[error] Throw proper error message when an Ndarray is passed in via t…

…i.template (#5457)

ti.types.ndarray itself is a template type so let's throw a better error
message when users misuse it.

python/taichi/lang/kernel_impl.py

@@ -335,6 +335,10 @@ def extract_arg(arg, anno):
                 return tuple(
                     TaichiCallableTemplateMapper.extract_arg(item, anno)
                     for item in arg)
+            if isinstance(arg, taichi.lang._ndarray.Ndarray):
+                raise TaichiRuntimeTypeError(
+                    'Ndarray shouldn\'t be passed in via `ti.template()`, please annotate your kernel using `ti.types.ndarray(...)` instead'
+                )
             return arg
         if isinstance(anno, texture_type.TextureType):
             return '#'

tests/python/test_ndarray.py

@@ -660,3 +660,17 @@ def func(a: ti.types.ndarray()):
             for k in range(2):
                 for p in range(2):
                     assert a2[i, j][k, p] == k * k
+
+
+@test_utils.test(arch=supported_archs_taichi_ndarray)
+def test_ndarray_as_template():
+    @ti.kernel
+    def func(arr_src: ti.template(), arr_dst: ti.template()):
+        for i, j in ti.ndrange(*arr_src.shape):
+            arr_dst[i, j] = arr_src[i, j]
+
+    arr_0 = ti.ndarray(ti.f32, shape=(5, 10))
+    arr_1 = ti.ndarray(ti.f32, shape=(5, 10))
+    with pytest.raises(ti.TaichiRuntimeTypeError,
+                       match=r"Ndarray shouldn't be passed in via"):
+        func(arr_0, arr_1)