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Bug#1122519: xterm: display corruption with double-width characters



On Thu, Dec 11, 2025 at 01:53:38AM +0100, Vincent Lefevre wrote:
> Package: xterm
> Version: 404-1
> Severity: important
> 
> Display is corrupted when double-width characters are displayed.
> In particular, this affects Mutt (receiving mail with such characters
> is common), and one consequence is that wrong mail can be deleted
> because the cursor does not appear on the right message! I've
> attached a part of a screenshot (20251211-003112.png) to show
> the kind of output I get.
> 
> There is no such issue with rxvt and GNOME Terminal.
> 
> To reproduce a display issue, open a 80-column xterm, and generate
> output so that the shell prompt is at the very bottom. Then paste
> the following command:
> 
> printf "🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝🧝\n"
> 
> The last 3 characters of the command (\n") do not appear (see attached
> screenshot 20251211-014531.png). They appear one character at a time
> when I type the left arrow. There is the same issue when I recall this
> command from the history (if the prompt is at the very bottom).

I can see some cursor-misplacement, using bash and zsh, not dash,
when pasting that text without a line-ending (so that the cursor
would be at the end of the line).

fwiw, all of the characters are U+1F9DD, which we're agreed should be two
cells, and the VS15/VS16 code shouldn't be a factor.  I'll have to bisect
my changes to see why this happens.

-- 
Thomas E. Dickey <dickey@invisible-island.net>
https://invisible-island.net

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