Add MapProperty attribute.

src/MapTo/Extensions/GeneratorExecutionContextExtensions.cs

@@ -35,7 +35,7 @@ namespace MapTo.Extensions
 
         internal static string GetBuildPropertyName(string propertyName) => $"build_property.{PropertyNameSuffix}{propertyName}";
 
-        internal static void AddSource(this GeneratorExecutionContext context, Source source) =>
-            context.AddSource(source.HintName, source.Code);
+        internal static void AddSource(this GeneratorExecutionContext context, SourceCode sourceCode) =>
+            context.AddSource(sourceCode.HintName, sourceCode.Text);
     }
 }

src/MapTo/MapToGenerator.cs

@@ -25,6 +25,7 @@ namespace MapTo
             context.AddSource(MapFromAttributeSource.Generate(options));
             context.AddSource(IgnorePropertyAttributeSource.Generate(options));
             context.AddSource(TypeConverterSource.Generate(options));
+            context.AddSource(MapPropertyAttributeSource.Generate(options));
             
             if (context.SyntaxReceiver is MapToSyntaxReceiver receiver && receiver.CandidateClasses.Any())
             {

src/MapTo/Sources/IgnorePropertyAttributeSource.cs

@@ -7,7 +7,7 @@ namespace MapTo.Sources
     {
         internal const string AttributeName = "IgnoreProperty";
 
-        internal static Source Generate(SourceGenerationOptions options)
+        internal static SourceCode Generate(SourceGenerationOptions options)
         {
             var builder = new SourceBuilder()
                 .WriteLine(GeneratedFilesHeader)

src/MapTo/Sources/MapClassSource.cs

@@ -6,7 +6,7 @@ namespace MapTo.Sources
 {
     internal static class MapClassSource
     {
-        internal static Source Generate(MapModel model)
+        internal static SourceCode Generate(MapModel model)
         {
             using var builder = new SourceBuilder()
                 .WriteLine(GeneratedFilesHeader)

src/MapTo/Sources/MapFromAttributeSource.cs

@@ -7,7 +7,7 @@ namespace MapTo.Sources
     {
         internal const string AttributeName = "MapFrom";
         
-        internal static Source Generate(SourceGenerationOptions options)
+        internal static SourceCode Generate(SourceGenerationOptions options)
         {
             using var builder = new SourceBuilder()
                 .WriteLine(GeneratedFilesHeader)

src/MapTo/Sources/MapPropertyAttributeSource.cs

@@ -0,0 +1,64 @@
+using MapTo.Models;
+using static MapTo.Sources.Constants;
+
+namespace MapTo.Sources
+{
+    internal static class MapPropertyAttributeSource
+    {
+        internal const string AttributeName = "MapProperty";
+
+        internal static SourceCode Generate(SourceGenerationOptions options)
+        {
+            using var builder = new SourceBuilder()
+                .WriteLine(GeneratedFilesHeader)
+                .WriteLine("using System;")
+                .WriteLine()
+                .WriteLine($"namespace {RootNamespace}")
+                .WriteOpeningBracket();
+
+            if (options.GenerateXmlDocument)
+            {
+                builder
+                    .WriteLine("/// <summary>")
+                    .WriteLine("/// Maps a property to property of another object.")
+                    .WriteLine("/// </summary>");
+            }
+
+            builder
+                .WriteLine("[AttributeUsage(AttributeTargets.Property, AllowMultiple = true)]")
+                .WriteLine($"public sealed class {AttributeName}Attribute : Attribute")
+                .WriteOpeningBracket();
+
+            if (options.GenerateXmlDocument)
+            {
+                builder
+                    .WriteLine("/// <summary>")
+                    .WriteLine("/// Initializes a new instance of <see cref=\"MapPropertyAttribute\"/>.")
+                    .WriteLine("/// </summary>")
+                    .WriteLine("/// <param name=\"converter\">The <see cref=\"ITypeConverter{TSource,TDestination}\" /> to convert the value of the annotated property.</param>");
+            }
+
+            builder
+                .WriteLine($"public {AttributeName}Attribute(Type converter = null)")
+                .WriteOpeningBracket()
+                .WriteLine("Converter = converter;")
+                .WriteClosingBracket()
+                .WriteLine();
+
+            if (options.GenerateXmlDocument)
+            {
+                builder
+                    .WriteLine("/// <summary>")
+                    .WriteLine("/// Gets the <see cref=\"ITypeConverter{TSource,TDestination}\" /> to convert the value of the annotated property.")
+                    .WriteLine("/// </summary>");
+            }
+
+            builder
+                .WriteLine("public Type Converter { get; }")
+                .WriteClosingBracket()
+                .WriteClosingBracket();
+
+            return new(builder.ToString(), $"{AttributeName}Attribute.g.cs");
+        }
+    }
+}

