[SR-11529] Xcode won't ever build the project nor finish indexing it when keyPath subscript overlaps with others. #53930

swift-ci · 2019-09-26T16:38:36Z


Previous ID	SR-11529
Radar	rdar://problem/55746272
Original Reporter	sunshinejr (JIRA User)
Type	Bug

Environment

macOS: Catalina beta 9, but I also had reports of these in mojave
Xcode: 11 but I tried 10.3 and it failed as well
Swift: only used bundled toolchains on given Xcode's, nothing fancy

Additional Detail from JIRA


Votes	0
Component/s	Compiler
Labels	Bug, KeyPaths
Assignee	None
Priority	Medium

md5: f131fa5fa4bfd8b3a7a76bfb7bceaf57

Issue Description:

So I was debugging this issue my whole day and it's really weird as my current workaround doesn't make sense to me so please bear with me. Finally I was able to recreate a small code sample that breaks both the indexer and compiler❓.

Given the code below (either in another module/package or free floating in a file)

public var CrashDefaults = SwiftCrashDefaults(keys: SwiftCrashDefaultsKeys(key: .init(bar: "")))

public protocol Base {
    associatedtype T
}

extension String: Base {
    public typealias T = String
}

extension Optional: Base where Wrapped: Base {
    public typealias T = Self
}

public struct SwiftCrashDefaultsKey<T: Base> {
    public let bar: T

    public init(bar: T) { self.bar = bar; }
}

public protocol SwiftCrashDefaultsKeyStore {}

public struct SwiftCrashDefaultsKeys: SwiftCrashDefaultsKeyStore {

    public let key: SwiftCrashDefaultsKey<String?>

    public init(key: SwiftCrashDefaultsKey<String?>) { self.key = key}
}

public struct SwiftCrashDefaults<KeyStore: SwiftCrashDefaultsKeyStore> {

    public let keys: KeyStore

    public init(keys: KeyStore) {
        self.keys = keys
    }

    public subscript<T: Base>(key: SwiftCrashDefaultsKey<T>) -> T.T {
        get { return 1 as! T.T }
        set {}
    }

    public subscript<T: Base>(keyPath: KeyPath<KeyStore, SwiftCrashDefaultsKey<T>>) -> T.T {
        get { return 1 as! T.T }
        set {}
    }
}

you are able to use it and assign it:

let compilerWontCrash = CrashDefaults[\.key]

but you are not able to use it in a conditional statement as it will result in an infinite indexing and never-ending build process:

if let compilerCrash = CrashDefaults[\.key]{
    NSLog("it should just log it but it won't :( \(compilerCrash)")
}

Workarounds

Don't use a global variable
E.g. when you specify your local `crashDefaults` variable you will be able to use it in the conditional statement:

let crashDefaults = SwiftCrashDefaults(keys: SwiftCrashDefaultsKeys(key: .init(bar: "foo")))
if let compilerCrash = crashDefaults[\.key]{
    NSLog("it should just log it and it will! \(compilerCrash)")
}

Add a label to your other subscript
So instead of having this:

public subscript<T: Base>(key: SwiftCrashDefaultsKey<T>) -> T.T {
    get { return 1 as! T.T }
    set {}
}

Use this:

public subscript<T: Base>(key key: SwiftCrashDefaultsKey<T>) -> T.T {
    get { return 1 as! T.T }
    set {}
}

and it will also build as expected.

belkadan · 2019-09-26T17:22:12Z

@swift-ci create

swift-ci transferred this issue from apple/swift-issues Apr 25, 2022

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[SR-11529] Xcode won't ever build the project nor finish indexing it when keyPath subscript overlaps with others. #53930

[SR-11529] Xcode won't ever build the project nor finish indexing it when keyPath subscript overlaps with others. #53930

swift-ci commented Sep 26, 2019

belkadan commented Sep 26, 2019

[SR-11529] Xcode won't ever build the project nor finish indexing it when keyPath subscript overlaps with others. #53930

[SR-11529] Xcode won't ever build the project nor finish indexing it when keyPath subscript overlaps with others. #53930

Comments

swift-ci commented Sep 26, 2019

Workarounds

belkadan commented Sep 26, 2019