bug#15987: 24.3; diary-add-to-list ignored by diary-mark-entries

[Roland Winkler]

On Wed Aug 21 2019 Stephen Berman wrote:
> If diary-goto-entry-function is replaced, I'll adapt the todo-mode
> code as needed.

The goal is not to replace diary-goto-entry-function with something
else, but instead diary-goto-entry becomes extensible so that
diary-goto-entry-function is not needed anymore.

For this, can you modify todo-mode such that it will put a text
property diary-goto-entry on "its" diary entries?  The value of this
text property should be a list (FUNCTION ARG1 ARG2 ...)  where
FUNCTION will handle the diary entry of todo-mode when called with
args ARG1 ARG2 ... So diary-goto-entry can branch accordingly.