rollup merge of #24487: erickt/syntax

This removes the usage of `#[feature(into_cow, slice_patterns, box_syntax, box_patterns, quote, unsafe_destructor)]` from being used in libsyntax. My main desire for this is that it brings me one step closer to letting [syntex](https://github.com/erickt/rust-syntex) compile with stable rust. Hopefully this doesn't inconvenience rust development.

1 files changed, 13 insertions, 0 deletions

diff --git a/src/libsyntax/str.rs b/src/libsyntax/str.rs
new file mode 100644
index 00000000000..d0f47629b10
--- /dev/null
+++ b/src/libsyntax/str.rs
@@ -0,0 +1,13 @@
+// Copyright 2012-2014 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.
+
+pub fn char_at(s: &str, byte: usize) -> char {
+    s[byte..].chars().next().unwrap()
+}