Code fix for CS8313, CS8363 (invalid default literal as case constant / pattern) to use default expression

src/Features/CSharp/Portable/CSharpFeaturesResources.resx

@@ -569,4 +569,7 @@
   <data name="Remove_unused_variables" xml:space="preserve">
     <value>Remove unused variables</value>
   </data>
+  <data name="Use_default_0" xml:space="preserve">
+    <value>Use 'default({0})'</value>
+  </data>
 </root>

src/Features/CSharp/Portable/UseDefaultExpression/CSharpUseDefaultExpressionCodeFixProvider.cs

@@ -0,0 +1,98 @@
+// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
+
+using System;
+using System.Collections.Immutable;
+using System.Composition;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.CodeAnalysis.CodeActions;
+using Microsoft.CodeAnalysis.CodeFixes;
+using Microsoft.CodeAnalysis.CSharp.Extensions;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Text;
+
+namespace Microsoft.CodeAnalysis.CSharp.UseDefaultExpression
+{
+    [ExportCodeFixProvider(LanguageNames.CSharp, Name = PredefinedCodeFixProviderNames.UseDefaultExpression), Shared]
+    internal sealed class CSharpUseDefaultExpressionCodeFixProvider : CodeFixProvider
+    {
+        private const string CS8313 = nameof(CS8313); // A default literal 'default' is not valid as a case constant. Use another literal (e.g. '0' or 'null') as appropriate. If you intended to write the default label, use 'default:' without 'case'.
+        private const string CS8363 = nameof(CS8363); // A default literal 'default' is not valid as a pattern. Use another literal (e.g. '0' or 'null') as appropriate. To match everything, use a discard pattern 'var _'.
+        private const string CS8107 = nameof(CS8107); // Feature is not available in C# 7.0. Please use language version X or greater.
+        private const string CS8059 = nameof(CS8059); // Feature is not available in C# 6. Please use language version X or greater.
+        private const string CS8026 = nameof(CS8026); // Feature is not available in C# 5. Please use language version X or greater.
+        private const string CS8025 = nameof(CS8025); // Feature is not available in C# 4. Please use language version X or greater.
+        private const string CS8024 = nameof(CS8024); // Feature is not available in C# 3. Please use language version X or greater.
+        private const string CS8023 = nameof(CS8023); // Feature is not available in C# 2. Please use language version X or greater.
+
+        public override ImmutableArray<string> FixableDiagnosticIds { get; } =
+            ImmutableArray.Create(CS8313, CS8363, CS8107, CS8059, CS8026, CS8025, CS8024, CS8023);
+
+        public override FixAllProvider GetFixAllProvider()
+        {
+            // This code fix addresses very specific compiler errors. It's unlikely there will be more than 1 of them at a time.
+            return null;
+        }
+
+        public override async Task RegisterCodeFixesAsync(CodeFixContext context)
+        {
+            var syntaxRoot = await context.Document.GetSyntaxRootAsync(context.CancellationToken).ConfigureAwait(false);
+            var token = syntaxRoot.FindToken(context.Span.Start);
+
+            if (token.Span == context.Span &&
+                token.IsKind(SyntaxKind.DefaultKeyword) &&
+                token.Parent.IsKind(SyntaxKind.DefaultLiteralExpression))
+            {
+                var defaultLiteral = (LiteralExpressionSyntax)token.Parent;
+                var semanticModel = await context.Document.GetSemanticModelAsync(context.CancellationToken).ConfigureAwait(false);
+
+                var type = semanticModel.GetTypeInfo(defaultLiteral, context.CancellationToken).ConvertedType;
+                if (type == null || type.TypeKind == TypeKind.Error)
+                {
+                    return;
+                }
+
+                if (type.IsAnonymousType)
+                {
+                    type = semanticModel.Compilation.GetSpecialType(SpecialType.System_Object);
+                }
+
+                // If there happens to be more than 1 diagnostic (for example a default literal in a case label in C# 7.0),
+                // we will fix all of them, so pass in context.Diagnostics, not just the first one.
+                context.RegisterCodeFix(
+                    new MyCodeAction(
+                        c => FixAsync(context.Document, context.Span, type, c),
+                        type.ToDisplayString(SymbolDisplayFormat.MinimallyQualifiedFormat)),
+                    context.Diagnostics);
+            }
+        }
+
+        private static async Task<Document> FixAsync(Document document, TextSpan span, ITypeSymbol type, CancellationToken cancellationToken)
+        {
+            var syntaxRoot = await document.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
+
+            var defaultToken = syntaxRoot.FindToken(span.Start);
+            var defaultLiteral = (LiteralExpressionSyntax)defaultToken.Parent;
+
+            var typeSyntax = type.GenerateTypeSyntax(allowVar: false);
+
+            var defaultExpression =
+                SyntaxFactory.DefaultExpression(
+                    defaultToken.WithoutTrivia(),
+                    SyntaxFactory.Token(SyntaxKind.OpenParenToken),
+                    typeSyntax,
+                    SyntaxFactory.Token(SyntaxKind.CloseParenToken)).WithTriviaFrom(defaultLiteral);
+
+            var newRoot = syntaxRoot.ReplaceNode(defaultLiteral, defaultExpression);
+            return document.WithSyntaxRoot(newRoot);
+        }
+
+        private sealed class MyCodeAction : CodeAction.DocumentChangeAction
+        {
+            public MyCodeAction(Func<CancellationToken, Task<Document>> createChangedDocument, string type)
+                : base(string.Format(CSharpFeaturesResources.Use_default_0, type), createChangedDocument, CSharpFeaturesResources.Use_default_0)
+            {
+            }
+        }
+    }
+}

