feat: Add code fix for INTL0301/INTL0302 (FavorDirectoryEnumerationCalls)

- Add public DiagnosticId301/302 constants to the analyzer (required by the code fix)
- Add FavorDirectoryEnumerationCalls CodeFixProvider that renames GetFiles/GetDirectories
  to their lazy Enumerate* counterparts, wrapping with .ToArray() when the result is
  assigned to / returned as string[]
- Add System.Runtime metadata reference to test helper to support LINQ-based code fixes
- Add 4 code fix tests covering both rename and .ToArray() wrapping scenarios

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: BenjaminMichaelis

IntelliTect.Analyzer/IntelliTect.Analyzer.CodeFixes/FavorDirectoryEnumerationCalls.cs

@@ -0,0 +1,207 @@
+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;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Formatting;
+using Microsoft.CodeAnalysis.Text;
+
+namespace IntelliTect.Analyzer.CodeFixes
+{
+    [ExportCodeFixProvider(LanguageNames.CSharp, Name = nameof(FavorDirectoryEnumerationCalls))]
+    [Shared]
+    public class FavorDirectoryEnumerationCalls : CodeFixProvider
+    {
+        private const string TitleGetFiles = "Use Directory.EnumerateFiles";
+        private const string TitleGetDirectories = "Use Directory.EnumerateDirectories";
+
+        public sealed override ImmutableArray<string> FixableDiagnosticIds =>
+            ImmutableArray.Create(
+                Analyzers.FavorDirectoryEnumerationCalls.DiagnosticId301,
+                Analyzers.FavorDirectoryEnumerationCalls.DiagnosticId302);
+
+        public sealed override FixAllProvider GetFixAllProvider() =>
+            WellKnownFixAllProviders.BatchFixer;
+
+        public sealed override async Task RegisterCodeFixesAsync(CodeFixContext context)
+        {
+            SyntaxNode root = await context.Document.GetSyntaxRootAsync(context.CancellationToken).ConfigureAwait(false);
+
+            Diagnostic diagnostic = context.Diagnostics.First();
+            TextSpan diagnosticSpan = diagnostic.Location.SourceSpan;
+
+            // The diagnostic span covers the full invocation expression (Directory.GetFiles(...))
+            InvocationExpressionSyntax invocation = root.FindToken(diagnosticSpan.Start)
+                .Parent.AncestorsAndSelf()
+                .OfType<InvocationExpressionSyntax>()
+                .First();
+
+            bool isGetFiles = diagnostic.Id == Analyzers.FavorDirectoryEnumerationCalls.DiagnosticId301;
+            string title = isGetFiles ? TitleGetFiles : TitleGetDirectories;
+            string newMethodName = isGetFiles ? "EnumerateFiles" : "EnumerateDirectories";
+
+            context.RegisterCodeFix(
+                CodeAction.Create(
+                    title: title,
+                    createChangedDocument: c => UseEnumerationMethodAsync(context.Document, invocation, newMethodName, c),
+                    equivalenceKey: title),
+                diagnostic);
+        }
+
+        private static async Task<Document> UseEnumerationMethodAsync(
+            Document document,
+            InvocationExpressionSyntax invocation,
+            string newMethodName,
+            CancellationToken cancellationToken)
+        {
+            var memberAccess = (MemberAccessExpressionSyntax)invocation.Expression;
+
+            SemanticModel semanticModel = await document.GetSemanticModelAsync(cancellationToken).ConfigureAwait(false);
+
+            // Rename: Directory.GetFiles(...) → Directory.EnumerateFiles(...)
+            InvocationExpressionSyntax renamedInvocation = invocation.WithExpression(
+                memberAccess.WithName(SyntaxFactory.IdentifierName(newMethodName)));
+
+            ExpressionSyntax replacement = NeedsToArrayWrapper(invocation, semanticModel, cancellationToken)
+                // Wrap as Directory.EnumerateFiles(...).ToArray()
+                ? SyntaxFactory.InvocationExpression(
+                    SyntaxFactory.MemberAccessExpression(
+                        SyntaxKind.SimpleMemberAccessExpression,
+                        renamedInvocation,
+                        SyntaxFactory.IdentifierName("ToArray")))
+                : renamedInvocation;
+
+            SyntaxNode oldRoot = await document.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
+            SyntaxNode newRoot = oldRoot.ReplaceNode(invocation, replacement.WithAdditionalAnnotations(Formatter.Annotation));
+
+            if (replacement != renamedInvocation && newRoot is CompilationUnitSyntax compilationUnit)
+            {
+                newRoot = AddUsingIfMissing(compilationUnit, "System.Linq");
+            }
+
+            return document.WithSyntaxRoot(newRoot);
+        }
+
+        private static bool NeedsToArrayWrapper(
+            InvocationExpressionSyntax invocation,
+            SemanticModel semanticModel,
+            CancellationToken ct)
+        {
