[Zero-Dim]Unsqueeze support 0d tensor (#49862)

* add unsqueeze test case

* add unsqueeze xpu test case

* fix unsqueeze test case

* fix unsqueeze test case

* fix unsqueeze test case

* fix unsqueeze test case

* add retain_grads

python/paddle/fluid/tests/unittests/test_zero_dim_tensor.py

@@ -1345,6 +1345,23 @@ class TestSundryAPI(unittest.TestCase):
         self.assertEqual(x.grad.shape, [])
         self.assertEqual(x.grad.numpy(), 1)
 
+    def test_unsqueeze(self):
+        x1 = paddle.full([], 2)
+        x1.stop_gradient = False
+        x1.retain_grads()
+        out1 = paddle.unsqueeze(x1, axis=0)
+        out1.retain_grads()
+        out1.backward()
+        self.assertEqual(out1.shape, [1])
+        self.assertEqual(x1.grad.shape, [])
+
+        x2 = paddle.full([], 0, dtype='int32')
+        out2 = paddle.unsqueeze(x1, axis=x2)
+        out2.retain_grads()
+        out2.backward()
+        self.assertEqual(out2.shape, [1])
+        self.assertEqual(x1.grad.shape, [])
+
     def test_t(self):
         x = paddle.full([], 2.0)
         x.stop_gradient = False
@@ -2091,6 +2108,34 @@ class TestSundryAPIStatic(unittest.TestCase):
         self.assertEqual(res[3].shape, ())
         self.assertEqual(res[3], 1)
 
+    @prog_scope()
+    def test_unsqueeze(self):
+        x1 = paddle.full([], 2)
+        out1 = paddle.unsqueeze(x1, axis=0)
+        x1.stop_gradient = False
+        paddle.static.append_backward(out1.sum())
+
+        x2 = paddle.full([], 3)
+        x3 = paddle.full([], 0, dtype='int32')
+        x2.stop_gradient = False
+        out2 = paddle.unsqueeze(x2, axis=x3)
+        paddle.static.append_backward(out2.sum())
+
+        prog = paddle.static.default_main_program()
+        res = self.exe.run(
+            prog,
+            fetch_list=[
+                out1,
+                out2,
+                x1.grad_name,
+                x2.grad_name,
+            ],
+        )
+        self.assertEqual(res[0].shape, (1,))
+        self.assertEqual(res[1].shape, (1,))
+        self.assertEqual(res[2].shape, ())
+        self.assertEqual(res[3].shape, ())
+
     @prog_scope()
     def test_t(self):
         x = paddle.full([], 2.0)

python/paddle/fluid/tests/unittests/xpu/test_zero_dim_tensor_xpu.py

@@ -824,6 +824,19 @@ class TestSundryAPI(unittest.TestCase):
         self.assertEqual(x.grad.shape, [])
         self.assertEqual(x.grad.numpy(), 1)
 
+    def test_unsqueeze(self):
+        x1 = paddle.full([], 2)
+        x1.stop_gradient = False
+        out1 = paddle.unsqueeze(x1, axis=0)
+        out1.backward()
+        self.assertEqual(out1.shape, [1])
+        self.assertEqual(x1.grad.shape, [])
+
+        x2 = paddle.full([], 0, dtype='int32')
+        out2 = paddle.unsqueeze(x1, axis=x2)
+        out2.backward()
+        self.assertEqual(out2.shape, [1])
+
 
 # Use to test API whose zero-dim input tensors don't have grad and not need to test backward in OpTest.