[Rd] use of the tcltk package crashes R 4.0.1 for Windows

[peter dalgaard]

So this wasn't tested for a month?

Anyways, Free() is just free() with a check that we're not freeing a null pointer, followed by setting the pointer to NULL. At that point of tcltk.c, we have

   for (objc = i = 0; i < length(avec); i++){
        const char *s;
        char *tmp;
        if (!isNull(nm) && strlen(s = translateChar(STRING_ELT(nm, i)))){
            //  tmp = calloc(strlen(s)+2, sizeof(char));
            tmp = Calloc(strlen(s)+2, char);
            *tmp = '-';
            strcpy(tmp+1, s);
            objv[objc++] = Tcl_NewStringObj(tmp, -1);
            free(tmp);
        }
        if (!isNull(t = VECTOR_ELT(avec, i)))
            objv[objc++] = (Tcl_Obj *) R_ExternalPtrAddr(t);
    }

and I can't see how tmp can be NULL at the free(), nor can I see it mattering if it is not set to NULL (notice that it goes out of scope with the for loop). 

-pd
 

> On 7 Jun 2020, at 16:00 , Jeroen Ooms <jeroenooms using gmail.com> wrote:
> 
> On Sun, Jun 7, 2020 at 3:13 AM Fox, John <jfox using mcmaster.ca> wrote:
>> 
>> Hi,
>> 
>> The following code, from the examples in ?TkWidgets , immediately crashes R 4.0.1 for Windows:
>> 
>> --------------------- snip --------------------
>> library("tcltk")
>> tt <- tktoplevel()
>> label.widget <- tklabel(tt, text = "Hello, World!")
>> button.widget <- tkbutton(tt, text = "Push",
>>         command = function()cat("OW!\n"))
>> tkpack(label.widget, button.widget) # geometry manager
>> --------------------- snip --------------------
> 
> 
> I can reproduce this. The backtrace shows the crash happens in
> dotTclObjv  [/src/library/tcltk/src/tcltk.c using 243 ]. This looks like a
> bug that was introduced by commit 78408/78409 about a month ago. I
> think the problem is that this commit changes 'calloc' to 'Calloc'
> without changing the corresponding 'free' to 'Free'.
> 
> This has nothing to do with the Windows build or installation. Nothing
> has changed in the windows build procedure between 4.0.0 and 4.0.1.
> 
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-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Office: A 4.23
Email: pd.mes using cbs.dk  Priv: PDalgd using gmail.com