+            SyntaxNode parent = invocation.Parent;
+
+            // string[] files = Directory.GetFiles(...)  or field/property initializer
+            if (parent is EqualsValueClauseSyntax equalsValue)
+            {
+                // Local variable or field: string[] files = ... / private string[] _files = ...
+                if (equalsValue.Parent is VariableDeclaratorSyntax
+                    && equalsValue.Parent.Parent is VariableDeclarationSyntax declaration
+                    && semanticModel.GetTypeInfo(declaration.Type, ct).Type is IArrayTypeSymbol)
+                {
+                    return true;
+                }
+
+                // Property initializer: public string[] Files { get; } = Directory.GetFiles(...)
+                if (equalsValue.Parent is PropertyDeclarationSyntax property
+                    && semanticModel.GetTypeInfo(property.Type, ct).Type is IArrayTypeSymbol)
+                {
+                    return true;
+                }
+            }
+
+            // files = Directory.GetFiles(...)
+            if (parent is AssignmentExpressionSyntax assignment
+                && semanticModel.GetTypeInfo(assignment.Left, ct).Type is IArrayTypeSymbol)
+            {
+                return true;
+            }
+
+            // return Directory.GetFiles(...)  in a method or local function returning string[]
+            if (parent is ReturnStatementSyntax)
+            {
+                TypeSyntax returnType = invocation.Ancestors()
+                    .Select(a => a switch
+                    {
+                        MethodDeclarationSyntax m => m.ReturnType,
+                        LocalFunctionStatementSyntax lf => lf.ReturnType,
+                        _ => null
+                    })
+                    .FirstOrDefault(t => t != null);
+                if (returnType != null
+                    && semanticModel.GetTypeInfo(returnType, ct).Type is IArrayTypeSymbol)
+                {
+                    return true;
+                }
+            }
+
+            // Expression-bodied members: string[] GetFiles() => Directory.GetFiles(...)
+            if (parent is ArrowExpressionClauseSyntax arrow)
+            {
+                TypeSyntax returnType = arrow.Parent switch
+                {
+                    MethodDeclarationSyntax m => m.ReturnType,
+                    LocalFunctionStatementSyntax lf => lf.ReturnType,
+                    PropertyDeclarationSyntax p => p.Type,
+                    _ => null
+                };
+                if (returnType != null && semanticModel.GetTypeInfo(returnType, ct).Type is IArrayTypeSymbol)
+                {
+                    return true;
+                }
+            }
+
+            // SomeMethod(Directory.GetFiles(...)) where the parameter type is string[]
+            if (parent is ArgumentSyntax argument
+                && argument.Parent is ArgumentListSyntax argumentList
+                && argumentList.Parent is InvocationExpressionSyntax outerInvocation
+                && semanticModel.GetSymbolInfo(outerInvocation, ct).Symbol is IMethodSymbol outerMethod)
+            {
+                IParameterSymbol targetParam;
+
+                // Named argument: SomeMethod(param: Directory.GetFiles(...))
+                if (argument.NameColon != null)
+                {
+                    string paramName = argument.NameColon.Name.Identifier.Text;
+                    targetParam = outerMethod.Parameters.FirstOrDefault(p => p.Name == paramName);
+                }
+                else
+                {
+                    int argIndex = argumentList.Arguments.IndexOf(argument);
+                    int paramCount = outerMethod.Parameters.Length;
+                    targetParam = argIndex >= 0 && argIndex < paramCount
+                        ? outerMethod.Parameters[argIndex]
+                        : argIndex >= 0 && paramCount > 0 && outerMethod.Parameters[paramCount - 1].IsParams
+                            ? outerMethod.Parameters[paramCount - 1]
+                            : null;
+                }
+
+                if (targetParam?.Type is IArrayTypeSymbol)
+                {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        private static SyntaxNode AddUsingIfMissing(CompilationUnitSyntax root, string namespaceName)
+        {
+            bool alreadyPresent = root.Usings.Any(u => u.Name?.ToString() == namespaceName);
+            if (alreadyPresent)
+            {
+                return root;
+            }
+
+            UsingDirectiveSyntax newUsing = SyntaxFactory.UsingDirective(
+                SyntaxFactory.ParseName(namespaceName))
+                .NormalizeWhitespace()
+                .WithTrailingTrivia(SyntaxFactory.ElasticCarriageReturnLineFeed);
+
+            return root.AddUsings(newUsing);
+        }
+    }
+}