feat: accept destination type as mapping method parameter (#398)

docs/docs/01-getting-started/03-generated-mapper-example.mdx

@@ -8,7 +8,7 @@ import GeneratedCarMapperSource from '!!raw-loader!../../src/data/generated/samp
 
 This example will show you what kind of code Mapperly generates.
 It is based on the [Mapperly sample](https://github.com/riok/mapperly/tree/main/samples/Riok.Mapperly.Sample).
-To view the generated code of your own mapper, refer to the [generated source configuration](../02-configuration/15-generated-source.mdx).
+To view the generated code of your own mapper, refer to the [generated source configuration](../02-configuration/16-generated-source.mdx).
 
 ## The source classes
 

docs/docs/02-configuration/01-mapper.md

@@ -84,7 +84,7 @@ To enforce strict mappings
 (all source members have to be mapped to a target member
 and all target members have to be mapped from a source member,
 except for ignored members)
-set the following two EditorConfig settings (see also [analyzer diagnostics](./14-analyzer-diagnostics.mdx)):
+set the following two EditorConfig settings (see also [analyzer diagnostics](./15-analyzer-diagnostics.mdx)):
 
 ```editorconfig title=".editorconfig"
 [*.cs]
@@ -94,4 +94,4 @@ dotnet_diagnostic.RMG020.severity = error # Unmapped source member
 
 ### Strict enum mappings
 
-To enforce strict enum mappings set 'RMG037' and 'RMG038' to error, see [strict enum mappings](./04-enum.mdx).
+To enforce strict enum mappings set `RMG037` and `RMG038` to error, see [strict enum mappings](./04-enum.mdx).

docs/docs/02-configuration/04-enum.mdx

@@ -57,7 +57,7 @@ public partial class CarMapper
 To enforce strict enum mappings
 (all source enum values have to be mapped to a target enum value
 and all target enum values have to be mapped from a source enum value)
-set the following two EditorConfig settings (see also [analyzer diagnostics](./14-analyzer-diagnostics.mdx)):
+set the following two EditorConfig settings (see also [analyzer diagnostics](./15-analyzer-diagnostics.mdx)):
 
 ```editorconfig title=".editorconfig"
 [*.cs]

docs/docs/02-configuration/10-derived-type-mapping.md

@@ -17,19 +17,19 @@ This can be configured with the `MapDerivedTypeAttribute`:
 public static partial class ModelMapper
 {
     // highlight-start
-    [MapDerivedType<Audi, AudiDto>] // for c# language level ≥ 11
-    [MapDerivedType(typeof(Porsche), typeof(PorscheDto))] // for c# language level < 11
+    [MapDerivedType<Banana, BananaDto>] // for c# language level ≥ 11
+    [MapDerivedType(typeof(Apple), typeof(AppleDto))] // for c# language level < 11
     // highlight-end
-    public static partial CarDto MapCar(Car source);
+    public static partial FruitDto MapFruit(Fruit source);
 }
 
-abstract class Car {}
-class Audi : Car {}
-class Porsche : Car {}
+abstract class Fruit {}
+class Banana : Fruit {}
+class Apple : Fruit {}
 
-abstract class CarDto {}
-class AudiDto : CarDto {}
-class PorscheDto : CarDto {}
+abstract class FruitDto {}
+class BananaDto : FruitDto {}
+class AppleDto : FruitDto {}
 ```
 
 </TabItem>
@@ -39,17 +39,17 @@ class PorscheDto : CarDto {}
 [Mapper]
 public static partial class ModelMapper
 {
-    public static partial CarDto MapCar(Car source)
+    public static partial FruitDto MapFruit(Fruit source)
     {
         return source switch
         {
-            Audi x => MapToAudiDto(x),
-            Porsche x => MapToPorscheDto(x),
-            _ => throw new System.ArgumentException($"Cannot map {source.GetType()} to CarDto as there is no known derived type mapping", nameof(source)),
+            Banana x => MapToBananaDto(x),
+            Apple x => MapToAppleDto(x),
+            _ => throw new System.ArgumentException($"Cannot map {source.GetType()} to FruitDto as there is no known derived type mapping", nameof(source)),
         };
     }
 
-    // ... implementations of MapToAudiDto and MapToPorscheDto
+    // ... implementations of MapToBananaDto and MapToAppleDto
 }
 ```
 