src/Features/CSharp/Portable/UseDefaultLiteral/CSharpUseDefaultLiteralCodeFixProvider.cs

@@ -17,7 +17,7 @@
 
 namespace Microsoft.CodeAnalysis.CSharp.UseDefaultLiteral
 {
-    [ExportCodeFixProvider(LanguageNames.CSharp), Shared]
+    [ExportCodeFixProvider(LanguageNames.CSharp, Name = PredefinedCodeFixProviderNames.UseDefaultLiteral), Shared]
     internal partial class CSharpUseDefaultLiteralCodeFixProvider : SyntaxEditorBasedCodeFixProvider
     {
         public override ImmutableArray<string> FixableDiagnosticIds { get; }

src/Features/CSharp/Portable/xlf/CSharpFeaturesResources.cs.xlf

@@ -97,6 +97,11 @@
         <target state="translated">Seřadit modifikátory dostupnosti</target>
         <note />
       </trans-unit>
+      <trans-unit id="Use_default_0">
+        <source>Use 'default({0})'</source>
+        <target state="new">Use 'default({0})'</target>
+        <note />
+      </trans-unit>
       <trans-unit id="if_statement_can_be_simplified">
         <source>'if' statement can be simplified</source>
         <target state="translated">Příkaz if lze zjednodušit.</target>

src/Features/CSharp/Portable/xlf/CSharpFeaturesResources.de.xlf

@@ -97,6 +97,11 @@
         <target state="translated">Zugriffsmodifizierer sortieren</target>
         <note />
       </trans-unit>
+      <trans-unit id="Use_default_0">
+        <source>Use 'default({0})'</source>
+        <target state="new">Use 'default({0})'</target>
+        <note />
+      </trans-unit>
       <trans-unit id="if_statement_can_be_simplified">
         <source>'if' statement can be simplified</source>
         <target state="translated">Die if-Anweisung kann vereinfacht werden.</target>

