Re: Distinguish between regional undo and undo to the beginning in undo-equiv-table

[Yuan Fu]

> On Mar 5, 2021, at 10:57 AM, Stefan Monnier <monnier@iro.umontreal.ca> wrote:
> 
>>>> Then should we add a mapping for the buffer-undo-list to t at that
>>>> point?  Or should we just do nothing?
>>> Good question.  I think you have a better understanding of how the equiv
>>> table should be filled than I do at this point, so I'd trust your judgment.
>> Ok, I looked into it in detail, undo-equiv-table is also used to check if
>> the previous command is really an undo, alongside with checking
>> last-command.
> 
> Indeed [ tho, this test is not 100% reliable, because the hash-table is
> weak, so entries may disappear from it, leading to entries that used to
> map to non-nil suddenly mapping to nil.  ]

I think that’s fine. If the entry disappeared, that means either the key or the 
value is no longer in the undo list, no?

Yuan