Re: pending-undo-list is not buffer local

[Lennart Borgman (gmail)]

martin rudalics wrote:
>  >      > I think for the reason above that it should be buffer local 
> and I also
>  >      > think that it should be permanent buffer local then.
>  >
>  >     I think this wouldn't make much sense since `buffer-undo-list' isn't
>  >     permanently buffer-local either.
>  >
>  > It is, practically speaking.  It is buffer-local, and changing major
>  > modes does not clear it out.
>
> Like `buffer-file-name'.  Would it make sense to introduce a variable,
> say `buffer-file-name-extension', assign its initial value from
> `buffer-file-name', make it a permanent buffer-local, and hope that the
> value of the new variable always correctly reflects the extension of
> `buffer-file-name' without any additional provisions?
>
> Various parts of Emacs manipulate `buffer-undo-list' in various ways.
> `revert-buffer' may reset it.  Some applications temporarily bind it to
> t to avoid, for example, recording text property changes.  Finally undo
> recording may be switched off.  Should `pending-undo-list' be affected
> by all these and how?

I actually assume that the logic around pending-undo-list is correct. 
That part will not break.

I am a bit worried that the wrong pending-undo-list will be used because 
of buffer switching, but not very much, since buffer-undo-list is buffer 
local and those two are used together. (It have to be tested of course.)