Add fixers project and implement a fixer for FieldReferenceForObservablePropertyFieldAnalyzer

dotnet Community Toolkit.sln

@@ -81,6 +81,8 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "CommunityToolkit.Mvvm.Exter
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "CommunityToolkit.Mvvm.ExternalAssembly.Roslyn431", "tests\CommunityToolkit.Mvvm.ExternalAssembly.Roslyn431\CommunityToolkit.Mvvm.ExternalAssembly.Roslyn431.csproj", "{4FCD501C-1BB5-465C-AD19-356DAB6600C6}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "CommunityToolkit.Mvvm.CodeFixers", "src\CommunityToolkit.Mvvm.CodeFixers\CommunityToolkit.Mvvm.CodeFixers.csproj", "{E79DCA2A-4C59-499F-85BD-F45215ED6B72}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -435,6 +437,26 @@ Global
 		{4FCD501C-1BB5-465C-AD19-356DAB6600C6}.Release|x64.Build.0 = Release|Any CPU
 		{4FCD501C-1BB5-465C-AD19-356DAB6600C6}.Release|x86.ActiveCfg = Release|Any CPU
 		{4FCD501C-1BB5-465C-AD19-356DAB6600C6}.Release|x86.Build.0 = Release|Any CPU
+		{E79DCA2A-4C59-499F-85BD-F45215ED6B72}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{E79DCA2A-4C59-499F-85BD-F45215ED6B72}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{E79DCA2A-4C59-499F-85BD-F45215ED6B72}.Debug|ARM.ActiveCfg = Debug|Any CPU
+		{E79DCA2A-4C59-499F-85BD-F45215ED6B72}.Debug|ARM.Build.0 = Debug|Any CPU
+		{E79DCA2A-4C59-499F-85BD-F45215ED6B72}.Debug|ARM64.ActiveCfg = Debug|Any CPU
+		{E79DCA2A-4C59-499F-85BD-F45215ED6B72}.Debug|ARM64.Build.0 = Debug|Any CPU
+		{E79DCA2A-4C59-499F-85BD-F45215ED6B72}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{E79DCA2A-4C59-499F-85BD-F45215ED6B72}.Debug|x64.Build.0 = Debug|Any CPU
+		{E79DCA2A-4C59-499F-85BD-F45215ED6B72}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{E79DCA2A-4C59-499F-85BD-F45215ED6B72}.Debug|x86.Build.0 = Debug|Any CPU
+		{E79DCA2A-4C59-499F-85BD-F45215ED6B72}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{E79DCA2A-4C59-499F-85BD-F45215ED6B72}.Release|Any CPU.Build.0 = Release|Any CPU
+		{E79DCA2A-4C59-499F-85BD-F45215ED6B72}.Release|ARM.ActiveCfg = Release|Any CPU
+		{E79DCA2A-4C59-499F-85BD-F45215ED6B72}.Release|ARM.Build.0 = Release|Any CPU
+		{E79DCA2A-4C59-499F-85BD-F45215ED6B72}.Release|ARM64.ActiveCfg = Release|Any CPU
+		{E79DCA2A-4C59-499F-85BD-F45215ED6B72}.Release|ARM64.Build.0 = Release|Any CPU
+		{E79DCA2A-4C59-499F-85BD-F45215ED6B72}.Release|x64.ActiveCfg = Release|Any CPU
+		{E79DCA2A-4C59-499F-85BD-F45215ED6B72}.Release|x64.Build.0 = Release|Any CPU
+		{E79DCA2A-4C59-499F-85BD-F45215ED6B72}.Release|x86.ActiveCfg = Release|Any CPU
+		{E79DCA2A-4C59-499F-85BD-F45215ED6B72}.Release|x86.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE

src/CommunityToolkit.HighPerformance/CommunityToolkit.HighPerformance.csproj

@@ -36,7 +36,7 @@
         <PackageReference Include="System.Runtime.CompilerServices.Unsafe" Version="6.0.0" />
       </ItemGroup>
 
