From 159e1d775aa229ff6fb01a173aceddfbad01062a Mon Sep 17 00:00:00 2001
From: Jonathan Algar <93204286+jonathanalgar@users.noreply.github.com>
Date: Sat, 22 Feb 2025 13:21:25 +0000
Subject: [PATCH 1/2] first shot

---
 src/CustomCode-Analyzer/Analyzer.cs           | 22 ++++++++++++++-----
 .../AnalyzerTests.cs                          | 18 +++++++--------
 2 files changed, 26 insertions(+), 14 deletions(-)

diff --git a/src/CustomCode-Analyzer/Analyzer.cs b/src/CustomCode-Analyzer/Analyzer.cs
index 05ce6a9..6621bdb 100644
--- a/src/CustomCode-Analyzer/Analyzer.cs
+++ b/src/CustomCode-Analyzer/Analyzer.cs
@@ -1298,11 +1298,24 @@ 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 (typeToCheck.OriginalDefinition.SpecialType == SpecialType.System_Nullable_T)
+            {
+                if (
+                    typeToCheck is INamedTypeSymbol namedType
+                    && namedType.TypeArguments.Length == 1
+                )
+                {
+                    typeToCheck = namedType.TypeArguments[0];
+                }
+            }
+
+            // Check if the (unwrapped) type is supported
             if (
-                !ValidParameterSpecialTypes.Contains(parameter.Type.SpecialType)
+                !ValidParameterSpecialTypes.Contains(typeToCheck.SpecialType)
                 && !(
-                    parameter.Type is IArrayTypeSymbol arrayType
+                    typeToCheck is IArrayTypeSymbol arrayType
                     && arrayType.ElementType.SpecialType == SpecialType.System_Byte
                 )
             )
@@ -1322,8 +1335,7 @@ 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;
         }
 
diff --git a/tests/CustomCode-Analyzer.Tests/AnalyzerTests.cs b/tests/CustomCode-Analyzer.Tests/AnalyzerTests.cs
index 4828f49..f100cb8 100644
--- a/tests/CustomCode-Analyzer.Tests/AnalyzerTests.cs
+++ b/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,

From b703ec12707155d676cf87a299f33743457c4f62 Mon Sep 17 00:00:00 2001
From: Jonathan Algar <93204286+jonathanalgar@users.noreply.github.com>
Date: Sat, 22 Feb 2025 13:55:19 +0000
Subject: [PATCH 2/2] merge ifs

---
 src/CustomCode-Analyzer/Analyzer.cs | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/src/CustomCode-Analyzer/Analyzer.cs b/src/CustomCode-Analyzer/Analyzer.cs
index 6621bdb..78a35ed 100644
--- a/src/CustomCode-Analyzer/Analyzer.cs
+++ b/src/CustomCode-Analyzer/Analyzer.cs
@@ -1300,15 +1300,13 @@ private static bool IsValidParameterDefaultValue(IParameterSymbol parameter)
 
             // Unwrap nullable types to check the underlying type
             ITypeSymbol typeToCheck = parameter.Type;
-            if (typeToCheck.OriginalDefinition.SpecialType == SpecialType.System_Nullable_T)
+            if (
+                typeToCheck.OriginalDefinition.SpecialType == SpecialType.System_Nullable_T
+                && typeToCheck is INamedTypeSymbol namedType
+                && namedType.TypeArguments.Length == 1
+            )
             {
-                if (
-                    typeToCheck is INamedTypeSymbol namedType
-                    && namedType.TypeArguments.Length == 1
-                )
-                {
-                    typeToCheck = namedType.TypeArguments[0];
-                }
+                typeToCheck = namedType.TypeArguments[0];
             }
 
             // Check if the (unwrapped) type is supported