QtScript considered dangerous

Thomas Friedrichsmeier thomas.friedrichsmeier at ruhr-uni-bochum.de
Thu May 24 10:28:41 BST 2012

-- Note: Reposting to follow Dominik's example of CCing kde-core-devel --


On Wednesday 23 May 2012, Milian Wolff wrote:
> We have port Kate away from QtScript.

I'm not sure, whether this is a serious suggestion, or just a way to catch 
attention. In the latter case: it worked. In the former case, I think there 
are some important reasons going against this:

1. AFAIR, there are some subtle differences between KJS and QtScript. I'd be 
hard pressed to provide an example, but I know for sure that I have run into 
some, personally. Some code that worked fine in QtScript did not work for me 
in KJS (note: I was using kjsembed via Kross, then).

1b. While, certainly, any such incompatibilities could easily be addressed 
inside the Kate code base, keep in mind that a switch of engine could also 
cause trouble for users' custom scripts.

1c. Even if the above incompatibilities were a mere figment of my imagination, 
KJS does have it's own set of bugs. These may (or may not) be more benign than 
those of QtScript. They may be easier for us to get fixed, but that's because 
there is no third party to point fingers at, in the first place.

2. Kate is not the only user of QtScript in the KDE world. Do we want to 
switch all other KDE apps to KJS, too? Will that really be the most efficient 

I think, on a theoretical level, we can easily agree that getting this fixed 
inside Qt would be the optimal solution. So is this really totally out-of-

Well, apparently, the people who should take care of this, don't. That's 
extremely annoying. But also, let's not turn to suboptimal solutions, too 
early, out of frustration. So they are not willing to invest the required 
amount of work, themselves. But would they accept a patch? And how hard would 
it be to produce a patch?

I don't know. I have neither the skills, nor the right number of bits to be of 
any help with debugging this. But I think this is the very first question to 
think about, before thinking about alternatives: What about the proposed 
solution, i.e. updating JSC(*)? Can you provide an estimate of how much work 
that would mean? If that patch would be too large to be acceptable, is it 
possible to identify and port the fix to this particular issue, in the JSC 


(*) Just to point out the obvious, though: The bug appears to have surfaced 
considerably later than the last update of JSC. Which doesn't prove anything, 
but softens the evidence pointing to JSC as the (only) cause of the bug.
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