1 files changed, 161 insertions, 0 deletions
diff --git a/third_party/rust/unicode-normalization/src/decompose.rs b/third_party/rust/unicode-normalization/src/decompose.rs
new file mode 100644
index 0000000000..23cdb1a4e6
--- /dev/null
+++ b/third_party/rust/unicode-normalization/src/decompose.rs
@@ -0,0 +1,161 @@
+// 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.
+use core::fmt::{self, Write};
+use core::iter::Fuse;
+use core::ops::Range;
+use tinyvec::TinyVec;
+
+#[derive(Clone)]
+enum DecompositionType {
+    Canonical,
+    Compatible,
+}
+
+/// External iterator for a string decomposition's characters.
+#[derive(Clone)]
+pub struct Decompositions<I> {
+    kind: DecompositionType,
+    iter: Fuse<I>,
+
+    // This buffer stores pairs of (canonical combining class, character),
+    // pushed onto the end in text order.
+    //
+    // It's divided into up to three sections:
+    // 1) A prefix that is free space;
+    // 2) "Ready" characters which are sorted and ready to emit on demand;
+    // 3) A "pending" block which stills needs more characters for us to be able
+    //    to sort in canonical order and is not safe to emit.
+    buffer: TinyVec<[(u8, char); 4]>,
+    ready: Range<usize>,
+}
+
+#[inline]
+pub fn new_canonical<I: Iterator<Item = char>>(iter: I) -> Decompositions<I> {
+    Decompositions {
+        kind: self::DecompositionType::Canonical,
+        iter: iter.fuse(),
+        buffer: TinyVec::new(),
+        ready: 0..0,
+    }
+}
+
+#[inline]
+pub fn new_compatible<I: Iterator<Item = char>>(iter: I) -> Decompositions<I> {
+    Decompositions {
+        kind: self::DecompositionType::Compatible,
+        iter: iter.fuse(),
+        buffer: TinyVec::new(),
+        ready: 0..0,
+    }
+}
+
+impl<I> Decompositions<I> {
+    #[inline]
+    fn push_back(&mut self, ch: char) {
+        let class = super::char::canonical_combining_class(ch);
+
+        if class == 0 {
+            self.sort_pending();
+            self.buffer.push((class, ch));
+            self.ready.end = self.buffer.len();
+        } else {
+            self.buffer.push((class, ch));
+        }
+    }
+
+    #[inline]
+    fn sort_pending(&mut self) {
+        // NB: `sort_by_key` is stable, so it will preserve the original text's
+        // order within a combining class.
+        self.buffer[self.ready.end..].sort_by_key(|k| k.0);
+    }
+
+    #[inline]
+    fn reset_buffer(&mut self) {
+        // Equivalent to `self.buffer.drain(0..self.ready.end)`
+        // but faster than drain() if the buffer is a SmallVec or TinyVec
+        let pending = self.buffer.len() - self.ready.end;
+        for i in 0..pending {
+            self.buffer[i] = self.buffer[i + self.ready.end];
+        }
+        self.buffer.truncate(pending);
+        self.ready = 0..0;
+    }
+
+    #[inline]
+    fn increment_next_ready(&mut self) {
+        let next = self.ready.start + 1;
+        if next == self.ready.end {
+            self.reset_buffer();
+        } else {
+            self.ready.start = next;
+        }
+    }
+}
+
+impl<I: Iterator<Item = char>> Iterator for Decompositions<I> {
+    type Item = char;
+
+    #[inline]
+    fn next(&mut self) -> Option<char> {
+        while self.ready.end == 0 {
+            match (self.iter.next(), &self.kind) {
+                (Some(ch), &DecompositionType::Canonical) => {
+                    super::char::decompose_canonical(ch, |d| self.push_back(d));
+                }
+                (Some(ch), &DecompositionType::Compatible) => {
+                    super::char::decompose_compatible(ch, |d| self.push_back(d));
+                }
+                (None, _) => {
+                    if self.buffer.is_empty() {
+                        return None;
+                    } else {
+                        self.sort_pending();
+                        self.ready.end = self.buffer.len();
+
+                        // This implementation means that we can call `next`
+                        // on an exhausted iterator; the last outer `next` call
+                        // will result in an inner `next` call. To make this
+                        // safe, we use `fuse`.
+                        break;
+                    }
+                }
+            }
+        }
+
+        // We can assume here that, if `self.ready.end` is greater than zero,
+        // it's also greater than `self.ready.start`. That's because we only
+        // increment `self.ready.start` inside `increment_next_ready`, and
+        // whenever it reaches equality with `self.ready.end`, we reset both
+        // to zero, maintaining the invariant that:
+        //      self.ready.start < self.ready.end || self.ready.end == self.ready.start == 0
+        //
+        // This less-than-obviously-safe implementation is chosen for performance,
+        // minimizing the number & complexity of branches in `next` in the common
+        // case of buffering then unbuffering a single character with each call.
+        let (_, ch) = self.buffer[self.ready.start];
+        self.increment_next_ready();
+        Some(ch)
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let (lower, _) = self.iter.size_hint();
+        (lower, None)
+    }
+}
+
+impl<I: Iterator<Item = char> + Clone> fmt::Display for Decompositions<I> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        for c in self.clone() {
+            f.write_char(c)?;
+        }
+        Ok(())
+    }
+}