bug#71085: text-scale-adjust does not adjust margin width

[Emre Yolcu <mail@emreyolcu.com>]

> I don't see a need for it, sorry.
Got it. Thanks for discussing it anyway. I don't want to keep the thread  
going for too long, but I want to reply to some of your comments and leave  
it at that. (Maybe the discussion will be useful in the future, on the off  
chance that the issue gets revisited.)

>>> I don't understand the expectations: the window and frame geometry are
>>> not changed by text-scale-adjust, so why did you expect the window
>>> margins to change?  The margins are part of the window geometry.
>> I was not thinking of the margins as part of the window geometry but as
>> a special part of the buffer that we set aside and do not interact with.
>
> Well, but the fact is the margins _are_ part of the window geometry.
> And window geometry doesn't change when text size is scaled.  So this
> is a de-facto behavior Emacs had for several releases now, and we must
> preserve it.
FWIW, some wording in the Emacs manual suggests, at least for me, the  
interpretation that margins are to be viewed as part of the buffer. From  
Section 41.16.5: "A buffer can have blank areas called display margins on  
the left and on the right. Ordinary text never appears in these areas,  
..." On the other hand, the function for setting margin widths is called  
"set-window-margins".

>> A much nicer workaround would be possible if there
>> existed a "margin" face: text-scale-mode could simply remap it as it
>> does the default face.
>
> Actually, you want a face that will _not_ be remapped, since you want
> to make sure the text in the margins will not get clipped.  The
> current behavior is that by default the text in the margin is already
> remapped, which is why it can get clipped if it becomes too wide.
By remap here I mean that it will remap the margin face *back* to the  
original height. The current behavior does not explicitly touch (remap)  
the text in the margin, so the height gets determined by the buffer-local  
height of the default face. If enabled, the option would make  
text-scale-mode remap the margin face back to the original height to  
prevent the text from getting clipped.