feat: support static mapping methods in non-static mappers (#681)

docs/docs/configuration/static-mappers.md

@@ -16,3 +16,24 @@ public static partial class CarMapper
     private static int TimeSpanToHours(TimeSpan t) => t.Hours;
 }
 ```
+
+## Static methods in instantiable class
+
+Static methods are supported in non-static mapper classes. This supports the static interface use case. When a static mapping method is present, to simplify mapping method resolution and reduce confusion about which mapping method Mapperly uses, all methods must be static.
+
+```csharp
+public interface ICarMapper
+{
+    static abstract CarDto ToDto(Car car);
+}
+
+[Mapper]
+// highlight-start
+public partial class CarMapper : ICarMapper
+// highlight-end
+{
+// highlight-start
+    public static partial CarDto ToDto(Car car);
+// highlight-end
+}
+```

docs/docs/contributing/architecture.md

@@ -30,9 +30,9 @@ The `DescriptorBuilder` is responsible to build a `MapperDescriptor` which holds
 The `DescriptorBuilder` does this by following this process:
 
 1. Extracting the configuration from the attributes
-2. Extracting user implemented object factories
-3. Extracting user implemented and user defined mapping methods.
+2. Extracting user implemented and user defined mapping methods.
    It instantiates a `User*Mapping` (eg. `UserDefinedNewInstanceMethodMapping`) for each discovered mapping method and adds it to the queue of mappings to work on.
+3. Extracting user implemented object factories
 4. Extracting external mappings
 5. For each mapping in the queue the `DescriptorBuilder` tries to build its implementation bodies.
    This is done by a so called `*MappingBodyBuilder`.

src/Riok.Mapperly/AnalyzerReleases.Shipped.md

@@ -126,3 +126,9 @@ Rule ID | Category | Severity | Notes
 RMG051  | Mapper   | Warning  | Invalid ignore source member found, nested ignores are not supported
 RMG052  | Mapper   | Warning  | Invalid ignore target member found, nested ignores are not supported
 RMG053  | Mapper   | Error    | The flag MemberVisibility.Accessible cannot be disabled, this feature requires .NET 8.0 or greater
+RMG054  | Mapper   | Error    | Mapper class containing 'static partial' method must not have any instance methods 
+
+### Removed Rules
+Rule ID | Category | Severity | Notes
+--------|----------|----------|-------
+RMG018  | Mapper   | Disabled | Partial static mapping method in an instance mapper

src/Riok.Mapperly/Descriptors/DescriptorBuilder.cs

@@ -6,6 +6,7 @@
 using Riok.Mapperly.Descriptors.MappingBodyBuilders;
 using Riok.Mapperly.Descriptors.MappingBuilders;
 using Riok.Mapperly.Descriptors.ObjectFactories;
+using Riok.Mapperly.Diagnostics;
 using Riok.Mapperly.Helpers;
 using Riok.Mapperly.Symbols;
 using Riok.Mapperly.Templates;
@@ -28,8 +29,6 @@ public class DescriptorBuilder
     private readonly UnsafeAccessorContext _unsafeAccessorContext;
     private readonly MapperConfigurationReader _configurationReader;
 
-    private ObjectFactoryCollection _objectFactories = ObjectFactoryCollection.Empty;
-
     public DescriptorBuilder(
         CompilationContext compilationContext,
         MapperDeclaration mapperDeclaration,
@@ -63,8 +62,10 @@ MapperConfiguration defaultMapperConfiguration
     {
         ConfigureMemberVisibility();
         ReserveMethodNames();
-        ExtractObjectFactories();
         ExtractUserMappings();
+        // ExtractObjectFactories needs to be called after ExtractUserMappings due to configuring mapperDescriptor.Static
+        var objectFactories = ExtractObjectFactories();
+        EnqueueUserMappings(objectFactories);
         ExtractExternalMappings();
         _mappingBodyBuilder.BuildMappingBodies(cancellationToken);
         BuildMappingMethodNames();
@@ -106,24 +107,57 @@ private void ReserveMethodNames()
         }
     }
 
-    private void ExtractObjectFactories()
+    private void ExtractUserMappings()
+    {
+        _mapperDescriptor.Static = _mapperDescriptor.Symbol.IsStatic;
+        IMethodSymbol? firstNonStaticUserMapping = null;
+
+        foreach (var userMapping in UserMethodMappingExtractor.ExtractUserMappings(_builderContext, _mapperDescriptor.Symbol))
+        {
+            // if a user defined mapping method is static, all of them need to be static to avoid confusion for mapping method resolution
+            // however, user implemented mapping methods are allowed to be static in a non-static context.
+            // Therefore we are only interested in partial method definitions here.
