Implement split_inclusive for slice and str, an splitting iterator that includes the matched part in the iterated substrings as a terminator.

src/liballoc/tests/lib.rs

@@ -12,6 +12,7 @@
 #![feature(binary_heap_into_iter_sorted)]
 #![feature(binary_heap_drain_sorted)]
 #![feature(vec_remove_item)]
+#![feature(split_inclusive)]
 
 use std::collections::hash_map::DefaultHasher;
 use std::hash::{Hash, Hasher};

src/liballoc/tests/slice.rs

@@ -851,6 +851,26 @@ fn test_splitator() {
     assert_eq!(xs.split(|x| *x == 5).collect::<Vec<&[i32]>>(), splits);
 }
 
+#[test]
+fn test_splitator_inclusive() {
+    let xs = &[1, 2, 3, 4, 5];
+
+    let splits: &[&[_]] = &[&[1, 2], &[3, 4], &[5]];
+    assert_eq!(xs.split_inclusive(|x| *x % 2 == 0).collect::<Vec<_>>(), splits);
+    let splits: &[&[_]] = &[&[1], &[2, 3, 4, 5]];
+    assert_eq!(xs.split_inclusive(|x| *x == 1).collect::<Vec<_>>(), splits);
+    let splits: &[&[_]] = &[&[1, 2, 3, 4, 5], &[]];
+    assert_eq!(xs.split_inclusive(|x| *x == 5).collect::<Vec<_>>(), splits);
+    let splits: &[&[_]] = &[&[1, 2, 3, 4, 5]];
+    assert_eq!(xs.split_inclusive(|x| *x == 10).collect::<Vec<_>>(), splits);
+    let splits: &[&[_]] = &[&[1], &[2], &[3], &[4], &[5], &[]];
+    assert_eq!(xs.split_inclusive(|_| true).collect::<Vec<&[i32]>>(), splits);
+
+    let xs: &[i32] = &[];
+    let splits: &[&[i32]] = &[&[]];
+    assert_eq!(xs.split_inclusive(|x| *x == 5).collect::<Vec<&[i32]>>(), splits);
+}
+
 #[test]
 fn test_splitnator() {
     let xs = &[1, 2, 3, 4, 5];

src/liballoc/tests/str.rs

@@ -1247,6 +1247,24 @@ fn test_split_char_iterator_no_trailing() {
     assert_eq!(split, ["", "Märy häd ä little lämb", "Little lämb"]);
 }
 
+#[test]
+fn test_split_char_iterator_inclusive() {
+    let data = "\nMäry häd ä little lämb\nLittle lämb\n";
+
+    let split: Vec<&str> = data.split_inclusive('\n').collect();
+    assert_eq!(split, ["\n", "Märy häd ä little lämb\n", "Little lämb\n", ""]);
+
+    let uppercase_separated = "SheePSharKTurtlECaT";
+    let mut first_char = true;
+    let split: Vec<&str> = uppercase_separated.split_inclusive(|c: char| {
+        let split = !first_char && c.is_uppercase();
+        first_char = split;
+        split
+    }).collect();
+    assert_eq!(split, ["SheeP", "SharK", "TurtlE", "CaT", ""]);
+}
+
+
 #[test]
 fn test_rsplit() {
     let data = "\nMäry häd ä little lämb\nLittle lämb\n";

src/libcore/slice/mod.rs

@@ -1155,6 +1155,72 @@ impl<T> [T] {
         SplitMut { v: self, pred, finished: false }
     }
 
