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[SwiftParse] Update for accessor block disambiguation marker #3171

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Oct 18, 2025
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[SwiftParse] Update for accessor block disambiguation marker #3171

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7 changes: 7 additions & 0 deletions Sources/SwiftParser/Lookahead.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -274,6 +274,13 @@ extension Parser.Lookahead {
var lookahead = self.lookahead()
lookahead.eat(.leftBrace)

// '@_accessorBlock' is a builtin disambiguation marker.
if lookahead.peek(isAt: .identifier),
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Don’t you also need to consume the @ before looking at the identifier? Also, I think a test case would be good.

Also, I think this would probably belong in the while lookahead.consume(if: .atSign) != nil { loop below to make it resilient so @_accessorBlock doesn’t necessarily need to be the first attribute.

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Don’t you also need to consume the @ before looking at the identifier?

We know the current token is @ at line 269 above.

I think this would probably belong in the while lookahead.consume(if: .atSign) != nil { loop below to make it resilient so @_accessorBlock doesn’t necessarily need to be the first attribute.

ASTPrinter only print @_accessorBlock right after {. I don't see a reason to put it in the loop

Also, I think a test case would be good.

Sure, I will add a test case.

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We know the current token is @ at line 269 above.

Ah, I got a little confused about nextToken and then using a fresh lookahead here. Opened #3172 to make this slightly easier to read.

ASTPrinter only print @_accessorBlock right after {. I don't see a reason to put it in the loop

OK, your choice. But I find it odd that order of attributes matters here when it doesn’t in any other cases.

lookahead.peek().tokenText == "_accessorBlock"
{
return true
}

// Eat attributes, if present.
while lookahead.consume(if: .atSign) != nil {
guard lookahead.consume(if: .identifier) != nil else {
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37 changes: 37 additions & 0 deletions Tests/SwiftParserTest/DeclarationTests.swift
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Expand Up @@ -3768,4 +3768,41 @@ final class UsingDeclarationTests: ParserTestCase {
"""
)
}

func testAccessorBlockDisambiguationMarker() {
assertParse(
"""
var value = initialValue { @_accessorBlock
get
}
""",
substructure: VariableDeclSyntax(
bindingSpecifier: .keyword(.var),
bindings: [
PatternBindingSyntax(
pattern: IdentifierPatternSyntax(identifier: .identifier("value")),
initializer: InitializerClauseSyntax(
value: DeclReferenceExprSyntax(baseName: .identifier("initialValue"))
),
accessorBlock: AccessorBlockSyntax(
leftBrace: .leftBraceToken(),
accessors: .accessors([
AccessorDeclSyntax(
attributes: [
.attribute(
AttributeSyntax(
atSign: .atSignToken(),
attributeName: IdentifierTypeSyntax(name: .identifier("_accessorBlock"))
)
)
],
accessorSpecifier: .keyword(.get)
)
])
)
)
]
)
)
}
}