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[SR-13842] Compiler fails to type check optional UIImage when SwiftUI is imported #56240

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swift-ci opened this issue Nov 10, 2020 · 4 comments
Closed

[SR-13842] Compiler fails to type check optional UIImage when SwiftUI is imported #56240

swift-ci opened this issue Nov 10, 2020 · 4 comments
Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself type checker Area → compiler: Semantic analysis

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@swift-ci
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Previous ID SR-13842
Radar None
Original Reporter rog (JIRA User)
Type Bug
Status Closed
Resolution Duplicate

Attachment: Download

Environment

BigSur 11.0.1
Xcode 12.2 beta 4

Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug, TypeChecker
Assignee None
Priority Medium

md5: dfabfdcb3a7fd0eae9dbab6e92195d38

duplicates:

  • SR-13815 Confusing unwrapping diagnostic when using implicit member access on Optionals.

Issue Description:

Here's a minimum reproducible:

import UIKit
import SwiftUI

extension UIImage {
    static let background = UIImage(named: "test")
}

let b = UIImageView(image: .background)

The expectation here is that the compiler should be able to resolve .background to an optional UIImage, and accept it as the argument to initialize via UIIImageView(image: ).

However, when SwiftUI is imported in this context, the type checker fails with the following error message

Value of optional type 'UIImage?' must be unwrapped to a value of type 'UIImage'

The output of running
@swift-ci
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Comment by Frederick Kellison-Linn (JIRA)

Some breadcrumbs from brief investigation:

It appears that because `Optional` has a conditional conformance to `View`, our initial lookup pass for `background` (on `UIImage?`) finds `View.background(_:alignment🙂` on `Optional<UIImage>`. Then, when we reach the point in `ConstraintSystem::performMemberLookup` where we would normally look into `UIImage` for unresolved member lookup on an optional type, we've already found a candidate so we don't proceed...

@swift-ci
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Comment by Frederick Kellison-Linn (JIRA)

Here's a reproducer which doesn't touch SwiftUI at all.

extension Optional {
    func foo(_: Int) {}
}

struct S {}

extension S {
    static let foo: S? = S()
}

func takesS(_: S?) {}

takesS(.foo)

@typesanitizer
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Is this the same as https://bugs.swift.org/browse/SR-13815 ?

@swift-ci
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Comment by Frederick Kellison-Linn (JIRA)

theindigamer (JIRA User) Yes, that looks like the same issue!

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
This issue was closed.
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Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself type checker Area → compiler: Semantic analysis
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@typesanitizer @swift-ci