8;
-#[path = "num/i16.rs"]  pub mod i16;
-#[path = "num/i32.rs"]  pub mod i32;
-#[path = "num/i64.rs"]  pub mod i64;
+#[path = "num/isize.rs"] pub mod isize;
+#[path = "num/i8.rs"]    pub mod i8;
+#[path = "num/i16.rs"]   pub mod i16;
+#[path = "num/i32.rs"]   pub mod i32;
+#[path = "num/i64.rs"]   pub mod i64;
 
 #[path = "num/usize.rs"] pub mod usize;
-#[path = "num/u8.rs"]   pub mod u8;
-#[path = "num/u16.rs"]  pub mod u16;
-#[path = "num/u32.rs"]  pub mod u32;
-#[path = "num/u64.rs"]  pub mod u64;
+#[path = "num/u8.rs"]    pub mod u8;
+#[path = "num/u16.rs"]   pub mod u16;
+#[path = "num/u32.rs"]   pub mod u32;
+#[path = "num/u64.rs"]   pub mod u64;
 
 #[path = "num/f32.rs"]   pub mod f32;
 #[path = "num/f64.rs"]   pub mod f64;
@@ -161,5 +161,6 @@ pub mod hash;
 pub mod fmt;
 
 // note: does not need to be public
+mod char_private;
 mod iter_private;
 mod tuple;
diff --git a/src/libcoretest/char.rs b/src/libcoretest/char.rs
index c8906fed3d2..4632419336d 100644
--- a/src/libcoretest/char.rs
+++ b/src/libcoretest/char.rs
@@ -124,6 +124,49 @@ fn test_is_digit() {
 }
 
 #[test]
+fn test_escape_debug() {
+    fn string(c: char) -> String {
+        c.escape_debug().collect()
+    }
+    let s = string('\n');
+    assert_eq!(s, "\\n");
+    let s = string('\r');
+    assert_eq!(s, "\\r");
+    let s = string('\'');
+    assert_eq!(s, "\\'");
+    let s = string('"');
+    assert_eq!(s, "\\\"");
+    let s = string(' ');
+    assert_eq!(s, " ");
+    let s = string('a');
+    assert_eq!(s, "a");
+    let s = string('~');
+    assert_eq!(s, "~");
+    let s = string('é');
+    assert_eq!(s, "é");
+    let s = string('\x00');
+    assert_eq!(s, "\\u{0}");
+    let s = string('\x1f');
+    assert_eq!(s, "\\u{1f}");
+    let s = string('\x7f');
+    assert_eq!(s, "\\u{7f}");
+    let s = string('\u{80}');
+    assert_eq!(s, "\\u{80}");
+    let s = string('\u{ff}');
+    assert_eq!(s, "\u{ff}");
+    let s = string('\u{11b}');
+    assert_eq!(s, "\u{11b}");
+    let s = string('\u{1d4b6}');
+    assert_eq!(s, "\u{1d4b6}");
+    let s = string('\u{200b}'); // zero width space
+    assert_eq!(s, "\\u{200b}");
+    let s = string('\u{e000}'); // private use 1
+    assert_eq!(s, "\\u{e000}");
+    let s = string('\u{100000}'); // private use 2
+    assert_eq!(s, "\\u{100000}");
+}
+
+#[test]
 fn test_escape_default() {
     fn string(c: char) -> String {
         c.escape_default().collect()
@@ -142,18 +185,28 @@ fn test_escape_default() {
     assert_eq!(s, "a");
     let s = string('~');
     assert_eq!(s, "~");
+    let s = string('é');
+    assert_eq!(s, "\\u{e9}");
     let s = string('\x00');
     assert_eq!(s, "\\u{0}");
     let s = string('\x1f');
     assert_eq!(s, "\\u{1f}");
     let s = string('\x7f');
     assert_eq!(s, "\\u{7f}");
+    let s = string('\u{80}');
+    assert_eq!(s, "\\u{80}");
     let s = string('\u{ff}');
     assert_eq!(s, "\\u{ff}");
     let s = string('\u{11b}');
     assert_eq!(s, "\\u{11b}");
     let s = string('\u{1d4b6}');
     assert_eq!(s, "\\u{1d4b6}");
+    let s = string('\u{200b}'); // zero width space
+    assert_eq!(s, "\\u{200b}");
+    let s = string('\u{e000}'); // private use 1
+    assert_eq!(s, "\\u{e000}");
+    let s = string('\u{100000}'); // private use 2
+    assert_eq!(s, "\\u{100000}");
 }
 
