Merge pull request #1256 from GrahamTheCoder/claude/fix-issue-892-char-empty-comparison

Claude/fix issue 892 char empty comparison

Author: GrahamTheCoder

CodeConverter/CSharp/BinaryExpressionConverter.cs

@@ -82,11 +82,15 @@ private async Task<CSharpSyntaxNode> ConvertBinaryExpressionAsync(VBasic.Syntax.
             case VisualBasicEqualityComparison.RequiredType.StringOnly:
                 if (lhsTypeInfo.ConvertedType?.SpecialType == SpecialType.System_String &&
                     rhsTypeInfo.ConvertedType?.SpecialType == SpecialType.System_String &&
-                    _visualBasicEqualityComparison.TryConvertToNullOrEmptyCheck(node, lhs, rhs, out CSharpSyntaxNode visitBinaryExpression)) {
+                    _visualBasicEqualityComparison.TryConvertToNullOrEmptyCheck(node, lhs, rhs, lhsTypeInfo, rhsTypeInfo, out CSharpSyntaxNode visitBinaryExpression)) {
                     return visitBinaryExpression;
                 }
-                (lhs, rhs) = _visualBasicEqualityComparison.AdjustForVbStringComparison(node.Left, lhs, lhsTypeInfo, false, node.Right, rhs, rhsTypeInfo, false);
-                omitConversion = true; // Already handled within for the appropriate types (rhs can become int in comparison)
+                if (lhsTypeInfo.Type?.SpecialType == SpecialType.System_Char && rhsTypeInfo.Type?.SpecialType == SpecialType.System_Char) {
+                    // Do nothing, char comparison
+                } else {
+                    (lhs, rhs) = _visualBasicEqualityComparison.AdjustForVbStringComparison(node.Left, lhs, lhsTypeInfo, false, node.Right, rhs, rhsTypeInfo, false);
+                    omitConversion = true; // Already handled within for the appropriate types (rhs can become int in comparison)
+                }
                 break;
             case VisualBasicEqualityComparison.RequiredType.Object:
                 return _visualBasicEqualityComparison.GetFullExpressionForVbObjectComparison(lhs, rhs, VisualBasicEqualityComparison.ComparisonKind.Equals, node.IsKind(VBasic.SyntaxKind.NotEqualsExpression));

CodeConverter/CSharp/VisualBasicEqualityComparison.cs

@@ -79,6 +79,7 @@ public RequiredType GetObjectEqualityType(params TypeInfo[] typeInfos)
 
         if (typeInfos.All(
                 t => t.Type == null || t.Type.SpecialType == SpecialType.System_String ||
+                     t.Type.SpecialType == SpecialType.System_Char ||
                      t.Type.IsArrayOf(SpecialType.System_Char) ) ) {
             return RequiredType.StringOnly;
         }
@@ -177,20 +178,38 @@ private static ObjectCreationExpressionSyntax NewStringFromArg(ExpressionSyntax
     }
 
     public bool TryConvertToNullOrEmptyCheck(VBSyntax.BinaryExpressionSyntax node, ExpressionSyntax lhs,
-        ExpressionSyntax rhs, out CSharpSyntaxNode? visitBinaryExpression)
+        ExpressionSyntax rhs, TypeInfo lhsTypeInfo, TypeInfo rhsTypeInfo, out CSharpSyntaxNode? visitBinaryExpression)
     {
-        if (OptionCompareTextCaseInsensitive)
-        {
-            visitBinaryExpression = null;
-            return false;
-        }
-
         bool lhsEmpty = IsNothingOrEmpty(node.Left);
         bool rhsEmpty = IsNothingOrEmpty(node.Right);
 
         if (lhsEmpty || rhsEmpty)
         {
             var arg = lhsEmpty ? rhs : lhs;
+            var argType = lhsEmpty ? rhsTypeInfo : lhsTypeInfo;
+
+            if (argType.Type?.SpecialType == SpecialType.System_Char) {
+                // char = "" in VB means char == '\0' (char.MinValue) in C#; not affected by OptionCompareText
+                var charMinValue = SyntaxFactory.MemberAccessExpression(SyntaxKind.SimpleMemberAccessExpression,
+                    SyntaxFactory.PredefinedType(SyntaxFactory.Token(SyntaxKind.CharKeyword)),
+                    ValidSyntaxFactory.IdentifierName("MinValue"));
+                var equalityKind = node.IsKind(VBasic.SyntaxKind.NotEqualsExpression) ? SyntaxKind.NotEqualsExpression : SyntaxKind.EqualsExpression;
+                var opToken = SyntaxFactory.Token(node.IsKind(VBasic.SyntaxKind.NotEqualsExpression) ? SyntaxKind.ExclamationEqualsToken : SyntaxKind.EqualsEqualsToken);
+                visitBinaryExpression = SyntaxFactory.BinaryExpression(equalityKind, arg, opToken, charMinValue);
+                return true;
+            }
+
+            if (OptionCompareTextCaseInsensitive)
+            {
+                visitBinaryExpression = null;
+                return false;
+            }
+
+            if (argType.Type?.SpecialType != SpecialType.System_String && argType.Type?.SpecialType != SpecialType.System_Object) {
+                visitBinaryExpression = null;
+                return false;
+            }
+
             var nullOrEmpty = SyntaxFactory.InvocationExpression(
                 SyntaxFactory.MemberAccessExpression(SyntaxKind.SimpleMemberAccessExpression,
                     SyntaxFactory.PredefinedType(SyntaxFactory.Token(SyntaxKind.StringKeyword)),
@@ -207,7 +226,7 @@ public bool TryConvertToNullOrEmptyCheck(VBSyntax.BinaryExpressionSyntax node, E
         return false;
     }
 
-    private bool IsNothingOrEmpty(VBSyntax.ExpressionSyntax expressionSyntax)
+    public bool IsNothingOrEmpty(VBSyntax.ExpressionSyntax expressionSyntax)
     {
         expressionSyntax = expressionSyntax.SkipIntoParens();
 

Tests/CSharp/ExpressionTests/StringExpressionTests.cs

@@ -541,6 +541,53 @@ public void Foo()
     {
         string x = Conversions.ToString(DateTime.Parse(""2022-01-01"")) + "" 15:00"";
     }
+}");
+    }
+
+    [Fact]
+    public async Task CharEqualityEmptyStringAsync()
+    {
+        await TestConversionVisualBasicToCSharpAsync(@"Class TestClass
+    Private Sub TestMethod()
+        Dim testChar As Char = Nothing
+        Dim testResult = testChar = """"
+        Dim testResult2 = """" = testChar
+        Dim testResult3 = testChar <> """"
+    End Sub
+End Class", @"
+internal partial class TestClass
+{
+    private void TestMethod()
+    {
+        char testChar = default;
+        bool testResult = testChar == char.MinValue;
+        bool testResult2 = testChar == char.MinValue;
+        bool testResult3 = testChar != char.MinValue;
+    }
+}");
+    }
+
+    [Fact]
+    public async Task CharEqualityInConditionAsync()
+    {
+        await TestConversionVisualBasicToCSharpAsync(@"Class TestClass
+    Private Function IsEmpty(c As Char) As Boolean
+        If c = """" Then
+            Return True
+        End If
+        Return False
+    End Function
+End Class", @"
+internal partial class TestClass
+{
+    private bool IsEmpty(char c)
+    {
+        if (c == char.MinValue)
+        {
+            return true;
+        }
+        return false;
+    }
 }");
     }
 }