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Fix #803: Use C# 9 relational patterns for VB Case Is <op> constant #1251

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Fix #803: Use C# 9 relational patterns for VB Case Is <op> constant #1251

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4b852d5
Fix #803: Use C# 9 relational patterns for VB `Case Is <op> constant`
claude Apr 13, 2026
dc08ad9
Fix #803 compile error: use CS.CSharpExtensions.Kind() to avoid VB ex…
claude Apr 13, 2026
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15 changes: 15 additions & 0 deletions CodeConverter/CSharp/MethodBodyExecutableStatementVisitor.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -843,6 +843,13 @@ public override async Task<SyntaxList<StatementSyntax>> VisitSelectBlock(VBSynta
if (isObjectComparison) {
caseSwitchLabelSyntax = WrapInCasePatternSwitchLabelSyntax(node, relational.Value, csRelationalValue, false, operatorKind);
}
else if (!isStringComparison && _semanticModel.GetConstantValue(relational.Value).HasValue) {
csRelationalValue = CommonConversions.TypeConversionAnalyzer.AddExplicitConversion(relational.Value, csRelationalValue);
var operatorToken = SyntaxFactory.Token(GetRelationalPatternTokenKind(operatorKind));
caseSwitchLabelSyntax = SyntaxFactory.CasePatternSwitchLabel(
SyntaxFactory.RelationalPattern(operatorToken, csRelationalValue),
SyntaxFactory.Token(SyntaxKind.ColonToken));
}
else {
var varName = CommonConversions.CsEscapedIdentifier(GetUniqueVariableNameInScope(node, "case"));
ExpressionSyntax csLeft = ValidSyntaxFactory.IdentifierName(varName);
Expand Down Expand Up @@ -1021,6 +1028,14 @@ private CasePatternSwitchLabelSyntax WrapInCasePatternSwitchLabelSyntax(VBSyntax
_ => throw new ArgumentOutOfRangeException(nameof(caseClauseKind), caseClauseKind, null)
};

private static CS.SyntaxKind GetRelationalPatternTokenKind(VBasic.SyntaxKind caseClauseKind) => caseClauseKind switch {
VBasic.SyntaxKind.CaseLessThanClause => CS.SyntaxKind.LessThanToken,
VBasic.SyntaxKind.CaseLessThanOrEqualClause => CS.SyntaxKind.LessThanEqualsToken,
VBasic.SyntaxKind.CaseGreaterThanOrEqualClause => CS.SyntaxKind.GreaterThanEqualsToken,
VBasic.SyntaxKind.CaseGreaterThanClause => CS.SyntaxKind.GreaterThanToken,
_ => throw new ArgumentOutOfRangeException(nameof(caseClauseKind), caseClauseKind, null)
};

private ExpressionSyntax ComparisonAdjustedForStringComparison(VBSyntax.SelectBlockSyntax node, VBSyntax.ExpressionSyntax vbCase, TypeInfo lhsTypeInfo, ExpressionSyntax csLeft, ExpressionSyntax csRight, TypeInfo rhsTypeInfo, ComparisonKind comparisonKind)
{
var vbEquality = CommonConversions.VisualBasicEqualityComparison;
Expand Down
15 changes: 15 additions & 0 deletions CodeConverter/VB/NodesVisitor.cs
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Expand Up @@ -1643,6 +1643,12 @@ public override VisualBasicSyntaxNode VisitThrowExpression(CSSyntax.ThrowExpress

public override VisualBasicSyntaxNode VisitCasePatternSwitchLabel(CSSyntax.CasePatternSwitchLabelSyntax node)
{
if (node.Pattern is CSSyntax.RelationalPatternSyntax relational) {
var value = (ExpressionSyntax)relational.Expression.Accept(TriviaConvertingVisitor);
var (caseClauseKind, tokenKind) = GetRelationalCaseClauseKinds(CS.CSharpExtensions.Kind(relational.OperatorToken));
return SyntaxFactory.RelationalCaseClause(caseClauseKind,
SyntaxFactory.Token(tokenKind), value);
}
var condition = node.WhenClause.Condition.SkipIntoParens();
switch (condition) {
case CSSyntax.BinaryExpressionSyntax bes when node.Pattern.ToString().StartsWith("var", StringComparison.InvariantCulture): //VarPatternSyntax (not available in current library version)
Expand All @@ -1654,6 +1660,15 @@ public override VisualBasicSyntaxNode VisitCasePatternSwitchLabel(CSSyntax.CaseP
throw new NotSupportedException(condition.GetType() + " in switch case");
}
}

private static (SyntaxKind CaseClauseKind, SyntaxKind TokenKind) GetRelationalCaseClauseKinds(CS.SyntaxKind csTokenKind) => csTokenKind switch {
CS.SyntaxKind.LessThanToken => (SyntaxKind.CaseLessThanClause, SyntaxKind.LessThanToken),
CS.SyntaxKind.LessThanEqualsToken => (SyntaxKind.CaseLessThanOrEqualClause, SyntaxKind.LessThanEqualsToken),
CS.SyntaxKind.GreaterThanToken => (SyntaxKind.CaseGreaterThanClause, SyntaxKind.GreaterThanToken),
CS.SyntaxKind.GreaterThanEqualsToken => (SyntaxKind.CaseGreaterThanOrEqualClause, SyntaxKind.GreaterThanEqualsToken),
_ => throw new NotSupportedException($"Relational operator token {csTokenKind} not supported in VB case clause")
};

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@GrahamTheCoder GrahamTheCoder Apr 14, 2026

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Implementation in C# -> VB direction with no test

private INamedTypeSymbol GetStructOrClassSymbol(CS.CSharpSyntaxNode node) {
return (INamedTypeSymbol)_semanticModel.GetDeclaredSymbol(node.Ancestors().First(x => x is CSSyntax.ClassDeclarationSyntax || x is CSSyntax.StructDeclarationSyntax));
}
Expand Down
55 changes: 46 additions & 9 deletions Tests/CSharp/StatementTests/MethodStatementTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -1089,13 +1089,13 @@ public static string TimeAgo(int daysAgo)
{
case var @case when 0 <= @case && @case <= 3:
case 4:
case var case1 when case1 >= 5:
case var case2 when case2 < 6:
case var case3 when case3 <= 7:
case >= 5:
case < 6:
case <= 7:
{
return ""this week"";
}
case var case4 when case4 > 0:
case > 0:
{
return daysAgo / 7 + "" weeks ago"";
}
Expand Down Expand Up @@ -1249,15 +1249,15 @@ public void DoesNotThrow()
var rand = new Random();
switch (rand.Next(8))
{
case var @case when @case < 4:
case < 4:
{
break;
}
case 4:
{
break;
}
case var case1 when case1 > 4:
case > 4:
{
break;
}
Expand All @@ -1268,9 +1268,46 @@ public void DoesNotThrow()
}
}
}
}
1 target compilation errors:
CS0825: The contextual keyword 'var' may only appear within a local variable declaration or in script code");
}");
}

[Fact]
public async Task Issue803SelectCaseIsRelationalUsesC9PatternAsync()
{
await TestConversionVisualBasicToCSharpAsync(@"Public Class TestClass
Function Rollo(Breite As Integer) As Integer
Select Case Breite
Case Is < 1000
Return 12
Case Is < 1200
Return 15
Case Else
Return 28
End Select
End Function
End Class", @"
public partial class TestClass
{
public int Rollo(int Breite)
{
switch (Breite)
{
case < 1000:
{
return 12;
}
case < 1200:
{
return 15;
}

default:
{
return 28;
}
}
}
}");
}

[Fact]
Expand Down
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