bug#25408: Remove Decorations Around Emacs Frame (Windows OS)

[martin rudalics]

> What happens when the line is full-width, i.e. the last character is
> flushed all the way to the right edge of the window?

Tested with normal continuation lines, truncated line and visual line
mode and all sorts of window widths.  No problems.

> What happens
> when you set wrap-prefix to some string value and then turn on
> visual-line-mode in a buffer with lines longer than the window width?

No special problems found but for one: If the window is narrower than
the wrap-prefix, Emacs may hang with all processor cycles it can get.
But this is easily reproducible here without setting the new parameter.

I use the following recipe: With emacs -Q I evaluate

(let ((frame (make-frame)))
  (find-file-noselect "dnd.el")
  (set-window-buffer (frame-root-window frame) "dnd.el")
  (with-current-buffer (window-buffer (frame-root-window frame))
    (setq wrap-prefix "-------------")
    (visual-line-mode 1)))

Then I make the new frame as narrow as possible by dragging one of its
borders with the mouse.  Now alternatively using (1) <down> to move the
cursor towards the end of the buffer _and_ (2) <wheel-down> to scroll
the buffer end out of view sooner or later hangs my Emacs 25.2 here.

>> Also, IIUC Clément has no intention to make such buffers scrollable,
>> editable or focusable.  So if necessary we can also forbid such actions.
>
> ??? This is a general-purpose feature, not something created for a
> single use case.  And I don't quite see how you can forbid cursor
> motion without also forbidding a lot of other useful features.

We could treat such frames like tooltip frames.  But I currently see no
need for such harsh measures.

martin