bug#44232: global-display-fill-column-indicator-mode vs. readonly buffers

[Lars Ingebrigtsen <larsi@gnus.org>]

Eli Zaretskii <eliz@gnu.org> writes:

> As for the specific suggestion: it sounds somewhat kludgey to me.  Why
> not take the Emacsy way: add a defcustom that lists major modes whose
> users are unlikely to want this mode turned on, and let the default
> value include the modes you think belong to that group.

Is this how other globalized minor modes work?  I tried poking around
but couldn't really see any patterns...

But here's one that works along this way:

---
highlight-changes-global-modes is a variable defined in ‘hilit-chg.el’.
Its value is t

  You can customize this variable.

Documentation:
Determine whether a buffer is suitable for global Highlight Changes mode.

A function means call that function to decide: if it returns non-nil,
the buffer is suitable.

A list means the elements are major modes suitable for Highlight
Changes mode, or a list whose first element is ‘not’ followed by major
modes which are not suitable.

A value of t means the buffer is suitable if it is visiting a file and
its name does not begin with ‘ ’ or ‘*’.

A value of nil means no buffers are suitable for ‘global-highlight-changes-mode’
(effectively disabling the mode).

Example:
	(c-mode c++-mode)
means that Highlight Changes mode is turned on for buffers in C and C++
modes only.
---

So it's a complex

(c-mode (not text-mode) ...)

kind of thing that sounds like it could be generalised for globalized
minor modes.  (Although I'd say use derived-mode-p instead of eq to
check.)

-- 
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   bloggy blog: http://lars.ingebrigtsen.no