feat: intorduce MapValueAttribute to map constant values and method p…

…rovided values

docs/docs/configuration/before-after-map.md

@@ -1,5 +1,5 @@
 ---
-sidebar_position: 4
+sidebar_position: 5
 description: Run custom logic before or after the generated mapping.
 ---
 

docs/docs/configuration/constant-generated-values.mdx

@@ -0,0 +1,48 @@
+---
+sidebar_position: 4
+description: Map constant and generated values
+---
+
+import Tabs from '@theme/Tabs';
+import TabItem from '@theme/TabItem';
+
+# Constant and generated values
+
+## Constant values
+
+To map a constant value to a member or a constructor parameter `MapValue` can be used.
+Make sure the value exactly matches the target type.
+
+<Tabs>
+  <TabItem value="declaration" label="Declaration" default>
+    ```csharp [MapValue(nameof(CarDto.SourceSystem), "C1")] partial CarDto
+    Map(Car car); ```
+  </TabItem>
+  <TabItem value="generated" label="Generated code" default>
+    ```csharp target.SourceSystem = "C1"; ```
+  </TabItem>
+</Tabs>
+
+## Method generated values
+
+To map a method generated value to a member or a constructor parameter `MapValue` can be used.
+Make sure the return type exactly matches the target type.
+
+<Tabs>
+    <TabItem value="declaration" label="Declaration" default>
+        ```csharp
+        [MapValue(nameof(CarDto.SourceSystem), nameof(GetSourceSystem))]
+        partial CarDto Map(Car car);
+
+        string GetSourceSystem() => "C1";
+        ```
+    </TabItem>
+    <TabItem value="generated" label="Generated code" default>
+        ```csharp
+        target.SourceSystem = GetSourceSystem();
+        ```
+    </TabItem>
+
+</Tabs>
+
+This also works for constructor parameters.

docs/docs/configuration/conversions.md

@@ -1,5 +1,5 @@
 ---
-sidebar_position: 14
+sidebar_position: 15
 description: A list of conversions supported by Mapperly
 ---
 

docs/docs/configuration/ctor-mappings.md

@@ -1,5 +1,5 @@
 ---
-sidebar_position: 6
+sidebar_position: 7
 description: Constructor mappings
 ---
 

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

@@ -1,5 +1,5 @@
 ---
-sidebar_position: 9
+sidebar_position: 10
 description: Map derived types and interfaces
 ---
 

docs/docs/configuration/enum.mdx

@@ -1,5 +1,5 @@
 ---
-sidebar_position: 3
+sidebar_position: 4
 description: Map enums
 ---
 

docs/docs/configuration/existing-target.md

@@ -1,5 +1,5 @@
 ---
-sidebar_position: 8
+sidebar_position: 9
 description: Map to an existing target object
 ---
 

docs/docs/configuration/flattening.md

@@ -1,5 +1,5 @@
 ---
-sidebar_position: 2
+sidebar_position: 3
 description: Flatten properties and fields
 ---
 

docs/docs/configuration/generated-source.mdx

@@ -1,5 +1,5 @@
 ---
-sidebar_position: 16
+sidebar_position: 17
 description: How to inspect and check in the generated source into a version control system (VCS, GIT, ...)
 ---
 

docs/docs/configuration/generic-mapping.md

@@ -1,5 +1,5 @@
 ---
-sidebar_position: 10
+sidebar_position: 11
 description: Create a generic mapping method
 ---
 

docs/docs/configuration/object-factories.md

@@ -1,5 +1,5 @@
 ---
-sidebar_position: 7
+sidebar_position: 8
 description: Construct and resolve objects using object factories
 ---
 

docs/docs/configuration/private-member-mapping.md

@@ -1,5 +1,5 @@
 ---
-sidebar_position: 12
+sidebar_position: 13
 description: Private member mapping
 ---
 

docs/docs/configuration/queryable-projections.mdx

@@ -1,5 +1,5 @@
 ---
-sidebar_position: 13
+sidebar_position: 14
 description: Use queryable projections to map queryable objects and optimize ORM performance
 ---
 

docs/docs/configuration/reference-handling.md

@@ -1,5 +1,5 @@
 ---
-sidebar_position: 11
+sidebar_position: 12
 description: Use reference handling to handle reference loops
 ---
 

docs/docs/configuration/user-implemented-methods.mdx

@@ -1,5 +1,5 @@
 ---
-sidebar_position: 5
+sidebar_position: 6
 description: Manually implement mappings
 ---
 

