Re: Problems with move_it_in_display_line_to X when tabs exist.

[Eli Zaretskii <eliz@gnu.org>]

> Date:  Sat, 02 Dec 2017 11:52:33 -0800
> From:  Keith David Bershatsky <esq@lawlist.com>
> Cc:  emacs-devel@gnu.org
> 
> The test assumes:
> 
> * The variable word-wrap is non-nil.
> 
> * The variable tab-width is 2.
> 
> * The buffer-display table entry for a tab is:  [(187 . 120) (9 . 121)].
> 
> * Native line numbers are _not_ enabled.
> 
> I have a long line that wraps at the window edge and I put a space to simulate a new word that should be wrapped to the following line.  To make it easier to read, I am using the backslash symbol (below) to signify a word-wrap with a space at the window edge.  The next line has three "x" followed by a tab and then the word "hello-world".  The STRETCH glyph is 22 pixels wide; however, it.pixel_width is erroneously (?) reporting that it is 11 pixels wide.
> 
> I have hard-coded an emacs_abort () when it.c == '\t', which means that we have just moved passed character 187 (aka "»") and we are now on a STRETCH tab-width.

What is the value of it.what and of it.char_to_display?  And what is
the value of it.method and it.current_x?

My crystal ball says that, since your display table shows a TAB as 2
characters, the first of which is a u+00bb, and is displayed as an
11-pixel glyph, that is the display element whose metrics you are
seeing.  The stretch glyph produced by the TAB from the display table
is after that.