Fix #76116. (#76747)

Author: eiriktsarpalis

src/libraries/System.Collections/tests/Generic/List/List.Generic.Tests.AddRange.cs

@@ -98,5 +98,28 @@ public void AddRange_AddSelfAsEnumerable_ThrowsExceptionWhenNotEmpty()
             Assert.Throws<InvalidOperationException>(() => list.AddRange(list.Where(_ => true)));
             Assert.Equal(6, list.Count);
         }
+
+        [Fact]
+        public void AddRange_CollectionWithLargeCount_ThrowsOverflowException()
+        {
+            List<T> list = GenericListFactory(count: 1);
+            ICollection<T> collection = new CollectionWithLargeCount();
+
+            Assert.Throws<OverflowException>(() => list.AddRange(collection));
+        }
+
+        private class CollectionWithLargeCount : ICollection<T>
+        {
+            public int Count => int.MaxValue;
+
+            public bool IsReadOnly => throw new NotImplementedException();
+            public void Add(T item) => throw new NotImplementedException();
+            public void Clear() => throw new NotImplementedException();
+            public bool Contains(T item) => throw new NotImplementedException();
+            public void CopyTo(T[] array, int arrayIndex) => throw new NotImplementedException();
+            public IEnumerator<T> GetEnumerator() => throw new NotImplementedException();
+            public bool Remove(T item) => throw new NotImplementedException();
+            IEnumerator IEnumerable.GetEnumerator() => throw new NotImplementedException();
+        }
     }
 }

src/libraries/System.Collections/tests/Generic/List/List.Generic.Tests.InsertRange.cs

@@ -47,5 +47,14 @@ public void InsertRange_MatchesExpectedContents()
             Assert.Equal(12, list.Count);
             Assert.Equal(new[] { 6, 5, 4, 100, 99, 98, 3, 2, 1, 0, -1, -2 }, list);
         }
+
+        [Fact]
+        public void InsertRange_CollectionWithLargeCount_ThrowsOverflowException()
+        {
+            List<T> list = GenericListFactory(count: 1);
+            ICollection<T> collection = new CollectionWithLargeCount();
+
+            Assert.Throws<OverflowException>(() => list.InsertRange(0, collection));
+        }
     }
 }

src/libraries/System.Private.CoreLib/src/System/Collections/Generic/List.cs

@@ -254,7 +254,7 @@ public void AddRange(IEnumerable<T> collection)
                 {
                     if (_items.Length - _size < count)
                     {
-                        Grow(_size + count);
+                        Grow(checked(_size + count));
                     }
 
                     c.CopyTo(_items, _size);
@@ -787,7 +787,7 @@ public void InsertRange(int index, IEnumerable<T> collection)
                 {
                     if (_items.Length - _size < count)
                     {
-                        Grow(_size + count);
+                        Grow(checked(_size + count));
                     }
                     if (index < _size)
                     {