Supplying a mix of "on_boundary" and integer subdomain DirichletBCs

[andreasbock]

I have inherited DirichletBC to set certain Discontinuous Lagrange Trace variables to zero on the interior mesh according to my variational problem. In this connection I have discovered a bug in line 490 of firedrake/firedrake/functionspacedata.py. I am providing a list of DirichletBCs objects e.g.:

bcs = [DirichletBC(V, val, "on_boundary"), MyCustomDirichletBC(V, val, dummy_domain, my_custom_params)

to the solve(a == L, bcs=bcs) interface leads to a

TypeError: '<' not supported between instances of 'tuple' and 'str'.

Only the self.nodes of my MyCustomDirichletBC is actually used, not the dummy_domain.

[wence-]

FWIW, very late to the party, this was fixed in #1418.