Ensure panic on length mismatch

src/zip_eq_impl.rs

@@ -52,18 +52,23 @@ where
         }
     }
 
-    #[inline]
     fn fold<B, F>(self, init: B, mut f: F) -> B
     where
         Self: Sized,
         F: FnMut(B, Self::Item) -> B,
     {
         let Self { a, mut b } = self;
 
-        a.fold(init, |acc, x| match b.next() {
+        let acc = a.fold(init, |acc, x| match b.next() {
             Some(y) => f(acc, (x, y)),
             None => panic!("itertools: .zip_eq() reached end of one iterator before the other"),
-        })
+        });
+
+        if b.next().is_some() {
+            panic!("itertools: .zip_eq() reached end of one iterator before the other")
+        }
+
+        acc
     }
 
     fn size_hint(&self) -> (usize, Option<usize>) {

tests/zip.rs

@@ -82,3 +82,12 @@ fn zip_eq_panic3() {
 
     zip_eq(&a, &b).fold(0, |acc, (x, y)| acc + x * y);
 }
+
+#[should_panic]
+#[test]
+fn zip_eq_panic4() {
+    let b = [1, 2];
+    let a = [1, 2, 3];
+
+    zip_eq(&a, &b).fold(0, |acc, (x, y)| acc + x * y);
+}