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diff --git a/third_party/rust/unicode-xid/src/lib.rs b/third_party/rust/unicode-xid/src/lib.rs
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+// Copyright 2012-2015 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.
+
+//! Determine if a `char` is a valid identifier for a parser and/or lexer according to
+//! [Unicode Standard Annex #31](http://www.unicode.org/reports/tr31/) rules.
+//!
+//! ```rust
+//! extern crate unicode_xid;
+//!
+//! use unicode_xid::UnicodeXID;
+//!
+//! fn main() {
+//!     let ch = 'a';
+//!     println!("Is {} a valid start of an identifier? {}", ch, UnicodeXID::is_xid_start(ch));
+//! }
+//! ```
+//!
+//! # features
+//!
+//! unicode-xid supports a `no_std` feature. This eliminates dependence
+//! on std, and instead uses equivalent functions from core.
+//!
+
+#![forbid(unsafe_code)]
+#![deny(missing_docs)]
+#![doc(
+    html_logo_url = "https://unicode-rs.github.io/unicode-rs_sm.png",
+    html_favicon_url = "https://unicode-rs.github.io/unicode-rs_sm.png"
+)]
+#![no_std]
+#![cfg_attr(feature = "bench", feature(test, unicode_internals))]
+
+#[cfg(test)]
+#[macro_use]
+extern crate std;
+
+#[cfg(feature = "bench")]
+extern crate test;
+
+use tables::derived_property;
+pub use tables::UNICODE_VERSION;
+
+mod tables;
+
+#[cfg(test)]
+mod tests;
+
+/// Methods for determining if a character is a valid identifier character.
+pub trait UnicodeXID {
+    /// Returns whether the specified character satisfies the 'XID_Start'
+    /// Unicode property.
+    ///
+    /// 'XID_Start' is a Unicode Derived Property specified in
+    /// [UAX #31](http://unicode.org/reports/tr31/#NFKC_Modifications),
+    /// mostly similar to ID_Start but modified for closure under NFKx.
+    fn is_xid_start(self) -> bool;
+
+    /// Returns whether the specified `char` satisfies the 'XID_Continue'
+    /// Unicode property.
+    ///
+    /// 'XID_Continue' is a Unicode Derived Property specified in
+    /// [UAX #31](http://unicode.org/reports/tr31/#NFKC_Modifications),
+    /// mostly similar to 'ID_Continue' but modified for closure under NFKx.
+    fn is_xid_continue(self) -> bool;
+}
+
+impl UnicodeXID for char {
+    #[inline]
+    fn is_xid_start(self) -> bool {
+        // Fast-path for ascii idents
+        ('a' <= self && self <= 'z')
+            || ('A' <= self && self <= 'Z')
+            || (self > '\x7f' && derived_property::XID_Start(self))
+    }
+
+    #[inline]
+    fn is_xid_continue(self) -> bool {
+        // Fast-path for ascii idents
+        ('a' <= self && self <= 'z')
+            || ('A' <= self && self <= 'Z')
+            || ('0' <= self && self <= '9')
+            || self == '_'
+            || (self > '\x7f' && derived_property::XID_Continue(self))
+    }
+}