 #[test]
diff --git a/src/libcoretest/lib.rs b/src/libcoretest/lib.rs
index 1ef2b58351f..ef0042808f9 100644
--- a/src/libcoretest/lib.rs
+++ b/src/libcoretest/lib.rs
@@ -14,6 +14,7 @@
 #![feature(borrow_state)]
 #![feature(box_syntax)]
 #![feature(cell_extras)]
+#![feature(char_escape_debug)]
 #![feature(const_fn)]
 #![feature(core_private_bignum)]
 #![feature(core_private_diy_float)]
@@ -29,10 +30,10 @@
 #![feature(slice_patterns)]
 #![feature(step_by)]
 #![feature(test)]
+#![feature(try_from)]
 #![feature(unboxed_closures)]
 #![feature(unicode)]
 #![feature(unique)]
-#![feature(try_from)]
 
 extern crate core;
 extern crate test;
diff --git a/src/librustc_unicode/char.rs b/src/librustc_unicode/char.rs
index 1ea0f8d70a8..81856cb87c7 100644
--- a/src/librustc_unicode/char.rs
+++ b/src/librustc_unicode/char.rs
@@ -36,7 +36,7 @@ use tables::{conversions, derived_property, general_category, property};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::char::{MAX, from_digit, from_u32, from_u32_unchecked};
 #[stable(feature = "rust1", since = "1.0.0")]
-pub use core::char::{EncodeUtf16, EncodeUtf8, EscapeDefault, EscapeUnicode};
+pub use core::char::{EncodeUtf16, EncodeUtf8, EscapeDebug, EscapeDefault, EscapeUnicode};
 
 // unstable reexports
 #[unstable(feature = "decode_utf8", issue = "33906")]
@@ -269,6 +269,41 @@ impl char {
 
     /// Returns an iterator that yields the literal escape code of a `char`.
     ///
+    /// This will escape the characters similar to the `Debug` implementations
+    /// of `str` or `char`.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// for i in '\n'.escape_default() {
+    ///     println!("{}", i);
+    /// }
+    /// ```
+    ///
+    /// This prints:
+    ///
+    /// ```text
+    /// \
+    /// n
+    /// ```
+    ///
+    /// Collecting into a `String`:
+    ///
+    /// ```
+    /// let quote: String = '\n'.escape_default().collect();
+    ///
+    /// assert_eq!(quote, "\\n");
+    /// ```
+    #[unstable(feature = "char_escape_debug", issue = "35068")]
+    #[inline]
+    pub fn escape_debug(self) -> EscapeDebug {
+        C::escape_debug(self)
+    }
+
+    /// Returns an iterator that yields the literal escape code of a `char`.
+    ///
     /// The default is chosen with a bias toward producing literals that are
     /// legal in a variety of languages, including C++11 and similar C-family
     /// languages. The exact rules are:
diff --git a/src/librustc_unicode/lib.rs b/src/librustc_unicode/lib.rs
index f91a754ab57..3ae905eba27 100644
--- a/src/librustc_unicode/lib.rs
+++ b/src/librustc_unicode/lib.rs
@@ -32,6 +32,7 @@
 #![cfg_attr(not(stage0), deny(warnings))]
 #![no_std]
 
+#![feature(char_escape_debug)]
 #![feature(core_char_ext)]
 #![feature(decode_utf8)]
 #![feature(lang_items)]
diff --git a/src/libstd/lib.rs b/src/libstd/lib.rs
index d05a5a09614..865d067cdb6 100644
--- a/src/libstd/lib.rs
+++ b/src/libstd/lib.rs
@@ -218,8 +218,9 @@
 #![feature(associated_consts)]
 #![feature(borrow_state)]
 #![feature(box_syntax)]
-#![feature(cfg_target_vendor)]
 #![feature(cfg_target_thread_local)]
+#![feature(cfg_target_vendor)]
+#![feature(char_escape_debug)]
 #![feature(char_internals)]
 #![feature(collections)]
 #![feature(collections_bound)]
@@ -229,10 +230,10 @@
 #![feature(dropck_parametricity)]
 #![feature(float_extras)]
 #![feature(float_from_str_radix)]
-#![feature(fnbox)]
 #![feature(fn_traits)]
-#![feature(heap_api)]
+#![feature(fnbox)]
 #![feature(hashmap_hasher)]
+#![feature(heap_api)]
 #![feature(inclusive_range)]
 #![feature(int_error_internals)]
 #![feature(into_cow)]
@@ -242,6 +243,7 @@
 #![feature(linkage)]
 #![feature(macro_reexport)]
 #![cfg_attr(test, feature(map_values_mut))]
+#![feature(needs_panic_runtime)]
 #![feature(num_bits_bytes)]
 #![feature(old_wrapping)]
 #![feature(on_unimplemented)]
@@ -249,10 +251,11 @@
 #![feature(optin_builtin_traits)]
 #![feature(panic_unwind)]
 #![feature(placement_in_syntax)]
+#![feature(question_mark)]
 #![feature(rand)]
 #![feature(raw)]
-#![feature(repr_simd)]
 #![feature(reflect_marker)]
+#![feature(repr_simd)]
 #![feature(rustc_attrs)]
 #![feature(shared)]
 #![feature(sip_hash_13)]
@@ -266,6 +269,7 @@
 #![feature(str_utf16)]
 #![feature(test, rustc_private)]
 #![feature(thread_local)]
+#![feature(try_from)]
 #![feature(unboxed_closures)]
 #![feature(unicode)]
 #![feature(unique)]
@@ -273,9 +277,6 @@
 #![feature(unwind_attributes)]
 #![feature(vec_push_all)]
 #![feature(zero_one)]
-#![feature(question_mark)]
-#![feature(try_from)]
-#![feature(needs_panic_runtime)]
 