-      <!-- On .NET Standard 2.0, the unit test project also needs access to internals-->
+      <!-- On .NET Standard 2.0, the unit test project also needs access to internals -->
       <ItemGroup>
         <InternalsVisibleTo Include="CommunityToolkit.HighPerformance.UnitTests, PublicKey=$(AssemblySignPublicKey)" />
       </ItemGroup>

src/CommunityToolkit.Mvvm.CodeFixers/CommunityToolkit.Mvvm.CodeFixers.csproj

@@ -0,0 +1,16 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>netstandard2.0</TargetFramework>
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp.Workspaces" Version="4.0.1" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\CommunityToolkit.Mvvm.SourceGenerators.Roslyn401\CommunityToolkit.Mvvm.SourceGenerators.Roslyn401.csproj" />
+  </ItemGroup>
+
+</Project>

src/CommunityToolkit.Mvvm.CodeFixers/FieldReferenceForObservablePropertyFieldFixer.cs

@@ -0,0 +1,86 @@
+// 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 System.Composition;
+using System.Threading;
+using System.Threading.Tasks;
+using CommunityToolkit.Mvvm.SourceGenerators;
+using CommunityToolkit.Mvvm.SourceGenerators.Diagnostics;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CodeActions;
+using Microsoft.CodeAnalysis.CodeFixes;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Text;
+
+namespace CommunityToolkit.Mvvm.CodeFixers;
+
+/// <summary>
+/// A code fixer that automatically updates references to fields with <c>[ObservableProperty]</c> to reference the generated property instead.
+/// </summary>
+[ExportCodeFixProvider(LanguageNames.CSharp)]
+[Shared]
+public sealed class FieldReferenceForObservablePropertyFieldCodeFixer : CodeFixProvider
+{
+    /// <inheritdoc/>
+    public override ImmutableArray<string> FixableDiagnosticIds { get; } = ImmutableArray.Create(DiagnosticDescriptors.FieldReferenceForObservablePropertyFieldId);
+
+    /// <inheritdoc/>
+    public override FixAllProvider? GetFixAllProvider()
+    {
+        return WellKnownFixAllProviders.BatchFixer;
+    }
+
+    /// <inheritdoc/>
+    public override async Task RegisterCodeFixesAsync(CodeFixContext context)
+    {
+        Diagnostic diagnostic = context.Diagnostics[0];
+        TextSpan diagnosticSpan = diagnostic.Location.SourceSpan;
+
+        // Retrieve the properties passed by the analyzer
+        if (diagnostic.Properties[FieldReferenceForObservablePropertyFieldAnalyzer.FieldNameKey] is not string fieldName ||
+            diagnostic.Properties[FieldReferenceForObservablePropertyFieldAnalyzer.PropertyNameKey] is not string propertyName)
+        {
+            return;
+        }
+
+        SyntaxNode? root = await context.Document.GetSyntaxRootAsync(context.CancellationToken).ConfigureAwait(false);
+
+        foreach (SyntaxNode syntaxNode in root!.FindNode(diagnosticSpan).DescendantNodesAndSelf())
+        {
+            // Find the first descendant node from the source of the diagnostic that is an identifier with the target name
+            if (syntaxNode is IdentifierNameSyntax { Identifier.Text: string identifierName } identifierNameSyntax &&
+                identifierName == fieldName)
+            {
+                // Register the code fix to update the field reference to use the generated property instead
+                context.RegisterCodeFix(
+                    CodeAction.Create(
+                        title: "Reference property",
+                        createChangedDocument: token => UpdateReference(context.Document, identifierNameSyntax, propertyName, token),
+                        equivalenceKey: "Reference property"),
+                    diagnostic);
+
+                return;
+            }
+        }
+    }
+
+    /// <summary>
+    /// Applies the code fix to a target identifier and returns an updated document.
+    /// </summary>
+    /// <param name="document">The original document being fixed.</param>
+    /// <param name="fieldReference">The <see cref="IdentifierNameSyntax"/> corresponding to the field reference to update.</param>
+    /// <param name="propertyName">The name of the generated property.</param>
+    /// <param name="cancellationToken">The cancellation token for the operation.</param>
+    /// <returns>An updated document with the applied code fix, and <paramref name="fieldReference"/> being replaced with a property reference.</returns>
+    private static async Task<Document> UpdateReference(Document document, IdentifierNameSyntax fieldReference, string propertyName, CancellationToken cancellationToken)
+    {
+        IdentifierNameSyntax propertyReference = SyntaxFactory.IdentifierName(propertyName);
+        SyntaxNode originalRoot = await fieldReference.SyntaxTree.GetRootAsync(cancellationToken).ConfigureAwait(false);
+        SyntaxTree updatedTree = originalRoot.ReplaceNode(fieldReference, propertyReference).SyntaxTree;
+
+        return document.WithSyntaxRoot(await updatedTree.GetRootAsync(cancellationToken).ConfigureAwait(false));
+    }
+}

src/CommunityToolkit.Mvvm.SourceGenerators/CommunityToolkit.Mvvm.SourceGenerators.props

