Problem with tkBind.c since Tk 8.6.10 (various assertions fail)

Robert Csok

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Sep 27, 2022, 5:50:11 AM9/27/22

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Hello, everybody

We have noticed that since Tk 8.6.10 our application crashes in connection with bindings. Different kinds of assertions fail in tkBind.c, for instance:
tkBind.c:2825: MatchPatterns: Assertion `(psPtr->object == NULL) == (physPtrPtr != NULL)'
tkBind.c:2489: Tk_BindEvent: Assertion `i + 1 < psEntry->psPtr->numPats'
tkBind.c:2827: MatchPatterns: Assertion `psPtr->numPats > patIndex'
tkBind.c:2824: MatchPatterns: Assertion `TEST_PSENTRY(psPtr)'

From what I can tell at a glance, major changes were made to tkBind.c between 8.6.9 and 8.6.10.

I have attached a small script that can be used to reproduce the crashes (see below).

Could you guys please take another look at this?

Kind regards,

Robert

#!/bin/sh
#\
exec wish "$0" ${1+"$@"}

# If you draw a line, the program crashes with Tk since 8.6.10.
#
# Tested under
# Ubuntu 18.04/Tk 8.6.8 (works)
# Ubuntu 20.04/Tk 8.6.10 (crashes)
# Ubuntu 22.04/Tk 8.6.12 (crashes)
# openSUSE 15.4/Tk 8.6.12 (crashes)
# among others
#
# (8.6.9 works, 8.6.11 crashes)
#
# If Tk was compiled without debugging information, it may take several
# attempts to crash the program.

proc startLin {c} {
unbindCan $c; # try without this (shouldn't crash then)

# Some array (move mouse after <ButtonRelease-1>):
set arr($c,foofoofoo) ""
set arr($c,barbarbar) 1

# or try this instead (and move mouse, leave canvas or draw another line after <ButtonRelease-1>):
# set arr($c,foo) ""
# set arr($c,bar) 1

# Try this (shouldn't crash then)
# unset arr

bindCan $c [array get arr]
}

proc bindCan {c args} {
bind $c <ButtonPress-1> "createLin %W %x %y"
bind $c <B1-Motion> "drawLin %W %x %y"
# Try without the next two lines (shouldn't crash then)
bind $c <B1-Motion><Leave> "leaveCan %W"
bind $c <B1-Motion><Enter> "enterCan %W"
bind $c <ButtonRelease-1> "startLin %W"
}

proc unbindCan {c} {
bind $c <ButtonPress-1> {}
bind $c <B1-Motion> {}
# Try without the next two lines (shouldn't crash then)
bind $c <B1-Motion><Leave> {}
bind $c <B1-Motion><Enter> {}
bind $c <ButtonRelease-1> {}
}

proc createLin {c x y} {
set x0 [$c canvasx $x]
set y0 [$c canvasy $y]

$c delete linTag
$c create line $x0 $y0 $x0 $y0 -tags linTag
}

proc drawLin {c x y} {
lassign [$c coords linTag] x0 y0
$c coords linTag [list $x0 $y0 [$c canvasx $x] [$c canvasy $y]]
}

proc leaveCan {c} {
# nothing
}

proc enterCan {c} {
# nothing
}

set c [canvas .c]
pack $c
startLin $c

Ralf Fassel

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Sep 27, 2022, 8:57:29 AM9/27/22

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* Robert Csok <rober...@gmail.com>

openSuse 15.3 8.6.12 crashes, too.

% wish /tmp/t.tcl
Segmentation fault (core dumped)

| I have attached a small script that can be used to reproduce the crashes (see below).
>
| Could you guys please take another look at this?

Consider to file a bug report on https://core.tcl.tk/tk

R'

Robert Csok

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Sep 27, 2022, 10:30:58 AM9/27/22

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> Consider to file a bug report on https://core.tcl.tk/tk

Thanks for the tip. I have now created a ticket:

https://core.tcl-lang.org/tk/tktview?name=43573999ca

Dave

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Sep 27, 2022, 11:04:03 AM9/27/22

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On 9/27/2022 4:50 AM, Robert Csok wrote:
> Hello, everybody
>
> We have noticed that since Tk 8.6.10 our application crashes in connection with bindings.

It also crashes on win7x64 8.6.11 and 8.7a5

clt.to...@dfgh.net

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Sep 27, 2022, 11:42:28 AM9/27/22

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The problem looks like it is related to the sequence of events.

If you replace the <B1-Motion><Enter> with <B1-Enter>
and similarly for <B1-Leave>
It appears to work (at least on 8.6.12).
I'm not sure what else might go wrong outside of your (very nicely) simplified example though.

It might be a workaround. In any case the Tcl segfault needs to be fixed.

Dave B