How to debug slow Swift compile times

Question

I have a Swift SpriteKit project with about 25 smallish files. The time to compile this project is 30-45 seconds! It's pure Swift with no ObjC.

I've watched the compile in the Report Navigator to try to find a single file that's taking the time. But, it's not really a single file. It's always the last file in the list that seems to take all the time. But that file can be different between compiles and still takes all the time.

The step right after the last file is Merge xxx.swiftmodule, which happens quickly, but I'm not sure if because it comes right after the slowness it might be related.

I've searched and tried various approaches to find the culprit. I read this post: Why is Swift compile time so slow? and tried those approaches. I've done a command line build using CTRL-\, but that does not show any useful information about the slowness.

I've gone through my project looking for places where type inference might be getting tripped up, but haven't found much (and really, if that was the case, I'd expect a single file to be the culprit).

Does anyone have any other suggestions for tracking this down? Coming from an Objective-C project that compiles nearly instantly, this is driving me crazy.

EDIT I worked on this a bit more and am including a screen shot of the build output, noting where the slowness happens. The thing is, if I comment out the code in the slow file, then the file before it in the list becomes the slow one (where it was fine before). If I comment that code out, then the one before that becomes the slow one, etc.

Answer 1

After more digging and debugging, I found the problem. It turns out it actually is type inference, as other posts have suggested. Part of the problem is that I did not notice that the build output in the Report Navigator shows an arrow for files still compiling and a checkmark for those that are done (my color blindness played a role). So I thought they were all finished compiling when one was not.

In any case, I read the article here: GM release of Xcode 6 compile and did a command line build of the entire project, which showed me the file that was the issue. Then, using the CTRL-\ approach noted above, I found the culprit.

It turns out that this line was the issue:

ourWindowCopy.position = CGPoint(x: ((26.5 + theXOffset) * self.multiplierWidth) + (4.0 * CGFloat(randomRow) * 2.0 * self.multiplierWidth), y: ((41.0 + theYOffset) * self.multiplierHeight) + (5.75 * CGFloat(randomColumn) * 2.0 * self.multiplierHeight))

I know it seems a mess - I was playing around with a bunch of different options early on and hadn't yet gone back to simplify. I replaced it with this (and will of course replace the literals as well as simply further):

let floatRandomRow = CGFloat(randomRow)
let floatRandomCol = CGFloat(randomColumn)
let pointX: CGFloat = ((26.5 + theXOffset) * self.multiplierWidth) + (4.0 * floatRandomRow * 2.0 * self.multiplierWidth)
let pointY: CGFloat = ((41.0 + theYOffset) * self.multiplierHeight) + (5.75 * floatRandomCol * 2.0 * self.multiplierHeight)

ourWindowCopy.position = CGPoint(x: pointX, y: pointY)

Now the compile speed is very fast!

I'm not sure there's really any new information here, but wanted to close this out with a solution in case someone runs across it.