fix: generic and runtime target type mappings with derived types

src/Riok.Mapperly/Descriptors/MappingBodyBuilders/RuntimeTargetTypeMappingBodyBuilder.cs

@@ -119,7 +119,11 @@ IEnumerable<ITypeMapping> childMappings
             .ThenBy(x => x.TargetType.IsNullable())
             .GroupBy(x => new TypeMappingKey(x, includeNullability: false))
             .Select(x => x.First())
-            .Select(x => new RuntimeTargetTypeMapping(x, ctx.Compilation.HasImplicitConversion(x.TargetType, ctx.Target)))
+            .Select(x => new RuntimeTargetTypeMapping(
+                x,
+                ctx.Compilation.HasImplicitConversion(x.TargetType, ctx.Target),
+                (x as UserDefinedNewInstanceMethodMapping)?.IsDerivedTypeMapping == true
+            ))
             .ToList();
 
         if (runtimeTargetTypeMappings.Count == 0)

src/Riok.Mapperly/Descriptors/Mappings/UserMappings/UserDefinedNewInstanceMethodMapping.cs

@@ -15,13 +15,16 @@ public class UserDefinedNewInstanceMethodMapping(
     MethodParameter sourceParameter,
     MethodParameter? referenceHandlerParameter,
     ITypeSymbol targetType,
-    bool enableReferenceHandling
+    bool enableReferenceHandling,
+    bool isDerivedTypeMapping
 ) : NewInstanceMethodMapping(method, sourceParameter, referenceHandlerParameter, targetType), INewInstanceUserMapping
 {
     private INewInstanceMapping? _delegateMapping;
 
     public new IMethodSymbol Method { get; } = method;
 
+    public bool IsDerivedTypeMapping => isDerivedTypeMapping;
+
     private MethodMapping? DelegateMethodMapping => _delegateMapping as MethodMapping;
 
     public bool? Default { get; } = isDefault;

src/Riok.Mapperly/Descriptors/Mappings/UserMappings/UserDefinedNewInstanceRuntimeTargetTypeMapping.cs

@@ -91,10 +91,16 @@ public override IEnumerable<StatementSyntax> BuildBody(TypeMappingBuildContext c
 
     protected virtual ExpressionSyntax? BuildSwitchArmWhenClause(ExpressionSyntax runtimeTargetType, RuntimeTargetTypeMapping mapping)
     {
-        // targetType.IsAssignableFrom(typeof(ADto))
+        var mappingTargetType = TypeOfExpression(FullyQualifiedIdentifier(mapping.Mapping.TargetType.NonNullable()));
+
+        // Derived type mapping: A => ADto (runtime target type) or A => BaseDto (runtime target type), BaseDto (mapping target type).
+        // typeof(BaseDto).IsAssignableFrom(runtimeTargetType)
+
+        // Non-derived type mapping: A => ADto (runtime target type) or A => BaseDto (runtime target type), ADto (mapping target type).
+        // runtimeTargetType.IsAssignableFrom(ADto)
         return InvocationWithoutIndention(
-            MemberAccess(runtimeTargetType, IsAssignableFromMethodName),
-            TypeOfExpression(FullyQualifiedIdentifier(mapping.Mapping.TargetType.NonNullable()))
+            MemberAccess(mapping.IsDerivedTypeMapping ? mappingTargetType : runtimeTargetType, IsAssignableFromMethodName),
+            mapping.IsDerivedTypeMapping ? runtimeTargetType : mappingTargetType
         );
     }
 

src/Riok.Mapperly/Descriptors/UserMethodMappingExtractor.cs

@@ -338,7 +338,8 @@ string sourceParameterName
             parameters.Source,
             parameters.ReferenceHandler,
             ctx.SymbolAccessor.UpgradeNullable(methodSymbol.ReturnType),
-            ctx.Configuration.Mapper.UseReferenceHandling
+            ctx.Configuration.Mapper.UseReferenceHandling,
+            ctx.AttributeAccessor.HasAttribute<MapDerivedTypeAttribute<object, object>>(methodSymbol)
         )
         {
             AdditionalSourceParameters = parameters.AdditionalParameters,

src/Riok.Mapperly/Symbols/RuntimeTargetTypeMapping.cs

@@ -2,4 +2,4 @@
 
 namespace Riok.Mapperly.Symbols;
 
-public record RuntimeTargetTypeMapping(INewInstanceMapping Mapping, bool IsAssignableToMethodTargetType);
+public record RuntimeTargetTypeMapping(INewInstanceMapping Mapping, bool IsAssignableToMethodTargetType, bool IsDerivedTypeMapping);

test/Riok.Mapperly.IntegrationTests/_snapshots/StaticMapperTest.SnapshotGeneratedSource_NET8_0.verified.cs

