Add additional shape information to basis evaluation.

Even if the basis scalar, it is worth to put a shape of (n, 1),
because that is how PDELab thinks about it. Not doing so can have
you end up with mismatches between `Dune::FieldVector<double, 1>` and `double`.

python/dune/perftool/pdelab/basis.py

@@ -92,7 +92,7 @@ def declare_cache_temporary(element, restriction, which):
 @kernel_cached
 def evaluate_basis(leaf_element, name, restriction):
     lfs = name_leaf_lfs(leaf_element, restriction)
-    temporary_variable(name, shape=(name_lfs_bound(lfs),), decl_method=declare_cache_temporary(leaf_element, restriction, 'Function'))
+    temporary_variable(name, shape=(name_lfs_bound(lfs), 1), decl_method=declare_cache_temporary(leaf_element, restriction, 'Function'))
     cache = name_localbasis_cache(leaf_element)
     qp = get_backend("qp_in_cell")(restriction)
     instruction(inames=get_backend("quad_inames")(),
@@ -113,7 +113,7 @@ def pymbolic_basis(leaf_element, restriction, number, context=''):
     evaluate_basis(leaf_element, name, restriction)
     iname, = lfs_inames(leaf_element, restriction, number, context=context)
 
-    return Subscript(Variable(name), (Variable(iname),))
+    return Subscript(Variable(name), (Variable(iname), 0))
 
 
 @backend(interface="evaluate_grad")
@@ -166,7 +166,7 @@ def evaluate_coefficient(visitor, element, name, container, restriction, index):
 
     lfs = name_lfs(element, restriction, index)
     basis = visitor.interface.pymbolic_basis(sub_element, restriction, 0, context='trial')
-    basisindex, = get_pymbolic_indices(basis)
+    basisindex, _ = get_pymbolic_indices(basis)
 
     if get_option("blockstructured"):
         from dune.perftool.blockstructured.argument import pymbolic_coefficient