Only make members required when RequiredMemberAttribute is present

Fixes #68478

Author: sharwell

src/Analyzers/CSharp/CodeFixes/MakeMemberRequired/CSharpMakeMemberRequiredCodeFixProvider.cs

@@ -58,6 +58,12 @@ public override async Task RegisterCodeFixesAsync(CodeFixContext context)
 
         var semanticModel = await document.GetRequiredSemanticModelAsync(cancellationToken).ConfigureAwait(false);
 
+        if (semanticModel.Compilation.GetBestTypeByMetadataName("System.Runtime.CompilerServices.RequiredMemberAttribute") is null)
+        {
+            // The attribute necessary to support required members is not present
+            return;
+        }
+
         var fieldOrPropertySymbol = semanticModel.GetDeclaredSymbol(node, cancellationToken);
         if (fieldOrPropertySymbol is IPropertySymbol propertySymbol)
         {

src/Analyzers/CSharp/Tests/MakeMemberRequired/MakeMemberRequiredTests.cs

@@ -8,6 +8,7 @@
 using Microsoft.CodeAnalysis.Editor.UnitTests.CodeActions;
 using Microsoft.CodeAnalysis.Test.Utilities;
 using Microsoft.CodeAnalysis.Testing;
+using Roslyn.Test.Utilities;
 using Xunit;
 
 namespace Microsoft.CodeAnalysis.CSharp.Analyzers.UnitTests.MakeMemberRequired
@@ -119,6 +120,28 @@ public static IEnumerable<object[]> AccessorAccessibilityModifierCombinationsWhe
             yield return new[] { "internal", "private protected" };
         }
 
+        [Fact]
+        [WorkItem("https://github.com/dotnet/roslyn/issues/68478")]
+        public async Task SimpleSetPropertyMissingRequiredAttribute()
+        {
+            var code =
+                """
+                #nullable enable
+                class MyClass
+                {
+                    public string {|CS8618:MyProperty|} { get; set; }
+                }
+                """;
+
+            await new VerifyCS.Test
+            {
+                TestCode = code,
+                FixedCode = code,
+                LanguageVersion = LanguageVersion.CSharp11,
+                ReferenceAssemblies = ReferenceAssemblies.Net.Net60,
+            }.RunAsync();
+        }
+
         [Fact]
         public async Task SimpleSetProperty()
         {