Use fully-qualified type names in generated partial method signatures (#1135)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>

Author: Copilot

src/ModelContextProtocol.Analyzers/XmlToDescriptionGenerator.cs

@@ -19,6 +19,14 @@ public sealed class XmlToDescriptionGenerator : IIncrementalGenerator
 {
     private const string GeneratedFileName = "ModelContextProtocol.Descriptions.g.cs";
 
+    /// <summary>
+    /// A display format that produces fully-qualified type names with "global::" prefix
+    /// and includes nullability annotations.
+    /// </summary>
+    private static readonly SymbolDisplayFormat s_fullyQualifiedFormatWithNullability =
+        SymbolDisplayFormat.FullyQualifiedFormat.AddMiscellaneousOptions(
+            SymbolDisplayMiscellaneousOptions.IncludeNullableReferenceTypeModifier);
+
     public void Initialize(IncrementalGeneratorInitializationContext context)
     {
         // Extract method information for all MCP tools, prompts, and resources.
@@ -125,7 +133,7 @@ private static MethodToGenerate ExtractMethodInfo(
             .Where(m => !m.IsKind(SyntaxKind.AsyncKeyword))
             .Select(m => m.Text);
         string modifiersStr = string.Join(" ", modifiers);
-        string returnType = methodSymbol.ReturnType.ToDisplayString(SymbolDisplayFormat.MinimallyQualifiedFormat);
+        string returnType = methodSymbol.ReturnType.ToDisplayString(s_fullyQualifiedFormatWithNullability);
         string methodName = methodSymbol.Name;
 
         // Extract parameters
@@ -137,7 +145,7 @@ private static MethodToGenerate ExtractMethodInfo(
             var paramSyntax = i < parameterSyntaxList.Count ? parameterSyntaxList[i] : null;
 
             parameters[i] = new ParameterInfo(
-                ParameterType: param.Type.ToDisplayString(SymbolDisplayFormat.MinimallyQualifiedFormat),
+                ParameterType: param.Type.ToDisplayString(s_fullyQualifiedFormatWithNullability),
                 Name: param.Name,
                 HasDescriptionAttribute: descriptionAttribute is not null && HasAttribute(param, descriptionAttribute),
                 XmlDescription: xmlDocs?.Parameters.TryGetValue(param.Name, out var pd) == true && !string.IsNullOrWhiteSpace(pd) ? pd : null,