This method is only available on newer versions.
The first available version (v2_6_3) is shown here.
possibilities()
public
(see Bundler::Molinillo::ResolutionState#possibilities)
# File lib/bundler/vendor/molinillo/lib/molinillo/delegates/resolution_state.rb, line 33
def possibilities
current_state = state || Bundler::Molinillo::ResolutionState.empty
current_state.possibilities
end