Bug: org-link-descriptive needs to be buffer-local [9.4.4 (release_9.4.4 @ /usr/local/share/emacs/28.0.50/lisp/org/)]

[Ingo Lohmar]

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I stumbled upon weird behavior when using `org-toggle-link-display', and
I finally checked what that is about.

Observation:
- use `org-toggle-link-display' in org buffer A, and (coming
  from the defaults) links are now shown in full (not just the
  description), but only in buffer A
- switch to org buffer B, still only showing the description part, and
  again use `o-t-l-d' --- nothing changes
- the state for new org buffers is as before, onle link descriptions are
  shown.

This behavior is very confusing, IMO.  The reason is simple.  The
display hiding comes from changing the `buffer-invisibility-spec', which
is automatically buffer-local.  But the state of the org toggle is kept
in `org-link-descriptive', which is global!

I suggest a simple fix that I just tested: make `org-link-descriptive'
automatically buffer-local, by adding ":local t" to the defcustom.

NB: This also fixes a related bug that

    eval: (org-toggle-link-display)

in the file-local works properly --- it did not work for me before.

Thanks.


Emacs  : GNU Emacs 28.0.50 (build 5, x86_64-pc-linux-gnu, GTK+ Version 3.24.24, 
cairo version 1.16.0)
 of 2021-03-27
Package: Org mode version 9.4.4 (release_9.4.4 @ 
/usr/local/share/emacs/28.0.50/lisp/org/)