Check parse options in UnsupportedCSharpLanguageVersionAnalyzer

Author: Sergio0694

CommunityToolkit.Mvvm.SourceGenerators/Diagnostics/Analyzers/UnsupportedCSharpLanguageVersionAnalyzer.cs

@@ -6,6 +6,7 @@
 using System.Collections.Immutable;
 using System.Linq;
 using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
 using Microsoft.CodeAnalysis.Diagnostics;
 using static CommunityToolkit.Mvvm.SourceGenerators.Diagnostics.DiagnosticDescriptors;
 
@@ -50,6 +51,12 @@ public override void Initialize(AnalysisContext context)
                 return;
             }
 
+            // Check that the language version is not high enough, otherwise no diagnostic should be produced
+            if (context.Symbol.DeclaringSyntaxReferences.FirstOrDefault() is not { SyntaxTree.Options: CSharpParseOptions { LanguageVersion: < LanguageVersion.CSharp8 } })
+            {
+                return;
+            }
+
             ImmutableArray<AttributeData> attributes = context.Symbol.GetAttributes();
 
             // If the symbol has no attributes, there's nothing left to do