+    /// Returns an iterator over subslices separated by elements that match
+    /// `pred`. The matched element is contained in the end of the previous
+    /// subslice as a terminator.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(split_inclusive)]
+    /// let slice = [10, 40, 33, 20];
+    /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
+    ///
+    /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
+    /// assert_eq!(iter.next().unwrap(), &[20]);
+    /// assert!(iter.next().is_none());
+    /// ```
+    ///
+    /// If the first element is matched, an empty slice will be the first item
+    /// returned by the iterator. Similarly, if the last element in the slice
+    /// is matched, an empty slice will be the last item returned by the
+    /// iterator:
+    ///
+    /// ```
+    /// #![feature(split_inclusive)]
+    /// let slice = [10, 40, 33];
+    /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
+    ///
+    /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
+    /// assert_eq!(iter.next().unwrap(), &[]);
+    /// assert!(iter.next().is_none());
+    /// ```
+    #[unstable(feature = "split_inclusive", issue = "0")]
+    #[inline]
+    pub fn split_inclusive<F>(&self, pred: F) -> SplitInclusive<'_, T, F>
+        where F: FnMut(&T) -> bool
+    {
+        SplitInclusive {
+            v: self,
+            pred,
+            finished: false
+        }
+    }
+
+    /// Returns an iterator over mutable subslices separated by elements that
+    /// match `pred`. The matched element is contained in the previous
+    /// subslice as a terminator.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(split_inclusive)]
+    /// let mut v = [10, 40, 30, 20, 60, 50];
+    ///
+    /// for group in v.split_inclusive_mut(|num| *num % 3 == 0) {
+    ///     let terminator_idx = group.len()-1;
+    ///     group[terminator_idx] = 1;
+    /// }
+    /// assert_eq!(v, [10, 40, 1, 20, 1, 1]);
+    /// ```
+    #[unstable(feature = "split_inclusive", issue = "0")]
+    #[inline]
+    pub fn split_inclusive_mut<F>(&mut self, pred: F) -> SplitInclusiveMut<'_, T, F>
+        where F: FnMut(&T) -> bool
+    {
+        SplitInclusiveMut { v: self, pred, finished: false }
+    }
+
     /// Returns an iterator over subslices separated by elements that match
     /// `pred`, starting at the end of the slice and working backwards.
     /// The matched element is not contained in the subslices.
@@ -3675,7 +3741,100 @@ where
 #[stable(feature = "fused", since = "1.26.0")]
 impl<T, P> FusedIterator for Split<'_, T, P> where P: FnMut(&T) -> bool {}
 
