api: fix evaluation with different time dims

devito/types/basic.py

@@ -762,7 +762,7 @@ def __new__(cls, *args, **kwargs):
         # Initialization. The following attributes must be available
         # when executing __init_finalize__
         newobj._name = name
-        newobj._dimensions = dimensions
+        newobj._dimensions = DimensionTuple(*dimensions, getters=dimensions)
         newobj._shape = cls.__shape_setup__(**kwargs)
         newobj._dtype = cls.__dtype_setup__(**kwargs)
 

devito/types/dense.py

@@ -1128,7 +1128,8 @@ def _eval_at(self, func):
         for d in self.dimensions:
             try:
                 if self.indices_ref[d] is not func.indices_ref[d]:
-                    mapper[self.indices_ref[d]] = func.indices_ref[d]
+                    f_idx = func.indices_ref[d]._subs(func.dimensions[d], d)
+                    mapper[self.indices_ref[d]] = f_idx
             except KeyError:
                 pass
 

tests/test_staggered_utils.py

@@ -187,3 +187,16 @@ def test_staggered_rebuild(stagg):
             assert f2.indices[nd] == nd + nd.spacing / 2
         else:
             assert f2.indices[nd] == nd
+
+
+def test_eval_at_different_dim():
+    grid = Grid(shape=(31, 17, 25))
+    nt = 5
+    x, _, _ = grid.dimensions
+
+    v = TimeFunction(name="v", grid=grid, staggered=x)
+    tau = TimeFunction(name="tau", grid=grid, save=nt)
+
+    eq = Eq(tau.forward, v).evaluate
+
+    assert grid.time_dim not in eq.rhs.free_symbols