Subject: Re: bug#23785: Emacs 25: 'Undo' overdoes things.

From: [email-masked] (Phillip Lord)
Date: Mon, 20 Jun 2016 13:47:59 +0100

Stefan Monnier <[email-masked]> writes:

>> The other fiddles with insert-file-contents and adds an undo. It is this
>> function that has specialized handling for the undo list that is causing
>> the problem. My patch in this case is questionable in that I have randomly
>> pushed a call to undo-boundary near the end. It should probably be
>> somewere better.
>
> Indeed, the problem is not that insert-file-contents fails to add
> a boundary, but rather that it removes an existing one, so we should
> figure out where/why it removes it and change the code to push one back
> after removing it.

I don't understand why you say this. AFAICT, the problem is that the
buffer-undo-list doesn't have a nil after the command has happened.

>> Another possibility would be to have insert-file-contents call
>> "undo-auto--undoable-change" -- this is the root cause of the problem.
>
> Figuring out why undo-auto--undoable-change isn't called for it would be
> good as well, indeed.  After all, it runs after-change-functions, so
> it should call undo-auto--undoable-change.

I think that it does -- it calls "insert_from_buffer" which then calls
"prepare_to_modify_buffer".

I *think* what is happening is that prepare_to_modify_buffer is being
called when buffer-undo-list is specbound to t -- hence the change does
not register as undoable change.

I am somewhat guessing here.

Phil