-/// An iterator over the subslices of the vector which are separated
+/// An iterator over subslices separated by elements that match a predicate
+/// function. Unlike `Split`, it contains the matched part as a terminator
+/// of the subslice.
+///
+/// This struct is created by the [`split_inclusive`] method on [slices].
+///
+/// [`split_inclusive`]: ../../std/primitive.slice.html#method.split_inclusive
+/// [slices]: ../../std/primitive.slice.html
+#[unstable(feature = "split_inclusive", issue = "0")]
+pub struct SplitInclusive<'a, T:'a, P> where P: FnMut(&T) -> bool {
+    v: &'a [T],
+    pred: P,
+    finished: bool
+}
+
+#[unstable(feature = "split_inclusive", issue = "0")]
+impl<T: fmt::Debug, P> fmt::Debug for SplitInclusive<'_, T, P> where P: FnMut(&T) -> bool {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("SplitInclusive")
+            .field("v", &self.v)
+            .field("finished", &self.finished)
+            .finish()
+    }
+}
+
+// FIXME(#26925) Remove in favor of `#[derive(Clone)]`
+#[unstable(feature = "split_inclusive", issue = "0")]
+impl<T, P> Clone for SplitInclusive<'_, T, P> where P: Clone + FnMut(&T) -> bool {
+    fn clone(&self) -> Self {
+        SplitInclusive {
+            v: self.v,
+            pred: self.pred.clone(),
+            finished: self.finished,
+        }
+    }
+}
+
+#[unstable(feature = "split_inclusive", issue = "0")]
+impl<'a, T, P> Iterator for SplitInclusive<'a, T, P> where P: FnMut(&T) -> bool {
+    type Item = &'a [T];
+
+    #[inline]
+    fn next(&mut self) -> Option<&'a [T]> {
+        if self.finished { return None; }
+
+        match self.v.iter().position(|x| (self.pred)(x)) {
+            None => self.finish(),
+            Some(idx) => {
+                let ret = Some(&self.v[..idx + 1]);
+                self.v = &self.v[idx + 1..];
+                ret
+            }
+        }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        if self.finished {
+            (0, Some(0))
+        } else {
+            (1, Some(self.v.len() + 1))
+        }
+    }
+}
+
+#[unstable(feature = "split_inclusive", issue = "0")]
+impl<'a, T, P> DoubleEndedIterator for SplitInclusive<'a, T, P> where P: FnMut(&T) -> bool {
+    #[inline]
+    fn next_back(&mut self) -> Option<&'a [T]> {
+        if self.finished { return None; }
+
+        match self.v.iter().rposition(|x| (self.pred)(x)) {
+            None => self.finish(),
+            Some(idx) => {
+                let ret = Some(&self.v[idx + 1..]);
+                self.v = &self.v[..idx];
+                ret
+            }
+        }
+    }
+}
+
+#[unstable(feature = "split_inclusive", issue = "0")]
+impl<'a, T, P> SplitIter for SplitInclusive<'a, T, P> where P: FnMut(&T) -> bool {
+    #[inline]
+    fn finish(&mut self) -> Option<&'a [T]> {
+        if self.finished { None } else { self.finished = true; Some(self.v) }
+    }
+}
+
+#[unstable(feature = "split_inclusive", issue = "0")]
+impl<T, P> FusedIterator for SplitInclusive<'_, T, P> where P: FnMut(&T) -> bool {}
+
+/// An iterator over the mutable subslices of the vector which are separated
 /// by elements that match `pred`.
 ///
 /// This struct is created by the [`split_mut`] method on [slices].
@@ -3789,6 +3948,106 @@ where
 #[stable(feature = "fused", since = "1.26.0")]
 impl<T, P> FusedIterator for SplitMut<'_, T, P> where P: FnMut(&T) -> bool {}
 
+/// An iterator over the mutable subslices of the vector which are separated
+/// by elements that match `pred`. Unlike `SplitMut`, it contains the matched
+/// parts in the ends of the subslices.
+///
+/// This struct is created by the [`split_inclusive_mut`] method on [slices].
+///
+/// [`split_inclusive_mut`]: ../../std/primitive.slice.html#method.split_inclusive_mut
+/// [slices]: ../../std/primitive.slice.html
+#[unstable(feature = "split_inclusive", issue = "0")]
+pub struct SplitInclusiveMut<'a, T:'a, P> where P: FnMut(&T) -> bool {
+    v: &'a mut [T],
+    pred: P,
+    finished: bool
+}
+
+#[unstable(feature = "split_inclusive", issue = "0")]
+impl<T: fmt::Debug, P> fmt::Debug for SplitInclusiveMut<'_, T, P> where P: FnMut(&T) -> bool {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("SplitInclusiveMut")
+            .field("v", &self.v)
+            .field("finished", &self.finished)
+            .finish()
+    }
+}
+
+#[unstable(feature = "split_inclusive", issue = "0")]
+impl<'a, T, P> SplitIter for SplitInclusiveMut<'a, T, P> where P: FnMut(&T) -> bool {
+    #[inline]
+    fn finish(&mut self) -> Option<&'a mut [T]> {
+        if self.finished {
+            None
+        } else {
+            self.finished = true;
+            Some(mem::replace(&mut self.v, &mut []))
+        }
+    }
+}
+
+#[unstable(feature = "split_inclusive", issue = "0")]
+impl<'a, T, P> Iterator for SplitInclusiveMut<'a, T, P> where P: FnMut(&T) -> bool {
+    type Item = &'a mut [T];
+
+    #[inline]
+    fn next(&mut self) -> Option<&'a mut [T]> {
+        if self.finished { return None; }
+
+        let idx_opt = { // work around borrowck limitations
+            let pred = &mut self.pred;
+            self.v.iter().position(|x| (*pred)(x))
+        };
+        match idx_opt {
+            None => self.finish(),
+            Some(idx) => {
+                let tmp = mem::replace(&mut self.v, &mut []);
+                let (head, tail) = tmp.split_at_mut(idx+1);
+                self.v = tail;
+                Some(head)
+            }
+        }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        if self.finished {
+            (0, Some(0))
+        } else {
+            // if the predicate doesn't match anything, we yield one slice
+            // if it matches every element, we yield len+1 empty slices.
+            (1, Some(self.v.len() + 1))
+        }
+    }
+}
+
+#[unstable(feature = "split_inclusive", issue = "0")]
+impl<'a, T, P> DoubleEndedIterator for SplitInclusiveMut<'a, T, P> where
+    P: FnMut(&T) -> bool,
+{
+    #[inline]
+    fn next_back(&mut self) -> Option<&'a mut [T]> {
+        if self.finished { return None; }
+
+        let idx_opt = { // work around borrowck limitations
+            let pred = &mut self.pred;
+            self.v.iter().rposition(|x| (*pred)(x))
+        };
+        match idx_opt {
+            None => self.finish(),
+            Some(idx) => {
+                let tmp = mem::replace(&mut self.v, &mut []);
+                let (head, tail) = tmp.split_at_mut(idx+1);
+                self.v = head;
+                Some(tail)
+            }
+        }
+    }
+}
+
+#[unstable(feature = "split_inclusive", issue = "0")]
+impl<T, P> FusedIterator for SplitInclusiveMut<'_, T, P> where P: FnMut(&T) -> bool {}
+
 /// An iterator over subslices separated by elements that match a predicate
 /// function, starting from the end of the slice.
 ///

