Fix, test set_arg with None argument

Closes gh-897

Author: inducer

src/wrap_cl_part_2.cpp

@@ -605,7 +605,10 @@ void pyopencl_expose_part_2(py::module_ &m)
                 { knl.set_arg_buf_pack(i, typechar, arg); },
                 indices_chars_and_args);
           })
-      .DEF_SIMPLE_METHOD(set_arg)
+      .def("set_arg", &cls::set_arg,
+          py::arg("arg_index"),
+          py::arg("arg").none(true)
+        )
 #if PYOPENCL_CL_VERSION >= 0x1020
       .DEF_SIMPLE_METHOD(get_arg_info)
 #endif

test/test_wrapper.py

@@ -1560,6 +1560,21 @@ def test_buffer_release(ctx_factory: cl.CtxFactory):
     b.release()
 
 
+def test_set_arg_none(ctx_factory: cl.CtxFactory):
+    # https://github.com/inducer/pyopencl/issues/897
+    ctx = ctx_factory()
+    prg = cl.Program(ctx, """
+    __kernel void sum(
+       __global const float *a_g, __global const float *b_g, __global float *res_g)
+    {
+     int gid = get_global_id(0);
+     res_g[gid] = a_g[gid] + b_g[gid];
+    }
+    """).build()
+
+    prg.sum.set_arg(0, None)
+
+
 if __name__ == "__main__":
     import sys
     if len(sys.argv) > 1: