  We attempt a clarification of geometric aspects of quantum field theory by
using the notion of smoothness introduced by Fr\"olicher and exploited by
several authors in the study of functional bundles. A discussion of momentum
and position representations in curved spacetime, in terms of generalized
semi-densities, leads to a definition of quantum configuration bundle which is
suitable for a treatment of that kind. A consistent approach to Lagrangian
field theories, vertical infinitesimal symmetries and related currents is then
developed, and applied to a formulation of BRST symmetry in a gauge theory of
the Yang-Mills type.
