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[SR-14646] Suggest to replace control flow condition to type-checking when result of downcasting is not used #56998

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WowbaggersLiquidLunch opened this issue May 19, 2021 · 6 comments
Closed

[SR-14646] Suggest to replace control flow condition to type-checking when result of downcasting is not used #56998

WowbaggersLiquidLunch opened this issue May 19, 2021 · 6 comments
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@WowbaggersLiquidLunch
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compiler The Swift compiler in itself diagnostics QoI Bug: Diagnostics Quality of Implementation good first issue Good for newcomers improvement

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@WowbaggersLiquidLunch
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Previous ID SR-14646
Radar rdar://problem/78276233
Original Reporter @WowbaggersLiquidLunch
Type Improvement
Status Closed
Resolution Done
Environment

Swift (Trunk) Development Snapshot 2021-05-17 (a)
Xcode 12.4 (12D4e)
macOS 10.15.7 (19H1030)

Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Improvement, DiagnosticsQoI, StarterBug
Assignee @WowbaggersLiquidLunch
Priority Medium

md5: 1cfced954c10e0b1e0facdc9ec346d1a

Issue Description:

2 examples:

func answer(of universe: Any?) -> Int {
    // current fix-it: Replace 'let bar = universe as? Foo' with '(universe as? Foo) != nil'
    // better fix-it: Replace 'let bar = universe as? Foo' with 'universe is Foo'
    if let bar = universe as? Foo {
        return 42
    } else {
        return 54
    }
}
let foo: Optional<Any> = 42 as Int

// current fix-it: Replace 'let bar = foo as? Int' with '(foo as? Int) != nil'
// better fix-it: Replace 'let bar = foo as? Int' with 'foo is Int'

if let bar = foo as? Int { 
    print("'foo' is of type 'Int'")
}
@typesanitizer
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That's strange. I see the following diagnostic:

Value 'bar' was defined but never used; consider replacing with boolean test
Replace 'let bar = foo as?' with 'foo is'

So the "better fix-it" behavior is what I see locally. Are you sure you're using the newer toolchain for testing?

@WowbaggersLiquidLunch
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My mistake. I was using the newer toolchain, but I overly-reduced the example without checking it first. The "current fix-it" occurs only when downcasting from Optional<Any>. I fixed the example, and added another one.

@typesanitizer
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@swift-ci create

@swift-ci
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Comment by Minhyuk Kim (JIRA)

I created a PR here! #37897

@xedin
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xedin commented Jun 22, 2021

Fixed by #37897 Thank you, mininny (JIRA User)! @WowbaggersLiquidLunch Please use the next available snapshot of main branch to verify and close.

@WowbaggersLiquidLunch
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Sorry for the delay. I just verified that this has been fixed as of the 2021-07-09 macOS toolchain

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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compiler The Swift compiler in itself diagnostics QoI Bug: Diagnostics Quality of Implementation good first issue Good for newcomers improvement
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@xedin @typesanitizer @swift-ci @WowbaggersLiquidLunch