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[SR-13303] Erroneous warning shown when casting protocol type to dictionary type #55743

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swift-ci opened this issue Jul 27, 2020 · 3 comments
Closed

[SR-13303] Erroneous warning shown when casting protocol type to dictionary type #55743

swift-ci opened this issue Jul 27, 2020 · 3 comments
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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-13303
Radar None
Original Reporter ketzusaka (JIRA User)
Type Bug
Status Resolved
Resolution Done
Environment

macOS X 10.15.6.

Bug is present in Xcode 11.6, Xcode 12 Beta 2. It is not present in Xcode 11.3.1

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

md5: e1b5118e1d41c3d0c99d8fe0ff8ba714

Issue Description:

I have a protocol that a dictionary conforms to. Types can be cast from this protocol to the concrete dictionary type. This has worked for us before, but is now showing a warning. It works correctly (not showing the warning) on Xcode 11.3.1. The warning shows on Xcode 11.6; we have not tested the in between Xcodes. This issue is still present in Xcode 12 beta 2.

Sample code to reproduce:

import Foundation


protocol Widget {}
extension String: Widget {}
extension Dictionary: Widget where Key == String, Value == Widget {}


var subject: Widget = ["Foo": "Bar"]


// Shows warning: Cast from 'Widget' to unrelated type '[String : String]' always fails
guard let castedSubject = subject as? [String: String] else { fatalError("Cast failed") }
print(castedSubject) // Prints successfully as ["Foo": "Bar"]
@theblixguy
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This was fixed by @LucianoPAlmeida in #32592 Could you verify using a trunk development snapshot from swift.org?

@swift-ci
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Comment by James Richard (JIRA)

Sweet![]( Verified its good with Xcode 12 Beta 2 and the July 22, 2020 toolchain. Thanks)

@theblixguy
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No worries! Good to hear that it's fixed for you.

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