@@ -790,7 +790,7 @@ string x when targetType.IsAssignableFrom(typeof(int)) => ParseableInt(x),
                 global::Riok.Mapperly.IntegrationTests.Models.AssemblyScopedModel x when targetType.IsAssignableFrom(typeof(global::Riok.Mapperly.IntegrationTests.Dto.AssemblyScopedDto)) => global::Riok.Mapperly.IntegrationTests.Mapper.AssemblyScopedMappers.ToDto(x),
                 global::System.Collections.Generic.IReadOnlyCollection<global::System.Collections.Generic.IReadOnlyList<global::System.Collections.Generic.IReadOnlyCollection<string>>> x when targetType.IsAssignableFrom(typeof(global::System.Collections.Generic.IReadOnlyList<global::System.Collections.Generic.IReadOnlyList<global::System.Collections.Generic.IReadOnlyCollection<int>>>)) => MapNestedLists(x),
                 global::System.Collections.Generic.IEnumerable<global::Riok.Mapperly.IntegrationTests.Models.TestObject> x when targetType.IsAssignableFrom(typeof(global::System.Collections.Generic.IEnumerable<global::Riok.Mapperly.IntegrationTests.Dto.TestObjectDto>)) => MapAllDtos(x),
-                object x when targetType.IsAssignableFrom(typeof(object)) => DerivedTypes(x),
+                object x when typeof(object).IsAssignableFrom(targetType) => DerivedTypes(x),
                 _ => throw new global::System.ArgumentException($"Cannot map {source.GetType()} to {targetType} as there is no known type mapping", nameof(source)),
             };
         }
@@ -817,7 +817,7 @@ string x when targetType.IsAssignableFrom(typeof(int)) => ParseableInt(x),
                 global::Riok.Mapperly.IntegrationTests.Models.AssemblyScopedModel x when targetType.IsAssignableFrom(typeof(global::Riok.Mapperly.IntegrationTests.Dto.AssemblyScopedDto)) => global::Riok.Mapperly.IntegrationTests.Mapper.AssemblyScopedMappers.ToDto(x),
                 global::System.Collections.Generic.IReadOnlyCollection<global::System.Collections.Generic.IReadOnlyList<global::System.Collections.Generic.IReadOnlyCollection<string>>> x when targetType.IsAssignableFrom(typeof(global::System.Collections.Generic.IReadOnlyList<global::System.Collections.Generic.IReadOnlyList<global::System.Collections.Generic.IReadOnlyCollection<int>>>)) => MapNestedLists(x),
                 global::System.Collections.Generic.IEnumerable<global::Riok.Mapperly.IntegrationTests.Models.TestObject> x when targetType.IsAssignableFrom(typeof(global::System.Collections.Generic.IEnumerable<global::Riok.Mapperly.IntegrationTests.Dto.TestObjectDto>)) => MapAllDtos(x),
-                object x when targetType.IsAssignableFrom(typeof(object)) => DerivedTypes(x),
+                object x when typeof(object).IsAssignableFrom(targetType) => DerivedTypes(x),
                 null => default,
                 _ => throw new global::System.ArgumentException($"Cannot map {source.GetType()} to {targetType} as there is no known type mapping", nameof(source)),
             };
@@ -845,7 +845,7 @@ string x when typeof(TTarget).IsAssignableFrom(typeof(int)) => (TTarget)(object)
                 global::Riok.Mapperly.IntegrationTests.Models.AssemblyScopedModel x when typeof(TTarget).IsAssignableFrom(typeof(global::Riok.Mapperly.IntegrationTests.Dto.AssemblyScopedDto)) => (TTarget)(object)global::Riok.Mapperly.IntegrationTests.Mapper.AssemblyScopedMappers.ToDto(x),
                 global::System.Collections.Generic.IReadOnlyCollection<global::System.Collections.Generic.IReadOnlyList<global::System.Collections.Generic.IReadOnlyCollection<string>>> x when typeof(TTarget).IsAssignableFrom(typeof(global::System.Collections.Generic.IReadOnlyList<global::System.Collections.Generic.IReadOnlyList<global::System.Collections.Generic.IReadOnlyCollection<int>>>)) => (TTarget)(object)MapNestedLists(x),
                 global::System.Collections.Generic.IEnumerable<global::Riok.Mapperly.IntegrationTests.Models.TestObject> x when typeof(TTarget).IsAssignableFrom(typeof(global::System.Collections.Generic.IEnumerable<global::Riok.Mapperly.IntegrationTests.Dto.TestObjectDto>)) => (TTarget)(object)MapAllDtos(x),
-                object x when typeof(TTarget).IsAssignableFrom(typeof(object)) => (TTarget)(object)DerivedTypes(x),
+                object x when typeof(object).IsAssignableFrom(typeof(TTarget)) => (TTarget)(object)DerivedTypes(x),
                 null => throw new global::System.ArgumentNullException(nameof(source)),
                 _ => throw new global::System.ArgumentException($"Cannot map {source.GetType()} to {typeof(TTarget)} as there is no known type mapping", nameof(source)),
             };

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

@@ -29,7 +29,7 @@ public void GenericWithDerivedTypes()
                 """
                 return source switch
                 {
-                    global::Base x when typeof(TTarget).IsAssignableFrom(typeof(global::BaseDto)) => (TTarget)(object)MapDerivedTypes(x),
+                    global::Base x when typeof(global::BaseDto).IsAssignableFrom(typeof(TTarget)) => (TTarget)(object)MapDerivedTypes(x),
                     null => throw new global::System.ArgumentNullException(nameof(source)),
                     _ => throw new global::System.ArgumentException($"Cannot map {source.GetType()} to {typeof(TTarget)} as there is no known type mapping", nameof(source)),
                 };

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

@@ -165,7 +165,7 @@ public void WithDerivedTypesShouldUseBaseType()
                 """
                 return source switch
                 {
-                    global::Base x when targetType.IsAssignableFrom(typeof(global::BaseDto)) => MapDerivedTypes(x),
+                    global::Base x when typeof(global::BaseDto).IsAssignableFrom(targetType) => MapDerivedTypes(x),
                     _ => throw new global::System.ArgumentException($"Cannot map {source.GetType()} to {targetType} as there is no known type mapping", nameof(source)),
                 };
                 """