Swift at scale tgebarowski (v3 revised) Tomasz Gebarowski Mobile Warsaw 24.07.2017 

mBank.pl tgebarowski 

tgebarowski 

some stats +10 developers 2 years of development +3200 Swift files 100’s of View Controllers, Cells We use code generation 3 migrations between Swift versions tgebarowski 

scale effect compilation times migrations tgebarowski 

compilation times https://xkcd.com/303/ tgebarowski 

1 minute? tgebarowski 

5 minutes? tgebarowski 

up to 40 minutes… tgebarowski 

https://github.com/riamf/XcodeBuildTimeMeasurement Day time (s) formatted time no builds 10.10.2016 7297 2h 1m 37s 24 11.10.2016 12221 3h 23m 41s 87 12.10.2016 7146 1h 59m 5s 79 13.10.2016 8885 2h 28m 5s 107 14.10.2016 4452 1h 14m 12s 33 tgebarowski 

Compilation times -Onone -whole-module- optimization Core i5 ~40 min ~11 min Core i7 ~30 min ~8 min tgebarowski 

Why -Onone is so slow? In a large project, single Swift file compilation takes ~1 second 

Why -Onone is so slow? -filelist argument contains a list of all Swift files in a project 

specialisation of generic functions for concrete types inlining dead function/method elimination source: swift.org whole-module optimization tgebarowski 

single invocation of frontend with -filelist argument whole-module optimization tgebarowski 

could it be faster? tgebarowski 

compilation times -Onone -whole-module- optimization SWIFT_WHOLE_MODULE_ OPTIMIZATION=YES Core i5 ~40 min ~11 min ~5 min Core i7 ~30 min ~8 min ~3 min tgebarowski 

swift -frontend -primary-file file1.swift -filelist file swift -whole-module-optimization file1.swift file2.swift file3.swift how it works? swift -Onone file1.swift file2.swift file3.swift swift -frontend -whole-module-optimization -filelist file swift -frontend -primary-file file2.swift -filelist file swift -frontend -primary-file file3.swift -filelist file spawn spawn spawn spawn -whole-module-optimization -Onone tgebarowski 

swift -whole-module-optimization file1.swift file2.swift file3.swift the trick swift -frontend -whole-module-optimization -Onone -filelist file spawn SWIFT_WHOLE_MODULE_OPTIMIZATION=YES tgebarowski 

Xcode 9 tgebarowski 

SWIFT_WHOLE_MODULE_OPTIMIZATION=YES still works tgebarowski 

what about? tgebarowski 

what about? nothing changed… 

beware of large targets! getconf ARG_MAX 262144 uses absolute path of every Swift file in project +1500 Swift files Assume long project dir path MacOS command line
 max length tgebarowski 

Frameworks! One Monolithic Mobile App MBFoundation MBServiceKit MBUtilityKit MBCoreKit MBGlueKit MobileApp dropping iOS 7 support tgebarowski 

-Onone -Owholemodule Core i5 ~18 min
 ~40 min ~10 min
 ~11 min Core i7 13 min
 ~30 min 8 min
 ~8 min compilation times after introducing frameworks tgebarowski 

Migrations Swift 1.2 Swift 2.1 Swift 2.2 2 days ~3 weeks author: Christophe Boisson Swift 3 7 days tgebarowski 

Swift 1.2 Swift 2.1 ~3 weeks Swift 2.2 Swift 3 7 days 8h Migration Tool 2 days Manual Fixes 2 devs 5 days Bypassing 
 compiler bug 3h Migration Tool 4 days Manual Fixes 3 devs ~3800 errors ~1600 errors 5 days Regression testing 2 days Regression testing 

migration process Auto migration Code Freeze Migrating Core frameworks Migrating App itself Migrating Unit and UI tests Regression and fixing issues Auto migration Migrating Core frameworks Estimating number and types of bugs to fix migration evaluation migration process tgebarowski 

Swift 3 Migration Issues • dequeueReusableCellWithIdentifier -> dequeueReusableCell(withIdentifier:for:) • hidden -> isHidden • enabled -> isEnabled • popViewControllerAnimated -> popViewController(animated:) • registerNib(_:forCellReuseIdentifier:) -> register(_:forCellReuseIdentifier:) • wszystkie błędy związane z rename’ing enumów ‚X’ has been renamed to ‚Y’ 551 errors extraneous argument label 250 errors explicitly marked unavailable here 570 errors has no case „X”, did you mean „x” 523 errors NSDate & Date related 114 errors tgebarowski 

The +1500 Swift files problem (Xcode 7.2) swiftc crash Migration Issues tgebarowski 

swift -frontend swiftc swift -frontend posix_spawn swift -frontend … crash The +1500 Swift files problem (Xcode 7.2) tgebarowski 

Reported problem to Apple (SR-280) Fixed in Xcode 7.3 Provided a workaround for 7.2 swiftc wrapper swiftc -num-threads 0 with fork instead of posix_spawn Xcode More info: https://github.com/tgebarowski/swiftc-wrapper The +1500 Swift files problem (Xcode 7.2) tgebarowski 

What’s next? tgebarowski 

• Swift 4 • Xcode 9 • precompiled frameworks • static libraries • Buck What’s next? tgebarowski 

Thank You! tgebarowski 

tgebarowski Swift at scale Tomasz Gebarowski Mobile Warsaw 24.07.2017