bug#44647: 27.1.50; `bibtex-contline-indentation' doesn't work as file local variable

[Roland Winkler]

On Mon Nov 16 2020 Teemu Likonen wrote:
> > Your patch implies that the buffer-local value of fill-prefix is not
> > what it should be (say, if any other command wants to use it).
> 
> Yes. Bibtex-mode's filling uses fill-prefix and that variable must
> be set to correct value before filling. The correct moment may not
> be when a bibtex-mode buffer is initialized with buffer-local
> values.

Defcustom supports the keyword :set that can handle the case when a
user variable such as bibtex-contline-indentation is changed which
implies updating another variable such as fill-prefix.  However, I
assume that this is a rather rare case in the present context.

On the other hand, it is a design principle of emacs that variables
such as fill-prefix can be and are used by different commands.  So
they should have their proper value instead of only let-binding them
on the fly.  Such let-bindings are used only when it is the intent
to use different values than the proper buffer-local values.