+            if (userMapping.Method is { IsStatic: true, IsPartialDefinition: true })
+            {
+                _mapperDescriptor.Static = true;
+            }
+            else if (firstNonStaticUserMapping == null && !userMapping.Method.IsStatic)
+            {
+                firstNonStaticUserMapping = userMapping.Method;
+            }
+
+            _mappings.Add(userMapping);
+        }
+
+        if (_mapperDescriptor.Static && firstNonStaticUserMapping is not null)
+        {
+            _diagnostics.Add(
+                Diagnostic.Create(
+                    DiagnosticDescriptors.MixingStaticPartialWithInstanceMethod,
+                    firstNonStaticUserMapping.Locations.FirstOrDefault(),
+                    _mapperDescriptor.Symbol.ToDisplayString()
+                )
+            );
+        }
+    }
+
+    private ObjectFactoryCollection ExtractObjectFactories()
     {
-        _objectFactories = ObjectFactoryBuilder.ExtractObjectFactories(_builderContext, _mapperDescriptor.Symbol);
+        return ObjectFactoryBuilder.ExtractObjectFactories(_builderContext, _mapperDescriptor.Symbol);
     }
 
-    private void ExtractUserMappings()
+    private void EnqueueUserMappings(ObjectFactoryCollection objectFactories)
     {
-        foreach (var userMapping in UserMethodMappingExtractor.ExtractUserMappings(_builderContext, _mapperDescriptor.Symbol))
+        foreach (var userMapping in _mappings.UserMappings)
         {
             var ctx = new MappingBuilderContext(
                 _builderContext,
-                _objectFactories,
+                objectFactories,
                 userMapping.Method,
                 userMapping.SourceType,
                 userMapping.TargetType
             );
 
-            _mappings.Add(userMapping);
             _mappings.EnqueueToBuildBody(userMapping, ctx);
         }
     }

src/Riok.Mapperly/Descriptors/MapperDescriptor.cs

@@ -16,6 +16,8 @@ public class MapperDescriptor
     private readonly List<IUnsafeAccessor> _unsafeAccessors = new();
     private readonly HashSet<TemplateReference> _requiredTemplates = new();
 
+    public bool Static { get; set; }
+
     public MapperDescriptor(MapperDeclaration declaration, UniqueNameBuilder nameBuilder)
     {
         _declaration = declaration;

src/Riok.Mapperly/Descriptors/ObjectFactories/ObjectFactoryBuilder.cs

@@ -28,6 +28,7 @@ public static ObjectFactoryCollection ExtractObjectFactories(SimpleMappingBuilde
             || methodSymbol.IsPartialDefinition
             || methodSymbol.MethodKind != MethodKind.Ordinary
             || methodSymbol.ReturnsVoid
+            || (!methodSymbol.IsStatic && ctx.Static)
         )
         {
             ctx.ReportDiagnostic(DiagnosticDescriptors.InvalidObjectFactorySignature, methodSymbol, methodSymbol.Name);

src/Riok.Mapperly/Descriptors/ObjectFactories/ObjectFactoryCollection.cs

@@ -5,8 +5,6 @@ namespace Riok.Mapperly.Descriptors.ObjectFactories;
 
 public class ObjectFactoryCollection
 {
-    public static readonly ObjectFactoryCollection Empty = new(Array.Empty<ObjectFactory>());
-
     private readonly IReadOnlyCollection<ObjectFactory> _objectFactories;
     private readonly Dictionary<ITypeSymbol, ObjectFactory> _concreteObjectFactories = new(SymbolEqualityComparer.IncludeNullability);
 

src/Riok.Mapperly/Descriptors/SimpleMappingBuilderContext.cs

@@ -58,6 +58,8 @@ protected SimpleMappingBuilderContext(SimpleMappingBuilderContext ctx)
 
     public WellKnownTypes Types => _compilationContext.Types;
 
+    public bool Static => _descriptor.Static;
+
     public SymbolAccessor SymbolAccessor { get; }
 
     public AttributeDataAccessor AttributeAccessor { get; }

src/Riok.Mapperly/Descriptors/UserMethodMappingExtractor.cs

@@ -17,8 +17,8 @@ internal static IEnumerable<IUserMapping> ExtractUserMappings(SimpleMappingBuild
         foreach (var methodSymbol in ExtractMethods(mapperSymbol))
         {
             var mapping =
-                BuilderUserDefinedMapping(ctx, methodSymbol, mapperSymbol.IsStatic)
-                ?? BuildUserImplementedMapping(ctx, methodSymbol, null, false, mapperSymbol.IsStatic);
+                BuilderUserDefinedMapping(ctx, methodSymbol)
+                ?? BuildUserImplementedMapping(ctx, methodSymbol, receiver: null, allowPartial: false, mapperSymbol.IsStatic);
             if (mapping != null)
                 yield return mapping;
         }
@@ -109,18 +109,11 @@ bool isStatic
             : new UserImplementedMethodMapping(receiver, method, parameters.Source, parameters.ReferenceHandler);
