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LaurenWhite
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Implement no cases with only fallthrough (swiftlang#68)
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‎Sources/Rules/NoCasesWithOnlyFallthrough.swift

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Original file line numberDiff line numberDiff line change
@@ -11,5 +11,136 @@ import SwiftSyntax
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///
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/// - SeeAlso: https://google.github.io/swift#fallthrough-in-switch-statements
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public final class NoCasesWithOnlyFallthrough: SyntaxFormatRule {
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public override func visit(_ node: SwitchStmtSyntax) -> StmtSyntax {
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var newCases: [SwitchCaseSyntax] = []
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var violations: [SwitchCaseLabelSyntax] = []
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for switchCase in node.cases {
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guard let switchCase = switchCase as? SwitchCaseSyntax else { continue }
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guard let label = switchCase.label as? SwitchCaseLabelSyntax else {
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newCases.append(switchCase)
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continue
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}
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if switchCase.statements.count == 1,
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let only = switchCase.statements.first,
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only.item is FallthroughStmtSyntax {
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diagnose(.collapseCase(name: "\(label)"), on: switchCase)
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violations.append(label)
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} else {
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guard violations.count > 0 else {
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newCases.append(switchCase)
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continue
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}
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if retrieveNumericCaseValue(caseLabel: label) != nil {
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let newCase = collapseIntegerCases(violations: violations,
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validCaseLabel: label,
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validCase: switchCase)
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newCases.append(newCase)
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} else {
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let newCase = collapseNonIntegerCases(violations: violations,
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validCaseLabel: label,
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validCase: switchCase)
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newCases.append(newCase)
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}
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violations = []
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}
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}
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return node.withCases(SyntaxFactory.makeSwitchCaseList(newCases))
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}
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// Puts all given cases on one line with range operator or commas
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func collapseIntegerCases(violations: [SwitchCaseLabelSyntax],
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validCaseLabel: SwitchCaseLabelSyntax, validCase: SwitchCaseSyntax) -> SwitchCaseSyntax {
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var isConsecutive = true
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var index = 0
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var caseNums: [Int] = []
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for item in violations {
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guard let caseNum = retrieveNumericCaseValue(caseLabel: item) else { continue }
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caseNums.append(caseNum)
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}
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guard let validCaseNum = retrieveNumericCaseValue(caseLabel: validCaseLabel) else {
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return validCase
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}
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caseNums.append(validCaseNum)
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while index <= caseNums.count - 2, isConsecutive {
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isConsecutive = caseNums[index] + 1 == caseNums[index + 1]
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index += 1
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}
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var newCaseItems: [CaseItemSyntax] = []
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let first = caseNums[0]
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let last = caseNums[caseNums.count - 1]
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if isConsecutive {
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// Create a case with a sequence expression based on the new range
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let start = SyntaxFactory.makeIntegerLiteralExpr(
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digits: SyntaxFactory.makeIntegerLiteral("\(first)"))
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let end = SyntaxFactory.makeIntegerLiteralExpr(
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digits: SyntaxFactory.makeIntegerLiteral("\(last)"))
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let newExpList = SyntaxFactory.makeExprList(
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[start,
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SyntaxFactory.makeBinaryOperatorExpr(operatorToken:
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SyntaxFactory.makeUnspacedBinaryOperator("...")),
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end])
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let newExpPat = SyntaxFactory.makeExpressionPattern(
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expression: SyntaxFactory.makeSequenceExpr(elements: newExpList))
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newCaseItems.append(
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SyntaxFactory.makeCaseItem(pattern: newExpPat, whereClause: nil, trailingComma: nil))
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} else {
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// Add each case item separated by a comma
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for num in caseNums {
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let newExpPat = SyntaxFactory.makeExpressionPattern(
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expression: SyntaxFactory.makeIntegerLiteralExpr(
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digits: SyntaxFactory.makeIntegerLiteral("\(num)")))
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let trailingComma = SyntaxFactory.makeCommaToken(trailingTrivia: .spaces(1))
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let newCaseItem = SyntaxFactory.makeCaseItem(
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pattern: newExpPat,
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whereClause: nil,
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trailingComma: num == last ? nil : trailingComma
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)
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newCaseItems.append(newCaseItem)
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}
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}
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let caseItemList = SyntaxFactory.makeCaseItemList(newCaseItems)
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return validCase.withLabel(validCaseLabel.withCaseItems(caseItemList))
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}
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// Gets integer value from case label, if possible
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func retrieveNumericCaseValue(caseLabel: SwitchCaseLabelSyntax) -> Int? {
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if let firstTok = caseLabel.caseItems.firstToken,
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let num = Int(firstTok.text) {
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return num
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}
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return nil
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}
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// Puts all given cases on one line separated by commas
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func collapseNonIntegerCases(violations: [SwitchCaseLabelSyntax],
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validCaseLabel: SwitchCaseLabelSyntax, validCase: SwitchCaseSyntax) -> SwitchCaseSyntax {
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var newCaseItems: [CaseItemSyntax] = []
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for violation in violations {
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for item in violation.caseItems {
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let newCaseItem = item.withTrailingComma(
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SyntaxFactory.makeCommaToken(trailingTrivia: .spaces(1)))
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newCaseItems.append(newCaseItem)
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}
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}
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for item in validCaseLabel.caseItems {
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newCaseItems.append(item)
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}
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let caseItemList = SyntaxFactory.makeCaseItemList(newCaseItems)
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return validCase.withLabel(validCaseLabel.withCaseItems(caseItemList))
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}
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}
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extension Diagnostic.Message {
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static func collapseCase(name: String) -> Diagnostic.Message {
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return .init(.warning,
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"\(name) only contains 'fallthrough' and can be combined with a following case")
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}
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}

‎Tests/SwiftFormatTests/NoCasesWithOnlyFallthroughTests.swift

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import Foundation
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import XCTest
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import SwiftSyntax
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@testable import Rules
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public class NoCasesWithOnlyFallthroughTests: DiagnosingTestCase {
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func testFallthroughCases() {
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XCTAssertFormatting(NoCasesWithOnlyFallthrough.self,
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input: """
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switch numbers {
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case 1: print("one")
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case 2: fallthrough
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case 3: fallthrough
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case 4: print("two to four")
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case 5: fallthrough
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case 7: print("five or seven")
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default: break
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}
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switch letters {
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case "a": fallthrough
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case "b", "c": fallthrough
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case "d": print("abcd")
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case "e": print("e")
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case "f": fallthrough
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case "z": print("fz")
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default: break
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}
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switch tokens {
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case .comma: print(",")
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case .rightBrace: fallthrough
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case .leftBrace: fallthrough
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case .braces: print("{}")
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case .period: print(".")
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case .empty: fallthrough
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default: break
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}
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""",
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expected: """
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switch numbers {
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case 1: print("one")
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case 2...4: print("two to four")
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case 5, 7: print("five or seven")
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default: break
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}
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switch letters {
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case "a", "b", "c", "d": print("abcd")
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case "e": print("e")
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case "f", "z": print("fz")
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default: break
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}
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switch tokens {
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case .comma: print(",")
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case .rightBrace, .leftBrace, .braces: print("{}")
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case .period: print(".")
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default: break
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}
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""")
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}
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#if !os(macOS)
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static let allTests = [
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NoCasesWithOnlyFallthroughTests.testFallthroughCases,
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]
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#endif
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}

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