Add production-ready incremental source generator for automatic Description attributes from XML comments

Directory.Packages.props

@@ -53,6 +53,10 @@
     <!-- Build Infra & Packaging -->
     <PackageVersion Include="Microsoft.SourceLink.GitHub" Version="8.0.0" />
 
+    <!-- Source Generator & Analyzer dependencies -->
+    <PackageVersion Include="Microsoft.CodeAnalysis.CSharp" Version="4.8.0" />
+    <PackageVersion Include="Microsoft.CodeAnalysis.Analyzers" Version="3.3.4" />
+
     <!-- Testing dependencies -->
     <PackageVersion Include="Anthropic.SDK" Version="5.6.0" />
     <PackageVersion Include="coverlet.collector" Version="6.0.4">

ModelContextProtocol.slnx

@@ -64,6 +64,7 @@
     <File Path="src/Directory.Build.props" />
     <Project Path="src/ModelContextProtocol.AspNetCore/ModelContextProtocol.AspNetCore.csproj" />
     <Project Path="src/ModelContextProtocol.Core/ModelContextProtocol.Core.csproj" />
+    <Project Path="src/ModelContextProtocol.SourceGenerators/ModelContextProtocol.SourceGenerators.csproj" />
     <Project Path="src/ModelContextProtocol/ModelContextProtocol.csproj" />
   </Folder>
   <Folder Name="/tests/">

src/ModelContextProtocol.Core/ModelContextProtocol.Core.csproj

@@ -47,4 +47,24 @@
     <None Include="README.md" pack="true" PackagePath="\" />
   </ItemGroup>
 
+  <!-- Include source generator as an analyzer -->
+  <ItemGroup>
+    <ProjectReference Include="..\ModelContextProtocol.SourceGenerators\ModelContextProtocol.SourceGenerators.csproj"
+                      OutputItemType="Analyzer"
+                      ReferenceOutputAssembly="false" />
+  </ItemGroup>
+
+  <!-- Direct analyzer reference for build-time source generation -->
+  <ItemGroup>
+    <Analyzer Include="$(ArtifactsDir)bin\ModelContextProtocol.SourceGenerators\netstandard2.0\ModelContextProtocol.SourceGenerators.dll" />
+  </ItemGroup>
+
+  <!-- Package the analyzer DLL into the NuGet package -->
+  <ItemGroup>
+    <None Include="$(ArtifactsDir)bin\ModelContextProtocol.SourceGenerators\netstandard2.0\ModelContextProtocol.SourceGenerators.dll" 
+          Pack="true" 
+          PackagePath="analyzers/dotnet/cs" 
+          Visible="false" />
+  </ItemGroup>
+
 </Project>

src/ModelContextProtocol.SourceGenerators/EXAMPLE.md

@@ -0,0 +1,70 @@
+# Source Generator Example
+
+This example demonstrates how to use the XmlToDescriptionGenerator source generator.
+
+## Without Source Generator (Traditional Approach)
+
+```csharp
+using ModelContextProtocol.Server;
+using System.ComponentModel;
+
+[McpServerToolType]
+public class WeatherTools
+{
+    /// <summary>
+    /// Get the current weather for a location.
+    /// </summary>
+    [McpServerTool]
+    [Description("Get the current weather for a location.")]  // Duplication!
+    public static string GetWeather(string location)
+    {
+        return $"Weather for {location}: Sunny, 72°F";
+    }
+}
+```
+
+## With Source Generator (Recommended)
+
+```csharp
+using ModelContextProtocol.Server;
+
+[McpServerToolType]
+public partial class WeatherTools
+{
+    /// <summary>
+    /// Get the current weather for a location.
+    /// </summary>
+    [McpServerTool]
+    public static partial string GetWeather(string location)
+    {
+        return $"Weather for {location}: Sunny, 72°F";
+    }
+}
+```
+
+The source generator automatically creates a partial method declaration with the `[Description]` attribute:
+
+```csharp
+// <auto-generated/>
+#nullable enable
+
+using System.ComponentModel;
+using ModelContextProtocol.Server;
+
+namespace YourNamespace;
+
+public partial class WeatherTools
+{
+    [Description("Get the current weather for a location.")]
+    public static partial string GetWeather(string location);
+}
+```
+
+## Key Changes Required
+
+1. Make the class `partial`
+2. Make the method `partial`
+3. Remove any existing `[Description]` attribute
+4. Keep your XML documentation comments
+
+The Description attribute will be automatically generated from your XML `<summary>` element!

