Re: [Patch]: Allow overlay arrows to be inserted before the text at column zero rather than splatting it.

[Eli Zaretskii]

> Date: Sun, 18 Aug 2019 13:48:04 +0000
> From: Alan Mackenzie <address@hidden>
> 
> Currently, when there are no fringes, inserting an overlay arrow
> overwrites the first two characters on the pertinent line.  This is fine
> for things like edebug, where the text is usually indented many columns
> anyway, and only whitespace gets overwritten.
> 
> This is less good for things like compilation-mode, where this arrow
> would obliterate the first two characters of a file name.
> 
> The following amendment fixes this by allowing the arrow to be displayed
> at the BOL, displacing the rest of the line two characters to the right.
> To do this, a new buffer local boolean variable, overlay-arrow-insert is
> introduced.

If you want the arrow be displayed before the line's text, why didn't
you just put a before-string at the beginning of the line, instead of
implementing this in the display engine?  AFAIU, that would give you
most of the patch for free, e.g. you wouldn't need to mess with the
set_cursor_from_row hair.

What am I missing?