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[SR-10466] Accepts invalid because where clause seems to be ignored. #52866

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jepers opened this issue Apr 12, 2019 · 4 comments
Closed

[SR-10466] Accepts invalid because where clause seems to be ignored. #52866

jepers opened this issue Apr 12, 2019 · 4 comments
Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior.

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@jepers
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jepers commented Apr 12, 2019

Previous ID SR-10466
Radar None
Original Reporter @jepers
Type Bug
Status Closed
Resolution Done
Environment

Xcode 10.2, macOS 10.14.4

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

md5: 6de39a7eeffdab4b0289c4abdfc194a9

relates to:

  • SR-5440 Typealias in constrained extension misinterprets the where clause

Issue Description:

The following (AFAICS invalid) program still compiles with Swift 5 / Xcode 10.2 and the latest dev snapshot (2019-04-10):

struct S<T> {
    var a : A
}
extension S where T == Never {
    typealias A = Int
}
let v = S<Int>(a: 123)
print(v)

Doesn't this imply/require Int == Never?

More details here:
https://forums.swift.org/t/22995
@belkadan
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I'm pretty sure type lookup just doesn't respect constraints at all. (@slavapestov, this is why I get so surprised when people do clever things with constrained extensions—some of them don't work.)

Jens, I don't think we need two bugs for this; can we dup this to SR-5440?

@slavapestov
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Yeah, we don't check constraints in all the places we should. Let's dupe this and once we fix it we can verify that all examples in the dupes are fixed.

@jepers
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jepers commented Apr 12, 2019

Sure, I only filed this as an isolated simplified case of SR-5440, since SR-5440 got a bit too broad and is kind of partly fixed.

@slavapestov
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#28275

@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.
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3 participants
@slavapestov @belkadan @jepers