src/Riok.Mapperly.Abstractions/MapValueAttribute.cs

@@ -0,0 +1,73 @@
+using System.Diagnostics;
+
+namespace Riok.Mapperly.Abstractions;
+
+/// <summary>
+/// Specifies a constant value mapping.
+/// </summary>
+[AttributeUsage(AttributeTargets.Method, AllowMultiple = true)]
+[Conditional("MAPPERLY_ABSTRACTIONS_SCOPE_RUNTIME")]
+public sealed class MapValueAttribute : Attribute
+{
+    private const string PropertyAccessSeparatorStr = ".";
+    private const char PropertyAccessSeparator = '.';
+
+    /// <summary>
+    /// Maps a constant value to a target member.
+    /// </summary>
+    /// <param name="target">The target member path.</param>
+    /// <param name="value">The value to assign to the <paramref name="target"/>, needs to be of the same type as the <paramref name="target"/>.</param>
+    public MapValueAttribute(string target, object? value)
+        : this(target.Split(PropertyAccessSeparator), value) { }
+
+    /// <summary>
+    /// Maps a constant value to a target member.
+    /// </summary>
+    /// <param name="target">The target member path.</param>
+    /// <param name="value">The value to assign to the <paramref name="target"/>, needs to be of the same type as the <paramref name="target"/>.</param>
+    public MapValueAttribute(string[] target, object? value)
+    {
+        Target = target;
+        Value = value;
+    }
+
+    /// <summary>
+    /// Maps a method generated value to a target member.
+    /// Requires the usage of the <see cref="Use"/> property.
+    /// </summary>
+    /// <param name="target">The target member path.</param>
+    public MapValueAttribute(string target)
+        : this(target, null) { }
+
+    /// <summary>
+    /// Maps a method generated value to a target member.
+    /// Requires the usage of the <see cref="Use"/> property.
+    /// </summary>
+    /// <param name="target">The target member path, the usage of nameof is encouraged.</param>
+    public MapValueAttribute(string[] target)
+        : this(target, null) { }
+
+    /// <summary>
+    /// Gets the name of the target property.
+    /// </summary>
+    public IReadOnlyCollection<string> Target { get; }
+
+    /// <summary>
+    /// Gets the full name of the target property path.
+    /// </summary>
+    public string TargetFullName => string.Join(PropertyAccessSeparatorStr, Target);
+
+    /// <summary>
+    /// Gets the value to be assigned to <see cref="Target"/>.
+    /// </summary>
+    public object? Value { get; }
+
+    /// <summary>
+    /// Gets or sets the method name of the method which generates the value to be assigned to <see cref="Target"/>.
+    /// Either this property or <see cref="Value"/> needs to be set.
+    /// The return type of the referenced method must exactly match the type of <see cref="Target"/>
+    /// and needs to be parameterless.
+    /// The usage of nameof is encouraged.
+    /// </summary>
+    public string? Use { get; set; }
+}

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

@@ -171,3 +171,13 @@ Riok.Mapperly.Abstractions.MapPropertyFromSourceAttribute.FormatProvider.get ->
 Riok.Mapperly.Abstractions.MapPropertyFromSourceAttribute.FormatProvider.set -> void
 Riok.Mapperly.Abstractions.MapPropertyFromSourceAttribute.Use.get -> string?
 Riok.Mapperly.Abstractions.MapPropertyFromSourceAttribute.Use.set -> void
+Riok.Mapperly.Abstractions.MapValueAttribute
+Riok.Mapperly.Abstractions.MapValueAttribute.Use.get -> string?
+Riok.Mapperly.Abstractions.MapValueAttribute.Use.set -> void
+Riok.Mapperly.Abstractions.MapValueAttribute.MapValueAttribute(string! target) -> void
+Riok.Mapperly.Abstractions.MapValueAttribute.MapValueAttribute(string! target, object? value) -> void
+Riok.Mapperly.Abstractions.MapValueAttribute.MapValueAttribute(string![]! target) -> void
+Riok.Mapperly.Abstractions.MapValueAttribute.MapValueAttribute(string![]! target, object? value) -> void
+Riok.Mapperly.Abstractions.MapValueAttribute.Target.get -> System.Collections.Generic.IReadOnlyCollection<string!>!
+Riok.Mapperly.Abstractions.MapValueAttribute.TargetFullName.get -> string!
+Riok.Mapperly.Abstractions.MapValueAttribute.Value.get -> object?

