Fix false positive for unsupported default values on nullable parameters (#29)

* first shot

* merge ifs

Author: jonathanalgar

src/CustomCode-Analyzer/Analyzer.cs

@@ -1323,11 +1323,22 @@ private static bool IsValidParameterDefaultValue(IParameterSymbol parameter)
                 return true;
             }
 
-            // Check if type is supported
+            // Unwrap nullable types to check the underlying type
+            ITypeSymbol typeToCheck = parameter.Type;
             if (
-                !ValidParameterSpecialTypes.Contains(parameter.Type.SpecialType)
+                typeToCheck.OriginalDefinition.SpecialType == SpecialType.System_Nullable_T
+                && typeToCheck is INamedTypeSymbol namedType
+                && namedType.TypeArguments.Length == 1
+            )
+            {
+                typeToCheck = namedType.TypeArguments[0];
+            }
+
+            // Check if the (unwrapped) type is supported
+            if (
+                !ValidParameterSpecialTypes.Contains(typeToCheck.SpecialType)
                 && !(
-                    parameter.Type is IArrayTypeSymbol arrayType
+                    typeToCheck is IArrayTypeSymbol arrayType
                     && arrayType.ElementType.SpecialType == SpecialType.System_Byte
                 )
             )
@@ -1347,8 +1358,7 @@ parameter.Type is IArrayTypeSymbol arrayType
                 return false;
             }
 
-            // Check if the default value is a literal expression
-            // This ensures that the default value is a compile-time constant
+            // Check if the default value is a literal expression (compile-time constant)
             return parameterSyntax.Default?.Value is LiteralExpressionSyntax;
         }
 

tests/CustomCode-Analyzer.Tests/AnalyzerTests.cs

@@ -1778,25 +1778,25 @@ public async Task UnsupportedDefaultValueRule_ValidLiterals_NoWarning()
 public interface ITestInterface 
 {
     void TestMethod(string text = ""hello"",
-                    int number = 42,
+                    int? number = 42,
                     long bigNumber = 123L,
                     double precise = 3.14,
                     decimal money = 10.5m,
                     bool flag = true,
-                    DateTime date = default,
+                    DateTime? date = default,
                     string nullString = null);
 }
 
 public class Implementation : ITestInterface 
 {
     public void TestMethod(string text = ""hello"",
-                        int number = 42,
-                        long bigNumber = 123L,
-                        double precise = 3.14,
-                        decimal money = 10.5m,
-                        bool flag = true,
-                        DateTime date = default,
-                        string nullString = null) { }
+                    int? number = 42,
+                    long bigNumber = 123L,
+                    double precise = 3.14,
+                    decimal money = 10.5m,
+                    bool flag = true,
+                    DateTime? date = default,
+                    string nullString = null) { }
 }";
             await CSharpAnalyzerVerifier<Analyzer>.VerifyAnalyzerAsync(
                 test,