feat: Add option to specify the string format of a property

docs/docs/configuration/mapper.mdx

@@ -216,7 +216,7 @@ the `RequiredMappingStrategy` can be used.
     // highlight-start
     [MapperRequiredMapping(RequiredMappingStrategy.Source)]
     // highlight-end
-    public partial CarDto MapMake(Car make);
+    public partial CarDto MapCar(Car car);
   }
   ```
 
@@ -227,6 +227,22 @@ the `RequiredMappingStrategy` can be used.
 
 To enforce strict enum mappings set `RMG037` and `RMG038` to error, see [strict enum mappings](./enum.mdx#strict-enum-mappings).
 
+### String format
+
+The string format passed to `ToString` calls when converting to a string can be customized
+by using the `StringFormat` property of the `MapPropertyAttribute`.
+
+```csharp
+[Mapper]
+public partial class CarMapper
+{
+  // highlight-start
+  [MapProperty(nameof(Car.Price), nameof(CarDto.Price), StringFormat = "C")]
+  // highlight-end
+  public partial CarDto MapCar(Car car);
+}
+```
+
 ## Default Mapper configuration
 
 The `MapperDefaultsAttribute` allows to set default configurations applied to all mappers on the assembly level.

src/Riok.Mapperly.Abstractions/MapPropertyAttribute.cs

@@ -43,6 +43,11 @@
     /// </summary>
     public IReadOnlyCollection<string> Target { get; }
 
+    /// <summary>
+    /// Gets or sets the format of the <c>ToString</c> conversion.
+    /// </summary>
+    public string? StringFormat { get; set; }
+
     /// <summary>
     /// Gets the full name of the target property path.
     /// </summary>

src/Riok.Mapperly.Abstractions/PublicAPI.Shipped.txt

@@ -55,6 +55,8 @@ Riok.Mapperly.Abstractions.MapPropertyAttribute.Source.get -> System.Collections
 Riok.Mapperly.Abstractions.MapPropertyAttribute.SourceFullName.get -> string!
 Riok.Mapperly.Abstractions.MapPropertyAttribute.Target.get -> System.Collections.Generic.IReadOnlyCollection<string!>!
 Riok.Mapperly.Abstractions.MapPropertyAttribute.TargetFullName.get -> string!
+Riok.Mapperly.Abstractions.MapPropertyAttribute.StringFormat.get -> string?
+Riok.Mapperly.Abstractions.MapPropertyAttribute.StringFormat.set -> void
 Riok.Mapperly.Abstractions.ObjectFactoryAttribute
 Riok.Mapperly.Abstractions.ObjectFactoryAttribute.ObjectFactoryAttribute() -> void
 Riok.Mapperly.Abstractions.PropertyNameMappingStrategy

src/Riok.Mapperly/AnalyzerReleases.Shipped.md

@@ -127,6 +127,7 @@ RMG051  | Mapper   | Warning  | Invalid ignore source member found, nested ignor
 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 
+RMG055  | Mapper   | Error    | The source type does not implement IFormattable, string format cannot be applied
 
 ### Removed Rules
 Rule ID | Category | Severity | Notes

src/Riok.Mapperly/Configuration/MapperConfigurationReader.cs

@@ -72,7 +72,7 @@ private PropertiesMappingConfiguration BuildPropertiesConfig(IMethodSymbol metho
             .Select(x => x.Target)
             .WhereNotNull()
             .ToList();
-        var explicitMappings = _dataAccessor.Access<MapPropertyAttribute, PropertyMappingConfiguration>(method).ToList();
+        var propertyConfigurations = _dataAccessor.Access<MapPropertyAttribute, PropertyMappingConfiguration>(method).ToList();
         var ignoreObsolete = _dataAccessor.Access<MapperIgnoreObsoleteMembersAttribute>(method).FirstOrDefault() is not { } methodIgnore
             ? _defaultConfiguration.Properties.IgnoreObsoleteMembersStrategy
             : methodIgnore.IgnoreObsoleteStrategy;
@@ -83,7 +83,7 @@ private PropertiesMappingConfiguration BuildPropertiesConfig(IMethodSymbol metho
         return new PropertiesMappingConfiguration(
             ignoredSourceProperties,
             ignoredTargetProperties,
-            explicitMappings,
+            propertyConfigurations,
             ignoreObsolete,
             requiredMapping
         );

src/Riok.Mapperly/Configuration/PropertyMappingConfiguration.cs

@@ -1,3 +1,10 @@
+using Riok.Mapperly.Descriptors;
+
 namespace Riok.Mapperly.Configuration;
 
-public record PropertyMappingConfiguration(StringMemberPath Source, StringMemberPath Target);
