Re: Problems with move_it_in_display_line_to X when tabs exist.

[Eli Zaretskii <eliz@gnu.org>]

> Date: Tue, 28 Nov 2017 22:12:35 -0800
> From: Keith David Bershatsky <esq@lawlist.com>
> 
> I can see that X and/or HPOS are wrong when tabs are present on the current line because I get superimposed letters and double of the same word slightly off to the left and/or the right of where the word should be.
> 
> HYPOTHESIS:  I would venture to say that what is displayed on screen does _not_ coincide with what IT reports when running move_it_in_display_line_to.

Does this happen only when line numbers are displayed?

In any case, your description provides a lot of details that are hard
to reason about, because most of the code is not shown.  OTOH, if
indeed there's a bug in move_it_in_display_line_to, then presenting
evidence for it is very simple: show a line of text and its line
number, and then show the X and HPOS values for each tab in that line
as calculated by move_it_in_display_line_to vs the same values in a
displayed line.  (For the latter, you can use the pgrowx command
defined in src/.gdbinit, or manually display the values using the
debugger.)

If you do that, any mismatches between displaying a line and moving
through it with move_it_in_display_line_to will be immediately
apparent, and it should be easy to fix them.