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

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

[Clément Pit--Claudel]

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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"))
  error("Changes to be undone by function different than announced")
  primitive-undo(1 ((apply -274 1289 9209 diff-context->unified 1289 9209) (apply -271 514 1289 diff-context->unified 514 1289) (#("---" 0 3 (fontified t face diff-header)) . 478) (481 . 484) (#("+++" 0 3 (fontified t face diff-header)) . 496) (t 22126 61486 433935 691000) (t 22126 61486 433935 691000) (499 . 502) (t 22126 61486 433935 691000)))
  undo-more(1)
  undo(nil)
  funcall-interactively(undo nil)
  call-interactively(undo nil nil)
  command-execute(undo)

Clément.

In GNU Emacs 25.1.50.7 (x86_64-pc-linux-gnu, GTK+ Version 3.18.9)
 of 2016-07-20 built on clem-w50-mint
Repository revision: a1a0c208e3e895a6ea0942e8e5c4077faf12c7ad
Windowing system distributor 'The X.Org Foundation', version 11.0.11803000
System Description:	Linux Mint 18 Sarah


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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)))))))))))


-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no