Re: master a7c65fc666: Allow nil value for filter-buffer-substring-function

[Robert Pluim]

>>>>> On Mon, 19 Sep 2022 16:37:04 -0400, Stefan Monnier 
>>>>> <monnier@iro.umontreal.ca> said:

    >> Ick. If `buffer-substring--filter' is the default function to call, it
    >> should not have the '--' internal function marker.

    Stefan> Why?  You're *not* supposed to call `buffer-substring--filter'.
    Stefan> Instead you're supposed to call the value contained in
    Stefan> `filter-buffer-substring-function`, whichever it is.  (and if you're
    Stefan> modifying this variable, then you're supposed to modify it with
    Stefan> `add-function` and your function will then receive the "previous"
    Stefan> function to call).

Itʼs not obvious to me that youʼre supposed to use `add-function'. And
even if it were, having '--' appear in the public api just feels
wrong. Oh well.

Robert
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