Xcode 8 very slow Swift compiling

Question

Ever since Swift 3 and Xcode 8 my project compiles quite slowly. Every time I add so much as an empty line to a file, recompiling takes a full minute. When I check the output, there is no particular file that takes very long. (I also used this tool to measure it: https://github.com/RobertGummesson/BuildTimeAnalyzer-for-Xcode)

It always appears to compile 4 files at once. The "rythm" is quite steady. Just very slow...

Also: Whenever I open or switch between files, it can take very long till I get autocomplete, or errors/warnings.

What things can I check? I almost feel like there is some flag I set that just drags down the build speed like crazy..

EDIT: This is not a solution to the underlying problem, but I spent some time on moving more code to frameworks. This made a difference (simply because it has to recompile less files every time). This shouldn't be necessary but it got unbearable... I'm of course still looking very much for a proper solution.

Answer 1

A issue with this problem is that we don't know where is the wrong initialization/declaration . A solution that my colleague suggest is to find which function take long time to compile so:

1. Go to Project select your target
2. Build Settings -> Swift Compiler - Custom Flags
3. Add to Other Swift Flags -Xfrontend -warn-long-function-bodies=50 (50 represent the time in milliseconds)

after that a warning should displayed as follow:

Getter 'frameDescription' took 108ms to type-check (limit: 50ms)

and after that you know what to do ;)

Answer 2

I've had the same issue only since upgrading to Swift 3/XCode 8 and it appears to be caused by large array literals, similar to this.

I was able to fix the issue by adding type annotations to the variables being assigned to the array literal, e.g.

let array: Array<String> = ["1", "2", "3", "4", "5", "6", "7", "8"] 

instead of

let array = ["1", "2", "3", "4", "5", "6", "7", "8"]