Tk Source Code

We received a bug report about an error in ::tk::ScrollByUnits:

can't read "Priv(xEvents)": no such element in array
    while executing
"if {($Priv(xEvents) + $Priv(yEvents) > 10) &&
		($axis eq "x" && $Priv(xEvents) < $Priv(yEvents) ||
		 $axis eq "y" && $Priv(yEvents) < $Priv(xEvents)..."
    (procedure "tk::ScrollByUnits" line 14)

We have not been able to reproduce it ourselves, but looking at the logic it seems like the <Enter> events was not (yet) resolved when ::tk::ScrollByUnits was entered. So a valid fix seems to be to make sure both "events" variables are initialized before doing the if statement, by adding

set otherAxis [expr {$axis eq "x" ? "y" : "x"}]
if {![info exists Priv(${otherAxis}Events)]} {
    set Priv(${otherAxis}Events) 0
}

The platform is Windows.

Fixed by commits [cca7d076] (main) and [2eb7e410] (core-9-0-branch). In addition, guarded against potential similar problems related to entry and notebook widgets.

Assigned to myself. The fix is coming soon.