bug#48269: 27.1: log-edit-generate-changelog-from-diff FAILURE

[Boruch Baum]

GNU Emacs 27.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.24,
cairo version 1.16.0) of 2021-03-27, modified by Debian

ref: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=47784#45

1] Attempting to run function log-edit-generate-changelog-from-diff
   returns an error message: 'Diff functionality has not been setup.'

2] The docstring for function log-edit-generate-changelog-from-diff
   gives no indication how to set up 'diff functionality' or otherwise
   guidance on how to use the function.

3] The source of the error message is function log-edit-show-diff. It,
   too, lacks a useful docstring.

4] The code in function log-edit-show-diff indicates that the
   configuration is performed via variable log-edit-diff-function.
   However:

   4.1] That variable lacks a docstring.

   4.2] Setting it to a 'reasonable' value of 'ediff returns an error
        (wrong-number-of-arguments (2 . 3) 0)

At this point, I stopped chasing down the issue. Counting three
documentation issues, one default configuration bug. If I'm the first
end-user world-wide trying to use this, do I get a valuable prize?

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