src/libcore/str/mod.rs

@@ -1132,6 +1132,21 @@ impl<'a, P: Pattern<'a>> SplitInternal<'a, P> {
         }
     }
 
+    #[inline]
+    fn next_inclusive(&mut self) -> Option<&'a str> {
+        if self.finished { return None }
+
+        let haystack = self.matcher.haystack();
+        match self.matcher.next_match() {
+            Some((_, b)) => unsafe {
+                let elt = haystack.get_unchecked(self.start..b);
+                self.start = b;
+                Some(elt)
+            },
+            None => self.get_end(),
+        }
+    }
+
     #[inline]
     fn next_back(&mut self) -> Option<&'a str>
     where
@@ -1168,6 +1183,34 @@ impl<'a, P: Pattern<'a>> SplitInternal<'a, P> {
             },
         }
     }
+
+    #[inline]
+    fn next_back_inclusive(&mut self) -> Option<&'a str>
+        where P::Searcher: ReverseSearcher<'a>
+    {
+        if self.finished { return None }
+
+        if !self.allow_trailing_empty {
+            self.allow_trailing_empty = true;
+            match self.next_back() {
+                Some(elt) if !elt.is_empty() => return Some(elt),
+                _ => if self.finished { return None }
+            }
+        }
+
+        let haystack = self.matcher.haystack();
+        match self.matcher.next_match_back() {
+            Some((_, b)) => unsafe {
+                let elt = haystack.get_unchecked(b..self.end);
+                self.end = b;
+                Some(elt)
+            },
+            None => unsafe {
+                self.finished = true;
+                Some(haystack.get_unchecked(self.start..self.end))
+            },
+        }
+    }
 }
 
 generate_pattern_iterators! {
@@ -3212,6 +3255,31 @@ impl str {
         })
     }
 
