Fix memory leaks in qt/guiutil.cpp #11156

on macOS: listSnapshot was leaking in findStartupItemInList() bitcoinAppUrl was leaking in [Get|Set]StartOnSystemStartup()

CFArrayGetCount dereferences listSnapshot and if it's nullptr then it crashes, so how have you tested this?

@promag Not sure I understand the question, do you mean

+    if (listSnapshot == nullptr) {
+        return nullptr;
+    }

added at 784-786?

This is just for safety, it's not really expected for listSnapshot to be nullptr. I think it makes sense to add this safety in the context of not doing CFRelease on nullptr at the end. You're right that even without the added lines above, in case of listSnapshot == nullptr there will probably be a crash even before we get to the CFRelease. Still, seems cleaner to me.

Also, in the unlikely case that listSnapshot is set to nullptr, we will return nullptr instead of crashing, which is probably nicer behavior anyway. (though, it's up to the caller whether it itself would crash or not)

utACK 9b348ff9eb75e04249dfa873a34e0d1a31993b9c. Seems right, though maybe it would be simpler with an RAII helper class:

struct CFReleaser
{
    CFReleaser(CFTypeRef cf) m_cf(cf) {}
    ~CFReleaser() { if (m_cf) CFRelease(m_cf); }
    CFTypeRef m_cf;
};

@ryanofsky I agree, just didn't want to do two things at once - introduce such a class as well as fix problematic code. Once this is merged I'm for doing a separate pull requests with a commit that introduces such a class, followed by commits which make use of it.

utACK 9b348ff9eb75e04249dfa873a34e0d1a31993b9c. I think we should also get rid of the OSX Growl support.

I really like the idea of using a RAII class here. Much easier to check whether all possible exit paths are covered, and exception-safety comes for free.

I agree an RAII approach would be much better. But until someone comes up with an RAII for that pure OSX stuff, I think this is an valid improvement.

Tested ACK 9b348ff9eb75e04249dfa873a34e0d1a31993b9c. Could not find any leaks with macOS instruments (leak detector) during notifications.