Don't generate 'INotifyPropertyChanging' code if not requested

src/CommunityToolkit.Mvvm.SourceGenerators/CommunityToolkit.Mvvm.SourceGenerators.projitems

@@ -55,6 +55,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Extensions\CompilationExtensions.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Extensions\DiagnosticsExtensions.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Extensions\INamedTypeSymbolExtensions.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Extensions\GeneratorAttributeSyntaxContextWithOptions.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Extensions\IncrementalGeneratorInitializationContextExtensions.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Extensions\IncrementalValuesProviderExtensions.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Extensions\MethodDeclarationSyntaxExtensions.cs" />

src/CommunityToolkit.Mvvm.SourceGenerators/ComponentModel/ObservablePropertyGenerator.Execute.cs

@@ -16,6 +16,7 @@
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Diagnostics;
 using static CommunityToolkit.Mvvm.SourceGenerators.Diagnostics.DiagnosticDescriptors;
 using static Microsoft.CodeAnalysis.CSharp.SyntaxFactory;
 
@@ -35,6 +36,7 @@ internal static class Execute
         /// <param name="fieldSyntax">The <see cref="FieldDeclarationSyntax"/> instance to process.</param>
         /// <param name="fieldSymbol">The input <see cref="IFieldSymbol"/> instance to process.</param>
         /// <param name="semanticModel">The <see cref="SemanticModel"/> instance for the current run.</param>
+        /// <param name="options">The options in use for the generator.</param>
         /// <param name="token">The cancellation token for the current operation.</param>
         /// <param name="propertyInfo">The resulting <see cref="PropertyInfo"/> value, if successfully retrieved.</param>
         /// <param name="diagnostics">The resulting diagnostics from the processing operation.</param>
@@ -43,6 +45,7 @@ public static bool TryGetInfo(
             FieldDeclarationSyntax fieldSyntax,
             IFieldSymbol fieldSymbol,
             SemanticModel semanticModel,
+            AnalyzerConfigOptions options,
             CancellationToken token,
             [NotNullWhen(true)] out PropertyInfo? propertyInfo,
             out ImmutableArray<DiagnosticInfo> diagnostics)
@@ -66,6 +69,11 @@ public static bool TryGetInfo(
 
             token.ThrowIfCancellationRequested();
 
+            // Override the property changing support if explicitly disabled
+            shouldInvokeOnPropertyChanging &= GetEnableINotifyPropertyChangingSupport(options);
+
+            token.ThrowIfCancellationRequested();
+
             // Get the property type and name
             string typeNameWithNullabilityAnnotations = fieldSymbol.Type.GetFullyQualifiedNameWithNullabilityAnnotations();
             string fieldName = fieldSymbol.Name;
@@ -320,6 +328,27 @@ public static bool TryGetInfo(
             return true;
         }
 
+        /// <summary>
+        /// Gets the value for the "MvvmToolkitEnableINotifyPropertyChangingSupport" property.
+        /// </summary>
+        /// <param name="options">The options in use for the generator.</param>
+        /// <returns>The value for the "MvvmToolkitEnableINotifyPropertyChangingSupport" property.</returns>
+        public static bool GetEnableINotifyPropertyChangingSupport(AnalyzerConfigOptions options)
+        {
+            if (options.TryGetValue("build_property.MvvmToolkitEnableINotifyPropertyChangingSupport", out string? propertyValue))
+            {
+                if (bool.TryParse(propertyValue, out bool enableINotifyPropertyChangingSupport))
+                {
+                    return enableINotifyPropertyChangingSupport;
+                }
+            }
+
+            // This setting is enabled by default, for backwards compatibility.
+            // Note that this path should never be reached, as the default
+            // value is also set in a .targets file bundled in the package.
+            return true;
+        }
+
         /// <summary>
         /// Validates the containing type for a given field being annotated.
         /// </summary>

src/CommunityToolkit.Mvvm.SourceGenerators/ComponentModel/ObservablePropertyGenerator.cs

@@ -25,8 +25,7 @@ public void Initialize(IncrementalGeneratorInitializationContext context)
     {
         // Gather info for all annotated fields
         IncrementalValuesProvider<(HierarchyInfo Hierarchy, Result<PropertyInfo?> Info)> propertyInfoWithErrors =
-            context.SyntaxProvider
-            .ForAttributeWithMetadataName(
+            context.ForAttributeWithMetadataNameAndOptions(
                 "CommunityToolkit.Mvvm.ComponentModel.ObservablePropertyAttribute",
                 static (node, _) => node is VariableDeclaratorSyntax { Parent: VariableDeclarationSyntax { Parent: FieldDeclarationSyntax { Parent: ClassDeclarationSyntax or RecordDeclarationSyntax, AttributeLists.Count: > 0 } } },
                 static (context, token) =>
@@ -44,7 +43,14 @@ public void Initialize(IncrementalGeneratorInitializationContext context)
 
                     token.ThrowIfCancellationRequested();
 
