bug#56357: Request for font size adaptation that fits window

[Eli Zaretskii <eliz@gnu.org>]

> Cc: 56357@debbugs.gnu.org
> From: Lars Ingebrigtsen <larsi@gnus.org>
> Date: Mon, 04 Jul 2022 13:01:20 +0200
> 
> carlmarcos@tutanota.com writes:
> 
> > Suppose a user uses a 13 pt font size.  Let there be some space
> > between the longest line in the buffer and the edge of the window.  It
> > would be super if the font size could be automatically increased, such
> > that the difference between the longest line and the window size in
> > minimised.
> 
> I think that sounds like a useful feature, and I'm kinda surprised that
> it doesn't exist yet.  Or does it?  Anybody know?
> 
> To implement this, I guess the obvious thing would be to have a global
> minor mode that'd listen to frame size changes, and then adjust the font
> size up/down to reach the desired number of characters in a frame?  So
> we'd have a user option font-size-adjust-target (defaulting to 80)
> and a font-size-adjust-mode?

That's not what the feature request asked for, AFAIU: it wanted
dynamic resizing, and it wanted the size to depend on the "longest
line" (not clear if "longest in the window" or "longest in the
buffer").

With your proposal, how would you determine the target value?  If it's
just an arbitrary value (80 sounds like an arbitrary one to me), then
the recently-added global-text-scale-adjust-resizes-frames variable
does the same, just from the other end: the user enlarges the font and
the frame follows suit.  And since our default frame width is already
set for 80 characters, it sounds like we already have the feature you
envisioned, no?