+public record PropertyMappingConfiguration(StringMemberPath Source, StringMemberPath Target)
+{
+    public string? StringFormat { get; set; }
+
+    public TypeMappingConfiguration ToTypeMappingConfiguration() => new(StringFormat);
+}

src/Riok.Mapperly/Descriptors/DescriptorBuilder.cs

@@ -126,7 +126,7 @@ private void ExtractUserMappings()
                 firstNonStaticUserMapping = userMapping.Method;
             }
 
-            _mappings.Add(userMapping);
+            _mappings.Add(userMapping, TypeMappingConfiguration.Default);
         }
 
         if (_mapperDescriptor.Static && firstNonStaticUserMapping is not null)
@@ -152,8 +152,7 @@ private void EnqueueUserMappings(ObjectFactoryCollection objectFactories)
                 _builderContext,
                 objectFactories,
                 userMapping.Method,
-                userMapping.SourceType,
-                userMapping.TargetType
+                new TypeMappingKey(userMapping.SourceType, userMapping.TargetType)
             );
 
             _mappings.EnqueueToBuildBody(userMapping, ctx);
@@ -164,7 +163,7 @@ private void ExtractExternalMappings()
     {
         foreach (var externalMapping in ExternalMappingsExtractor.ExtractExternalMappings(_builderContext, _mapperDescriptor.Symbol))
         {
-            _mappings.Add(externalMapping);
+            _mappings.Add(externalMapping, TypeMappingConfiguration.Default);
         }
     }
 

src/Riok.Mapperly/Descriptors/InlineExpressionMappingBuilderContext.cs

@@ -3,7 +3,6 @@
 using Riok.Mapperly.Descriptors.Mappings;
 using Riok.Mapperly.Descriptors.Mappings.ExistingTarget;
 using Riok.Mapperly.Descriptors.Mappings.UserMappings;
-using Riok.Mapperly.Helpers;
 
 namespace Riok.Mapperly.Descriptors;
 
@@ -16,16 +15,11 @@ public class InlineExpressionMappingBuilderContext : MappingBuilderContext
     private readonly MappingCollection _inlineExpressionMappings;
     private readonly MappingBuilderContext _parentContext;
 
-    public InlineExpressionMappingBuilderContext(MappingBuilderContext ctx, ITypeSymbol sourceType, ITypeSymbol targetType)
-        : this(ctx, (ctx.FindMapping(sourceType, targetType) as IUserMapping)?.Method, sourceType, targetType) { }
+    public InlineExpressionMappingBuilderContext(MappingBuilderContext ctx, TypeMappingKey mappingKey)
+        : this(ctx, (ctx.FindMapping(mappingKey) as IUserMapping)?.Method, mappingKey) { }
 
-    private InlineExpressionMappingBuilderContext(
-        MappingBuilderContext ctx,
-        IMethodSymbol? userSymbol,
-        ITypeSymbol source,
-        ITypeSymbol target
-    )
-        : base(ctx, userSymbol, source, target, false)
+    private InlineExpressionMappingBuilderContext(MappingBuilderContext ctx, IMethodSymbol? userSymbol, TypeMappingKey mappingKey)
+        : base(ctx, userSymbol, mappingKey, false)
     {
         _parentContext = ctx;
         _inlineExpressionMappings = new MappingCollection();
@@ -34,11 +28,10 @@ ITypeSymbol target
     private InlineExpressionMappingBuilderContext(
         InlineExpressionMappingBuilderContext ctx,
         IMethodSymbol? userSymbol,
-        ITypeSymbol source,
-        ITypeSymbol target,
+        TypeMappingKey mappingKey,
         bool clearDerivedTypes
     )
-        : base(ctx, userSymbol, source, target, clearDerivedTypes)
+        : base(ctx, userSymbol, mappingKey, clearDerivedTypes)
     {
         _parentContext = ctx;
         _inlineExpressionMappings = ctx._inlineExpressionMappings;
@@ -55,25 +48,24 @@ conversionType is not MappingConversionType.EnumToString and not MappingConversi
         && base.IsConversionEnabled(conversionType);
 
     /// <summary>
-    /// Tries to find an existing mapping for the provided types.
+    /// Tries to find an existing mapping for the provided types + config.
     /// The nullable annotation of reference types is ignored and always set to non-nullable.
     /// Only inline expression mappings and user implemented mappings are considered.