docs/docs/02-configuration/11-runtime-target-type-mapping.md

@@ -0,0 +1,39 @@
+# Runtime target type mapping
+
+If the target type of a mapping is not known at compile time,
+a mapping method with a `Type` parameter can be used.
+Mapperly implements this mapping method
+using all mappings the user defined in the mapper.
+
+```csharp
+[Mapper]
+public static partial class ModelMapper
+{
+    // highlight-start
+    public static partial object Map(object source, Type targetType);
+    // highlight-end
+
+    private static partial BananaDto MapBanana(Banana source);
+    private static partial AppleDto MapApple(Apple source);
+}
+
+class Banana {}
+class Apple {}
+
+class BananaDto {}
+class AppleDto {}
+```
+
+If the source or target type of a runtime target type mapping is not `object`,
+only user mappings of which the source/target type is assignable to the source/target type of the mapping method are considered.
+
+Runtime target type mappings support [derived type mappings](./10-derived-type-mapping.md).
+The `MapDerivedTypeAttribute` can be directly applied to a runtime target type mapping method.
+
+:::info
+Mapperly runtime target type mappings
+only support source/target type combinations which are defined
+as mappings in the same mapper.
+If an unknown source/target type combination is provided at runtime,
+an `ArgumentException` is thrown.
+:::

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

@@ -37,6 +37,9 @@ public void BuildMappingBodies()
                 case UserDefinedExistingTargetMethodMapping mapping:
                     UserMethodMappingBodyBuilder.BuildMappingBody(ctx, mapping);
                     break;
+                case UserDefinedNewInstanceRuntimeTargetTypeMapping mapping:
+                    RuntimeTargetTypeMappingBodyBuilder.BuildMappingBody(ctx, mapping);
+                    break;
             }
         }
     }

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

@@ -0,0 +1,40 @@
+using Riok.Mapperly.Descriptors.MappingBuilders;
+using Riok.Mapperly.Descriptors.Mappings;
+using Riok.Mapperly.Helpers;
+
+namespace Riok.Mapperly.Descriptors.MappingBodyBuilders;
+
+public static class RuntimeTargetTypeMappingBodyBuilder
+{
+    public static void BuildMappingBody(MappingBuilderContext ctx, UserDefinedNewInstanceRuntimeTargetTypeMapping mapping)
+    {
+        // source nulls are filtered out by the type switch arms,
+        // therefore set source type always to nun-nullable
+        // as non-nullables are also assignable to nullables.
+        IEnumerable<ITypeMapping> mappings = ctx.CallableUserMappings.Where(
+            x =>
+                x.SourceType.NonNullable().IsAssignableTo(ctx.Compilation, mapping.SourceType)
+                && x.TargetType.IsAssignableTo(ctx.Compilation, mapping.TargetType)
+        );
+
+        // include derived type mappings declared on this user defined method
+        var derivedTypeMappings = DerivedTypeMappingBuilder.TryBuildContainedMappings(ctx, true);
+        if (derivedTypeMappings != null)
+        {
+            mappings = derivedTypeMappings.Concat(mappings);
+        }
+
+        // prefer non-nullable return types
+        // and prefer types with a higher inheritance level
+        // over types with a lower inheritance level
+        // in the type switch
+        // to use the most specific mapping
+        mappings = mappings
+            .OrderByDescending(x => x.SourceType.GetInheritanceLevel())
+            .ThenByDescending(x => x.TargetType.GetInheritanceLevel())
+            .ThenBy(x => x.TargetType.IsNullable())
+            .GroupBy(x => new TypeMappingKey(x, false))
+            .Select(x => x.First());
+        mapping.AddMappings(mappings);
+    }
+}

src/Riok.Mapperly/Descriptors/MappingBuilderContext.cs

@@ -42,6 +42,9 @@ protected MappingBuilderContext(MappingBuilderContext ctx, IMethodSymbol? userSy
 
     public ObjectFactoryCollection ObjectFactories { get; }
 
+    /// <inheritdoc cref="MappingBuilderContext.CallableUserMappings"/>
+    public IReadOnlyCollection<IUserMapping> CallableUserMappings => MappingBuilder.CallableUserMappings;
+
     public T GetConfigurationOrDefault<T>()
         where T : Attribute => Configuration.GetOrDefault<T>(_userSymbol);
 

src/Riok.Mapperly/Descriptors/MappingBuilders/DerivedTypeMappingBuilder.cs

@@ -11,31 +11,40 @@ public static class DerivedTypeMappingBuilder
 {
     public static ITypeMapping? TryBuildMapping(MappingBuilderContext ctx)
     {
-        var configs = ctx.ListConfiguration<MapDerivedTypeAttribute, MapDerivedType>()
-            .Concat(ctx.ListConfiguration<MapDerivedTypeAttribute<object, object>, MapDerivedType>())
-            .ToList();
-        if (configs.Count == 0)
+        var derivedTypeMappings = TryBuildContainedMappings(ctx);
+        if (derivedTypeMappings == null)
             return null;
 
