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.

Solution 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 ;)

Solution 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"]

Solution 3

This is an issue with Xcode 8 where it does not perform incremental builds correctly. If you edit a single swift file it should compile only that file only. This has already been raised here: Xcode 8 does full project rebuild

The 4 files at a time build sounds like Xcode is performing a full rebuild of the project which should not happen again if you only modified a single line in one file.

Solution 4

In my case I was using a helper function to save some data in Firebase. That function was returning a dictionary with about 20 elements and it would take about 40 mins to compile. My solution was to initialize an empty dictionary and then add the items one by one to someDict . Now it compiles in less than 30 seconds. I hope it helps.

Before

func toAnyObject() -> AnyObject {
  return
      ["BookingAmount":BookingAmount,
     "BookingNumber":BookingNumber,
     "PostCode":PostCode,
     "SelectedBathRow":SelectedBathRow,
     "SelectedBedRow":SelectedBedRow,
     "DateAndTime":DateAndTime,
     "TimeStampDateAndTime":TimeStampDateAndTime,
     "TimeStampBookingSavedInDB": TimeStampBookingSavedInDB,
     "FrequencyName":FrequencyName,
     "FrequecyAmount":FrequecyAmount,
     "insideCabinets": insideCabinets,
     "insideFridge": insideFridge,
     "insideOven": insideOven,
     "laundryWash": laundryWash,
     "interiorWindows": interiorWindows,
     "FullName":FullName,
     "SuppliesName":SuppliesName,
     "SuppliesAmount":SuppliesAmount,
     "FlatNumber":FlatNumber,
     "StreetAddress":StreetAddress,
     "PhoneNumber":PhoneNumber,
     "EmailAddress":EmailAddress] as AnyObject

}

After

  func toAnyObject() -> AnyObject {

    var someDict = [String : AnyObject]()
    someDict["BookingAmount"] = self.BookingAmount as AnyObject?
    someDict["BookingNumber"] = self.BookingNumber as AnyObject?
    someDict["PostCode"] = self.PostCode as AnyObject?
    someDict["SelectedBathRow"] = self.SelectedBathRow as AnyObject?
    someDict["SelectedBedRow"] = self.SelectedBedRow as AnyObject?
    someDict["DateAndTime"] = self.DateAndTime as AnyObject?
    someDict["TimeStampDateAndTime"] = self.TimeStampDateAndTime as AnyObject?
    someDict["TimeStampBookingSavedInDB"] = self.TimeStampBookingSavedInDB as AnyObject?
    someDict["FrequencyName"] = self.FrequencyName as AnyObject?
    someDict["FrequecyAmount"] = self.FrequecyAmount as AnyObject?
    someDict["insideCabinets"] = self.insideCabinets as AnyObject?
    someDict["insideFridge"] = self.insideFridge as AnyObject?
    someDict["insideOven"] = self.insideOven  as AnyObject?
    someDict["laundryWash"] = self.laundryWash as AnyObject?
    someDict["interiorWindows"] = self.interiorWindows as AnyObject?
    someDict["FullName"] = self.FullName as AnyObject?
    someDict["SuppliesName"] = self.SuppliesName as AnyObject?
    someDict["SuppliesAmount"] = self.SuppliesAmount as AnyObject?
    someDict["FlatNumber"] = self.FlatNumber as AnyObject?
    someDict["StreetAddress"] = self.StreetAddress as AnyObject?
    someDict["PhoneNumber"] = self.PhoneNumber as AnyObject?
    someDict["EmailAddress"] = self.EmailAddress as AnyObject?

    return someDict as AnyObject
}

Solution 5

I was able to greatly reduce my swift project compile times by avoiding the use the Nil-Coalescing Operator and string concatenation.

In otherwords where I had something like:

let x = "one" + object.nullableProperty ?? ""

I changed it to

let x = String(format: "one %@", object.nullableProperty ?? "")

My compile times have dropped drastically- from 20 minutes to 20 seconds.

View more solutions

Comments

[fancy]

Having large array literals currently do lead to performance issues. But (as stated in my question) there are no classes that particularly stand out in compile time. If somebody suffers from long build times he should definitely check out this possibility, but in my case it's something different.

[John Gibb]

I saw a note here (forums.developer.apple.com/thread/19342) that if any files have warnings, xcode will rebuild the entire project rather than the incremental changes. I removed my warnings and it seemed to help—ymmv

[SmileBot]

Did you report this in a radar? This is should not be happening. I notice that it doesn't work if you say :[String] as the type. Only using the generic notation seems to solve the issue. Thanx for posting.

[hardikdevios]

You are the Best My BRo

[Darius]

@hardik.shah his colleague is the best ;)

[d4Rk]

for me, "module optimization" decreased the build time by 30%, "no implicit dependencies" by around 70-80% (even though the latter is more a temporary setting, as it won't work after a clean, at least when using pods).