Added an underscore prefix analyzer

app/SourceCodeRules/SourceCodeRules/AnalyzerReleases.Shipped.md

@@ -6,3 +6,4 @@
 -----------|----------|----------|------------------------
  MWAIS0001 | Usage    | Error    | ProviderAccessAnalyzer
  MWAIS0002 | Naming | Error | ConstStaticAnalyzer
+ MWAIS0003 | Naming | Error | UnderscorePrefixAnalyzer

app/SourceCodeRules/SourceCodeRules/Identifier.cs

@@ -4,4 +4,5 @@ public static class Identifier
 {
     public const string PROVIDER_ACCESS_ANALYZER = $"{Tools.ID_PREFIX}0001";
     public const string CONST_STATIC_ANALYZER = $"{Tools.ID_PREFIX}0002";
+    public const string UNDERSCORE_PREFIX_ANALYZER = $"{Tools.ID_PREFIX}0003";
 }

app/SourceCodeRules/SourceCodeRules/NamingAnalyzers/UnderscorePrefixAnalyzer.cs

@@ -0,0 +1,46 @@
+using System.Collections.Immutable;
+
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Diagnostics;
+
+namespace SourceCodeRules.NamingAnalyzers;
+
+#pragma warning disable RS1038
+[DiagnosticAnalyzer(LanguageNames.CSharp)]
+#pragma warning restore RS1038
+public sealed class UnderscorePrefixAnalyzer : DiagnosticAnalyzer
+{
+    private const string DIAGNOSTIC_ID = Identifier.UNDERSCORE_PREFIX_ANALYZER;
+    
+    private static readonly string TITLE = "Variable names cannot start with underscore";
+    
+    private static readonly string MESSAGE_FORMAT = "The variable name '{0}' starts with an underscore which is not allowed";
+    
+    private static readonly string DESCRIPTION = "Variable names cannot start with an underscore prefix.";
+    
+    private const string CATEGORY = "Naming";
+    
+    private static readonly DiagnosticDescriptor RULE = new(DIAGNOSTIC_ID, TITLE, MESSAGE_FORMAT, CATEGORY, DiagnosticSeverity.Error, isEnabledByDefault: true, description: DESCRIPTION);
+    
+    public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics => [RULE];
+    
+    public override void Initialize(AnalysisContext context)
+    {
+        context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None);
+        context.EnableConcurrentExecution();
+        context.RegisterSyntaxNodeAction(AnalyzeVariableDeclaration, SyntaxKind.VariableDeclarator);
+    }
+    
+    private static void AnalyzeVariableDeclaration(SyntaxNodeAnalysisContext context)
+    {
+        var variableDeclarator = (VariableDeclaratorSyntax)context.Node;
+        var variableName = variableDeclarator.Identifier.Text;
+        if (variableName.StartsWith("_"))
+        {
+            var diagnostic = Diagnostic.Create(RULE, variableDeclarator.Identifier.GetLocation(), variableName);
+            context.ReportDiagnostic(diagnostic);
+        }
+    }
+}

app/SourceCodeRules/SourceCodeRules/NamingCodeFixes/UnderscorePrefixCodeFixProvider.cs

@@ -0,0 +1,54 @@
+using System.Collections.Immutable;
+using System.Composition;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CodeActions;
+using Microsoft.CodeAnalysis.CodeFixes;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Rename;
+
+namespace SourceCodeRules.NamingCodeFixes;
+
+[ExportCodeFixProvider(LanguageNames.CSharp, Name = nameof(UnderscorePrefixCodeFixProvider)), Shared]
+public sealed class UnderscorePrefixCodeFixProvider : CodeFixProvider
+{
+    public override ImmutableArray<string> FixableDiagnosticIds => [Identifier.UNDERSCORE_PREFIX_ANALYZER];
+    
+    public override FixAllProvider GetFixAllProvider() => WellKnownFixAllProviders.BatchFixer;
+    
+    public override async Task RegisterCodeFixesAsync(CodeFixContext context)
+    {
+        var root = await context.Document.GetSyntaxRootAsync(context.CancellationToken);
+        var diagnostic = context.Diagnostics.First();
+        var diagnosticSpan = diagnostic.Location.SourceSpan;
+        var declaration = root?.FindToken(diagnosticSpan.Start).Parent?.AncestorsAndSelf().OfType<VariableDeclaratorSyntax>().First();
+        if (declaration is null)
+            return;
+        
+        context.RegisterCodeFix(
+            CodeAction.Create(
+                title: "Remove underscore prefix", 
+                createChangedDocument: c => this.RemoveUnderscorePrefixAsync(context.Document, declaration, c), 
+                equivalenceKey: nameof(UnderscorePrefixCodeFixProvider)), 
+            diagnostic);
+    }
+    
+    private async Task<Document> RemoveUnderscorePrefixAsync(Document document, VariableDeclaratorSyntax declarator, CancellationToken cancellationToken)
+    {
+        var oldName = declarator.Identifier.Text;
+        var newName = oldName.TrimStart('_');
+        
+        var semanticModel = await document.GetSemanticModelAsync(cancellationToken);
+        var symbol = semanticModel?.GetDeclaredSymbol(declarator, cancellationToken);
+        if (symbol is null)
+            return document;
+        
+        var solution = document.Project.Solution;
+        var newSolution = await Renamer.RenameSymbolAsync(solution, symbol, new SymbolRenameOptions(), newName, cancellationToken);
+        
+        return newSolution.GetDocument(document.Id) ?? document;
+    }
+}