fix: Nullable<T>.Value is no longer treated as a member

src/Riok.Mapperly/Descriptors/SymbolAccessor.cs

@@ -136,7 +136,9 @@ private IEnumerable<IMappableMember> FindMemberPath(ITypeSymbol type, IEnumerabl
     {
         foreach (var name in path)
         {
-            if (GetMappableMembers(type, name, comparer).FirstOrDefault() is not { } member)
+            // get T if type is Nullable<T>, prevents Value being treated as a member
+            var actualType = type.NonNullableValueType() ?? type;
+            if (GetMappableMembers(actualType, name, comparer).FirstOrDefault() is not { } member)
                 break;
 
             type = member.Type;

src/Riok.Mapperly/Helpers/NullableSymbolExtensions.cs

@@ -83,6 +83,13 @@ internal static bool IsNullable(this ITypeSymbol symbol) =>
 
     internal static bool IsNullableValueType(this ITypeSymbol symbol) => symbol.NonNullableValueType() != null;
 
+    internal static ITypeSymbol? NonNullableValueType(this ITypeSymbol symbol)
+    {
+        if (symbol.IsValueType && symbol is INamedTypeSymbol { OriginalDefinition.SpecialType: SpecialType.System_Nullable_T } namedType)
+            return namedType.TypeArguments[0];
+        return null;
+    }
+
     /// <summary>
     /// Whether or not the <see cref="ITypeParameterSymbol"/> is nullable.
     /// </summary>
@@ -104,11 +111,4 @@ internal static bool IsNullable(this ITypeParameterSymbol typeParameter, Nullabl
     }
 
     private static bool IsNullable(this NullableAnnotation nullable) => nullable is NullableAnnotation.Annotated or NullableAnnotation.None;
-
-    private static ITypeSymbol? NonNullableValueType(this ITypeSymbol symbol)
-    {
-        if (symbol.IsValueType && symbol is INamedTypeSymbol { OriginalDefinition.SpecialType: SpecialType.System_Nullable_T } namedType)
-            return namedType.TypeArguments[0];
-        return null;
-    }
 }

test/Riok.Mapperly.Tests/Mapping/ObjectPropertyFlatteningTest.cs

@@ -1,3 +1,5 @@
+using Riok.Mapperly.Diagnostics;
+
 namespace Riok.Mapperly.Tests.Mapping;
 
 [UsesVerify]
@@ -126,6 +128,79 @@ public void AutoFlattenedMultiplePropertiesNullablePath()
             );
     }
 
+    [Fact]
+    public void AutoFlattenedPropertyNullableValueTypePath()
+    {
+        var source = TestSourceBuilder.Mapping(
+            "A",
+            "B",
+            "public class A { public C Id { get; set; } }",
+            "public class B { public int IdValue { get; set; } }",
+            "public class C { public int? Value { get; set; } }"
+        );
+        TestHelper
+            .GenerateMapper(source)
+            .Should()
+            .HaveSingleMethodBody(
+                """
+                var target = new global::B();
+                if (source.Id.Value != null)
+                {
+                    target.IdValue = source.Id.Value.Value;
+                }
+
+                return target;
+                """
+            );
+    }
+
+    [Fact]
+    public void AutoFlattenedPropertyNullableValueTypePathShouldResolve()
+    {
+        var source = TestSourceBuilder.Mapping(
+            "A",
+            "B",
+            "public class A { public C? Prop { get; set; } }",
+            "public class B { public string PropInteger { get; set; } }",
+            "public struct C { public int Integer { get; set; } }"
+        );
+        TestHelper
+            .GenerateMapper(source)
+            .Should()
+            .HaveSingleMethodBody(
+                """
+                var target = new global::B();
+                if (source.Prop != null)
+                {
+                    target.PropInteger = source.Prop.Value.Integer.ToString();
+                }
+
+                return target;
+                """
+            );
+    }
+
+    [Fact]
+    public void AutoFlattenedPropertyNullableValueTypePathShouldDiagnostic()
+    {
+        var source = TestSourceBuilder.Mapping(
+            "A",
+            "B",
+            "public record A(int? Id);",
+            "public record B { public int IdValue { get; set; } }"
+        );
+        TestHelper
+            .GenerateMapper(source, TestHelperOptions.AllowDiagnostics)
+            .Should()
+            .HaveDiagnostic(DiagnosticDescriptors.SourceMemberNotFound)
+            .HaveSingleMethodBody(
+                """
+                var target = new global::B();
+                return target;
+                """
+            );
+    }
+
     [Fact]
     public void AutoFlattenedMultiplePropertiesPathDisabledNullable()
     {