src/Features/CSharp/Portable/xlf/CSharpFeaturesResources.es.xlf

@@ -97,6 +97,11 @@
         <target state="translated">Ordenar modificadores de accesibilidad</target>
         <note />
       </trans-unit>
+      <trans-unit id="Use_default_0">
+        <source>Use 'default({0})'</source>
+        <target state="new">Use 'default({0})'</target>
+        <note />
+      </trans-unit>
       <trans-unit id="if_statement_can_be_simplified">
         <source>'if' statement can be simplified</source>
         <target state="translated">La instrucción "if" se puede simplificar</target>

src/Features/CSharp/Portable/xlf/CSharpFeaturesResources.fr.xlf

@@ -97,6 +97,11 @@
         <target state="translated">Trier les modificateurs d'accessibilité</target>
         <note />
       </trans-unit>
+      <trans-unit id="Use_default_0">
+        <source>Use 'default({0})'</source>
+        <target state="new">Use 'default({0})'</target>
+        <note />
+      </trans-unit>
       <trans-unit id="if_statement_can_be_simplified">
         <source>'if' statement can be simplified</source>
         <target state="translated">L'instruction 'if' peut être simplifiée</target>

src/Features/CSharp/Portable/xlf/CSharpFeaturesResources.it.xlf

@@ -97,6 +97,11 @@
         <target state="translated">Ordina i modificatori di accessibilità</target>
         <note />
       </trans-unit>
+      <trans-unit id="Use_default_0">
+        <source>Use 'default({0})'</source>
+        <target state="new">Use 'default({0})'</target>
+        <note />
+      </trans-unit>
       <trans-unit id="if_statement_can_be_simplified">
         <source>'if' statement can be simplified</source>
         <target state="translated">L'istruzione 'if' può essere semplificata</target>

src/Features/CSharp/Portable/xlf/CSharpFeaturesResources.ja.xlf

@@ -97,6 +97,11 @@
         <target state="translated">アクセシビリティ修飾子を並べ替える</target>
         <note />
       </trans-unit>
+      <trans-unit id="Use_default_0">
+        <source>Use 'default({0})'</source>
+        <target state="new">Use 'default({0})'</target>
+        <note />
+      </trans-unit>
       <trans-unit id="if_statement_can_be_simplified">
         <source>'if' statement can be simplified</source>
         <target state="translated">'if' ステートメントは簡素化できます</target>

src/Features/CSharp/Portable/xlf/CSharpFeaturesResources.ko.xlf

@@ -97,6 +97,11 @@
         <target state="translated">접근성 한정자 정렬</target>
         <note />
       </trans-unit>
+      <trans-unit id="Use_default_0">
+        <source>Use 'default({0})'</source>
+        <target state="new">Use 'default({0})'</target>
+        <note />
+      </trans-unit>
       <trans-unit id="if_statement_can_be_simplified">
         <source>'if' statement can be simplified</source>
         <target state="translated">'if' 문을 간단하게 줄일 수 있습니다.</target>

src/Features/CSharp/Portable/xlf/CSharpFeaturesResources.pl.xlf

@@ -97,6 +97,11 @@
         <target state="translated">Sortuj modyfikatory dostępności</target>
         <note />
       </trans-unit>
+      <trans-unit id="Use_default_0">
+        <source>Use 'default({0})'</source>
+        <target state="new">Use 'default({0})'</target>
+        <note />
+      </trans-unit>
       <trans-unit id="if_statement_can_be_simplified">
         <source>'if' statement can be simplified</source>
         <target state="translated">Instrukcja „if” może zostać uproszczona</target>

src/Features/CSharp/Portable/xlf/CSharpFeaturesResources.pt-BR.xlf

@@ -97,6 +97,11 @@
         <target state="translated">Classificar modificadores de acessibilidade</target>
         <note />
       </trans-unit>
+      <trans-unit id="Use_default_0">
+        <source>Use 'default({0})'</source>
+        <target state="new">Use 'default({0})'</target>
+        <note />
+      </trans-unit>
       <trans-unit id="if_statement_can_be_simplified">
         <source>'if' statement can be simplified</source>
         <target state="translated">A instrução 'if' pode ser simplificada</target>

