Closure arguments parsed as attribute parameters

[SimplyDanny]

Issue Kind

Parse of Valid Source Produced Invalid Syntax Tree

Source Code

f { @Sendable (e: Int) in }

Description

Parsing the code snippet, swift-parser-cli print-tree produces the tree

SourceFileSyntax
├─statements: CodeBlockItemListSyntax
│ ╰─[0]: CodeBlockItemSyntax
│   ╰─item: FunctionCallExprSyntax
│     ├─calledExpression: DeclReferenceExprSyntax
│     │ ╰─baseName: identifier("f")
│     ├─arguments: LabeledExprListSyntax
│     ├─trailingClosure: ClosureExprSyntax
│     │ ├─leftBrace: leftBrace
│     │ ├─signature: ClosureSignatureSyntax
│     │ │ ├─attributes: AttributeListSyntax
│     │ │ │ ╰─[0]: AttributeSyntax
│     │ │ │   ├─atSign: atSign
│     │ │ │   ├─attributeName: IdentifierTypeSyntax
│     │ │ │   │ ╰─name: identifier("Sendable")
│     │ │ │   ├─leftParen: leftParen
│     │ │ │   ├─arguments: LabeledExprListSyntax
│     │ │ │   │ ╰─[0]: LabeledExprSyntax
│     │ │ │   │   ├─label: identifier("e")
│     │ │ │   │   ├─colon: colon
│     │ │ │   │   ╰─expression: DeclReferenceExprSyntax
│     │ │ │   │     ╰─baseName: identifier("Int")
│     │ │ │   ╰─rightParen: rightParen
│     │ │ ╰─inKeyword: keyword(SwiftSyntax.Keyword.in)
│     │ ├─statements: CodeBlockItemListSyntax
│     │ ╰─rightBrace: rightBrace
│     ╰─additionalTrailingClosures: MultipleTrailingClosureElementListSyntax
╰─endOfFileToken: endOfFile

which shows that (e: Int) is interpreted as the parameter list of @Sendable while it is actually meant to be the argument list for the closure.

Is this an ambiguity only the compiler can resolve with full type information available?

[ahoppen]

Tracked in Apple’s issue tracker as rdar://118608697

[SimplyDanny]

@ahoppen: I think @Sendable is not the primary reason for the behavior. I see f { @A (e: Int) in } is parsed in the same way, namely (e: Int) as an argument list.

[ahoppen]

AFAIK @A (e: Int) isn’t valid at the moment either.

_ = { @MainActor (e: Int) in 
  print(e) // error: /tmp/a.swift:2:9: error: cannot find 'e' in scope
}

You need to write this as

_ = { @MainActor
  (e: Int) in 
  print(e)
}

I’m open to discussing whether the first variant should be allowed but that would be a separate issue since it’s not a discrepancy between the new and the old parser.

[SimplyDanny]

Okay. I see the difference. What behaves like the current parser is not a bug.