src/Riok.Mapperly/AnalyzerReleases.Shipped.md

@@ -173,6 +173,12 @@ RMG073  | Mapper   | Warning  | The target type of the referenced mapping does n
 Rule ID | Category | Severity | Notes
 --------|----------|----------|-------
 RMG074  | Mapper   | Error    | Multiple mappings are configured for the same target member
+RMG075  | Mapper   | Error    | Invalid usage of the MapValueAttribute
+RMG076  | Mapper   | Warning  | Cannot assign null to non-nullable member
+RMG077  | Mapper   | Error    | Cannot assign constant value because the type of the value does not match the type of the target
+RMG078  | Mapper   | Error    | Cannot assign method return type because the type of the value does not match the type of the target
+RMG079  | Mapper   | Error    | The referenced method could not be found or has an unsupported signature
+RMG080  | Mapper   | Error    | The MapValueAttribute does not support types and arrays
 
 ### Removed Rules
 

src/Riok.Mapperly/Configuration/AttributeDataAccessor.cs

@@ -123,6 +123,8 @@ IReadOnlyList<AttributeArgumentSyntax> argumentSyntax
     {
         return arg.Kind switch
         {
+            _ when (targetType == typeof(AttributeValue?) || targetType == typeof(AttributeValue)) && syntax != null
+                => new AttributeValue(arg, syntax.Expression),
             _ when arg.IsNull => null,
             _ when targetType == typeof(StringMemberPath) => CreateMemberPath(arg, syntax),
             TypedConstantKind.Enum => GetEnumValue(arg, targetType),

src/Riok.Mapperly/Configuration/AttributeValue.cs

@@ -0,0 +1,12 @@
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+
+namespace Riok.Mapperly.Configuration;
+
+/// <summary>
+/// Represents an attribute value provided by the user.
+/// Allows access to the intepreted value as well as the source syntax.
+/// </summary>
+/// <param name="ConstantValue">The interpreted compile-time constant value.</param>
+/// <param name="Expression">The syntax as written by the user.</param>
+public readonly record struct AttributeValue(TypedConstant ConstantValue, ExpressionSyntax Expression);

src/Riok.Mapperly/Configuration/MapperConfigurationReader.cs

@@ -34,7 +34,7 @@ MapperConfiguration defaultMapperConfiguration
                 [],
                 mapper.RequiredMappingStrategy
             ),
-            new MembersMappingConfiguration([], [], [], [], mapper.IgnoreObsoleteMembersStrategy, mapper.RequiredMappingStrategy),
+            new MembersMappingConfiguration([], [], [], [], [], mapper.IgnoreObsoleteMembersStrategy, mapper.RequiredMappingStrategy),
             []
         );
     }
@@ -75,6 +75,7 @@ private MembersMappingConfiguration BuildMembersConfig(MappingConfigurationRefer
             .Select(x => x.Target)
             .WhereNotNull()
             .ToList();
+        var memberValueConfigurations = _dataAccessor.Access<MapValueAttribute, MemberValueMappingConfiguration>(configRef.Method).ToList();
         var memberConfigurations = _dataAccessor
             .Access<MapPropertyAttribute, MemberMappingConfiguration>(configRef.Method)
             .Concat(_dataAccessor.Access<MapPropertyFromSourceAttribute, MemberMappingConfiguration>(configRef.Method))
@@ -106,6 +107,11 @@ private MembersMappingConfiguration BuildMembersConfig(MappingConfigurationRefer
             return MapperConfiguration.Members;
         }
 
+        foreach (var invalidMemberConfig in memberValueConfigurations.Where(x => !x.IsValid))
+        {
+            diagnostics.ReportDiagnostic(DiagnosticDescriptors.InvalidMapValueAttributeUsage, invalidMemberConfig.Location);
+        }
+
         foreach (var invalidMemberConfig in memberConfigurations.Where(x => !x.IsValid))
         {
             diagnostics.ReportDiagnostic(DiagnosticDescriptors.InvalidMapPropertyAttributeUsage, invalidMemberConfig.Location);
@@ -114,6 +120,7 @@ private MembersMappingConfiguration BuildMembersConfig(MappingConfigurationRefer
         return new MembersMappingConfiguration(
             ignoredSourceMembers,
             ignoredTargetMembers,
+            memberValueConfigurations,
             memberConfigurations,
             nestedMembersConfigurations,
             ignoreObsolete ?? MapperConfiguration.Members.IgnoreObsoleteMembersStrategy,

