Do not offer 'convert' namespace when the ns has sibling types

src/Analyzers/CSharp/Analyzers/ConvertNamespace/ConvertNamespaceAnalysis.cs

@@ -2,7 +2,6 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-using System.Collections.Immutable;
 using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using Microsoft.CodeAnalysis.CodeStyle;
@@ -68,16 +67,14 @@ internal static bool CanOfferUseFileScoped(
         if (!canOffer)
             return false;
 
-        // even if we could offer this here, we have to make sure it would be legal.  A file scoped namespace is
-        // only legal if it's the only namespace in the file and there are no top level statements.
-        var tooManyNamespaces = root.DescendantNodesAndSelf(n => n is CompilationUnitSyntax or BaseNamespaceDeclarationSyntax)
-                                    .OfType<BaseNamespaceDeclarationSyntax>()
-                                    .Take(2)
-                                    .Count() != 1;
-        if (tooManyNamespaces)
+        // even if we could offer this here, we have to make sure it would be legal.
+
+        // A file scoped namespace is only legal if it's the only top level member in the file.
+        if (root.Members is not [var singleMember] || singleMember != namespaceDeclaration)
             return false;
 
-        if (root.Members.Any(m => m is GlobalStatementSyntax))
+        // A file scoped namespace is only legal if it's the only namespace in the file.
+        if (namespaceDeclaration.Members.Any(static m => m is BaseNamespaceDeclarationSyntax))
             return false;
 
         return true;

src/Analyzers/CSharp/Tests/ConvertNamespace/ConvertToFileScopedNamespaceAnalyzerTests.cs

@@ -1544,4 +1544,46 @@ limit 1
             }
         }.RunAsync();
     }
+
+    [Fact, WorkItem("https://github.com/dotnet/roslyn/issues/74214")]
+    public async Task TestNotWithClassAfter()
+    {
+        await new VerifyCS.Test
+        {
+            TestCode = """
+            namespace N
+            {
+                class Inner { }
+            }
+
+            class Outer { }
+            """,
+            LanguageVersion = LanguageVersion.CSharp10,
+            Options =
+            {
+                { CSharpCodeStyleOptions.NamespaceDeclarations, NamespaceDeclarationPreference.FileScoped }
+            }
+        }.RunAsync();
+    }
+
+    [Fact, WorkItem("https://github.com/dotnet/roslyn/issues/74214")]
+    public async Task TestNotWithClassBefore()
+    {
+        await new VerifyCS.Test
+        {
+            TestCode = """
+            class Outer { }
+
+            namespace N
+            {
+                class Inner { }
+            }
+            """,
+            LanguageVersion = LanguageVersion.CSharp10,
+            Options =
+            {
+                { CSharpCodeStyleOptions.NamespaceDeclarations, NamespaceDeclarationPreference.FileScoped }
+            }
+        }.RunAsync();
+    }
 }

src/Features/CSharp/Portable/ConvertNamespace/ConvertNamespaceCodeRefactoringProvider.cs

@@ -24,14 +24,10 @@ namespace Microsoft.CodeAnalysis.CSharp.ConvertNamespace;
 using static ConvertNamespaceTransform;
 
 [ExportCodeRefactoringProvider(LanguageNames.CSharp, Name = PredefinedCodeRefactoringProviderNames.ConvertNamespace), Shared]
-internal class ConvertNamespaceCodeRefactoringProvider : SyntaxEditorBasedCodeRefactoringProvider
+[method: ImportingConstructor]
+[method: SuppressMessage("RoslynDiagnosticsReliability", "RS0033:Importing constructor should be [Obsolete]", Justification = "Used in test code: https://github.com/dotnet/roslyn/issues/42814")]
+internal class ConvertNamespaceCodeRefactoringProvider() : SyntaxEditorBasedCodeRefactoringProvider
 {
-    [ImportingConstructor]
-    [SuppressMessage("RoslynDiagnosticsReliability", "RS0033:Importing constructor should be [Obsolete]", Justification = "Used in test code: https://github.com/dotnet/roslyn/issues/42814")]
-    public ConvertNamespaceCodeRefactoringProvider()
-    {
-    }
-
     protected override ImmutableArray<FixAllScope> SupportedFixAllScopes
         => [FixAllScope.Project, FixAllScope.Solution];