Re: Changing of line format and undo

[Lennart Borgman <lennart.borgman.073@student.lu.se>]

Stuart D. Herring wrote:
> Lennart Borgman wrote:
>   
>> Eli Zaretskii wrote:
>>     
>>> If you mean "C-x RET f", then it doesn't really change anything.  It
>>> just sets a buffer-local variable to some value.  So there's nothing
>>> to undo.
>>>
>>>       
>> That is an internal Emacs perpective. From a users point of view there
>> is truly a change. If you for example change the line endings the file
>> will be saved with this new line endings.
>>     
>
> Doing
>
> (add-hook 'local-write-file-functions 'erase-buffer)
>
> also would change how files were written out.  Changing how Emacs works
> (via variables like the coding systems, hooks, or outright rewriting
> functions) is not within the scope of the undo mechanism, which is for
> modifications to text, not Emacs.
>   
I would say that the line endings is a border case. I would expect most 
users to look like it like changing the text (even if that is not what 
is done internally). However I realize it is a lot of work to fix this 
border case and it is perhaps not worth the trouble.
>   
>> BTW should not changes of this kind also set the buffer to modified?
>>     
>
> If and only if they should be undoable (which they shouldn't, IMHO).  It
> would be very odd to have a buffer unmodified before and after an undo, or
> to be marked modified with no way (via undo) to remove that marking.
>   
My mistake. As David pointed out the buffer is marked modified if you 
change the line endings in a supported way. It is natural to make the 
buffer modified since perhaps it will not get saved otherwise. 
Unfortunately this change is not undoable and that is a bit confusing 
sometimes.