get(s..=usize::MAX) should be fine when s != 0

Test for coverage

Author: Philippe-Cholet

src/iter_index.rs

@@ -48,11 +48,17 @@ impl<I> IteratorIndex<I> for RangeInclusive<usize>
 where
     I: Iterator,
 {
-    type Output = Skip<Take<I>>;
+    type Output = Take<Skip<I>>;
 
     fn index(self, iter: I) -> Self::Output {
-        assert_ne!(*self.end(), usize::MAX);
-        iter.take(self.end() + 1).skip(*self.start())
+        // end - start + 1 without overflowing if possible
+        let length = if *self.end() == usize::MAX {
+            assert_ne!(*self.start(), 0);
+            self.end() - self.start() + 1
+        } else {
+            (self.end() + 1).saturating_sub(*self.start())
+        };
+        iter.skip(*self.start()).take(length)
     }
 }
 

src/lib.rs

@@ -511,7 +511,7 @@ pub trait Itertools: Iterator {
     ///
     /// Works similarly to [`slice::get`](https://doc.rust-lang.org/std/primitive.slice.html#method.get).
     ///
-    /// **Panics** if the range includes `usize::MAX`.
+    /// **Panics** for ranges `..=usize::MAX` and `0..=usize::MAX`.
     ///
     /// It's a generalisation of [`Iterator::take`] and [`Iterator::skip`],
     /// and uses these under the hood.

tests/test_core.rs

@@ -40,6 +40,19 @@ fn get_dei_esi_then_dei_esi<I: DoubleEndedIterator + ExactSizeIterator + Clone>(
     is_dei_esi(it.get(..));
 }
 
+#[test]
+fn get_1_max() {
+    let mut it = (0..5).get(1..=usize::MAX);
+    assert_eq!(it.next(), Some(1));
+    assert_eq!(it.next_back(), Some(4));
+}
+
+#[test]
+#[should_panic]
+fn get_full_range_inclusive() {
+    let _it = (0..5).get(0..=usize::MAX);
+}
+
 #[test]
 fn product0() {
     let mut prod = iproduct!();