api: Fix deprecation of symbolic coeffs

devito/deprecations.py

@@ -11,5 +11,12 @@ def coeff_warn(self):
              DeprecationWarning, stacklevel=2)
         return
 
+    @cached_property
+    def symbolic_warn(self):
+        warn("coefficients='symbolic' is deprecated, coefficients should"
+             "be passed directly to the derivative object `u.dx(weights=...)",
+             DeprecationWarning, stacklevel=2)
+        return
+
 
 deprecations = DevitoDeprecation()

devito/types/dense.py

@@ -12,6 +12,7 @@
 from devito.data import (DOMAIN, OWNED, HALO, NOPAD, FULL, LEFT, CENTER, RIGHT,
                          Data, default_allocator)
 from devito.data.allocators import DataReference
+from devito.deprecations import deprecations
 from devito.exceptions import InvalidArgument
 from devito.logger import debug, warning
 from devito.mpi import MPI
@@ -73,10 +74,7 @@ def __init_finalize__(self, *args, function=None, **kwargs):
         super().__init_finalize__(*args, **kwargs)
 
         # Symbolic (finite difference) coefficients
-        self._coefficients = kwargs.get('coefficients', self._default_fd)
-        if self._coefficients not in fd_weights_registry:
-            raise ValueError("coefficients must be one of %s"
-                             " not %s" % (str(fd_weights_registry), self._coefficients))
+        self._coefficients = self.__coefficients_setup__(**kwargs)
 
         # Data-related properties
         self._data = None
@@ -169,6 +167,19 @@ def __dtype_setup__(cls, **kwargs):
         else:
             return np.float32
 
+    def __coefficients_setup__(self, **kwargs):
+        """
+        Setup finite-differences coefficients mode
+        """
+        coeffs = kwargs.get('coefficients', self._default_fd)
+        if coeffs not in fd_weights_registry:
+            if coeffs == 'symbolic':
+                deprecations.symbolic_warn
+            else:
+                raise ValueError("coefficients must be one of %s"
+                                 " not %s" % (str(fd_weights_registry), coeffs))
+        return coeffs
+
     def __staggered_setup__(self, **kwargs):
         """
         Setup staggering-related metadata. This method assigns:

tests/test_symbolic_coefficients.py

@@ -25,7 +25,7 @@ class TestSC:
     def test_coefficients(self, expr, sorder, dorder, dim, weights, expected):
         """Test that custom coefficients return the expected result"""
         grid = Grid(shape=(10, 10))
-        u = Function(name='u', grid=grid, space_order=sorder)
+        u = Function(name='u', grid=grid, space_order=sorder, coefficients='symbolic')
         x, y = grid.dimensions
         h_x, h_y = grid.spacing_symbols  # noqa