Add 'UnsupportedRoslynVersionForPartialPropertyAnalyzer'

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

@@ -85,3 +85,4 @@ Rule ID | Category | Severity | Notes
 MVVMTK0041 | CommunityToolkit.Mvvm.SourceGenerators.ObservablePropertyGenerator | Error | See https://aka.ms/mvvmtoolkit/errors/mvvmtk0041
 MVVMTK0042 | CommunityToolkit.Mvvm.SourceGenerators.ObservablePropertyGenerator | Info | See https://aka.ms/mvvmtoolkit/errors/mvvmtk0042
 MVVMTK0043| CommunityToolkit.Mvvm.SourceGenerators.ObservablePropertyGenerator | Error | See https://aka.ms/mvvmtoolkit/errors/mvvmtk0043
+MVVMTK0044| CommunityToolkit.Mvvm.SourceGenerators.ObservablePropertyGenerator | Error | See https://aka.ms/mvvmtoolkit/errors/mvvmtk0043

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

@@ -46,6 +46,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Diagnostics\Analyzers\ClassUsingAttributeInsteadOfInheritanceAnalyzer.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Diagnostics\Analyzers\FieldWithOrphanedDependentObservablePropertyAttributesAnalyzer.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Diagnostics\Analyzers\FieldReferenceForObservablePropertyFieldAnalyzer.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Diagnostics\Analyzers\UnsupportedRoslynVersionForPartialPropertyAnalyzer.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Diagnostics\Analyzers\RequiresCSharpLanguageVersionPreviewAnalyzer.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Diagnostics\Analyzers\InvalidPropertyLevelObservablePropertyAttributeAnalyzer.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Diagnostics\Analyzers\UseObservablePropertyOnPartialPropertyAnalyzer.cs" />

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

@@ -0,0 +1,60 @@
+// 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_11_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 a property, if the Roslyn version in use is not high enough.
+/// </summary>
+[DiagnosticAnalyzer(LanguageNames.CSharp)]
+public sealed class UnsupportedRoslynVersionForPartialPropertyAnalyzer : DiagnosticAnalyzer
+{
+    /// <inheritdoc/>
+    public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics { get; } = ImmutableArray.Create(UnsupportedRoslynVersionForObservablePartialPropertySupport);
+
+    /// <inheritdoc/>
+    public override void Initialize(AnalysisContext context)
+    {
+        context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.Analyze | GeneratedCodeAnalysisFlags.ReportDiagnostics);
+        context.EnableConcurrentExecution();
+
+        context.RegisterCompilationStartAction(static context =>
+        {
+            // Get the symbol for [ObservableProperty]
+            if (context.Compilation.GetTypeByMetadataName("CommunityToolkit.Mvvm.ComponentModel.ObservablePropertyAttribute") is not INamedTypeSymbol observablePropertySymbol)
+            {
+                return;
+            }
+
+            context.RegisterSymbolAction(context =>
+            {
+                // We're intentionally only looking for properties here
+                if (context.Symbol is not IPropertySymbol propertySymbol)
+                {
+                    return;
+                }
+
+                // If the property has [ObservableProperty], emit an error in all cases
+                if (propertySymbol.TryGetAttributeWithType(observablePropertySymbol, out AttributeData? observablePropertyAttribute))
+                {
+                    context.ReportDiagnostic(Diagnostic.Create(
+                        UnsupportedRoslynVersionForObservablePartialPropertySupport,
+                        observablePropertyAttribute.GetLocation(),
+                        propertySymbol.ContainingType,
+                        propertySymbol));
+                }
+            }, SymbolKind.Property);
+        });
+    }
+}
+
+#endif

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

@@ -727,4 +727,20 @@ internal static class DiagnosticDescriptors
         isEnabledByDefault: true,
         description: "Properties annotated with [ObservableProperty] must be partial properties with a getter and a setter that is not init-only.",
         helpLinkUri: "https://aka.ms/mvvmtoolkit/errors/mvvmtk0043");
+
+    /// <summary>
+    /// Gets a <see cref="DiagnosticDescriptor"/> indicating when <c>[ObservableProperty]</c> is applied to a property when an unsupported version of Roslyn is used.
+    /// <para>
+    /// Format: <c>"The property {0}.{1} cannot be used to generate an observable property, as the current Roslyn version being used is not high enough (remove [ObservableProperty] or target a field instead, or upgrade to at least Visual Studio 2022 version 17.12 and the .NET 9 SDK)"</c>.
+    /// </para>
+    /// </summary>
+    public static readonly DiagnosticDescriptor UnsupportedRoslynVersionForObservablePartialPropertySupport = new DiagnosticDescriptor(
+        id: "MVVMTK0044",
+        title: "Unsupported Roslyn version for using [ObservableProperty] on partial properties",
+        messageFormat: "The property {0}.{1} cannot be used to generate an observable property, as the current Roslyn version being used is not high enough (remove [ObservableProperty] or target a field instead, or upgrade to at least Visual Studio 2022 version 17.12 and the .NET 9 SDK)",
+        category: typeof(ObservablePropertyGenerator).FullName,
+        defaultSeverity: DiagnosticSeverity.Error,
+        isEnabledByDefault: true,
+        description: "Using [ObservableProperty] with (partial) properties requires a higher version of Roslyn (remove [ObservableProperty] or target a field instead, or upgrade to at least Visual Studio 2022 version 17.12 and the .NET 9 SDK).",
+        helpLinkUri: "https://aka.ms/mvvmtoolkit/errors/mvvmtk0044");
 }