From a4747bcd8bc029c478150fbf5027bea3143ba188 Mon Sep 17 00:00:00 2001
From: Colin Green <colin.green@focus-solutions.co.uk>
Date: Tue, 19 Apr 2022 21:38:13 +0100
Subject: [PATCH] Change: IsGeneratableType will return false for Syste.Guid,
 DateOnly, and TimeOnly. These types report as SpecialType.None, but are
 System value/struct types that do not require a wrapper type.

Note. DateOnly and TimeOnly were added in .NEt 6.0, and therefore are not part of NetStandard2.0 (and therefore are not currently known to Microsoft.CodeAnalysis).
---
 .../GeneratedTypeFilter.cs                           | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/JsonMergePatch.SourceGenerator/GeneratedTypeFilter.cs b/src/JsonMergePatch.SourceGenerator/GeneratedTypeFilter.cs
index c37e5bd..662b827 100644
--- a/src/JsonMergePatch.SourceGenerator/GeneratedTypeFilter.cs
+++ b/src/JsonMergePatch.SourceGenerator/GeneratedTypeFilter.cs
@@ -12,7 +12,17 @@ public static bool IsGeneratableType(ITypeSymbol typeInfo)
             bool generic = false;
             if (typeInfo is INamedTypeSymbol namedTypeInfo)
                 generic = namedTypeInfo.IsGenericType;
-            return typeInfo.SpecialType == SpecialType.None && !typeInfo.IsAnonymousType && !typeInfo.IsAbstract && !generic && !typeInfo.IsStatic && typeInfo.TypeKind != TypeKind.Enum;
+
+            // Check for System types that have SpecialType.None.
+            string typeName = typeInfo.ToDisplayString();
+            bool isNonSpecialSystemType = typeName == "System.Guid" || typeName == "System.DateOnly" || typeName == "System.TimeOnly";
+
+            return typeInfo.SpecialType == SpecialType.None
+                && !isNonSpecialSystemType
+                && !typeInfo.IsAnonymousType
+                && !typeInfo.IsAbstract
+                && !generic && !typeInfo.IsStatic
+                && typeInfo.TypeKind != TypeKind.Enum;
         }