-        var derivedTypeMappings = BuildDerivedTypeMappings(ctx, configs);
         return ctx.IsExpression
             ? new DerivedTypeIfExpressionMapping(ctx.Source, ctx.Target, derivedTypeMappings)
             : new DerivedTypeSwitchMapping(ctx.Source, ctx.Target, derivedTypeMappings);
     }
 
-    private static IReadOnlyCollection<ITypeMapping> BuildDerivedTypeMappings(
+    public static IReadOnlyCollection<ITypeMapping>? TryBuildContainedMappings(
+        MappingBuilderContext ctx,
+        bool duplicatedSourceTypesAllowed = false
+    )
+    {
+        var configs = ctx.ListConfiguration<MapDerivedTypeAttribute, MapDerivedType>()
+            .Concat(ctx.ListConfiguration<MapDerivedTypeAttribute<object, object>, MapDerivedType>())
+            .ToList();
+        return configs.Count == 0 ? null : BuildContainedMappings(ctx, configs, duplicatedSourceTypesAllowed);
+    }
+
+    private static IReadOnlyCollection<ITypeMapping> BuildContainedMappings(
         MappingBuilderContext ctx,
-        IReadOnlyCollection<MapDerivedType> configs
+        IReadOnlyCollection<MapDerivedType> configs,
+        bool duplicatedSourceTypesAllowed
     )
     {
         var derivedTypeMappingSourceTypes = new HashSet<ITypeSymbol>(SymbolEqualityComparer.Default);
         var derivedTypeMappings = new List<ITypeMapping>(configs.Count);
 
         foreach (var config in configs)
         {
-            // set reference types non-nullable as they can never be null when type-switching.
-            var sourceType = config.SourceType.WithNullableAnnotation(NullableAnnotation.NotAnnotated);
-            if (!derivedTypeMappingSourceTypes.Add(sourceType))
+            // set types non-nullable as they can never be null when type-switching.
+            var sourceType = config.SourceType.NonNullable();
+            if (!duplicatedSourceTypesAllowed && !derivedTypeMappingSourceTypes.Add(sourceType))
             {
                 ctx.ReportDiagnostic(DiagnosticDescriptors.DerivedSourceTypeDuplicated, sourceType);
                 continue;
@@ -47,7 +56,7 @@ IReadOnlyCollection<MapDerivedType> configs
                 continue;
             }
 
-            var targetType = config.TargetType.WithNullableAnnotation(NullableAnnotation.NotAnnotated);
+            var targetType = config.TargetType.NonNullable();
             if (!targetType.IsAssignableTo(ctx.Compilation, ctx.Target))
             {
                 ctx.ReportDiagnostic(DiagnosticDescriptors.DerivedTargetTypeIsNotAssignableToReturnType, targetType, ctx.Target);

src/Riok.Mapperly/Descriptors/MappingBuilders/MappingBuilder.cs

@@ -36,6 +36,9 @@ public MappingBuilder(MappingCollection mappings)
         _mappings = mappings;
     }
 
+    /// <inheritdoc cref="MappingCollection.CallableUserMappings"/>
+    public IReadOnlyCollection<IUserMapping> CallableUserMappings => _mappings.CallableUserMappings;
+
     /// <inheritdoc cref="MappingBuilderContext.FindMapping"/>
     public ITypeMapping? Find(ITypeSymbol sourceType, ITypeSymbol targetType) => _mappings.Find(sourceType, targetType);
 

src/Riok.Mapperly/Descriptors/MappingCollection.cs

@@ -7,20 +7,37 @@ namespace Riok.Mapperly.Descriptors;
 
 public class MappingCollection
 {
-    // this includes mappings to build and already built mappings
+    /// <summary>
+    /// The first callable mapping of each type pair.
+    /// Contains mappings to build and already built mappings
+    /// </summary>
     private readonly Dictionary<TypeMappingKey, ITypeMapping> _mappings = new();
 
-    // a list of all method mappings (extra mappings and mappings)
+    /// <summary>
+    /// A list of all method mappings (extra mappings and mappings)
+    /// </summary>
     private readonly List<MethodMapping> _methodMappings = new();
 
-    // queue of mappings which don't have the body built yet
+    /// <summary>
+    /// A list of all callable user mappings with <see cref="ITypeMapping.CallableByOtherMappings"/> <c>true</c>.
+    /// </summary>
+    private readonly List<IUserMapping> _callableUserMappings = new();
+
+    /// <summary>
+    /// Queue of mappings which don't have the body built yet
+    /// </summary>
     private readonly Queue<(IMapping, MappingBuilderContext)> _mappingsToBuildBody = new();
 
