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diff --git a/vendor/string_cache/src/static_sets.rs b/vendor/string_cache/src/static_sets.rs
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+// Copyright 2014 The Servo Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution.
+//
+// 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.
+
+/// A static `PhfStrSet`
+///
+/// This trait is implemented by static sets of interned strings generated using
+/// `string_cache_codegen`, and `EmptyStaticAtomSet` for when strings will be added dynamically.
+///
+/// It is used by the methods of [`Atom`] to check if a string is present in the static set.
+///
+/// [`Atom`]: struct.Atom.html
+pub trait StaticAtomSet: Ord {
+    /// Get the location of the static string set in the binary.
+    fn get() -> &'static PhfStrSet;
+    /// Get the index of the empty string, which is in every set and is used for `Atom::default`.
+    fn empty_string_index() -> u32;
+}
+
+/// A string set created using a [perfect hash function], specifically
+/// [Hash, Displace and Compress].
+///
+/// See the CHD document for the meaning of the struct fields.
+///
+/// [perfect hash function]: https://en.wikipedia.org/wiki/Perfect_hash_function
+/// [Hash, Displace and Compress]: http://cmph.sourceforge.net/papers/esa09.pdf
+pub struct PhfStrSet {
+    #[doc(hidden)]
+    pub key: u64,
+    #[doc(hidden)]
+    pub disps: &'static [(u32, u32)],
+    #[doc(hidden)]
+    pub atoms: &'static [&'static str],
+    #[doc(hidden)]
+    pub hashes: &'static [u32],
+}
+
+/// An empty static atom set for when only dynamic strings will be added
+#[derive(PartialEq, Eq, PartialOrd, Ord)]
+pub struct EmptyStaticAtomSet;
+
+impl StaticAtomSet for EmptyStaticAtomSet {
+    fn get() -> &'static PhfStrSet {
+        // The name is a lie: this set is not empty (it contains the empty string)
+        // but that’s only to avoid divisions by zero in rust-phf.
+        static SET: PhfStrSet = PhfStrSet {
+            key: 0,
+            disps: &[(0, 0)],
+            atoms: &[""],
+            // "" SipHash'd, and xored with u64_hash_to_u32.
+            hashes: &[0x3ddddef3],
+        };
+        &SET
+    }
+
+    fn empty_string_index() -> u32 {
+        0
+    }
+}