 // Issue# 30592: Systematically use alloc_system during stage0 since jemalloc
 // might be unavailable or disabled
diff --git a/src/libstd/sys/common/wtf8.rs b/src/libstd/sys/common/wtf8.rs
index 2c1a656290f..c0e6ec46b55 100644
--- a/src/libstd/sys/common/wtf8.rs
+++ b/src/libstd/sys/common/wtf8.rs
@@ -390,7 +390,7 @@ impl fmt::Debug for Wtf8 {
     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
         fn write_str_escaped(f: &mut fmt::Formatter, s: &str) -> fmt::Result {
             use fmt::Write;
-            for c in s.chars().flat_map(|c| c.escape_default()) {
+            for c in s.chars().flat_map(|c| c.escape_debug()) {
                 f.write_char(c)?
             }
             Ok(())
@@ -1064,9 +1064,9 @@ mod tests {
 
     #[test]
     fn wtf8buf_show() {
-        let mut string = Wtf8Buf::from_str("a\té 💩\r");
+        let mut string = Wtf8Buf::from_str("a\té \u{7f}💩\r");
         string.push(CodePoint::from_u32(0xD800).unwrap());
-        assert_eq!(format!("{:?}", string), r#""a\t\u{e9} \u{1f4a9}\r\u{D800}""#);
+        assert_eq!(format!("{:?}", string), "\"a\\té \\u{7f}\u{1f4a9}\\r\\u{D800}\"");
     }
 
     #[test]
diff --git a/src/test/run-pass/ifmt.rs b/src/test/run-pass/ifmt.rs
index ed56519d236..8b5536de12e 100644
--- a/src/test/run-pass/ifmt.rs
+++ b/src/test/run-pass/ifmt.rs
@@ -70,15 +70,15 @@ pub fn main() {
     t!(format!("{}", '☃'), "☃");
     t!(format!("{}", 10), "10");
     t!(format!("{}", 10_usize), "10");
-    t!(format!("{:?}", '☃'), "'\\u{2603}'");
+    t!(format!("{:?}", '☃'), "'☃'");
     t!(format!("{:?}", 10), "10");
     t!(format!("{:?}", 10_usize), "10");
     t!(format!("{:?}", "true"), "\"true\"");
     t!(format!("{:?}", "foo\nbar"), "\"foo\\nbar\"");
     t!(format!("{:?}", "foo\n\"bar\"\r\n\'baz\'\t\\qux\\"),
        r#""foo\n\"bar\"\r\n\'baz\'\t\\qux\\""#);
-    t!(format!("{:?}", "foo\0bar\x01baz\u{3b1}q\u{75}x"),
-       r#""foo\u{0}bar\u{1}baz\u{3b1}qux""#);
+    t!(format!("{:?}", "foo\0bar\x01baz\u{7f}q\u{75}x"),
+       r#""foo\u{0}bar\u{1}baz\u{7f}qux""#);
     t!(format!("{:o}", 10_usize), "12");
     t!(format!("{:x}", 10_usize), "a");
     t!(format!("{:X}", 10_usize), "A");
diff --git a/src/test/run-pass/sync-send-iterators-in-libcore.rs b/src/test/run-pass/sync-send-iterators-in-libcore.rs
index 93178994815..d12bdf182fa 100644
--- a/src/test/run-pass/sync-send-iterators-in-libcore.rs
+++ b/src/test/run-pass/sync-send-iterators-in-libcore.rs
@@ -67,7 +67,7 @@ macro_rules! is_sync_send {
 
 fn main() {
     // for char.rs
-    all_sync_send!("Я", escape_default, escape_unicode);
+    all_sync_send!("Я", escape_debug, escape_default, escape_unicode);
 
     // for iter.rs
     all_sync_send_mutable_ref!([1], iter);