bug#5018: 23.1.50; Feature request: truncate-lines text property

[Eli Zaretskii <eliz@gnu.org>]

> From: Michael Brand <michael.ch.brand@gmail.com>
> Date: Sun, 4 Jun 2017 20:11:51 +0200
> 
> I would like to express my serious interest in this.

Would you like to work on implementing this feature?  I can provide
guidance if needed.

> I would like to add that this new feature would have to allow to a)
> truncate all lines, b) truncate only the lines with the new text
> property or c) not truncate any line.

I would propose to come up with an agreed set of requirements for the
feature.  The original request is quite vague and leaves a lot TBD.
For example:

  . is the override supposed to work in reverse, i.e. when the
    buffer-specific value of truncate-lines is non-nil, but the
    property's value is nil, is it expected that the line with the
    property will wrap instead of being truncated?
  . what text is supposed to have this property to mark the line as
    truncated, and how will Emacs know where the effect of the
    property ends?  e.g., will we require the property to be set on
    the entire line, including the newline, or will it be enough to
    set it only on part of the line?
  . should truncate-partial-width-windows obey this property as well?
  . when point moves along a line which is being truncated, and goes
    outside of the visible portion of the window, how do we want to
    hscroll the text in the window, in those parts that display lines
    which wrap?
  . should we also truncate if this property is on a display string or
    on an overlay string, or only if it's on buffer text?

Needless to say, the more we require from the feature, the harder it
will be to implement correctly.  We should choose wisely.