Add 'InvalidPartialPropertyLevelObservablePropertyAttributeAnalyzer'

src/CommunityToolkit.Mvvm.SourceGenerators/AnalyzerReleases.Shipped.md

@@ -92,4 +92,7 @@ MVVMTK0047 | CommunityToolkit.Mvvm.SourceGenerators.ObservablePropertyGenerator
 MVVMTK0048 | CommunityToolkit.Mvvm.SourceGenerators.RelayCommandGenerator | Warning | See https://aka.ms/mvvmtoolkit/errors/mvvmtk0048
 MVVMTK0049 | CommunityToolkit.Mvvm.SourceGenerators.INotifyPropertyChangedGenerator | Warning | See https://aka.ms/mvvmtoolkit/errors/mvvmtk0049
 MVVMTK0050 | CommunityToolkit.Mvvm.SourceGenerators.ObservableObjectGenerator | Warning | See https://aka.ms/mvvmtoolkit/errors/mvvmtk0050
-MVVMTK0051 | CommunityToolkit.Mvvm.SourceGenerators.ObservablePropertyGenerator | Info | See https://aka.ms/mvvmtoolkit/errors/mvvmtk0050
+MVVMTK0051 | CommunityToolkit.Mvvm.SourceGenerators.ObservablePropertyGenerator | Info | See https://aka.ms/mvvmtoolkit/errors/mvvmtk0051
+MVVMTK0052 | CommunityToolkit.Mvvm.SourceGenerators.ObservablePropertyGenerator | Error | See https://aka.ms/mvvmtoolkit/errors/mvvmtk0052
+MVVMTK0053 | CommunityToolkit.Mvvm.SourceGenerators.ObservablePropertyGenerator | Error | See https://aka.ms/mvvmtoolkit/errors/mvvmtk0053
+MVVMTK0054 | CommunityToolkit.Mvvm.SourceGenerators.ObservablePropertyGenerator | Error | See https://aka.ms/mvvmtoolkit/errors/mvvmtk0054

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

@@ -41,6 +41,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)ComponentModel\TransitiveMembersGenerator.Execute.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Diagnostics\Analyzers\AsyncVoidReturningRelayCommandMethodAnalyzer.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Diagnostics\Analyzers\InvalidGeneratedPropertyObservablePropertyAttributeAnalyzer.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Diagnostics\Analyzers\InvalidPartialPropertyLevelObservablePropertyAttributeAnalyzer.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Diagnostics\Analyzers\WinRTClassUsingNotifyPropertyChangedAttributesAnalyzer.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Diagnostics\Analyzers\WinRTGeneratedBindableCustomPropertyWithBasesMemberAnalyzer.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Diagnostics\Analyzers\WinRTRelayCommandIsNotGeneratedBindableCustomPropertyCompatibleAnalyzer.cs" />

