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[SR-12856] Swift rejects valid array type literal containing closure #55302

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nicklockwood opened this issue May 22, 2020 · 4 comments
Open

[SR-12856] Swift rejects valid array type literal containing closure #55302

nicklockwood opened this issue May 22, 2020 · 4 comments
Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself parser Area → compiler: The legacy C++ parser

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@nicklockwood
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Previous ID SR-12856
Radar None
Original Reporter @nicklockwood
Type Bug
Environment

Swift 5.2, Xcode 11.4

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

md5: 6b3b7fd38d8c9ac6fbf92e4492b5844f

Issue Description:

The following code is rejected by the Swift compiler with the error message "Expected ',' separator":

var handlers = [(_ image: Data?) -> Void]()

However the following all work:

var handlers: [(_ image: Data?) -> Void]
var handlers = Array<(_ image: Data?) -> Void>()
var handlers = [(image: Data?) -> Void]()
var handlers = [(Data?) -> Void]()
@nicklockwood
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It also fails with the same error for Dictionary and Optional literals:

var handlers = [String: (_ image: Data?) -> Void]()
var handler = ((_ image: Data?) -> Void)?

@theblixguy
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It doesn't seem like it is limited to function types - var handlers = [(_ image: Data?)]() throws a similar error.

@nicklockwood
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But

(_ image: Data?)

isn't a valid type though. Tuple labels cannot be prefixed with `_` to make them anonymous (nor would it really make sense to do so).

The bug seems to be specifically triggered by using `_` for anonymous arguments in closures.

@theblixguy
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Yes, I was just referring to the diagnostic being the same (i.e expected ',' separator) which seems wrong here. I think in either scenarios it's trying to parse it as a discard assignment expression and failing.

@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 parser Area → compiler: The legacy C++ parser
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@nicklockwood @theblixguy