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[SR-14071] Enum case as protocol witness uses incorrect ARC semantics for payload #56460

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kabiroberai opened this issue Jan 20, 2021 · 2 comments
Closed

[SR-14071] Enum case as protocol witness uses incorrect ARC semantics for payload #56460

kabiroberai opened this issue Jan 20, 2021 · 2 comments
Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself

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@kabiroberai
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Previous ID SR-14071
Radar rdar://problem/73406514
Original Reporter @kabiroberai
Type Bug
Status Resolved
Resolution Duplicate
Environment

Operating System: macOS Big Sur 11.1 (20C69)

Toolchain: Xcode 12.3 (12C33)

Target Platform: macOS

Additional Detail from JIRA
Votes 1
Component/s Compiler
Labels Bug
Assignee None
Priority Medium

md5: ec3380d9c01408ad14573d2d139a63ff

duplicates:

  • SR-14041 Protocol allows to create a nested enum without explicit indirect keyword resulting in a runtime crash

Issue Description:

When using an (enum case with a reference-type associated value) as a protocol witness, the Swift compiler appears to be using incorrect ARC semantics while passing the associated value argument, resulting in an over-release or memory leak of the passed object.

For example:

class MyClass {}

protocol MyProtocol {
    static func value(_: MyClass) -> Self
}

enum MyEnum: MyProtocol {
    case value(MyClass)
}

func doCrash<P: MyProtocol>(_ type: P.Type) {
    // malloc: Double free of object 0x...
    _ = P.value(MyClass())
}

doCrash(MyEnum.self)

Furthermore, using a regular static method as a protocol witness fixes the issue:

class MyClass {}

protocol MyProtocol {
    static func value(_: MyClass) -> Self
}

enum MyEnum: MyProtocol {
    case _value(MyClass)
    static func value(_ obj: MyClass) -> MyEnum {
        ._value(obj)
    }
}

func doCrash<P: MyProtocol>(_ type: P.Type) {
    // No crash!
    _ = P.value(MyClass())
}

doCrash(MyEnum.self)
@typesanitizer
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@swift-ci create

@kabiroberai
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Just tested this out using Xcode 12.4 as well as development snapshot 2021-02-02-a (Swift 5.4) and I can confirm that the issue is still reproducible.

@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
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@typesanitizer @kabiroberai