-                    _ = Execute.TryGetInfo(fieldDeclaration, fieldSymbol, context.SemanticModel, token, out PropertyInfo? propertyInfo, out ImmutableArray<DiagnosticInfo> diagnostics);
+                    _ = Execute.TryGetInfo(
+                        fieldDeclaration,
+                        fieldSymbol,
+                        context.SemanticModel,
+                        context.GlobalOptions,
+                        token,
+                        out PropertyInfo? propertyInfo,
+                        out ImmutableArray<DiagnosticInfo> diagnostics);
 
                     token.ThrowIfCancellationRequested();
 

src/CommunityToolkit.Mvvm.SourceGenerators/Extensions/GeneratorAttributeSyntaxContextWithOptions.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 System.Collections.Immutable;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Diagnostics;
+
+namespace CommunityToolkit.Mvvm.SourceGenerators.Extensions;
+
+/// <summary>
+/// <inheritdoc cref="GeneratorAttributeSyntaxContext" path="/summary/node()"/>
+/// </summary>
+/// <param name="syntaxContext">The original <see cref="GeneratorAttributeSyntaxContext"/> value.</param>
+/// <param name="globalOptions">The original <see cref="AnalyzerConfigOptions"/> value.</param>
+internal readonly struct GeneratorAttributeSyntaxContextWithOptions(
+    GeneratorAttributeSyntaxContext syntaxContext,
+    AnalyzerConfigOptions globalOptions)
+{
+    /// <inheritdoc cref="GeneratorAttributeSyntaxContext.TargetNode"/>
+    public SyntaxNode TargetNode { get; } = syntaxContext.TargetNode;
+
+    /// <inheritdoc cref="GeneratorAttributeSyntaxContext.TargetSymbol"/>
+    public ISymbol TargetSymbol { get; } = syntaxContext.TargetSymbol;
+
+    /// <inheritdoc cref="GeneratorAttributeSyntaxContext.SemanticModel"/>
+    public SemanticModel SemanticModel { get; } = syntaxContext.SemanticModel;
+
+    /// <inheritdoc cref="GeneratorAttributeSyntaxContext.Attributes"/>
+    public ImmutableArray<AttributeData> Attributes { get; } = syntaxContext.Attributes;
+
+    /// <inheritdoc cref="AnalyzerConfigOptionsProvider.GlobalOptions"/>
+    public AnalyzerConfigOptions GlobalOptions { get; } = globalOptions;
+}

src/CommunityToolkit.Mvvm.SourceGenerators/Extensions/IncrementalGeneratorInitializationContextExtensions.cs

@@ -4,7 +4,11 @@
 
 using System;
 using System.Collections.Immutable;
+using System.Threading;
 using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Diagnostics;
+
+#pragma warning disable CS1574
 
 namespace CommunityToolkit.Mvvm.SourceGenerators.Extensions;
 
@@ -13,6 +17,31 @@ namespace CommunityToolkit.Mvvm.SourceGenerators.Extensions;
 /// </summary>
 internal static class IncrementalGeneratorInitializationContextExtensions
 {
+    /// <inheritdoc cref="SyntaxValueProvider.ForAttributeWithMetadataName"/>
+    public static IncrementalValuesProvider<T> ForAttributeWithMetadataNameAndOptions<T>(
+        this IncrementalGeneratorInitializationContext context,
+        string fullyQualifiedMetadataName,
+        Func<SyntaxNode, CancellationToken, bool> predicate,
+        Func<GeneratorAttributeSyntaxContextWithOptions, CancellationToken, T> transform)
+    {
+        // Invoke 'ForAttributeWithMetadataName' normally, but just return the context directly
+        IncrementalValuesProvider<GeneratorAttributeSyntaxContext> syntaxContext = context.SyntaxProvider.ForAttributeWithMetadataName(
+            fullyQualifiedMetadataName,
+            predicate,
+            static (context, token) => context);
+
+        // Do the same for the analyzer config options
+        IncrementalValueProvider<AnalyzerConfigOptions> configOptions = context.AnalyzerConfigOptionsProvider.Select(static (provider, token) => provider.GlobalOptions);
+
+        // Merge the two and invoke the provided transform on these two values. Neither value
+        // is equatable, meaning the pipeline will always re-run until this point. This is
+        // intentional: we don't want any symbols or other expensive objects to be kept alive
+        // across incremental steps, especially if they could cause entire compilations to be
+        // rooted, which would significantly increase memory use and introduce more GC pauses.
+        // In this specific case, flowing non equatable values in a pipeline is therefore fine.
+        return syntaxContext.Combine(configOptions).Select((input, token) => transform(new GeneratorAttributeSyntaxContextWithOptions(input.Left, input.Right), token));
+    }
+
     /// <summary>
     /// Conditionally invokes <see cref="IncrementalGeneratorInitializationContext.RegisterSourceOutput{TSource}(IncrementalValueProvider{TSource}, Action{SourceProductionContext, TSource})"/>
     /// if the value produced by the input <see cref="IncrementalValueProvider{TValue}"/> is <see langword="true"/>.

src/CommunityToolkit.Mvvm/CommunityToolkit.Mvvm.FeatureSwitches.targets

@@ -5,6 +5,14 @@
     <MvvmToolkitEnableINotifyPropertyChangingSupport Condition="'$(MvvmToolkitEnableINotifyPropertyChangingSupport)' == ''">true</MvvmToolkitEnableINotifyPropertyChangingSupport>
   </PropertyGroup>
 
+  <!--
+    Make the properties visible to the source generators as well, to allow
+    them to emit optimized codegen ahead of time depending on their values.
+  -->
+  <ItemGroup>
+    <CompilerVisibleProperty Include="MvvmToolkitEnableINotifyPropertyChangingSupport" />
+  </ItemGroup>
+
   <!--
     Configuration for the feature switches (to support IL trimming).
     See the 'ILLink.Substitutions.xml' file for more details on that.