From 8ecf274960d3c2b1de27522d729ce246afad441e Mon Sep 17 00:00:00 2001
From: Matthew Steeples <matthew@ledgerscope.com>
Date: Sat, 9 May 2026 14:18:49 +0100
Subject: [PATCH] Exclude private and protected fields from source generators

---
 .../MemberCollector.cs                        |  8 ++
 .../SourceGeneratorEdgeCaseTests.cs           | 93 +++++++++++++++++++
 2 files changed, 101 insertions(+)

diff --git a/src/FastCloner.SourceGenerator/MemberCollector.cs b/src/FastCloner.SourceGenerator/MemberCollector.cs
index fbc06e6..e74fcb9 100644
--- a/src/FastCloner.SourceGenerator/MemberCollector.cs
+++ b/src/FastCloner.SourceGenerator/MemberCollector.cs
@@ -36,6 +36,14 @@ public static List<MemberAnalysis> GetMembers(
                 if (member.IsStatic || member.IsImplicitlyDeclared)
                     continue;
 
+                bool hasAccessibleVisibility =
+                    member.DeclaredAccessibility == Accessibility.Public ||
+                    member.DeclaredAccessibility == Accessibility.Internal ||
+                    member.DeclaredAccessibility == Accessibility.ProtectedOrInternal;
+
+                if (!hasAccessibleVisibility)
+                    continue;
+
                 // Skip if we've already seen this member name (base class members override derived)
                 if (!seenNames.Add(member.Name))
                     continue;
diff --git a/src/FastCloner.Tests/SourceGeneratorEdgeCaseTests.cs b/src/FastCloner.Tests/SourceGeneratorEdgeCaseTests.cs
index 2519dcf..8af3a5d 100644
--- a/src/FastCloner.Tests/SourceGeneratorEdgeCaseTests.cs
+++ b/src/FastCloner.Tests/SourceGeneratorEdgeCaseTests.cs
@@ -256,6 +256,99 @@ public async Task PrivateSetter_Properties_Should_Be_Skipped()
         await Assert.That(clone.PrivateSetterProperty).IsEqualTo(0);
     }
 
+    [FastClonerClonable]
+    public class ClassWithPrivateField
+    {
+        public int PublicProperty { get; set; }
+        private int privateField;
+
+        public int PrivateFieldValue => privateField;
+
+        public void SetPrivateField(int value) => privateField = value;
+    }
+
+    [Test]
+    [SourceGeneratorCompatible]
+    public async Task Private_Fields_Should_Be_Skipped()
+    {
+        // Arrange
+        ClassWithPrivateField original = new ClassWithPrivateField
+        {
+            PublicProperty = 100
+        };
+        original.SetPrivateField(200);
+
+        // Act
+        ClassWithPrivateField clone = original.FastDeepClone();
+
+        // Assert
+        await Assert.That(clone).IsNotNull();
+        await Assert.That(clone!.PublicProperty).IsEqualTo(100);
+        await Assert.That(clone.PrivateFieldValue).IsEqualTo(0);
+    }
+
+    [FastClonerClonable]
+    public class ClassWithProtectedField
+    {
+        public int PublicProperty { get; set; }
+        protected int protectedField;
+
+        public int ProtectedFieldValue => protectedField;
+
+        public void SetProtectedField(int value) => protectedField = value;
+    }
+
+    [Test]
+    [SourceGeneratorCompatible]
+    public async Task Protected_Fields_Should_Be_Skipped()
+    {
+        // Arrange
+        ClassWithProtectedField original = new ClassWithProtectedField
+        {
+            PublicProperty = 100
+        };
+        original.SetProtectedField(300);
+
+        // Act
+        ClassWithProtectedField clone = original.FastDeepClone();
+
+        // Assert
+        await Assert.That(clone).IsNotNull();
+        await Assert.That(clone!.PublicProperty).IsEqualTo(100);
+        await Assert.That(clone.ProtectedFieldValue).IsEqualTo(0);
+    }
+
+    [FastClonerClonable]
+    public class ClassWithInternalField
+    {
+        public int PublicProperty { get; set; }
+        internal int internalField;
+
+        public int InternalFieldValue => internalField;
+
+        public void SetInternalField(int value) => internalField = value;
+    }
+
+    [Test]
+    [SourceGeneratorCompatible]
+    public async Task Internal_Fields_Should_Be_Cloned()
+    {
+        // Arrange
+        ClassWithInternalField original = new ClassWithInternalField
+        {
+            PublicProperty = 100
+        };
+        original.SetInternalField(400);
+
+        // Act
+        ClassWithInternalField clone = original.FastDeepClone();
+
+        // Assert
+        await Assert.That(clone).IsNotNull();
+        await Assert.That(clone!.PublicProperty).IsEqualTo(100);
+        await Assert.That(clone.InternalFieldValue).IsEqualTo(400);
+    }
+
     #endregion
 
     #region Issue 5: Delegate and Behavioral Types (Lazy, Func, Task)