From f5c6a33cc2a9ebc4b5e6b19d003484037101675b Mon Sep 17 00:00:00 2001
From: latonz <lars@riok.ch>
Date: Mon, 14 Oct 2024 19:19:49 +0200
Subject: [PATCH] allow assignments of MapValue constant value types to
 nullable value types

---
 .../MappingBodyBuilders/SourceValueBuilder.cs |  6 +++--
 .../Mapping/ObjectPropertyValueTest.cs        | 24 +++++++++++++++++++
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/src/Riok.Mapperly/Descriptors/MappingBodyBuilders/SourceValueBuilder.cs b/src/Riok.Mapperly/Descriptors/MappingBodyBuilders/SourceValueBuilder.cs
index ddd4290b43..6ebf0f1f78 100644
--- a/src/Riok.Mapperly/Descriptors/MappingBodyBuilders/SourceValueBuilder.cs
+++ b/src/Riok.Mapperly/Descriptors/MappingBodyBuilders/SourceValueBuilder.cs
@@ -114,7 +114,9 @@ private static bool TryBuildConstantSourceValue(
             return true;
         }
 
-        if (!SymbolEqualityComparer.Default.Equals(value.ConstantValue.Type, memberMappingInfo.TargetMember.MemberType))
+        // use non-nullable target type to allow non-null value type assignments
+        // to nullable value types
+        if (!SymbolEqualityComparer.Default.Equals(value.ConstantValue.Type, memberMappingInfo.TargetMember.MemberType.NonNullable()))
         {
             ctx.BuilderContext.ReportDiagnostic(
                 DiagnosticDescriptors.MapValueTypeMismatch,
@@ -135,7 +137,7 @@ private static bool TryBuildConstantSourceValue(
                 // expand enum member access to fully qualified identifier
                 // use simple member name approach instead of slower visitor pattern on the expression
                 var enumMemberName = ((MemberAccessExpressionSyntax)value.Expression).Name.Identifier.Text;
-                var enumTypeFullName = FullyQualifiedIdentifier(memberMappingInfo.TargetMember.MemberType);
+                var enumTypeFullName = FullyQualifiedIdentifier(memberMappingInfo.TargetMember.MemberType.NonNullable());
                 sourceValue = new ConstantSourceValue(MemberAccess(enumTypeFullName, enumMemberName));
                 return true;
             case TypedConstantKind.Type:
diff --git a/test/Riok.Mapperly.Tests/Mapping/ObjectPropertyValueTest.cs b/test/Riok.Mapperly.Tests/Mapping/ObjectPropertyValueTest.cs
index f8d94cc84f..aee5111321 100644
--- a/test/Riok.Mapperly.Tests/Mapping/ObjectPropertyValueTest.cs
+++ b/test/Riok.Mapperly.Tests/Mapping/ObjectPropertyValueTest.cs
@@ -114,6 +114,30 @@ public void StringToNestedNullableProperty()
             );
     }
 
+    [Fact]
+    public void ValueTypeToNestedNullableProperty()
+    {
+        var source = TestSourceBuilder.MapperWithBodyAndTypes(
+            """[MapValue("Nested.Value", E.E1)] partial B Map(A source);""",
+            "class A;",
+            "class B { public C? Nested { get; set; } }",
+            "class C { public E? Value { get; set; } }",
+            "enum E { E1 }"
+        );
+
+        TestHelper
+            .GenerateMapper(source)
+            .Should()
+            .HaveSingleMethodBody(
+                """
+                var target = new global::B();
+                target.Nested ??= new global::C();
+                target.Nested.Value = global::E.E1;
+                return target;
+                """
+            );
+    }
+
     [Fact]
     public void StringToNestedPropertyWithMapProperty()
     {