Text segfault with Modified event after delete

8.4 text widget has problems when processing <<Modified>> event caused by delete. This segfaults once the widget gets focus (sorry, I cannot test 8.5):

#!/usr/bin/wish8.4
text .t
.t insert insert x
bind .t <<Modified>> update
.t edit modified 0
pack .t

update
after 4000
.t delete 1.0 1.1

Alternatively, use just the first 6 lines, click in the left halve of the window and press Backspace to get Segmentation fault as well.

This is a minimalistic example and rather strange one, doing "update" does not make much sense. However it ilustrates likely data corruption which has other symptoms as well.

I wanted to invoke procedure after every text change and I found that after delete and <<Modified>> event, this procedure still reports text as it was BEFORE delete (while inserting chars is fine). Example:

proc modified {} {
if {![.t edit modified]} {
# invoked by itself
return
}
.t edit modified 0
puts text:[.t get 1.0 end]
}
text .t
bind .t <<Modified>> modified
pack .t

Now type "A" in text widget, delete it and type "X". Response is:

text:A <-- OK
text:A <-- WRONG! Text is empty now!
text:X <-- OK

Text widget itself looks as it should ("A" appears, disappears, "X" appears). Things also look OK when inspected outside of the event processing procedure. Just after delete, while processing <<Modified>>, data structures seem to be inconsistent, leading to slight errors or even segfaults.

Vaclav Hanzl

hanzl (at) noel dot feld dot cvut dot cz