bug#19395: 25.0.50; Setting left fringe to 0 messes up window-width

[martin rudalics <rudalics@gmx.at>]

 >> You mean as far as the Emacs display engine is concerned, right?  But
 >> the caller of `face-font' doesn't know that the display engine operates
 >> on the current buffer regardless of whether it is displayed or not.
 >
 > She doesn't need to know: the effect doesn't depend on that.

If I want to right-adjust the last word of a buffer line I apparently
have to provide the buffer _and_ the frame in order to know how many
spaces to insert.

 >> What means "applied"?  Is it merged or does it replace the
 >> frame-specific face?
 >
 > It replaces the original frame-specific face.

IIUC this contradicts an earlier observation by Titus that

   if the buffer in the specified window is displayed in two frames,
   the returned character width was always the one used in the current
   frame which is not necessarily the character width in the specified
   window (the window may be in the other frame).  This is a problem
   because character width can be different, if the two frames use
   different default fonts.

martin