Move partial filtering logic to new extension

Author: Sergio0694

CommunityToolkit.Mvvm.SourceGenerators/Extensions/SyntaxNodeExtensions.cs

@@ -0,0 +1,34 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using Microsoft.CodeAnalysis;
+
+namespace CommunityToolkit.Mvvm.SourceGenerators.Extensions;
+
+/// <summary>
+/// Extension methods for the <see cref="SyntaxNode"/> type.
+/// </summary>
+internal static class SyntaxNodeExtensions
+{
+    /// <summary>
+    /// Checks whether a given <see cref="SyntaxNode"/> represents the first (partial) declaration of a given symbol.
+    /// </summary>
+    /// <param name="syntaxNode">The input <see cref="SyntaxNode"/> instance.</param>
+    /// <param name="symbol">The target <see cref="ISymbol"/> instance to check the syntax declaration for.</param>
+    /// <returns>Whether <paramref name="syntaxNode"/> is the first (partial) declaration for <paramref name="symbol"/>.</returns>
+    /// <remarks>
+    /// This extension can be used to avoid accidentally generating repeated members for types that have multiple partial declarations.
+    /// In order to keep this check efficient and without the need to collect all items and build some sort of hashset from them to
+    /// remove duplicates, each syntax node is symply compared against the available declaring syntax references for the target symbol.
+    /// If the syntax node matches the first syntax reference for the symbol, it is kept, otherwise it is considered a duplicate.
+    /// </remarks>
+    public static bool IsFirstSyntaxDeclarationForSymbol(this SyntaxNode syntaxNode, ISymbol symbol)
+    {
+        return
+            symbol.DeclaringSyntaxReferences.Length > 0 &&
+            symbol.DeclaringSyntaxReferences[0] is SyntaxReference syntaxReference &&
+            syntaxReference.SyntaxTree == syntaxNode.SyntaxTree &&
+            syntaxReference.Span == syntaxNode.Span;
+    }
+}

CommunityToolkit.Mvvm.SourceGenerators/Messaging/IMessengerRegisterAllGenerator.cs

@@ -4,13 +4,11 @@
 
 using System.Collections.Immutable;
 using System.Linq;
-using System.Text;
 using CommunityToolkit.Mvvm.SourceGenerators.Extensions;
 using CommunityToolkit.Mvvm.SourceGenerators.Input.Models;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
-using Microsoft.CodeAnalysis.Text;
 
 namespace CommunityToolkit.Mvvm.SourceGenerators;
 
@@ -32,11 +30,7 @@ public void Initialize(IncrementalGeneratorInitializationContext context)
             .CreateSyntaxProvider(
                 static (node, _) => node is ClassDeclarationSyntax,
                 static (context, _) => (context.Node, Symbol: (INamedTypeSymbol)context.SemanticModel.GetDeclaredSymbol(context.Node)!))
-            .Where(static item =>
-                item.Symbol.DeclaringSyntaxReferences.Length > 0 &&
-                item.Symbol.DeclaringSyntaxReferences[0] is SyntaxReference syntaxReference &&
-                syntaxReference.SyntaxTree == item.Node.SyntaxTree &&
-                syntaxReference.Span == item.Node.Span)
+            .Where(static item => item.Node.IsFirstSyntaxDeclarationForSymbol(item.Symbol))
             .Select(static (item, _) => item.Symbol);
 
         // Get the target IRecipient<TMessage> interfaces and filter out other types