Add 'Generate additional part' refactoring

Author: sharwell

StyleCop.Analyzers/StyleCop.Analyzers.PrivateCodeFixes/GeneratePartCodeRefactoringProvider.cs

@@ -0,0 +1,76 @@
+// Copyright (c) Tunnel Vision Laboratories, LLC. All Rights Reserved.
+// Licensed under the MIT License. See LICENSE in the project root for license information.
+
+namespace StyleCop.Analyzers.PrivateCodeFixes;
+
+using System.IO;
+using System.Text;
+using System.Threading.Tasks;
+using Analyzer.Utilities;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CodeActions;
+using Microsoft.CodeAnalysis.CodeRefactorings;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Text;
+
+[ExportCodeRefactoringProvider(LanguageNames.CSharp, Name = nameof(GeneratePartCodeRefactoringProvider))]
+internal sealed class GeneratePartCodeRefactoringProvider
+    : CodeRefactoringProvider
+{
+    public override async Task ComputeRefactoringsAsync(CodeRefactoringContext context)
+    {
+        var partialType = await context.TryGetRelevantNodeAsync<ClassDeclarationSyntax>(CSharpRefactoringHelpers.Instance).ConfigureAwait(false);
+        if (partialType is not { Modifiers: var modifiers }
+            || !modifiers.Any(SyntaxKind.PartialKeyword))
+        {
+            return;
+        }
+
+        context.RegisterRefactoring(CodeAction.Create(
+            "Generate additional part",
+            async cancellationToken =>
+            {
+                var namespaceDeclaration = partialType.FirstAncestorOrSelf<BaseNamespaceDeclarationSyntax>();
+                if (namespaceDeclaration is null)
+                {
+                    return context.Document.Project.Solution;
+                }
+
+                var firstUsing = namespaceDeclaration.Usings.FirstOrDefault()?.Name.ToString();
+
+                var namespaceName = namespaceDeclaration.Name.ToString();
+                var subNamespace = namespaceName;
+                var rootNamespace = context.Document.Project.DefaultNamespace;
+                if (!string.IsNullOrEmpty(rootNamespace) && namespaceName.StartsWith(rootNamespace + "."))
+                {
+                    subNamespace = namespaceName[(rootNamespace.Length + 1)..];
+                }
+
+                var content = $@"// Copyright (c) Tunnel Vision Laboratories, LLC. All Rights Reserved.
+// Licensed under the MIT License. See LICENSE in the project root for license information.
+
+namespace {namespaceName};
+
+using {firstUsing};
+
+public partial class {partialType.Identifier.ValueText} {partialType.BaseList}
+{{
+}}
+";
+
+                var fileName = partialType.Identifier.ValueText + ".cs";
+                var directory = Path.GetDirectoryName(context.Document.Project.FilePath)!;
+                var existingText = await context.Document.GetTextAsync(cancellationToken).ConfigureAwait(false);
+
+                var addedDocument = context.Document.Project.AddDocument(
+                    fileName,
+                    SourceText.From(content, new UTF8Encoding(true), existingText.ChecksumAlgorithm),
+                    folders: subNamespace.Split('.'),
+                    filePath: Path.Combine(directory, Path.Combine(subNamespace.Split('.')), fileName));
+
+                return addedDocument.Project.Solution;
+            },
+            nameof(GeneratePartCodeRefactoringProvider)));
+    }
+}