For Excorporate's diary integration I had to add some advice to work
around the side effects of a diary-make-entry workaround in
icalendar--add-diary-entry, and side effects of diary-make-entry itself.
I'm filing this bug report to try to eliminate the need for any of these
workarounds.

diary-make-entry adds a trailing space to its entry.
icalendar--add-diary-entry works around this by deleting the trailing
space.  It saves the window excursion, but diary-make-entry still leaves
the diary file where (other-buffer (current-buffer)) will return it,
which is a usability bug.

The attached patch, icalendar-diary-make-entry-fix-1.patch, adds
omit-trailing-space and do-not-show parameters to diary-make-entry to
allow it to operate more like a library function and less like an
interactive function.

To keep the code mostly the same (so that I don't need to factor out
another function), I've changed the original logic by adding a
with-current-buffer wrapper, as shown in simplified form in
diary-make-entry-with-current-buffer.patch.  I'm hoping this keeps the
default diary-make-entry logic exactly the same, but I'd like
confirmation from someone more familiar with the subtleties of window
and buffer manipulation.

Thanks,
Thomas