@@ -35,4 +35,9 @@
     <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="$(MvvmToolkitSourceGeneratorRoslynVersion)" PrivateAssets="all" Pack="false" />
   </ItemGroup>
 
+  <!-- Give access to the code fixers project for the exported diagnostic ids and properties -->
+  <ItemGroup>
+    <InternalsVisibleTo Include="CommunityToolkit.Mvvm.CodeFixers, PublicKey=$(AssemblySignPublicKey)" />
+  </ItemGroup>
+
 </Project>

src/CommunityToolkit.Mvvm.SourceGenerators/Diagnostics/Analyzers/FieldReferenceForObservablePropertyFieldAnalyzer.cs

@@ -16,6 +16,16 @@ namespace CommunityToolkit.Mvvm.SourceGenerators;
 [DiagnosticAnalyzer(LanguageNames.CSharp)]
 public sealed class FieldReferenceForObservablePropertyFieldAnalyzer : DiagnosticAnalyzer
 {
+    /// <summary>
+    /// The key for the name of the target field to update.
+    /// </summary>
+    internal const string FieldNameKey = "FieldName";
+
+    /// <summary>
+    /// The key for the name of the generated property to update a field reference to.
+    /// </summary>
+    internal const string PropertyNameKey = "PropertyName";
+
     /// <inheritdoc/>
     public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics { get; } = ImmutableArray.Create(FieldReferenceForObservablePropertyFieldWarning);
 
@@ -59,7 +69,13 @@ public override void Initialize(AnalysisContext context)
                     SymbolEqualityComparer.Default.Equals(attributeClass, attributeSymbol))
                 {
                     // Emit a warning to redirect users to access the generated property instead
-                    context.ReportDiagnostic(Diagnostic.Create(FieldReferenceForObservablePropertyFieldWarning, context.Operation.Syntax.GetLocation(), fieldSymbol));
+                    context.ReportDiagnostic(Diagnostic.Create(
+                        FieldReferenceForObservablePropertyFieldWarning,
+                        context.Operation.Syntax.GetLocation(),
+                        ImmutableDictionary.Create<string, string?>()
+                            .Add(FieldNameKey, fieldSymbol.Name)
+                            .Add(PropertyNameKey, ObservablePropertyGenerator.Execute.GetGeneratedPropertyName(fieldSymbol)),
+                        fieldSymbol));
 
                     return;
                 }

src/CommunityToolkit.Mvvm.SourceGenerators/Diagnostics/DiagnosticDescriptors.cs

@@ -14,6 +14,11 @@ namespace CommunityToolkit.Mvvm.SourceGenerators.Diagnostics;
 /// </summary>
 internal static class DiagnosticDescriptors
 {
+    /// <summary>
+    /// The diagnostic id for <see cref="FieldReferenceForObservablePropertyFieldWarning"/>.
+    /// </summary>
+    public const string FieldReferenceForObservablePropertyFieldId = "MVVMTK0034";
+
     /// <summary>
     /// Gets a <see cref="DiagnosticDescriptor"/> indicating when a duplicate declaration of <see cref="INotifyPropertyChanged"/> would happen.
     /// <para>
@@ -550,7 +555,7 @@ internal static class DiagnosticDescriptors
     /// </para>
     /// </summary>
     public static readonly DiagnosticDescriptor FieldReferenceForObservablePropertyFieldWarning = new DiagnosticDescriptor(
-        id: "MVVMTK0034",
+        id: FieldReferenceForObservablePropertyFieldId,
         title: "Direct field reference to [ObservableProperty] backing field",
         messageFormat: "The field {0} is annotated with [ObservableProperty] and should not be directly referenced (use the generated property instead)",
         category: typeof(ObservablePropertyGenerator).FullName,

src/CommunityToolkit.Mvvm/CommunityToolkit.Mvvm.csproj

@@ -34,10 +34,11 @@
     <PackageReference Include="System.Runtime.CompilerServices.Unsafe" Version="6.0.0" />
   </ItemGroup>
 
