bug#28844: 26.0.90; display-line-numbers-mode should call window-configuration-change-hook

[martin rudalics <rudalics@gmx.at>]

 >> ‘window-configuration-change-hook’ is still run way too often, for
 >> example, when windows get resized.  ‘window-size-change-functions’ might
 >> be better.  But if you need such a hook, wouldn't you also need it when
 >> line numbers occupy more or less columns, for example, during scrolling?
 >>
 >> Otherwise, why can't you use ‘display-line-numbers-mode-hook’?
 >

 > Thanks for pointing me to display-line-numbers-mode-hook, but I’ve
 > found that it’s not enough to just check when the mode is enabled. We
 > need to alert other concerned modes whenever display-line-numbers-mode
 > changes the margins, e.g. due to scrolling from line 99 to 100 (which
 > will increase the width from 2 to 3).

That's what I meant when I said that

   "if you need such a hook, wouldn't you also need it when line numbers
   occupy more or less columns, for example, during scrolling?"

You could use ‘window-scroll-functions’ (remembering the old line number
widths) for scrolling but this would not handle simple point movements.

Eli will decide what to do.  If an existing hook must be chosen, I'd
rather (mis-)use ‘window-size-change-functions’ - strictly spoken,
display of line numbers never affects the size of windows (something
which is not true vice-versa IIUC).  But better, provide a separate hook
like ‘line-number-width-changed-functions’ with the corresponding window
as argument (and maybe the old line number width as second).

martin