Rollup merge of #82289 - SkiFire13:fix-issue-82282, r=m-ou-se

Fix underflow in specialized ZipImpl::size_hint

Fixes #82282

Author: m-ou-se

library/core/src/iter/adapters/zip.rs

@@ -200,6 +200,7 @@ where
         } else if A::MAY_HAVE_SIDE_EFFECT && self.index < self.a.size() {
             let i = self.index;
             self.index += 1;
+            self.len += 1;
             // match the base implementation's potential side effects
             // SAFETY: we just checked that `i` < `self.a.len()`
             unsafe {
@@ -258,7 +259,7 @@ where
             if sz_a != sz_b {
                 let sz_a = self.a.size();
                 if A::MAY_HAVE_SIDE_EFFECT && sz_a > self.len {
-                    for _ in 0..sz_a - cmp::max(self.len, self.index) {
+                    for _ in 0..sz_a - self.len {
                         self.a.next_back();
                     }
                 }

library/core/tests/iter/adapters/zip.rs

@@ -245,3 +245,23 @@ fn test_double_ended_zip() {
     assert_eq!(it.next_back(), Some((3, 3)));
     assert_eq!(it.next(), None);
 }
+
+#[test]
+fn test_issue_82282() {
+    fn overflowed_zip(arr: &[i32]) -> impl Iterator<Item = (i32, &())> {
+        static UNIT_EMPTY_ARR: [(); 0] = [];
+
+        let mapped = arr.into_iter().map(|i| *i);
+        let mut zipped = mapped.zip(UNIT_EMPTY_ARR.iter());
+        zipped.next();
+        zipped
+    }
+
+    let arr = [1, 2, 3];
+    let zip = overflowed_zip(&arr).zip(overflowed_zip(&arr));
+
+    assert_eq!(zip.size_hint(), (0, Some(0)));
+    for _ in zip {
+        panic!();
+    }
+}