bug#24556: 25.1.50; Undo partially broken in patch mode

[Lars Ingebrigtsen]

Clément Pit--Claudel <clement.pitclaudel@live.com> writes:

> Recipe in emacs -Q:
>
> * Open a patch or diff file
> * Press C-c C-d [diff-unified->context]
> * Press C-_ [undo]
>
> Undo fails with the following backtrace:
>
> Debugger entered--Lisp error: (error "Changes to be undone by function 
> different than announced")
>   signal(error ("Changes to be undone by function different than announced"))

I can confirm that this is still the case.

This code in diff-unified->context certainly looks like a likely culprit:

                (unless (or (not reversible) (eq buffer-undo-list t))
                  ;; Drop the many undo entries and replace them with
                  ;; a single entry that uses diff-context->unified to do
                  ;; the work.
                  (setq buffer-undo-list
                        (cons (list 'apply (- old-end end) start (point-max)
                                    'diff-context->unified start (point-max))
                              old-undo)))))))))))


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