chore: import upstream snapshot with attribution

test/cpp/compat/ATen_dense_sparse_conversion_test.cc

@@ -0,0 +1,61 @@
+// Copyright (c) 2026 PaddlePaddle Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <ATen/Functions.h>
+#include <ATen/core/TensorBody.h>
+#include <ATen/cuda/EmptyTensor.h>
+#include <ATen/native/cuda/Resize.h>
+#include <ATen/ops/tensor.h>
+#include <c10/core/Layout.h>
+#include <c10/core/ScalarType.h>
+#include <c10/core/TensorOptions.h>
+#if defined(PADDLE_WITH_CUDA) || defined(PADDLE_WITH_HIP)
+#include <c10/cuda/CUDAFunctions.h>
+#include <c10/cuda/CUDAGuard.h>
+#endif
+#include "ATen/ATen.h"
+#include "gtest/gtest.h"
+#include "paddle/phi/common/float16.h"
+#include "torch/all.h"
+#include "utils/dense_sparse_conversion.h"
+
+// ============================================================
+// Tests for compat::_PD_ConvertToSparseIfNeeded()
+// ============================================================
+
+// Helper: create a small 2-D dense float tensor.
+static paddle::Tensor make_dense_2d(int rows = 3, int cols = 3) {
+  // Use at::ones, but get the underlying paddle::Tensor.
+  at::Tensor t = at::ones({rows, cols}, at::kFloat);
+  return t._PD_GetInner();
+}
+
+// ---- kStrided -> dense (no conversion) ----
+
+TEST(DenseSparseConversionTest, kStrided_ReturnsDense) {
+  paddle::Tensor dense = make_dense_2d();
+  at::Tensor result = compat::_PD_ConvertToSparseIfNeeded(dense, c10::kStrided);
+
+  ASSERT_EQ(result.layout(), c10::kStrided);
+}
+
+// ---- unsupported layout throws ----
+
+TEST(DenseSparseConversionTest, UnsupportedLayout_Throws) {
+  paddle::Tensor dense = make_dense_2d();
+
+  // kSparseBsr is not handled in the switch => PD_CHECK(false, ...) fires.
+  ASSERT_THROW(compat::_PD_ConvertToSparseIfNeeded(dense, c10::kSparseBsr),
+               std::exception);
+}