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[SR-12063] Swift should warn for switch case '.none' vs '.none?' ambiguity #54499

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keith opened this issue Jan 21, 2020 · 4 comments
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[SR-12063] Swift should warn for switch case '.none' vs '.none?' ambiguity #54499

keith opened this issue Jan 21, 2020 · 4 comments
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@theblixguy
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compiler The Swift compiler in itself diagnostics QoI Bug: Diagnostics Quality of Implementation improvement type checker Area → compiler: Semantic analysis

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@keith
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keith commented Jan 21, 2020

Previous ID SR-12063
Radar None
Original Reporter @keith
Type Improvement
Status Resolved
Resolution Done
Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Improvement, DiagnosticsQoI, TypeChecker
Assignee @theblixguy
Priority Medium

md5: 17a3bec14e602d0feaaa8c2f85e8aae7

Issue Description:

With this code:

enum Foo {
    case bar
    case none
}

let a: Foo? = Foo.none

switch a {
case .none: // Should be '.none?'
    print(".none")
case .bar:
    print(".bar")
default:
    print("default")
}

Everything compiles, but you may have surprising behavior where the `default` case is matched instead of `case .none`.

Following by the example of the great warning you get when you have `let a: Foo? = .none`, it would be great if there was a similar warning for the "ambiguity" here
@keith
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keith commented Jan 21, 2020

Looks like this concern was brought up on the other PR allowing the removal of the `?` in the first place #22486 (comment)

@theblixguy
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Good idea, I’ll take a look tomorrow! I think the fix-it should be to change it to 'nil' if you want to match against Optional.none. This is what the official documentation does as well (see https://docs.swift.org/swift-book/ReferenceManual/Patterns.html#ID424).

@theblixguy
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Fixed by #29356 Please verify using the next available snapshot.

@keith
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keith commented Jan 23, 2020

Thanks!

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

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compiler The Swift compiler in itself diagnostics QoI Bug: Diagnostics Quality of Implementation improvement type checker Area → compiler: Semantic analysis
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@keith @theblixguy