Erase in Line CSI sequence does not erase line content beyond the terminal width

[rprichard]

I noticed that with mintty, the Erase in Line CSI sequence (\x1b[<n>K) only erases the currently visible part of the line. If the line extends past the right end of the window, those characters aren't erased. If the window is later expanded horizontally, the previously invisible part of the erased line comes back into view.

This behavior seems wrong to me. It also doesn't match what other terminals do (particularly, xterm, VTE, and Konsole).

Like mintty, xterm also keeps track of obscured line content beyond the right edge of the terminal, but both \x1b[0K and \x1b[2K erase the obscured characters.

Example:

• Resize a terminal to (say) 50x50.
• Run: echo -e '\x1b[2J\x1b[1;1HAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA'
• Reduce the terminal's width so that the AAA string is truncated.
• Run: echo -e '\x1b[1;1H\x1b[2K'
• Increase the terminal's width.

FWIW: This issue is affecting my winpty project, which frequently rewrites lines when the terminal/console is resized.

[rprichard]

(particularly, xterm, VTE, and Konsole)

I retested, and I was wrong about xterm. Actually, it doesn't restore truncated line content when shrinking and expanding a terminal, so it's not relevant to this issue.

[mintty]

Fixed:
CSI K Erase in Line
CSI J Erase in Display
CSI X Erase Characters
CSI @ Insert Characters
CSI P Delete Characters
CSI 4 h/l Insert Mode

test script:

#! /bin/sh

# mintty issue #480
# Erase in Line CSI sequence does not erase line content beyond the terminal width

echo -en "\e[8;;88t"
echo -en "\e[2J"
o40="ooooo______________________________ooooo"
for n in 1 2 3 4 5 6 7 8 9 0
do  echo; echo; echo; echo
done
echo -en "\e[1G${o40}XXXXX______________________________________XXXXX"
echo -en "\e[1;1H"

echo -en "\e[1;1H${o40}XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX"
echo -en "\e[2;1H${o40}123456789012345678901234567890123456789012345678"
echo -en "\e[3;1H${o40}XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX"
echo -en "\e[4;1H${o40}123456789012345678901234567890123456789012345678"
echo -en "\e[5;1H${o40}XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX"
echo -en "\e[6;1H${o40}12345678901234567890123456789012345678901睷4睷78"
echo -en "\e[7;1H${o40}12345678901234567890123456789012345678901睷4睷78"
echo -en "\e[8;1H${o40}XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX"
echo -en "\e[9;1H${o40}睷睷睷睷睷睷睷睷睷睷睷睷睷睷睷睷睷睷睷睷睷睷睷睷"
echo -en "\e[10;1H${o40} 睷睷睷睷睷睷睷睷睷睷睷睷睷睷睷睷睷睷睷睷睷睷睷"
echo -en "\e[11;1H"
sleep 1
echo -en "\e[8;;80t"
sleep 1

echo -en "\e[2;40H\e[1J"
sleep 1
echo -en "\e[3;41H\e[K"
sleep 1
echo -en "\e[4;77H\e[4hii\e[4l"
sleep 1
echo -en "\e[5;77H\e[8X"
sleep 1
echo -en "\e[6;77H\e[2@"
sleep 1
echo -en "\e[7;77H\e[2P"
sleep 1
echo -en "\e[8;41H\e[J"

sleep 1
echo -en "\e[8;;88t"
echo -en "\e[11;1H"

[rprichard]

Looks good to me. Thanks.

I also looked at how Konsole and gnome-terminal (an old version that didn't rewrap lines) handled some of the other CSI sequences, and curiously, Delete Characters (P) would slide obscured content into view, but Insert Characters (@) and insert mode (h/l) instead cleared the obscured characters. The two terminals handled Erase Characters (X) differently, with gnome-terminal matching the new mintty behavior, and Konsole clearing all the obscured characters. I have no idea if behavior is intentional. The new mintty behavior seems fine to me.

[mintty]

Thanks for the feedback.

[mintty]

Released in 2.2.1.