     /// </summary>
-    /// <param name="sourceType">The source type.</param>
-    /// <param name="targetType">The target type.</param>
+    /// <param name="mappingKey">The mapping key.</param>
     /// <returns>The <see cref="INewInstanceMapping"/> if a mapping was found or <c>null</c> if none was found.</returns>
-    public override INewInstanceMapping? FindMapping(ITypeSymbol sourceType, ITypeSymbol targetType)
+    public override INewInstanceMapping? FindMapping(TypeMappingKey mappingKey)
     {
-        if (_inlineExpressionMappings.Find(sourceType, targetType) is { } mapping)
+        if (_inlineExpressionMappings.Find(mappingKey) is { } mapping)
             return mapping;
 
         // User implemented mappings are also taken into account.
         // This works as long as the user implemented methods
         // follow the expression tree limitations:
         // https://learn.microsoft.com/en-us/dotnet/csharp/advanced-topics/expression-trees/#limitations
-        if (_parentContext.FindMapping(sourceType, targetType) is UserImplementedMethodMapping userMapping)
+        if (_parentContext.FindMapping(mappingKey) is UserImplementedMethodMapping userMapping)
         {
-            _inlineExpressionMappings.Add(userMapping);
+            _inlineExpressionMappings.Add(userMapping, mappingKey.Configuration);
             return userMapping;
         }
 
@@ -88,33 +80,29 @@ conversionType is not MappingConversionType.EnumToString and not MappingConversi
     /// This ensures, the configuration of the user defined method is reused.
     /// <seealso cref="MappingBuilderContext.FindOrBuildMapping"/>
     /// </summary>
-    /// <param name="sourceType">The source type.</param>
-    /// <param name="targetType">The target type.</param>
+    /// <param name="mappingKey">The mapping key.</param>
     /// <param name="options">The options, <see cref="MappingBuildingOptions.MarkAsReusable"/> is ignored.</param>
     /// <returns></returns>
     public override INewInstanceMapping? FindOrBuildMapping(
-        ITypeSymbol sourceType,
-        ITypeSymbol targetType,
+        TypeMappingKey mappingKey,
         MappingBuildingOptions options = MappingBuildingOptions.Default
     )
     {
-        sourceType = sourceType.UpgradeNullable();
-        targetType = targetType.UpgradeNullable();
-        var mapping = FindMapping(sourceType, targetType);
+        var mapping = FindMapping(mappingKey);
         if (mapping != null)
             return mapping;
 
         var userSymbol = options.HasFlag(MappingBuildingOptions.KeepUserSymbol) ? UserSymbol : null;
 
-        userSymbol ??= (MappingBuilder.Find(sourceType, targetType) as IUserMapping)?.Method;
+        userSymbol ??= (MappingBuilder.Find(mappingKey) as IUserMapping)?.Method;
 
         // unset MarkAsReusable and KeepUserSymbol as they have special handling for inline mappings
         options &= ~(MappingBuildingOptions.MarkAsReusable | MappingBuildingOptions.KeepUserSymbol);
 
-        mapping = BuildMapping(userSymbol, sourceType, targetType, options);
+        mapping = BuildMapping(userSymbol, mappingKey, options);
         if (mapping != null)
         {
-            _inlineExpressionMappings.Add(mapping);
+            _inlineExpressionMappings.Add(mapping, mappingKey.Configuration);
         }
 
         return mapping;
@@ -123,26 +111,22 @@ conversionType is not MappingConversionType.EnumToString and not MappingConversi
     /// <summary>
     /// Existing target instance mappings are not supported.
     /// </summary>
-    /// <param name="sourceType">The source type, ignored.</param>
-    /// <param name="targetType">The target type, ignored.</param>
+    /// <param name="mappingKey">The mapping key, ignored.</param>
     /// <param name="options">The options to build a new mapping, ignored.</param>
     /// <returns><c>null</c></returns>
     public override IExistingTargetMapping? FindOrBuildExistingTargetMapping(
-        ITypeSymbol sourceType,
-        ITypeSymbol targetType,
+        TypeMappingKey mappingKey,
         MappingBuildingOptions options = MappingBuildingOptions.Default
     ) => null;
 
     /// <summary>
     /// Existing target instance mappings are not supported.