src/ModelContextProtocol.SourceGenerators/ModelContextProtocol.SourceGenerators.csproj

@@ -0,0 +1,24 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>netstandard2.0</TargetFramework>
+    <LangVersion>latest</LangVersion>
+    <Nullable>enable</Nullable>
+    <EnforceExtendedAnalyzerRules>true</EnforceExtendedAnalyzerRules>
+    <IsRoslynComponent>true</IsRoslynComponent>
+    <IsPackable>false</IsPackable>
+    <IncludeBuildOutput>false</IncludeBuildOutput>
+    <GenerateDocumentationFile>false</GenerateDocumentationFile>
+  </PropertyGroup>
+
+  <!-- Remove auto-included polyfills from Directory.Build.props -->
+  <ItemGroup>
+    <Compile Remove="..\Common\Polyfills\**\*.cs" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" PrivateAssets="all" />
+    <PackageReference Include="Microsoft.CodeAnalysis.Analyzers" PrivateAssets="all" />
+  </ItemGroup>
+
+</Project>

src/ModelContextProtocol.SourceGenerators/README.md

@@ -0,0 +1,78 @@
+# ModelContextProtocol.SourceGenerators
+
+This project contains source generators for the Model Context Protocol C# SDK.
+
+## XmlToDescriptionGenerator
+
+This source generator automatically creates `Description` attributes from XML documentation comments for partial methods tagged with `[McpServerTool]`.
+
+### How it works
+
+When you write a partial method with:
+1. An `[McpServerTool]` attribute
+2. XML documentation comments (specifically a `<summary>` tag)
+3. NO existing `[Description]` attribute
+
+The generator will create a partial method declaration with a `[Description]` attribute containing the text from the XML `<summary>` element.
+
+### Example Usage
+
+**Your code:**
+```csharp
+using ModelContextProtocol.Server;
+using System.ComponentModel;
+
+[McpServerToolType]
+public partial class MyTools
+{
+    /// <summary>
+    /// This tool echoes the input message back to the user.
+    /// </summary>
+    [McpServerTool]
+    public static partial string Echo(string message)
+    {
+        return $"Echo: {message}";
+    }
+}
+```
+
+**Generated code:**
+```csharp
+// <auto-generated/>
+#nullable enable
+
+using System.ComponentModel;
+using ModelContextProtocol.Server;
+
+namespace YourNamespace;
+
+public partial class MyTools
+{
+    [Description("This tool echoes the input message back to the user.")]
+    public static partial string Echo(string message);
+}
+```
+
+### Benefits
+
+- **Reduces duplication**: You don't need to write both XML comments AND Description attributes
+- **Single source of truth**: XML comments are used for both documentation and runtime tool descriptions
+- **Automatic synchronization**: Changes to XML comments are automatically reflected in the Description attributes
+
+### Requirements
+
+- Your method must be marked as `partial`
+- Your method must have the `[McpServerTool]` attribute
+- Your method must have XML documentation comments with a `<summary>` tag
+- Your method must NOT already have a `[Description]` attribute
+- Your project must reference `ModelContextProtocol.Core` directly (the source generator is distributed with this package)
+
+### Availability
+
+The source generator is distributed as part of the `ModelContextProtocol.Core` NuGet package and will be automatically available when you reference that package in your project.
+
+### Notes
+
+- The generator only extracts text from the `<summary>` element
+- Multi-line summaries are combined into a single line
+- Only partial methods with implementations (method bodies) are supported