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[SR-11054] “Expression failed to parse, unknown error” only in Xcode 10.2.1 playgrounds #53446

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swift-ci opened this issue Jul 2, 2019 · 2 comments
Open

[SR-11054] “Expression failed to parse, unknown error” only in Xcode 10.2.1 playgrounds #53446

swift-ci opened this issue Jul 2, 2019 · 2 comments
Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself PlaygroundTransform

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@swift-ci
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swift-ci commented Jul 2, 2019

Previous ID SR-11054
Radar rdar://problem/52527289
Original Reporter TizianoCoroneo (JIRA User)
Type Bug
Environment

macOS Mojave 10.14.5

Xcode 10.2.1 Playgrounds

Swift 5.0

Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug, PlaygroundTransform
Assignee mattpat (JIRA)
Priority Medium

md5: 2012d30ee71bc653128fbacd64c97987

Issue Description:

Expression failed to parse, unknown error

The following code triggers this strange error message in the console area at the bottom of Xcode 10.2.1 Playgrounds.

class TestViewController: UIViewController {
    var mainLabel: UILabel!
}

class TestPresenter {
    init(_ vc: TestViewController) {
        self.vc = vc
    }
    
    var vc: TestViewController!
    
    func updateLabel(withString str: String) {
        vc.mainLabel.text = str
    }
}

The issue is fixed by or adding a question mark after mainLabel to make the optional chaining kick in:

class TestViewController: UIViewController {
    var mainLabel: UILabel!
}

class TestPresenter {
    init(_ vc: TestViewController) {
        self.vc = vc
    }
    
    var vc: TestViewController!
    
    func updateLabel(withString str: String) {
        vc.mainLabel?.text = str
    }
}

Or by removing the exclamation mark from the vc property, making the implicit optional unwrapping only one level deep instead of two:

class TestViewController: UIViewController {
    var mainLabel: UILabel!
}

class TestPresenter {
    init(_ vc: TestViewController) {
        self.vc = vc
    }
    
    var vc: TestViewController
    
    func updateLabel(withString str: String) {
        vc.mainLabel.text = str
    }
}

This error only appears in Xcode 10.2.1 Playgrounds. It compiles successfully in Xcode 10.2.1 projects. We also discussed this issue for a bit in the Swift forum here: https://forums.swift.org/t/expression-failed-to-parse-unknown-error-only-in-xcode-10-2-1-playgrounds
@belkadan
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belkadan commented Jul 2, 2019

@swift-ci create

@dcci
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Mannequin

dcci mannequin commented Jul 18, 2019

This seems to be a Playgrounds issue.

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself PlaygroundTransform
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