Columns and proportional fonts (was: bug#19872: 24.4; UTF8 characters of unusual width (Gnus markers))

[Stefan Monnier]

> I agree in general, but cannot see why this particular case couldn't
> be resolved reasonably well, e.g. by adding one more column "just in
> case", before the :align-to property.

In mpc.el I list the current songs with various of their info (duration,
title, artist, ...) in columns, so I have the same problem there.

I use truncate-string-to-width and do keep one extra column, but it's
not always sufficient to avoid misalignment when the proportional font
has some "very wide" chars.  Also, I suffer from the reverse problem,
that for columns where the text contains lots of narrow chars,
truncate-string-to-width ends up being pessimistic, which is less
harmful but wastes valuable screen estate and looks weird.

My understanding of the redisplay engine makes me believe that
a `:truncate-at' display property (and/or
a combined :truncate-at-or-align-to) should be doable with good
efficiency without too much extra gymnastics.
And no, sorry, I'm not volunteering to implement it.


        Stefan