src/Riok.Mapperly/Configuration/MemberValueMappingConfiguration.cs

@@ -0,0 +1,25 @@
+using System.Diagnostics;
+
+namespace Riok.Mapperly.Configuration;
+
+[DebuggerDisplay("{Target}: {DescribeValue()}")]
+public record MemberValueMappingConfiguration(StringMemberPath Target, AttributeValue? Value) : HasSyntaxReference
+{
+    /// <summary>
+    /// Constructor used by <see cref="AttributeDataAccessor"/>.
+    /// </summary>
+    public MemberValueMappingConfiguration(StringMemberPath target)
+        : this(target, null) { }
+
+    public string? Use { get; set; }
+
+    public bool IsValid => Use != null ^ Value != null;
+
+    public string DescribeValue()
+    {
+        if (Use != null)
+            return Use + "()";
+
+        return Value?.Expression.ToFullString() ?? string.Empty;
+    }
+}

src/Riok.Mapperly/Configuration/MembersMappingConfiguration.cs

@@ -6,6 +6,7 @@ namespace Riok.Mapperly.Configuration;
 public record MembersMappingConfiguration(
     IReadOnlyCollection<string> IgnoredSources,
     IReadOnlyCollection<string> IgnoredTargets,
+    IReadOnlyCollection<MemberValueMappingConfiguration> ValueMappings,
     IReadOnlyCollection<MemberMappingConfiguration> ExplicitMappings,
     IReadOnlyCollection<NestedMembersMappingConfiguration> NestedMappings,
     IgnoreObsoleteMembersStrategy IgnoreObsoleteMembersStrategy,
@@ -17,7 +18,8 @@ public IEnumerable<string> GetMembersWithExplicitConfigurations(MappingSourceTar
         var members = sourceTarget switch
         {
             MappingSourceTarget.Source => ExplicitMappings.Where(x => x.Source.Path.Count > 0).Select(x => x.Source.Path[0]),
-            MappingSourceTarget.Target => ExplicitMappings.Select(x => x.Target.Path[0]),
+            MappingSourceTarget.Target
+                => ExplicitMappings.Select(x => x.Target.Path[0]).Concat(ValueMappings.Select(x => x.Target.Path[0])),
             _ => throw new ArgumentOutOfRangeException(nameof(sourceTarget), sourceTarget, "Neither source or target"),
         };
         return members.Distinct();

src/Riok.Mapperly/Descriptors/DescriptorBuilder.cs

@@ -55,6 +55,7 @@ MapperConfiguration defaultMapperConfiguration
 
         _builderContext = new SimpleMappingBuilderContext(
             compilationContext,
+            mapperDeclaration,
             configurationReader,
             _symbolAccessor,
             new GenericTypeChecker(_symbolAccessor, _types),

src/Riok.Mapperly/Descriptors/MappingBodyBuilders/BuilderContext/IMembersBuilderContext.cs

@@ -17,7 +17,7 @@ public interface IMembersBuilderContext<out T>
 
     void SetTargetMemberMapped(IMappableMember targetMember);
 
-    void ConsumeMemberConfig(MemberMappingInfo members);
+    void ConsumeMemberConfigs(MemberMappingInfo members);
 
     IEnumerable<IMappableMember> EnumerateUnmappedTargetMembers();
 

src/Riok.Mapperly/Descriptors/MappingBodyBuilders/BuilderContext/MemberMappingDiagnosticReporter.cs

@@ -34,7 +34,7 @@ private static void AddUnmappedSourceMembersDiagnostics(MappingBuilderContext ct
 
     private static void AddUnmappedTargetMembersDiagnostics(MappingBuilderContext ctx, MembersMappingState state)
     {
-        foreach (var targetMember in state.UnmappedTargetMembers)
+        foreach (var targetMember in state.EnumerateUnmappedTargetMembers())
         {
             if (targetMember.IsRequired)
             {

src/Riok.Mapperly/Descriptors/MappingBodyBuilders/BuilderContext/MembersContainerBuilderContext.cs

@@ -25,6 +25,12 @@ public class MembersContainerBuilderContext<T>(MappingBuilderContext builderCont
     /// <param name="memberMapping">The member mapping to be applied if the source member is not null</param>
     public void AddNullDelegateMemberAssignmentMapping(IMemberAssignmentMapping memberMapping)
     {
+        if (memberMapping.MemberInfo.SourceMember == null)
+        {
+            AddMemberAssignmentMapping(memberMapping);
+            return;
+        }
+
         var nullConditionSourcePath = new NonEmptyMemberPath(
             memberMapping.MemberInfo.SourceMember.RootType,
             memberMapping.MemberInfo.SourceMember.PathWithoutTrailingNonNullable().ToList()