1 files changed, 154 insertions, 0 deletions
diff --git a/third_party/rust/itertools/src/peeking_take_while.rs b/third_party/rust/itertools/src/peeking_take_while.rs
new file mode 100644
index 0000000000..b3a9c5ccb4
--- /dev/null
+++ b/third_party/rust/itertools/src/peeking_take_while.rs
@@ -0,0 +1,154 @@
+use std::iter::Peekable;
+use crate::PutBack;
+#[cfg(feature = "use_alloc")]
+use crate::PutBackN;
+
+/// An iterator that allows peeking at an element before deciding to accept it.
+///
+/// See [`.peeking_take_while()`](crate::Itertools::peeking_take_while)
+/// for more information.
+///
+/// This is implemented by peeking adaptors like peekable and put back,
+/// but also by a few iterators that can be peeked natively, like the slice’s
+/// by reference iterator (`std::slice::Iter`).
+pub trait PeekingNext : Iterator {
+    /// Pass a reference to the next iterator element to the closure `accept`;
+    /// if `accept` returns true, return it as the next element,
+    /// else None.
+    fn peeking_next<F>(&mut self, accept: F) -> Option<Self::Item>
+        where F: FnOnce(&Self::Item) -> bool;
+}
+
+impl<I> PeekingNext for Peekable<I>
+    where I: Iterator,
+{
+    fn peeking_next<F>(&mut self, accept: F) -> Option<Self::Item>
+        where F: FnOnce(&Self::Item) -> bool
+    {
+        if let Some(r) = self.peek() {
+            if !accept(r) {
+                return None;
+            }
+        }
+        self.next()
+    }
+}
+
+impl<I> PeekingNext for PutBack<I>
+    where I: Iterator,
+{
+    fn peeking_next<F>(&mut self, accept: F) -> Option<Self::Item>
+        where F: FnOnce(&Self::Item) -> bool
+    {
+        if let Some(r) = self.next() {
+            if !accept(&r) {
+                self.put_back(r);
+                return None;
+            }
+            Some(r)
+        } else {
+            None
+        }
+    }
+}
+
+#[cfg(feature = "use_alloc")]
+impl<I> PeekingNext for PutBackN<I>
+    where I: Iterator,
+{
+    fn peeking_next<F>(&mut self, accept: F) -> Option<Self::Item>
+        where F: FnOnce(&Self::Item) -> bool
+    {
+        if let Some(r) = self.next() {
+            if !accept(&r) {
+                self.put_back(r);
+                return None;
+            }
+            Some(r)
+        } else {
+            None
+        }
+    }
+}
+
+/// An iterator adaptor that takes items while a closure returns `true`.
+///
+/// See [`.peeking_take_while()`](crate::Itertools::peeking_take_while)
+/// for more information.
+#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
+pub struct PeekingTakeWhile<'a, I: 'a, F>
+    where I: Iterator,
+{
+    iter: &'a mut I,
+    f: F,
+}
+
+impl<'a, I: 'a, F> std::fmt::Debug for PeekingTakeWhile<'a, I, F>
+where
+    I: Iterator + std::fmt::Debug,
+{
+    debug_fmt_fields!(PeekingTakeWhile, iter);
+}
+
+/// Create a `PeekingTakeWhile`
+pub fn peeking_take_while<I, F>(iter: &mut I, f: F) -> PeekingTakeWhile<I, F>
+    where I: Iterator,
+{
+    PeekingTakeWhile {
+        iter,
+        f,
+    }
+}
+
+impl<'a, I, F> Iterator for PeekingTakeWhile<'a, I, F>
+    where I: PeekingNext,
+          F: FnMut(&I::Item) -> bool,
+
+{
+    type Item = I::Item;
+    fn next(&mut self) -> Option<Self::Item> {
+        self.iter.peeking_next(&mut self.f)
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (0, self.iter.size_hint().1)
+    }
+}
+
+// Some iterators are so lightweight we can simply clone them to save their
+// state and use that for peeking.
+macro_rules! peeking_next_by_clone {
+    ([$($typarm:tt)*] $type_:ty) => {
+        impl<$($typarm)*> PeekingNext for $type_ {
+            fn peeking_next<F>(&mut self, accept: F) -> Option<Self::Item>
+                where F: FnOnce(&Self::Item) -> bool
+            {
+                let saved_state = self.clone();
+                if let Some(r) = self.next() {
+                    if !accept(&r) {
+                        *self = saved_state;
+                    } else {
+                        return Some(r)
+                    }
+                }
+                None
+            }
+        }
+    }
+}
+
+peeking_next_by_clone! { ['a, T] ::std::slice::Iter<'a, T> }
+peeking_next_by_clone! { ['a] ::std::str::Chars<'a> }
+peeking_next_by_clone! { ['a] ::std::str::CharIndices<'a> }
+peeking_next_by_clone! { ['a] ::std::str::Bytes<'a> }
+peeking_next_by_clone! { ['a, T] ::std::option::Iter<'a, T> }
+peeking_next_by_clone! { ['a, T] ::std::result::Iter<'a, T> }
+peeking_next_by_clone! { [T] ::std::iter::Empty<T> }
+#[cfg(feature = "use_alloc")]
+peeking_next_by_clone! { ['a, T] alloc::collections::linked_list::Iter<'a, T> }
+#[cfg(feature = "use_alloc")]
+peeking_next_by_clone! { ['a, T] alloc::collections::vec_deque::Iter<'a, T> }
+
+// cloning a Rev has no extra overhead; peekable and put backs are never DEI.
+peeking_next_by_clone! { [I: Clone + PeekingNext + DoubleEndedIterator]
+                         ::std::iter::Rev<I> }