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

@@ -0,0 +1,98 @@
+// 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.
+
+#if ROSLYN_4_12_0_OR_GREATER
+
+using System.Collections.Immutable;
+using CommunityToolkit.Mvvm.SourceGenerators.Extensions;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Diagnostics;
+using static CommunityToolkit.Mvvm.SourceGenerators.Diagnostics.DiagnosticDescriptors;
+
+namespace CommunityToolkit.Mvvm.SourceGenerators;
+
+/// <summary>
+/// A diagnostic analyzer that generates an error whenever <c>[ObservableProperty]</c> is used on an invalid partial property declaration.
+/// </summary>
+[DiagnosticAnalyzer(LanguageNames.CSharp)]
+public sealed class InvalidPartialPropertyLevelObservablePropertyAttributeAnalyzer : DiagnosticAnalyzer
+{
+    /// <inheritdoc/>
+    public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics { get; } = ImmutableArray.Create(
+        InvalidObservablePropertyDeclarationIsNotIncompletePartialDefinition,
+        InvalidObservablePropertyDeclarationReturnsByRef,
+        InvalidObservablePropertyDeclarationReturnsRefLikeType);
+
+    /// <inheritdoc/>
+    public override void Initialize(AnalysisContext context)
+    {
+        context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None);
+        context.EnableConcurrentExecution();
+
+        context.RegisterCompilationStartAction(static context =>
+        {
+            // Get the [ObservableProperty] and [GeneratedCode] symbols
+            if (context.Compilation.GetTypeByMetadataName("CommunityToolkit.Mvvm.ComponentModel.ObservablePropertyAttribute") is not INamedTypeSymbol observablePropertySymbol ||
+                context.Compilation.GetTypeByMetadataName("System.CodeDom.Compiler.GeneratedCodeAttribute") is not { } generatedCodeAttributeSymbol)
+            {
+                return;
+            }
+
+            context.RegisterSymbolAction(context =>
+            {
+                // Ensure that we have some target property to analyze (also skip implementation parts)
+                if (context.Symbol is not IPropertySymbol { PartialDefinitionPart: null } propertySymbol)
+                {
+                    return;
+                }
+
+                // If the property is not using [ObservableProperty], there's nothing to do
+                if (!context.Symbol.TryGetAttributeWithType(observablePropertySymbol, out AttributeData? observablePropertyAttribute))
+                {
+                    return;
+                }
+
+                // Emit an error if the property is not a partial definition with no implementation...
+                if (propertySymbol is not { IsPartialDefinition: true, PartialImplementationPart: null })
+                {
+                    // ...But only if it wasn't actually generated by the [ObservableProperty] generator.
+                    bool isImplementationAllowed =
+                        propertySymbol is { IsPartialDefinition: true, PartialImplementationPart: IPropertySymbol implementationPartSymbol } &&
+                        implementationPartSymbol.TryGetAttributeWithType(generatedCodeAttributeSymbol, out AttributeData? generatedCodeAttributeData) &&
+                        generatedCodeAttributeData.TryGetConstructorArgument(0, out string? toolName) &&
+                        toolName == typeof(ObservablePropertyGenerator).FullName;
+
+                    // Emit the diagnostic only for cases that were not valid generator outputs
+                    if (!isImplementationAllowed)
+                    {
+                        context.ReportDiagnostic(Diagnostic.Create(
+                            InvalidObservablePropertyDeclarationIsNotIncompletePartialDefinition,
+                            observablePropertyAttribute.GetLocation(),
+                            context.Symbol));
+                    }
+                }
+
+                // Emit an error if the property returns a value by ref
+                if (propertySymbol.ReturnsByRef || propertySymbol.ReturnsByRefReadonly)
+                {
+                    context.ReportDiagnostic(Diagnostic.Create(
+                        InvalidObservablePropertyDeclarationReturnsByRef,
+                        observablePropertyAttribute.GetLocation(),
+                        context.Symbol));
+                }
+
+                // Emit an error if the property type is a ref struct
+                if (propertySymbol.Type.IsRefLikeType)
+                {
+                    context.ReportDiagnostic(Diagnostic.Create(
+                        InvalidObservablePropertyDeclarationReturnsRefLikeType,
+                        observablePropertyAttribute.GetLocation(),
+                        context.Symbol));
+                }
+            }, SymbolKind.Property);
+        });
+    }
+}
+
+#endif

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

@@ -718,17 +718,17 @@ internal static class DiagnosticDescriptors
     /// <summary>
     /// Gets a <see cref="DiagnosticDescriptor"/> indicating when <c>[ObservableProperty]</c> is applied to a property with an invalid declaration.
     /// <para>
-    /// Format: <c>"The property {0}.{1} cannot be used to generate an observable property, as its declaration is not valid (it must be a partial property with a getter and a setter that is not init-only)"</c>.
+    /// Format: <c>"The property {0}.{1} cannot be used to generate an observable property, as its declaration is not valid (it must be an instance (non static) partial property with a getter and a setter that is not init-only)"</c>.
     /// </para>
     /// </summary>
     public static readonly DiagnosticDescriptor InvalidPropertyDeclarationForObservableProperty = new DiagnosticDescriptor(
         id: "MVVMTK0043",
         title: "Invalid property declaration for [ObservableProperty]",
-        messageFormat: "The property {0}.{1} cannot be used to generate an observable property, as its declaration is not valid (it must be a partial property with a getter and a setter that is not init-only)",
+        messageFormat: "The property {0}.{1} cannot be used to generate an observable property, as its declaration is not valid (it must be an instance (non static) partial property with a getter and a setter that is not init-only)",
         category: typeof(ObservablePropertyGenerator).FullName,
         defaultSeverity: DiagnosticSeverity.Error,
         isEnabledByDefault: true,
-        description: "Properties annotated with [ObservableProperty] must be partial properties with a getter and a setter that is not init-only.",
+        description: "Properties annotated with [ObservableProperty] must be instance (non static) partial properties with a getter and a setter that is not init-only.",
         helpLinkUri: "https://aka.ms/mvvmtoolkit/errors/mvvmtk0043");
 
