Fix a bug and add tests.

We didn't offer move type to new file if there was a single outer type
in a document with a nested type in it. Move to new file should be
offered for the nested type here.

src/EditorFeatures/CSharpTest/CodeActions/MoveType/MoveTypeTests.RenameFile.cs

@@ -19,6 +19,20 @@ public async Task SingleClassInFile_RenameFile()
             await TestRenameFileToMatchTypeAsync(code, expectedDocumentName);
         }
 
+        [WpfFact, Trait(Traits.Feature, Traits.Features.CodeActionsMoveType)]
+        public async Task MoreThanOneTypeInFile_RenameFile()
+        {
+            var code =
+@"[||]class Class1
+{ 
+    class Inner { }
+}";
+
+            var expectedDocumentName = "Class1.cs";
+
+            await TestRenameFileToMatchTypeAsync(code, expectedDocumentName);
+        }
+
         [WpfFact, Trait(Traits.Feature, Traits.Features.CodeActionsMoveType)]
         public async Task TypeNameMatchesFileName_RenameFile()
         {
@@ -31,7 +45,7 @@ public async Task TypeNameMatchesFileName_RenameFile()
         }
 
         [WpfFact, Trait(Traits.Feature, Traits.Features.CodeActionsMoveType)]
-        public async Task MoreThanOneTypeInFile_RenameFile()
+        public async Task MoreThanOneTopLevelTypeInFile_RenameFile()
         {
             var code =
 @"[||]class Class1 { }

src/EditorFeatures/CSharpTest/CodeActions/MoveType/MoveTypeTests.RenameType.cs

@@ -20,6 +20,24 @@ public async Task SingleClassInFile_RenameType()
             await TestRenameTypeToMatchFileAsync(code, codeWithTypeRenamedToMatchFileName);
         }
 
+        [WpfFact, Trait(Traits.Feature, Traits.Features.CodeActionsMoveType)]
+        public async Task MoreThanOneTypeInFile_RenameType()
+        {
+            var code =
+@"[||]class Class1
+{ 
+    class Inner { }
+}";
+
+            var codeWithTypeRenamedToMatchFileName =
+@"class [|test1|] 
+{ 
+    class Inner { }
+}";
+
+            await TestRenameTypeToMatchFileAsync(code, codeWithTypeRenamedToMatchFileName);
+        }
+
         [WpfFact, Trait(Traits.Feature, Traits.Features.CodeActionsMoveType)]
         public async Task TypeNameMatchesFileName_RenameType()
         {
@@ -32,7 +50,7 @@ public async Task TypeNameMatchesFileName_RenameType()
         }
 
         [WpfFact, Trait(Traits.Feature, Traits.Features.CodeActionsMoveType)]
-        public async Task MoreThanOneTypeInFile_RenameType()
+        public async Task MoreThanOneTopLevelTypeInFile_RenameType()
         {
             var code =
 @"[||]class Class1 { }

src/Features/Core/Portable/CodeRefactorings/MoveType/AbstractMoveTypeService.cs

@@ -41,10 +41,10 @@ protected virtual SyntaxNode GetNodeToAnalyze(SyntaxNode root, TextSpan span)
         /// <summary>
         /// checks if there is a single top level type declaration in a document
         /// </summary>
-        private bool IsSingleTypeDeclarationInSourceDocument(SyntaxNode root) =>
-            root.DescendantNodes()
+        private bool MultipleTopLevelTypeDeclarationInSourceDocument(SyntaxNode root) =>
+            root.DescendantNodes(n => (n is TCompilationUnitSyntax || n is TNamespaceDeclarationSyntax))
             .OfType<TTypeDeclarationSyntax>()
-            .Count() == 1;
+            .Count() > 1;
 
         public async Task<CodeRefactoring> GetRefactoringAsync(Document document, TextSpan textSpan, CancellationToken cancellationToken)
         {
@@ -73,9 +73,15 @@ public async Task<CodeRefactoring> GetRefactoringAsync(Document document, TextSp
         private List<CodeAction> CreateActions(State state, CancellationToken cancellationToken)
         {
             var actions = new List<CodeAction>();
-            var singleType = IsSingleTypeDeclarationInSourceDocument(state.SemanticDocument.Root);
+            var manyTypes = MultipleTopLevelTypeDeclarationInSourceDocument(state.SemanticDocument.Root);
 
-            if (singleType)
+            if (manyTypes || IsNestedType(state.TypeNode))
+            {
+                // If there are multiple type declarations in current document. offer, move to new file.
+                // Or if this is a nested type, offer to move to new file.
+                actions.Add(GetCodeAction(state, operationKind: OperationKind.MoveType));
+            }
+            else
             {
                 // one type declaration in current document. No moving around required, just sync
                 // document name and type name by offering rename in both directions between type and document.
@@ -88,11 +94,6 @@ private List<CodeAction> CreateActions(State state, CancellationToken cancellati
                     actions.Add(GetCodeAction(state, operationKind: OperationKind.RenameType));
                 }
             }
-            else
-            {
-                // multiple type declarations in current document. so, move to new file.
-                actions.Add(GetCodeAction(state, operationKind: OperationKind.MoveType));
-            }
 
             return actions;
         }