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[SR-9399] Source compatibility regression (swift December 1, 2018) #51865

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Agarunov opened this issue Dec 2, 2018 · 4 comments
Closed

[SR-9399] Source compatibility regression (swift December 1, 2018) #51865

Agarunov opened this issue Dec 2, 2018 · 4 comments
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@Agarunov
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself regression source compatibility swift 5.0 type checker Area → compiler: Semantic analysis

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@Agarunov
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Agarunov commented Dec 2, 2018

Previous ID SR-9399
Radar None
Original Reporter @Agarunov
Type Bug
Status Resolved
Resolution Invalid
Environment

macOS 10.14.1, Xcode 10.1, swift December 1, 2018

Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug, 5.0Regression, SourceCompatibility, TypeChecker
Assignee @Agarunov
Priority Medium

md5: 1c30299f8ccef30dd6fa0b93f3bb97ea

Issue Description:

Source compatibility regression in this example code

let optionalArray: [Int]?

if true {
    optionalArray = [1, 2, 3, 4]
} else {
    optionalArray = [5, 6, 7, 8]
    
    // Xcode 10.1
    // swift 4.2.1: no compilation error
    // swift toolchain December 1, 2018: Mutating method 'removeFirst' may not be used on immutable value 'optionalArray'
    optionalArray?.removeFirst()
}
@belkadan
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belkadan commented Dec 3, 2018

Hm. Arguably the new toolchain is correct, but that doesn't mean it's not a source compat break. @rudkx, @xedin?

@rudkx
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rudkx commented Dec 3, 2018

This diagnostic is emitted by DI.

It looks like expected fallout from #18839.

/cc: @rjmccall

@rjmccall
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rjmccall commented Dec 3, 2018

Yeah, this example seems like an obvious bug that we don't need to maintain source compatibility with.

@xedin
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xedin commented Dec 3, 2018

Based on the discussion in comments, it looks like new behavior is correct.

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

Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself regression source compatibility swift 5.0 type checker Area → compiler: Semantic analysis
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@xedin @rudkx @belkadan @rjmccall @Agarunov @AnthonyLatsis