[C++] Add regression test for SparseCSFIndex::Equals segfault

Author: Alirana2829

cpp/src/arrow/sparse_tensor_test.cc

@@ -1676,4 +1676,29 @@ TEST(TestSparseCSFMatrixForUInt64Index, Make) {
   ASSERT_RAISES(Invalid, SparseCSFTensor::Make(dense_tensor, uint64()));
 }
 
+TEST(TestSparseCSFIndex, EqualsMismatchedDimensions) {
+  std::vector<int64_t> axis_order_4d = {0, 1, 2, 3};
+  std::vector<int64_t> axis_order_2d = {0, 1};
+
+  // Create empty tensors for indptr/indices
+  auto empty_buffer = std::make_shared<Buffer>(nullptr, 0);
+  auto tensor_4d = std::make_shared<Tensor>(int32(), empty_buffer, std::vector<int64_t>{0});
+  auto tensor_2d = std::make_shared<Tensor>(int32(), empty_buffer, std::vector<int64_t>{0});
+
+  // Create a 4D index
+  std::vector<std::shared_ptr<Tensor>> indptr_4d = {tensor_4d, tensor_4d, tensor_4d};
+  std::vector<std::shared_ptr<Tensor>> indices_4d = {tensor_4d, tensor_4d, tensor_4d, tensor_4d};
+  auto si_4d = std::make_shared<SparseCSFIndex>(indptr_4d, indices_4d, axis_order_4d);
+
+  // Create a 2D index
+  std::vector<std::shared_ptr<Tensor>> indptr_2d = {tensor_2d};
+  std::vector<std::shared_ptr<Tensor>> indices_2d = {tensor_2d, tensor_2d};
+  auto si_2d = std::make_shared<SparseCSFIndex>(indptr_2d, indices_2d, axis_order_2d);
+
+  // Before fix: This would segfault.
+  // After fix: Returns false safely.
+  ASSERT_FALSE(si_4d->Equals(*si_2d));
+  ASSERT_FALSE(si_2d->Equals(*si_4d));
+}
+
 }  // namespace arrow