     /// <summary>
@@ -859,4 +859,52 @@ internal static class DiagnosticDescriptors
         description: "This project producing one or more 'MVVMTK0045' warnings due to [ObservableProperty] being used on fields, which is not AOT compatible in WinRT scenarios, should set 'LangVersion' to 'preview' to enable partial properties and the associated code fixer (setting 'LangVersion=preview' is required to use [ObservableProperty] on partial properties and address these warnings).",
         helpLinkUri: "https://aka.ms/mvvmtoolkit/errors/mvvmtk0051",
         customTags: WellKnownDiagnosticTags.CompilationEnd);
+
+    /// <summary>
+    /// Gets a <see cref="DiagnosticDescriptor"/> for when <c>[ObservableProperty]</c> is used on a property that is not an incomplete partial definition.
+    /// <para>
+    /// Format: <c>"The property {0}.{1} is not an incomplete partial definition ([ObservableProperty] must be used on partial property definitions with no implementation part)"</c>.
+    /// </para>
+    /// </summary>
+    public static readonly DiagnosticDescriptor InvalidObservablePropertyDeclarationIsNotIncompletePartialDefinition = new(
+        id: "MVVMTK0052",
+        title: "Using [ObservableProperty] on an invalid property declaration (not incomplete partial definition)",
+        messageFormat: """The property {0}.{1} is not an incomplete partial definition ([ObservableProperty] must be used on partial property definitions with no implementation part)""",
+        category: typeof(ObservablePropertyGenerator).FullName,
+        defaultSeverity: DiagnosticSeverity.Error,
+        isEnabledByDefault: true,
+        description: "A property using [ObservableProperty] is not a partial implementation part ([ObservableProperty] must be used on partial property definitions with no implementation part).",
+        helpLinkUri: "https://aka.ms/mvvmtoolkit/errors/mvvmtk0052");
+
+    /// <summary>
+    /// Gets a <see cref="DiagnosticDescriptor"/> for when <c>[ObservableProperty]</c> is used on a property that returns a ref value.
+    /// <para>
+    /// Format: <c>"The property {0}.{1} returns a ref value ([ObservableProperty] must be used on properties returning a type by value)"</c>.
+    /// </para>
+    /// </summary>
+    public static readonly DiagnosticDescriptor InvalidObservablePropertyDeclarationReturnsByRef = new(
+        id: "MVVMTK0053",
+        title: "Using [ObservableProperty] on a property that returns byref",
+        messageFormat: """The property {0}.{1} returns a ref value ([ObservableProperty] must be used on properties returning a type by value)""",
+        category: typeof(ObservablePropertyGenerator).FullName,
+        defaultSeverity: DiagnosticSeverity.Error,
+        isEnabledByDefault: true,
+        description: "A property using [ObservableProperty] returns a value by reference ([ObservableProperty] must be used on properties returning a type by value).",
+        helpLinkUri: "https://aka.ms/mvvmtoolkit/errors/mvvmtk0053");
+
+    /// <summary>
+    /// Gets a <see cref="DiagnosticDescriptor"/> for when <c>[ObservableProperty]</c> is used on a property that returns a byref-like value.
+    /// <para>
+    /// Format: <c>"The property {0}.{1} returns a byref-like value ([ObservableProperty] must be used on properties of a non byref-like type)"</c>.
+    /// </para>
+    /// </summary>
+    public static readonly DiagnosticDescriptor InvalidObservablePropertyDeclarationReturnsRefLikeType = new(
+        id: "MVVMTK0054",
+        title: "Using [ObservableProperty] on a property that returns byref-like",
+        messageFormat: """The property {0}.{1} returns a byref-like value ([ObservableProperty] must be used on properties of a non byref-like type)""",
+        category: typeof(ObservablePropertyGenerator).FullName,
+        defaultSeverity: DiagnosticSeverity.Error,
+        isEnabledByDefault: true,
+        description: "A property using [ObservableProperty] returns a byref-like value ([ObservableProperty] must be used on properties of a non byref-like type).",
+        helpLinkUri: "https://aka.ms/mvvmtoolkit/errors/mvvmtk0054");
 }