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[SR-7339] Incorrect keypath error for invalid typecast #49887

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swift-ci opened this issue Apr 3, 2018 · 3 comments
Closed

[SR-7339] Incorrect keypath error for invalid typecast #49887

swift-ci opened this issue Apr 3, 2018 · 3 comments
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@gregomni
Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself diagnostics QoI Bug: Diagnostics Quality of Implementation type checker Area → compiler: Semantic analysis

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@swift-ci
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swift-ci commented Apr 3, 2018

Previous ID SR-7339
Radar rdar://problem/39142001
Original Reporter paiv (JIRA User)
Type Bug
Status Resolved
Resolution Done
Environment

Apple Swift version 4.1 (swiftlang-902.0.48 clang-902.0.37.1)

Xcode 9.3

Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug, DiagnosticsQoI, TypeChecker
Assignee @gregomni
Priority Medium

md5: 45aa5b2c9a05c9665672583ae8bf0723

Issue Description:

Given this code

class Some<T, V> {
    init(keyPath: KeyPath<T, ((V) -> Void)?>) {
    }
}

class Demo {
    var here: (() -> Void)?
}

and trying to create variable

let some = Some(keyPath: \Demo.here)

I'm getting this error

error: x.playground:4:32: error: type '_' has no member 'here'
let some = Some(keyPath: \Demo.here)
                               ^

Which is misleading, since Demo has member here.

If changed to

let kk = \Demo.here
let some = Some(keyPath: kk)

Error changes to

error: x.playground:5:26: error: cannot convert value of type 'ReferenceWritableKeyPath<Demo, (() -> Void)?>' to expected argument type 'KeyPath<_, ((_) -> Void)?>'
let some = Some(keyPath: kk)
                         ^~
@belkadan
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belkadan commented Apr 3, 2018

@swift-ci create

@mdiep
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mdiep commented Jun 5, 2018

Since it wasn't obvious to me:

The actual error here is because Demo.here takes 0 arguments but the Some.init takes a function that's generic over an argument V. That doesn't match a 0-arg function.

But that doesn't excuse the poor diagnostic.

This is still an issue in Apple Swift version 4.2 (swiftlang-1000.0.16.7 clang-1000.10.25.3).

@gregomni
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gregomni commented Aug 5, 2018

error improved in #18329

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
This issue was closed.
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@gregomni gregomni

Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself diagnostics QoI Bug: Diagnostics Quality of Implementation type checker Area → compiler: Semantic analysis
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@mdiep @belkadan @swift-ci @gregomni