-  <!-- Reference the various multi-targeted versions of the source generator project (one per Roslyn version) -->
+  <!-- Reference the various multi-targeted versions of the source generator project (one per Roslyn version), and the code fixer -->
   <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
     <ProjectReference Include="..\CommunityToolkit.Mvvm.SourceGenerators.Roslyn401\CommunityToolkit.Mvvm.SourceGenerators.Roslyn401.csproj" ReferenceOutputAssembly="false" />
     <ProjectReference Include="..\CommunityToolkit.Mvvm.SourceGenerators.Roslyn431\CommunityToolkit.Mvvm.SourceGenerators.Roslyn431.csproj" ReferenceOutputAssembly="false" />
+    <ProjectReference Include="..\CommunityToolkit.Mvvm.CodeFixers\CommunityToolkit.Mvvm.CodeFixers.csproj" ReferenceOutputAssembly="false" />
   </ItemGroup>
 
   <!-- Add the [InternalsVisibleTo] attribute for the test project -->
@@ -73,9 +74,17 @@
     <!--
       Pack the source generator to the right package folders (each matching the target Roslyn version).
       Roslyn will automatically load the highest version compatible with Roslyn's version in the SDK.
+      Also pack the code fixer along with each target analyzer, the multi-targeting take care of it.
+      Note: the code fixer is not currently multi-targeting, as there are no Roslyn APIs it needs from
+      versions later than 4.0.1. As such, we can just use a single project (without the shared project
+      and two multi-targeted ones), and pack the resulting assembly twice along with the generators.
+      Even though the fixer only references the 4.0.1 generator target, both versions export the same
+      APIs that the code fixer project needs, and Roslyn versions are also forward compatible.
     -->
     <None Include="..\CommunityToolkit.Mvvm.SourceGenerators.Roslyn401\bin\$(Configuration)\netstandard2.0\CommunityToolkit.Mvvm.SourceGenerators.dll" PackagePath="analyzers\dotnet\roslyn4.0\cs" Pack="true" Visible="false" />
     <None Include="..\CommunityToolkit.Mvvm.SourceGenerators.Roslyn431\bin\$(Configuration)\netstandard2.0\CommunityToolkit.Mvvm.SourceGenerators.dll" PackagePath="analyzers\dotnet\roslyn4.3\cs" Pack="true" Visible="false" />
+    <None Include="..\CommunityToolkit.Mvvm.CodeFixers\bin\$(Configuration)\netstandard2.0\CommunityToolkit.Mvvm.CodeFixers.dll" PackagePath="analyzers\dotnet\roslyn4.0\cs" Pack="true" Visible="false" />
+    <None Include="..\CommunityToolkit.Mvvm.CodeFixers\bin\$(Configuration)\netstandard2.0\CommunityToolkit.Mvvm.CodeFixers.dll" PackagePath="analyzers\dotnet\roslyn4.3\cs" Pack="true" Visible="false" />
   </ItemGroup>
 
 </Project>

tests/CommunityToolkit.Mvvm.SourceGenerators.Roslyn401.UnitTests/CommunityToolkit.Mvvm.SourceGenerators.Roslyn401.UnitTests.csproj

@@ -6,6 +6,8 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.CodeAnalysis.CSharp.Analyzer.Testing.MSTest" Version="1.1.1" />
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp.CodeFix.Testing" Version="1.1.1" />
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp.CodeFix.Testing.MSTest" Version="1.1.1" />
     <PackageReference Include="Microsoft.CodeAnalysis.CSharp.Workspaces" Version="4.4.0" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.4.1" />
     <PackageReference Include="MSTest.TestAdapter" Version="3.0.1" />
@@ -14,6 +16,7 @@
 
   <ItemGroup>
     <ProjectReference Include="..\..\src\CommunityToolkit.Mvvm\CommunityToolkit.Mvvm.csproj" />
+    <ProjectReference Include="..\..\src\CommunityToolkit.Mvvm.CodeFixers\CommunityToolkit.Mvvm.CodeFixers.csproj" />
     <ProjectReference Include="..\..\src\CommunityToolkit.Mvvm.SourceGenerators.Roslyn401\CommunityToolkit.Mvvm.SourceGenerators.Roslyn401.csproj" />
   </ItemGroup>