src/Features/CSharp/Portable/xlf/CSharpFeaturesResources.ru.xlf

@@ -97,6 +97,11 @@
         <target state="translated">Сортировать модификаторы доступности</target>
         <note />
       </trans-unit>
+      <trans-unit id="Use_default_0">
+        <source>Use 'default({0})'</source>
+        <target state="new">Use 'default({0})'</target>
+        <note />
+      </trans-unit>
       <trans-unit id="if_statement_can_be_simplified">
         <source>'if' statement can be simplified</source>
         <target state="translated">Оператор if можно упростить</target>

src/Features/CSharp/Portable/xlf/CSharpFeaturesResources.tr.xlf

@@ -97,6 +97,11 @@
         <target state="translated">Erişilebilirlik değiştiricilerini sırala</target>
         <note />
       </trans-unit>
+      <trans-unit id="Use_default_0">
+        <source>Use 'default({0})'</source>
+        <target state="new">Use 'default({0})'</target>
+        <note />
+      </trans-unit>
       <trans-unit id="if_statement_can_be_simplified">
         <source>'if' statement can be simplified</source>
         <target state="translated">'if' deyimi basitleştirilebilir</target>

src/Features/CSharp/Portable/xlf/CSharpFeaturesResources.zh-Hans.xlf

@@ -97,6 +97,11 @@
         <target state="translated">对可访问性修饰符排序</target>
         <note />
       </trans-unit>
+      <trans-unit id="Use_default_0">
+        <source>Use 'default({0})'</source>
+        <target state="new">Use 'default({0})'</target>
+        <note />
+      </trans-unit>
       <trans-unit id="if_statement_can_be_simplified">
         <source>'if' statement can be simplified</source>
         <target state="translated">可简化“if”语句</target>

src/Features/CSharp/Portable/xlf/CSharpFeaturesResources.zh-Hant.xlf

@@ -97,6 +97,11 @@
         <target state="translated">排序協助工具修飾詞</target>
         <note />
       </trans-unit>
+      <trans-unit id="Use_default_0">
+        <source>Use 'default({0})'</source>
+        <target state="new">Use 'default({0})'</target>
+        <note />
+      </trans-unit>
       <trans-unit id="if_statement_can_be_simplified">
         <source>'if' statement can be simplified</source>
         <target state="translated">'if' 陳述式可簡化</target>

src/Features/Core/Portable/CodeFixes/PredefinedCodeFixProviderNames.cs

@@ -53,6 +53,8 @@ internal static class PredefinedCodeFixProviderNames
         public const string Suppression = nameof(Suppression);
         public const string AddOverloads = nameof(AddOverloads);
         public const string AddNew = nameof(AddNew);
+        public const string UseDefaultExpression = nameof(UseDefaultExpression);
+        public const string UseDefaultLiteral = nameof(UseDefaultLiteral);
         public const string UseImplicitType = nameof(UseImplicitType);
         public const string UseExplicitType = nameof(UseExplicitType);
         public const string UseCollectionInitializer = nameof(UseCollectionInitializer);

src/Test/Utilities/Portable/Traits/Traits.cs

@@ -127,6 +127,7 @@ public static class Features
             public const string CodeActionsUseCompoundAssignment = "CodeActions.UseCompoundAssignment";
             public const string CodeActionsUseConditionalExpression = "CodeActions.UseConditionalExpression";
             public const string CodeActionsUseDeconstruction = "CodeActions.UseDeconstruction";
+            public const string CodeActionsUseDefaultExpression = "CodeActions.UseDefaultExpression";
             public const string CodeActionsUseDefaultLiteral = "CodeActions.UseDefaultLiteral";
             public const string CodeActionsUseInferredMemberName = "CodeActions.UseInferredMemberName";
             public const string CodeActionsUseExpressionBody = "CodeActions.UseExpressionBody";