Fix analyzer RCS1203 (#1683)

Author: josefpihrt

ChangeLog.md

@@ -17,6 +17,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Fix analyzer [RCS1246](https://josefpihrt.github.io/docs/roslynator/analyzers/RCS1246) ([PR](https://github.com/dotnet/roslynator/pull/1676))
 - Fix analyzer [RCS1248](https://josefpihrt.github.io/docs/roslynator/analyzers/RCS1248) ([PR](https://github.com/dotnet/roslynator/pull/1677))
+- Fix analyzer [RCS1203](https://josefpihrt.github.io/docs/roslynator/analyzers/RCS1203) ([PR](https://github.com/dotnet/roslynator/pull/1683))
 - Fix refactoring [Check expression for null](https://josefpihrt.github.io/docs/roslynator/refactorings/RR0024) ([PR](https://github.com/dotnet/roslynator/pull/1682))
 
 ## [4.14.0] - 2025-07-26

src/Analyzers.CodeFixes/CSharp/CodeFixes/ClassDeclarationCodeFixProvider.cs

@@ -128,7 +128,17 @@ private static Task<Document> UseAttributeUsageAttributeAsync(
                     NameEquals(IdentifierName("AllowMultiple")),
                     FalseLiteralExpression())));
 
-        ClassDeclarationSyntax newNode = classDeclaration.AddAttributeLists(AttributeList(attribute));
+        ClassDeclarationSyntax newClassDeclaration = classDeclaration;
+        AttributeListSyntax attributeList = AttributeList(attribute);
+        SyntaxTrivia comment = classDeclaration.GetDocumentationCommentTrivia();
+
+        if (!comment.IsKind(SyntaxKind.None))
+        {
+            attributeList = attributeList.WithLeadingTrivia(classDeclaration.GetLeadingTrivia());
+            newClassDeclaration = newClassDeclaration.WithoutLeadingTrivia();
+        }
+
+        ClassDeclarationSyntax newNode = newClassDeclaration.AddAttributeLists(attributeList);
 
         return document.ReplaceNodeAsync(classDeclaration, newNode, cancellationToken);
     }

src/Tests/Analyzers.Tests/RCS1203UseAttributeUsageAttributeTests.cs

@@ -24,6 +24,31 @@ class [|FooAttribute|] : Attribute
 ", @"
 using System;
 
+[AttributeUsage(AttributeTargets.All, AllowMultiple = false)]
+class FooAttribute : Attribute
+{
+}
+");
+    }
+
+    [Fact, Trait(Traits.Analyzer, DiagnosticIdentifiers.UseAttributeUsageAttribute)]
+    public async Task Test_WithComment()
+    {
+        await VerifyDiagnosticAndFixAsync(@"
+using System;
+
+/// <summary>
+/// x
+/// <summary>
+class [|FooAttribute|] : Attribute
+{
+}
+", @"
+using System;
+
+/// <summary>
+/// x
+/// <summary>
 [AttributeUsage(AttributeTargets.All, AllowMultiple = false)]
 class FooAttribute : Attribute
 {