     /// </summary>
-    /// <param name="sourceType">The source type, ignored.</param>
-    /// <param name="targetType">The target type, ignored.</param>
+    /// <param name="mappingKey">The mapping key, ignored.</param>
     /// <param name="options">The options to build a new mapping, ignored.</param>
     /// <returns><c>null</c></returns>
     public override IExistingTargetMapping? BuildExistingTargetMapping(
-        ITypeSymbol sourceType,
-        ITypeSymbol targetType,
+        TypeMappingKey mappingKey,
         MappingBuildingOptions options = MappingBuildingOptions.Default
     ) => null;
 
@@ -151,15 +135,15 @@ protected override NullFallbackValue GetNullFallbackValue(ITypeSymbol targetType
 
     protected override MappingBuilderContext ContextForMapping(
         IMethodSymbol? userSymbol,
-        ITypeSymbol sourceType,
-        ITypeSymbol targetType,
+        TypeMappingKey mappingKey,
         MappingBuildingOptions options
-    ) =>
-        new InlineExpressionMappingBuilderContext(
+    )
+    {
+        return new InlineExpressionMappingBuilderContext(
             this,
             userSymbol,
-            sourceType,
-            targetType,
+            mappingKey,
             options.HasFlag(MappingBuildingOptions.ClearDerivedTypes)
         );
+    }
 }

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

@@ -132,22 +132,22 @@ IReadOnlyCollection<PropertyMappingConfiguration> memberConfigs
             return;
         }
 
-        BuildInitMemberMapping(ctx, targetMember, sourceMemberPath);
+        BuildInitMemberMapping(ctx, targetMember, sourceMemberPath, memberConfig);
     }
 
     private static void BuildInitMemberMapping(
         INewInstanceBuilderContext<IMapping> ctx,
         IMappableMember targetMember,
-        MemberPath sourcePath
+        MemberPath sourcePath,
+        PropertyMappingConfiguration? memberConfig = null
     )
     {
         var targetPath = new MemberPath(new[] { targetMember });
         if (!ObjectMemberMappingBodyBuilder.ValidateMappingSpecification(ctx, sourcePath, targetPath, true))
             return;
 
-        var delegateMapping =
-            ctx.BuilderContext.FindMapping(sourcePath.MemberType, targetMember.Type)
-            ?? ctx.BuilderContext.FindOrBuildMapping(sourcePath.MemberType.NonNullable(), targetMember.Type.NonNullable());
+        var mappingKey = new TypeMappingKey(sourcePath.MemberType, targetMember.Type, memberConfig?.ToTypeMappingConfiguration());
+        var delegateMapping = ctx.BuilderContext.FindOrBuildLooseNullableMapping(mappingKey);
 
         if (delegateMapping == null)
         {
@@ -254,7 +254,7 @@ private static bool TryBuildConstructorMapping(
         var skippedOptionalParam = false;
         foreach (var parameter in ctor.Parameters)
         {
-            if (!TryFindConstructorParameterSourcePath(ctx, parameter, out var sourcePath))
+            if (!TryFindConstructorParameterSourcePath(ctx, parameter, out var sourcePath, out var memberConfig))
             {
                 // expressions do not allow skipping of optional parameters
                 if (!parameter.IsOptional || ctx.BuilderContext.IsExpression)
@@ -266,9 +266,8 @@ private static bool TryBuildConstructorMapping(
 
             // nullability is handled inside the member mapping
             var paramType = parameter.Type.WithNullableAnnotation(parameter.NullableAnnotation);
-            var delegateMapping =
-                ctx.BuilderContext.FindMapping(sourcePath.MemberType, paramType)
-                ?? ctx.BuilderContext.FindOrBuildMapping(sourcePath.Member.Type.NonNullable(), paramType.NonNullable());
+            var typeMapping = new TypeMappingKey(sourcePath.MemberType, paramType, memberConfig?.ToTypeMappingConfiguration());
+            var delegateMapping = ctx.BuilderContext.FindOrBuildLooseNullableMapping(typeMapping);
 
             if (delegateMapping == null)
             {
@@ -311,10 +310,12 @@ private static bool TryBuildConstructorMapping(
     private static bool TryFindConstructorParameterSourcePath(
         INewInstanceBuilderContext<IMapping> ctx,
         IParameterSymbol parameter,
-        [NotNullWhen(true)] out MemberPath? sourcePath
+        [NotNullWhen(true)] out MemberPath? sourcePath,
+        out PropertyMappingConfiguration? memberConfig
     )
     {
         sourcePath = null;
+        memberConfig = null;
 
         if (!ctx.MemberConfigsByRootTargetName.TryGetValue(parameter.Name, out var memberConfigs))
         {
@@ -338,7 +339,7 @@ out sourcePath
             );
         }
 
-        var memberConfig = memberConfigs.First();
+        memberConfig = memberConfigs.First();
         if (memberConfig.Target.Path.Count > 1)
         {
             ctx.BuilderContext.ReportDiagnostic(