Auto merge of #48735 - 1011X:master, r=alexcrichton

Move ascii::escape_default to libcore

As requested in #46409, the `ascii::escape_default` method has been added to the core library. All I did was copy over the `std::ascii` module file, remove the (redundant) `AsciiExt` trait, and change some of the documentation to match. None of the tests were changed.

I wasn't sure how to handle the annotations. For `EscapeDefault` and `escape_default()`, I changed them to `#[unstable(feature = "core_ascii", issue = "46409")]`. Is that alright? Or should I leave them as they were?

src/libcore/ascii.rs

@@ -0,0 +1,147 @@
+// Copyright 2013-2014 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.
+
+//! Operations on ASCII strings and characters.
+//!
+//! Most string operations in Rust act on UTF-8 strings. However, at times it
+//! makes more sense to only consider the ASCII character set for a specific
+//! operation.
+//!
+//! The [`escape_default`] function provides an iterator over the bytes of an
+//! escaped version of the character given.
+//!
+//! [`escape_default`]: fn.escape_default.html
+
+#![stable(feature = "core_ascii", since = "1.26.0")]
+
+use fmt;
+use ops::Range;
+use iter::FusedIterator;
+
+/// An iterator over the escaped version of a byte.
+///
+/// This `struct` is created by the [`escape_default`] function. See its
+/// documentation for more.
+///
+/// [`escape_default`]: fn.escape_default.html
+#[stable(feature = "core_ascii", since = "1.26.0")]
+pub struct EscapeDefault {
+    range: Range<usize>,
+    data: [u8; 4],
+}
+
+/// Returns an iterator that produces an escaped version of a `u8`.
+///
+/// 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:
+///
+/// * Tab is escaped as `\t`.
+/// * Carriage return is escaped as `\r`.
+/// * Line feed is escaped as `\n`.
+/// * Single quote is escaped as `\'`.
+/// * Double quote is escaped as `\"`.
+/// * Backslash is escaped as `\\`.
+/// * Any character in the 'printable ASCII' range `0x20` .. `0x7e`
+///   inclusive is not escaped.
+/// * Any other chars are given hex escapes of the form '\xNN'.
+/// * Unicode escapes are never generated by this function.
+///
+/// # Examples
+///
+/// ```
+/// use std::ascii;
+///
+/// let escaped = ascii::escape_default(b'0').next().unwrap();
+/// assert_eq!(b'0', escaped);
+///
+/// let mut escaped = ascii::escape_default(b'\t');
+///
+/// assert_eq!(b'\\', escaped.next().unwrap());
+/// assert_eq!(b't', escaped.next().unwrap());
+///
+/// let mut escaped = ascii::escape_default(b'\r');
+///
+/// assert_eq!(b'\\', escaped.next().unwrap());
+/// assert_eq!(b'r', escaped.next().unwrap());
+///
+/// let mut escaped = ascii::escape_default(b'\n');
+///
+/// assert_eq!(b'\\', escaped.next().unwrap());
+/// assert_eq!(b'n', escaped.next().unwrap());
+///
+/// let mut escaped = ascii::escape_default(b'\'');
+///
+/// assert_eq!(b'\\', escaped.next().unwrap());
+/// assert_eq!(b'\'', escaped.next().unwrap());
+///
+/// let mut escaped = ascii::escape_default(b'"');
+///
+/// assert_eq!(b'\\', escaped.next().unwrap());
+/// assert_eq!(b'"', escaped.next().unwrap());
+///
+/// let mut escaped = ascii::escape_default(b'\\');
+///
+/// assert_eq!(b'\\', escaped.next().unwrap());
+/// assert_eq!(b'\\', escaped.next().unwrap());
+///
+/// let mut escaped = ascii::escape_default(b'\x9d');
+///
+/// assert_eq!(b'\\', escaped.next().unwrap());
+/// assert_eq!(b'x', escaped.next().unwrap());
+/// assert_eq!(b'9', escaped.next().unwrap());
+/// assert_eq!(b'd', escaped.next().unwrap());
+/// ```
+#[stable(feature = "core_ascii", since = "1.26.0")]
+pub fn escape_default(c: u8) -> EscapeDefault {
+    let (data, len) = match c {
+        b'\t' => ([b'\\', b't', 0, 0], 2),
+        b'\r' => ([b'\\', b'r', 0, 0], 2),
+        b'\n' => ([b'\\', b'n', 0, 0], 2),
+        b'\\' => ([b'\\', b'\\', 0, 0], 2),
+        b'\'' => ([b'\\', b'\'', 0, 0], 2),
+        b'"' => ([b'\\', b'"', 0, 0], 2),
+        b'\x20' ... b'\x7e' => ([c, 0, 0, 0], 1),
+        _ => ([b'\\', b'x', hexify(c >> 4), hexify(c & 0xf)], 4),
+    };
+
+    return EscapeDefault { range: 0..len, data };
+
+    fn hexify(b: u8) -> u8 {
+        match b {
+            0 ... 9 => b'0' + b,
+            _ => b'a' + b - 10,
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Iterator for EscapeDefault {
+    type Item = u8;
+    fn next(&mut self) -> Option<u8> { self.range.next().map(|i| self.data[i]) }
+    fn size_hint(&self) -> (usize, Option<usize>) { self.range.size_hint() }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl DoubleEndedIterator for EscapeDefault {
+    fn next_back(&mut self) -> Option<u8> {
+        self.range.next_back().map(|i| self.data[i])
+    }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl ExactSizeIterator for EscapeDefault {}
+#[stable(feature = "fused", since = "1.26.0")]
+impl FusedIterator for EscapeDefault {}
+
+#[stable(feature = "std_debug", since = "1.16.0")]
+impl fmt::Debug for EscapeDefault {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("EscapeDefault { .. }")
+    }
+}

src/libcore/lib.rs

@@ -167,6 +167,7 @@ pub mod borrow;
 
 pub mod any;
 pub mod array;
+pub mod ascii;
 pub mod sync;
 pub mod cell;
 pub mod char;