     }
 
-    private static IUserMapping? BuilderUserDefinedMapping(SimpleMappingBuilderContext ctx, IMethodSymbol methodSymbol, bool isStatic)
+    private static IUserMapping? BuilderUserDefinedMapping(SimpleMappingBuilderContext ctx, IMethodSymbol methodSymbol)
     {
         if (!methodSymbol.IsPartialDefinition)
             return null;
 
-        if (!isStatic && methodSymbol.IsStatic)
-        {
-            ctx.ReportDiagnostic(DiagnosticDescriptors.PartialStaticMethodInInstanceMapper, methodSymbol, methodSymbol.Name);
-
-            return null;
-        }
-
         if (methodSymbol.IsAsync)
         {
             ctx.ReportDiagnostic(DiagnosticDescriptors.UnsupportedMappingMethodSignature, methodSymbol, methodSymbol.Name);

src/Riok.Mapperly/Diagnostics/DiagnosticDescriptors.cs

@@ -159,15 +159,6 @@ public static class DiagnosticDescriptors
         true
     );
 
-    public static readonly DiagnosticDescriptor PartialStaticMethodInInstanceMapper = new DiagnosticDescriptor(
-        "RMG018",
-        "Partial static mapping method in an instance mapper",
-        "{0} is a partial static mapping method in an instance mapper. Static mapping methods are only supported in static mappers.",
-        DiagnosticCategories.Mapper,
-        DiagnosticSeverity.Error,
-        true
-    );
-
     public static readonly DiagnosticDescriptor SourceMemberNotMapped = new DiagnosticDescriptor(
         "RMG020",
         "Source member is not mapped to any target member",
@@ -473,4 +464,13 @@ public static class DiagnosticDescriptors
         DiagnosticSeverity.Error,
         true
     );
+
+    public static readonly DiagnosticDescriptor MixingStaticPartialWithInstanceMethod = new DiagnosticDescriptor(
+        "RMG054",
+        "Mapper class containing 'static partial' method must not have any instance methods",
+        "Mapper class {0} contains 'static partial' method. Use only instance method or only static methods.",
+        DiagnosticCategories.Mapper,
+        DiagnosticSeverity.Error,
+        true
+    );
 }

src/Riok.Mapperly/Emit/SourceEmitter.cs

@@ -14,7 +14,7 @@ public static class SourceEmitter
     public static CompilationUnitSyntax Build(MapperDescriptor descriptor, CancellationToken cancellationToken)
     {
         var ctx = new SourceEmitterContext(
-            descriptor.Symbol.IsStatic,
+            descriptor.Static,
             descriptor.NameBuilder,
             new SyntaxFactoryHelper(descriptor.Symbol.ContainingAssembly.Name)
         );

src/Riok.Mapperly/MapperGenerator.cs

@@ -1,4 +1,4 @@
-using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp;
 using Riok.Mapperly.Abstractions;
 using Riok.Mapperly.Configuration;

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

@@ -164,7 +164,11 @@ public void DictionaryToCustomDictionary()
     public void DictionaryToCustomDictionaryWithObjectFactory()
     {
         var source = TestSourceBuilder.MapperWithBodyAndTypes(
-            "[ObjectFactory] A CreateA() => new();" + "partial A Map(IDictionary<string, int> source);",
+            """
+            [ObjectFactory]
+            A CreateA() => new();
+            partial A Map(IDictionary<string, int> source);
+            """,
             "class A : Dictionary<string, int> {}"
         );
         TestHelper
@@ -354,7 +358,11 @@ string IDictionary<string, string>.this[string key]
     public void DictionaryToExplicitDictionaryWithObjectFactoryShouldCast()
     {
         var source = TestSourceBuilder.MapperWithBodyAndTypes(
-            "[ObjectFactory] A CreateA() => new();" + "partial A Map(Dictionary<string, string> source);",
+            """
+            [ObjectFactory]
+            A CreateA() => new();
+            partial A Map(Dictionary<string, string> source);
+            """,
             """
             public class A : IDictionary<string, string>
             {
@@ -387,7 +395,11 @@ string IDictionary<string, string>.this[string key]
     public void DictionaryToImplicitDictionaryWithObjectFactoryShouldNotCast()
     {
         var source = TestSourceBuilder.MapperWithBodyAndTypes(
-            "[ObjectFactory] A CreateA() => new();" + "partial A Map(Dictionary<string, string> source);",
+            """
+            [ObjectFactory]
+            A CreateA() => new();
+            partial A Map(Dictionary<string, string> source);
+            """,
             """
             public class A : IDictionary<string, string>
             {