Handle cval as a np attr in stencil generation.

As title.

Fixes numba#7286

numba/stencils/stencil.py

@@ -585,6 +585,11 @@ def _stencil_wrapper(self, result, sigret, return_type, typemap, calltypes, *arg
         # If we have to allocate the output array (the out argument was not used)
         # then us numpy.full if the user specified a cval stencil decorator option
         # or np.zeros if they didn't to allocate the array.
+        def cval_as_str(cval):
+            if getattr(np, str(cval), False) is cval:
+                return f"np.{cval}"
+            else:
+                return str(cval)
         if result is None:
             return_type_name = numpy_support.as_dtype(
                                return_type.dtype).type.__name__
@@ -594,7 +599,8 @@ def _stencil_wrapper(self, result, sigret, return_type, typemap, calltypes, *arg
                     raise ValueError(
                         "cval type does not match stencil return type.")
                 out_init ="{} = np.full({}, {}, dtype=np.{})\n".format(
-                            out_name, shape_name, cval, return_type_name)
+                            out_name, shape_name, cval_as_str(cval),
+                            return_type_name)
             else:
                 out_init ="{} = np.zeros({}, dtype=np.{})\n".format(
                             out_name, shape_name, return_type_name)
@@ -606,7 +612,7 @@ def _stencil_wrapper(self, result, sigret, return_type, typemap, calltypes, *arg
                 if not self._typingctx.can_convert(cval_ty, return_type.dtype):
                     msg = "cval type does not match stencil return type."
                     raise ValueError(msg)
-                out_init = "{}[:] = {}\n".format(out_name, cval)
+                out_init = "{}[:] = {}\n".format(out_name, cval_as_str(cval))
                 func_text += "    " + out_init
 
         offset = 1

numba/tests/test_stencils.py

@@ -611,6 +611,34 @@ def wrapped():
             else:
                 raise AssertionError("Expected error was not raised")
 
+    @skip_unsupported
+    def test_out_kwarg_w_cval_np_attr(self):
+        """ Tests issue #7286 where cval is an attr on the np module"""
+        def kernel(a):
+            return (a[0, 0] - a[1, 0])
+
+        stencil_fn = numba.stencil(kernel, cval=np.inf)
+
+        def wrapped():
+            A = np.arange(12.).reshape((3, 4))
+            ret = np.ones_like(A)
+            stencil_fn(A, out=ret)
+            return ret
+
+        # stencil function case
+        A = np.arange(12.).reshape((3, 4))
+        expected = np.full_like(A, -4)
+        expected[-1, :] = np.inf
+        ret = np.ones_like(A)
+        stencil_fn(A, out=ret)
+        np.testing.assert_almost_equal(ret, expected)
+
+        # wrapped function case, check njit, then njit(parallel=True)
+        impls = self.compile_all(wrapped,)
+        for impl in impls:
+            got = impl.entry_point()
+            np.testing.assert_almost_equal(got, expected)
+
 
 class pyStencilGenerator:
     """
@@ -2795,5 +2823,14 @@ def kernel(a):
         a = np.arange(20, dtype=np.uint32).reshape(4, 5)
         self.check(kernel, a)
 
+    def test_basic98(self):
+        """ Test issue #7286 where the cval is a np attr"""
+        def kernel(a):
+            return a[0, 0]
+        a = np.arange(6.).reshape((2, 3))
+        self.check(kernel, a, options={'neighborhood': ((-1, 1), (-1, 1),),
+                   'cval':np.nan})
+
+
 if __name__ == "__main__":
     unittest.main()