+    /// An iterator over substrings of this string slice, separated by
+    /// characters matched by a pattern. Differs from the iterator produced by
+    /// `split` in that `split_inclusive` leaves the matched part as the
+    /// terminator of the substring.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(split_inclusive)]
+    /// let v: Vec<&str> = "Mary had a little lamb\nlittle lamb\nlittle lamb."
+    ///     .split_inclusive('\n').collect();
+    /// assert_eq!(v, ["Mary had a little lamb\n", "little lamb\n", "little lamb."]);
+    /// ```
+    #[unstable(feature = "split_inclusive", issue = "0")]
+    #[inline]
+    pub fn split_inclusive<'a, P: Pattern<'a>>(&'a self, pat: P) -> SplitInclusive<'a, P> {
+        SplitInclusive(SplitInternal {
+            start: 0,
+            end: self.len(),
+            matcher: pat.into_searcher(self),
+            allow_trailing_empty: true,
+            finished: false,
+        })
+    }
+
     /// An iterator over substrings of the given string slice, separated by
     /// characters matched by a pattern and yielded in reverse order.
     ///
@@ -4405,6 +4473,19 @@ pub struct SplitAsciiWhitespace<'a> {
     inner: Map<Filter<SliceSplit<'a, u8, IsAsciiWhitespace>, BytesIsNotEmpty>, UnsafeBytesToStr>,
 }
 
+/// An iterator over the substrings of a string,
+/// terminated by a substring matching to a predicate function
+/// Unlike `Split`, it contains the matched part as a terminator
+/// of the subslice.
+///
+/// This struct is created by the [`split_inclusive`] method on [`str`].
+/// See its documentation for more.
+///
+/// [`split_inclusive`]: ../../std/primitive.str.html#method.split_inclusive
+/// [`str`]: ../../std/primitive.str.html
+#[unstable(feature = "split_inclusive", issue = "0")]
+pub struct SplitInclusive<'a, P: Pattern<'a>>(SplitInternal<'a, P>);
+
 impl_fn_for_zst! {
     #[derive(Clone)]
     struct IsWhitespace impl Fn = |c: char| -> bool {
@@ -4433,6 +4514,8 @@ impl_fn_for_zst! {
     };
 }
 
+
+
 #[stable(feature = "split_whitespace", since = "1.1.0")]
 impl<'a> Iterator for SplitWhitespace<'a> {
     type Item = &'a str;
@@ -4495,6 +4578,46 @@ impl<'a> DoubleEndedIterator for SplitAsciiWhitespace<'a> {
 #[stable(feature = "split_ascii_whitespace", since = "1.34.0")]
 impl FusedIterator for SplitAsciiWhitespace<'_> {}
 
+#[unstable(feature = "split_inclusive", issue = "0")]
+impl<'a, P: Pattern<'a>> Iterator for SplitInclusive<'a, P> {
+    type Item = &'a str;
+
+    #[inline]
+    fn next(&mut self) -> Option<&'a str> {
+        self.0.next_inclusive()
+    }
+}
+
+#[unstable(feature = "split_inclusive", issue = "0")]
+impl<'a, P: Pattern<'a, Searcher: fmt::Debug>> fmt::Debug for SplitInclusive<'a, P> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("SplitInclusive")
+            .field("0", &self.0)
+            .finish()
+    }
+}
+
+// FIXME(#26925) Remove in favor of `#[derive(Clone)]`
+#[unstable(feature = "split_inclusive", issue = "0")]
+impl<'a, P: Pattern<'a, Searcher: Clone>> Clone for SplitInclusive<'a, P> {
+    fn clone(&self) -> Self {
+        SplitInclusive(self.0.clone())
+    }
+}
+
+#[unstable(feature = "split_inclusive", issue = "0")]
+impl<'a, P: Pattern<'a, Searcher: ReverseSearcher<'a>>> DoubleEndedIterator
+    for SplitInclusive<'a, P>
+{
+    #[inline]
+    fn next_back(&mut self) -> Option<&'a str> {
+        self.0.next_back_inclusive()
+    }
+}
+
+#[unstable(feature = "split_inclusive", issue = "0")]
+impl<'a, P: Pattern<'a>> FusedIterator for SplitInclusive<'a, P> {}
+
 /// An iterator of [`u16`] over the string encoded as UTF-16.
 ///
 /// [`u16`]: ../../std/primitive.u16.html