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terminal: fix crash after shrinking columns splits a wide char - #14509
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fornwall
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Narrowing without reflow cleared only the cells past the new width, so a wide char whose spacer tail was cut kept its head in the new last column. Every operation pairing a head with the cell after it then reached past the row end: insertBlanks and eraseLine(.left) panic in Screen.clearCells, and rowWillBeShifted writes cells[cols]. Clear the orphaned head along with the cut columns. Signed-off-by: Fredrik Fornwall <fredrik@fornwall.net>
mitchellh
approved these changes
Oct 4, 2026
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Narrowing the terminal without reflow (wraparound off, or the alternate screen) can cut a wide char in half, leaving its head in the last column with no spacer tail.
Later edits on that row (e.g. ICH) then clear the missing tail too, reaching one cell past the row end, which leads to a bounds assertion failure in safe builds or an out-of-bounds write otherwise.
To reproduce, run the below script inside a safe build:
Screen.clearCells.survived, column 80 is blank.AI disclosure: Created with claude code using opus 5.5. Iterated on and reviewed by me.