Xcode 8.0 Swift 3.0 slow indexing and building

Go to project settings, then Editor > Add Build Setting > Add User-Defined Setting, and add the following:

SWIFT_WHOLE_MODULE_OPTIMIZATION = YES

Adding this flag dropped our clean-build compile times from 7 mins to 65s for a 40KLOC swift project, miraculously. Also can confirm 2 friends have seen similar improvements on enterprise projects.

I can only assume this is some kind of bug in Xcode 8.0

I solved the problem by commenting all files and then removing comments one by one. I found that the problem is still in the array declaration as described here.

I had code like this and project was not indexing:

class {    var first: String!    var second: String!    var third: String!    var fourth: String!    var fifth: String!    func abc() -> [String] {        var array = [first, second, third, fourth, fifth]    }}

I've changed it to this and indexing started working:

class {    var first: String!    var second: String!    var third: String!    var fourth: String!    var fifth: String!    func abc() -> [String] {        var array = [first]        array.append(second)        array.append(third)        array.append(fourth)        array.append(fifth)    }}

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

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"]