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🚥 Introduce a new Lexical query lookupControlStructure to the SwiftLexicalLookup Library #3216

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🚥 Introduce a new Lexical query lookupControlStructure to the SwiftLexicalLookup Library #3216

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37 changes: 37 additions & 0 deletions Sources/SwiftLexicalLookup/SimpleLookupQueries.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,43 @@
import SwiftSyntax

extension SyntaxProtocol {

@_spi(Experimental) public func lookupControlStructure() -> Syntax? {
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@rintaro rintaro Dec 22, 2025 •
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I don't feel comfortable with having this method on SyntaxProtocol.
Instead, how about making

@_spi(Experimental) public protocol ControlTransferStmtSyntax {
  var controlTransferTarget: Syntax? { get }
}

And make break, continue, return, throw, and fallthrough conform to it?

let syntax = Syntax(self)

switch syntax.as(SyntaxEnum.self) {
case .throwStmt, .returnStmt:
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@rintaro rintaro Dec 23, 2025

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The target of throw can be do-catch statements.

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@rintaro rintaro Dec 23, 2025

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Actually, SyntaxProtoco.lookupCatchNode() should be usable for throw case.

return lookupEnclosingControlStructure(for: [
FunctionDeclSyntax.self,
InitializerDeclSyntax.self,
DeinitializerDeclSyntax.self,
AccessorDeclSyntax.self,
ClosureExprSyntax.self,
])
case .breakStmt, .continueStmt:
return lookupEnclosingControlStructure(for: [
Comment on lines +29 to +30
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@rintaro rintaro Dec 22, 2025 •
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Unfortunately, break and continue target is not that simple. You'd need to handle labels e.g. break LOOP.
Also, they can target other non-loop labeled statements , e.g.

OUTER: do {
  for val in values {
    if val.condition {
      break OUTER
    }
  }
}

In the actual compiler, the rule is implemented in swift::findBreakOrContinueStmtTarget

WhileStmtSyntax.self,
RepeatStmtSyntax.self,
ForStmtSyntax.self,
])
default:
return nil
}
}

private func lookupEnclosingControlStructure(for types: [SyntaxProtocol.Type]) -> Syntax? {
var nextSyntax: Syntax? = Syntax(self).parent

while let currentSyntax = nextSyntax {
if types.contains(where: { currentSyntax.is($0) }) {
return currentSyntax
}
nextSyntax = currentSyntax.parent
}

return nil
}

/// Returns all labeled statements available at a particular syntax node.
///
/// - Returns: Available labeled statements at a particular syntax node
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