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[SR-4378] Swift 3.1 regression inferring type of tuple with generics #46957

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NachoSoto opened this issue Mar 27, 2017 · 5 comments
Closed

[SR-4378] Swift 3.1 regression inferring type of tuple with generics #46957

NachoSoto opened this issue Mar 27, 2017 · 5 comments
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@slavapestov
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself type checker Area → compiler: Semantic analysis

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@NachoSoto
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Previous ID SR-4378
Radar rdar://problem/31283568
Original Reporter @NachoSoto
Type Bug
Status Resolved
Resolution Won't Do
Environment

Apple Swift version 3.1 (swiftlang-802.0.48 clang-802.0.38)
Target: x86_64-apple-macosx10.9

Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug, 3.1Regression, TypeChecker
Assignee @slavapestov
Priority Medium

md5: 7304cd4263852c034a45e9816087b6ee

Issue Description:

The code (that used to compile):

self.pages = MutableProperty((
    data: [0: .notLoaded(expectedCount: 1)],
    totalCount: 0
))

More info on the types:

public final class InfiniteScrollingCollectionView <
    DataSource: InfiniteScrollingCollectionViewDataSource,
    Delegate: InfiniteScrollingCollectionViewDelegate,
    CellConfiguration: InfiniteScrollingCollectionCellConfigurator
> : UIView
    where
    DataSource.Element == CellConfiguration.Element,
    Delegate.Element == CellConfiguration.Element
{
    typealias Element = DataSource.Element
    typealias Error = DataSource.Error
    typealias Cell = CellConfiguration.Cell
    
    fileprivate typealias Page = DataSourcePage<Element, Error>
    fileprivate typealias Pages = (data: [Int : Page], totalCount: Int)
  
    private let pages: MutableProperty<Pages>

    ....
}

fileprivate enum DataSourcePage<T: Equatable, E: Swift.Error> {
    case loaded([T])
    case notLoaded(expectedCount: Int)
    case error(E, expectedCount: Int)
}
final public class MutableProperty<Value> {
    public init(_ initialValue: Value)
    ....
}

Expected result: code still compiles
Actual result: "Type of expression is ambiguous without more context"

Explicitly defining the tuple type works around the ambiguity:

let initialPages: Pages = (
    data: [0: .notLoaded(expectedCount: 1)],
    totalCount: 0
)
self.pages = MutableProperty(initialPages)
@jckarter
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@swift-ci create

@slavapestov
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Here is a reduced test case:

final public class MutableProperty<Value> {
    public init(_ initialValue: Value) {}
}

enum DataSourcePage<T> {
    case notLoaded
}

let pages1: MutableProperty<(data: DataSourcePage<Int>, totalCount: Int)> = MutableProperty((
    data: .notLoaded,
    totalCount: 0
))


let pages2: MutableProperty<(data: DataSourcePage<Int>, totalCount: Int)> = MutableProperty((
    data: DataSourcePage.notLoaded,
    totalCount: 0
))


let pages3: MutableProperty<(data: DataSourcePage<Int>, totalCount: Int)> = MutableProperty((
    data: DataSourcePage<Int>.notLoaded,
    totalCount: 0
))

All three examples type check correctly in -swift-version 4 mode, so this is something we fixed already as part of SE-0110. I'll add some tests.

@slavapestov
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I added a test case: #8877

@NachoSoto
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I imagine this is still not fixed?

@slavapestov
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Swift 3 mode is going away. The code works in Swift 4 mode.

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
This issue was closed.
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@slavapestov slavapestov

Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself type checker Area → compiler: Semantic analysis
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@slavapestov @jckarter @NachoSoto