-    // a list of existing target mappings
+    /// <summary>
+    /// All existing target mappings
+    /// </summary>
     private readonly Dictionary<TypeMappingKey, IExistingTargetMapping> _existingTargetMappings = new();
 
     public IReadOnlyCollection<MethodMapping> MethodMappings => _methodMappings;
 
+    /// <inheritdoc cref="_callableUserMappings"/>
+    public IReadOnlyCollection<IUserMapping> CallableUserMappings => _callableUserMappings;
+
     public ITypeMapping? Find(ITypeSymbol sourceType, ITypeSymbol targetType)
     {
         _mappings.TryGetValue(new TypeMappingKey(sourceType, targetType), out var mapping);
@@ -37,6 +54,11 @@ public class MappingCollection
 
     public void Add(ITypeMapping mapping)
     {
+        if (mapping is IUserMapping { CallableByOtherMappings: true } userMapping)
+        {
+            _callableUserMappings.Add(userMapping);
+        }
+
         if (mapping is MethodMapping methodMapping)
         {
             _methodMappings.Add(methodMapping);
@@ -52,42 +74,4 @@ public void AddExistingTargetMapping(IExistingTargetMapping mapping) =>
         _existingTargetMappings.Add(new TypeMappingKey(mapping), mapping);
 
     public IEnumerable<(IMapping, MappingBuilderContext)> DequeueMappingsToBuildBody() => _mappingsToBuildBody.DequeueAll();
-
-    private readonly struct TypeMappingKey
-    {
-        private static readonly IEqualityComparer<ISymbol?> _comparer = SymbolEqualityComparer.IncludeNullability;
-
-        private readonly ITypeSymbol _source;
-        private readonly ITypeSymbol _target;
-
-        public TypeMappingKey(ITypeMapping mapping)
-            : this(mapping.SourceType, mapping.TargetType) { }
-
-        public TypeMappingKey(IExistingTargetMapping mapping)
-            : this(mapping.SourceType, mapping.TargetType) { }
-
-        public TypeMappingKey(ITypeSymbol source, ITypeSymbol target)
-        {
-            _source = source;
-            _target = target;
-        }
-
-        private bool Equals(TypeMappingKey other) => _comparer.Equals(_source, other._source) && _comparer.Equals(_target, other._target);
-
-        public override bool Equals(object? obj) => obj is TypeMappingKey other && Equals(other);
-
-        public override int GetHashCode()
-        {
-            unchecked
-            {
-                var hashCode = _comparer.GetHashCode(_source);
-                hashCode = (hashCode * 397) ^ _comparer.GetHashCode(_target);
-                return hashCode;
-            }
-        }
-
-        public static bool operator ==(TypeMappingKey left, TypeMappingKey right) => left.Equals(right);
-
-        public static bool operator !=(TypeMappingKey left, TypeMappingKey right) => !left.Equals(right);
-    }
 }

src/Riok.Mapperly/Descriptors/Mappings/DerivedTypeSwitchMapping.cs

@@ -11,7 +11,7 @@ namespace Riok.Mapperly.Descriptors.Mappings;
 /// </summary>
 public class DerivedTypeSwitchMapping : TypeMapping
 {
-    private const string GetTypeMethodName = "GetType";
+    private const string GetTypeMethodName = nameof(GetType);
 
     private readonly IReadOnlyCollection<ITypeMapping> _typeMappings;
 
@@ -33,7 +33,7 @@ public override ExpressionSyntax Build(TypeMappingBuildContext ctx)
             )
         );
 
-        // source switch { A x => MapToA(x), B x => MapToB(x) }
+        // source switch { A x => MapToADto(x), B x => MapToBDto(x) }
         var (typeArmContext, typeArmVariableName) = ctx.WithNewSource();
         var arms = _typeMappings
             .Select(x => BuildSwitchArm(typeArmVariableName, x.SourceType, x.Build(typeArmContext)))
@@ -43,7 +43,7 @@ public override ExpressionSyntax Build(TypeMappingBuildContext ctx)
 
     private SwitchExpressionArmSyntax BuildSwitchArm(string typeArmVariableName, ITypeSymbol type, ExpressionSyntax mapping)
     {
-        // A x => MapToA(x),
+        // A x => MapToADto(x),
         var declaration = DeclarationPattern(FullyQualifiedIdentifier(type), SingleVariableDesignation(Identifier(typeArmVariableName)));
         return SwitchExpressionArm(declaration, mapping);
     }