Compile Time Incredibly Slow

Question

My project consists of ~350 Swift files and ~40 cocoa pod dependencies.

As soon as the entire project was migrated to Swift 3, build times have been INCREDIBLY slow and took a little over 3 minutes to completely compile.
I've noticed that if I rebuild after not changing any files, it builds within a reasonable amount of time. However, if I add a new function, it takes the 3+ minutes.
Cocoapods does not seem to be causing the problem as it delays on Compiling Swift source files state.

I followed this to investigate:

1. Added the -Xfrontend -debug-time-function-bodies flag to my Other Swift Flags in my target's build settings

2. Build the project

3. 

4. 

5. Copied this into terminal and ran pbpaste | egrep '\.[0-9]ms' | sort -t "." -k 1 -n | tail -100

However, I didn't see anything of concern. The file that took the longest to compile was only 250ms. The next closest was 100ms, even if all 350 files took 250ms to compile, that would only be a total of 73 seconds which is way off from the 3+ minute builds I am seeing.

What could be causing these long compile times?

It was never as slow before updating to Xcode 8 and Swift 3.

Answer 1

Update 1:

I created a new project without running the Swift 3 conversion, imported my Swift 3 files, but the build time remains the same.

Update 2:

I've tried SWIFT_WHOLE_MODULE_OPTIMIZATION = YES, but as soon as you make changes to more than 1 file, the incremental build fails and it triggers a re-build which lasts for more than 4-5 minutes.

Update 3:

I've now re-written my entire code base from Swift 3 to Swift 2.3. It didn't make any difference, the problem lies with the Xcode 8 compiler.

Update 4:

I can confirm that unchecking these two will alleviate the pain for a while, the Xcode 8 bug does seem to be tied to how it checks dependencies between files.

Update 5:

I've converted my code base to Swift 3 from Swift 2.3 since Xcode 8.2 beta requires it, the beta should include a fix for "Xcode will not rebuild an entire target when only small changes have occurred. (28892475)". Sad to say, they haven't fixed the bug and my compile times are exactly the same with Xcode 8.2 Beta.

Original post:

I don't have enough reputation to comment, but I still wanted to share some resources. I've been stuck in this misery for days, upgrading to Swift 3 has been a complete disaster.

I'm using this to track slow files, even though just like you, that's not my problem. Something else in xcode is taking literally 4 minutes to complete: https://github.com/irskep/swift_compile_times_parser https://github.com/RobertGummesson/BuildTimeAnalyzer-for-Xcode

I've also made sure I don't have any lazy vars or closures that swift doesn't like. Don't use the + operator when concatenating strings, etc. see this.

I'll update this answer if I find anything, it's just about impossible to be productive with Swift 3 ATM.