We get the f1 from args if it's merge and check that whether that exists in
sparse checkout or not. If that does not, we add that for merging.
The error comes from very low-level where we try to read data of a
working-filectx which does not exists in the working directory. It will be
extremely ugly to plug in logic to update sparse copy with new file at such a
We already have logic related to updating the checkout with required files in
calculateupdates() and let's handle this case there only. calculateupdates()
call sparse.filterupdatesactions() and the logic is added into the latter
To get the exact traceback, this patch can be backed out and
test-sparse-merges.t can be run with ui.traceback=True.