src/MapTo/Sources/Source.cs

@@ -1,4 +0,0 @@
-namespace MapTo.Sources
-{
-    internal record Source(string Code, string HintName);
-}

src/MapTo/Sources/SourceCode.cs

@@ -0,0 +1,4 @@
+namespace MapTo.Sources
+{
+    internal record SourceCode(string Text, string HintName);
+}

src/MapTo/Sources/TypeConverterSource.cs

@@ -7,7 +7,7 @@ namespace MapTo.Sources
     {
         internal const string InterfaceName = "ITypeConverter";
 
-        internal static Source Generate(SourceGenerationOptions options)
+        internal static SourceCode Generate(SourceGenerationOptions options)
         {
             using var builder = new SourceBuilder()
                 .WriteLine(GeneratedFilesHeader)

test/MapTo.Tests/Tests.cs

@@ -512,5 +512,37 @@ namespace MapTo
             diagnostics.ShouldBeSuccessful();
             compilation.SyntaxTrees.ShouldContainSource(TypeConverterSource.InterfaceName, expectedInterface);
         }
+        
+        [Fact]
+        public void VerifyMapPropertyAttribute()
+        {
+            // Arrange
+            const string source = "";
+            var expectedInterface = $@"
+{Constants.GeneratedFilesHeader}
+using System;
+
+namespace MapTo
+{{
+    [AttributeUsage(AttributeTargets.Property, AllowMultiple = true)]
+    public sealed class MapPropertyAttribute : Attribute
+    {{
+        public MapPropertyAttribute(Type converter = null)
+        {{
+            Converter = converter;
+        }}
+
+        public Type Converter {{ get; }}
+    }}
+}}
+".Trim();
+
+            // Act
+            var (compilation, diagnostics) = CSharpGenerator.GetOutputCompilation(source, analyzerConfigOptions: DefaultAnalyzerOptions);
+
+            // Assert
+            diagnostics.ShouldBeSuccessful();
+            compilation.SyntaxTrees.ShouldContainSource(MapPropertyAttributeSource.AttributeName, expectedInterface);
+        }
     }
 }

test/TestConsoleApp/ViewModels/User.cs

@@ -7,6 +7,10 @@ namespace TestConsoleApp.ViewModels
     [MapFrom(typeof(Data.Models.User))]
     public partial class User
     {
+        public int Id { get; }
+        
         public string FirstName { get; }
+        
+        public string LastName { get; }
     }
 }

test/TestConsoleApp/ViewModels/UserViewModel.cs

@@ -7,7 +7,16 @@ namespace TestConsoleApp.ViewModels
     {
         public string FirstName { get; }
 
-        // [IgnoreProerty]
+        [IgnoreProperty]
         public string LastName { get; }
+        
+        [MapProperty(converter: typeof(LastNameConverter))]
+        public string Key { get; }
+
+        private class LastNameConverter : ITypeConverter<int, string>
+        {
+            /// <inheritdoc />
+            public string Convert(int source) => $"{source} :: With Type Converter";
+        }
     }
 }