time-dependent functions with time stepping schemes other than implicit Euler
GetDP automatically handles time-dependent constraints when they are provided using the TimeFunction mechanism in an Assign-type Constraint.
However, GetDP cannot automatically transform general time-dependent source terms in weak formulations. Such source terms will be correctly treated only for implicit Euler, as the expression in the Galerkin term is evaluated at the current time step.
For other schemes, the source term should be written explicitly, by splitting it in two (theta f_n+1 + (1-theta) f_n), making use of the AtAnteriorTimeStep for the second part, and specifying NeverDt in the Galerkin term.