It’s quite a while since my last blog now. I’m still planning to present all the essential C++ support features in KDevelop4, but my plan is to polish each feature up a bit before I actually blog about it. This also serves as a nice motivation.
In the last weeks, I have mainly worked on DUChain backend stuff, especially making it more efficient. Some important coneceptual scalability problems have been solved, although I have yet quite a few tricks in line to make the actual parsing faster. Temporarily I lost my motivation a little on this boring backend stuff, but in the last days I regained it, and implemented some long planned nice features that I’m going to present to you now.
Most Qt programmers love the signals and slots, since they allow getting stuff up and running really fast. But there is also some annoying things about them. For example that they are managed through simple strings, where Qt doesn’t even know about the real scope of the involved types, which leads to simple string-matching instead of comparing the real types. Also you need to write the complete function signature whenever you use a singal/slot, and me personally, I tend to do little mistakes while doing that, which can lead to really annoying little bugs, that aren’t catched by the compiler. It becomes even worse when you try to do refactoring like renaming signals, slots, or some of the involved types. Since the SIGNAL and SLOT macros translate the signatures to strings, grep is until now the only thing that can be of assistance here.
Now, KDevelop4 is coming to rescue.
The first thing needed was additionally recording the signatures of signals/slots in exactly the same way Qt sees them. This way, we can theoretically do exactly the same matching Qt does. But then there’s the problem of the SIGNAL/SLOT macros. With a correctly working preprocessor, those will leave relatively useless strings to the C++ parser. I have completely blocked these macros and internally replaced them with new macros, a new token, and some new structures in the parsing infrastructure, to _not_ do the same thing the compiler does. Instead, our C++ parser now completely processes the signature, and allows building uses for all involved types, and of course for the signals/slots themselves.
Together with these uses, now KDevelop4 allows you to see all places where a signal/slot is connected, intelligently rename it, and to intelligently rename any types involved in the signature. Of course, the uses are only built if a signal/slot with the given exact signature actually exists. Together with highlighting, this already now gives you an excellent tool to detect broken connections.
Essentially, this makes signal/slot connections a real well-understood first-class citizen of the DUChain.
Since people like screenshots, here you see how the uses of a slot are shown, and can be renamed.
Now the duchain integration allows excellent tracking of already existing connections. But the annoyance of actually writing the connections remains. In KDevelop3, there already was a quite cool code-completion for signals/slots, that inserted the correct complete signature four you, and thus saved you from typing. In KDevelop4 I had this thing on my list for a long time, and now finally I’ve implemented it. However since KDevelop4 is aiming a lot higher then the earlier version, this feature of course needed to be improved as well.
So here you see the new Signal/Slot completion, with complete realistic signature-matching, which helps you conveniently connecting only fitting signals/slots to each other. As you see I’ve also worked a bit on the completion-widget. The highlighting colors are much softer now. This picture doesn’t show the interesting “matching” part yet, since every signal matches the connect(..) function.
In this picture, you see how the correct signature was inserted, and a new completion-list was opened, this time asking for the slot that he signal should be connected to. As you see, the only 2 perfectly matching slots are shown directly at the top. Since you can connect signals to slots with less arguments, the argument-less slots are shown as matches too, although with lower match-quality.
That’s it with signals/slots for now.
Builtin Operator Completion
One more thing that has been on my list for a long time, and that I’ve finally implemented, is completion for all builtin operators in C++, not only the overloaded ones. By completion I mean mainly getting the match-quality highlighted, and getting the “Best Matches” list at top. You will be wondering how often you use some kind of builtin operator, from my experience this saves from a _lot_ of typing, since in many cases the wanted item is right at the top.
Also I have added argument-hinting for the “return” keyword, which means you can also get best matches when returning a value from a function:
And that’s it for today. Hope you like the stuff, and as always, if you want KDevelop4 to get ready faster, consider getting your hands dirty.