feat: Add CodeFix for LockObjectsMustBeReadonlyAnalyzer (PH2066) with configurable modifier ordering and comprehensive test coverage

Documentation/Diagnostics/PH2066.md

@@ -6,7 +6,7 @@
 | Diagnostic ID | PH2066 |
 | Category  | [Maintainability](../Maintainability.md) |
 | Analyzer | [LockObjectsMustBeReadonlyAnalyzer](https://github.com/philips-software/roslyn-analyzers/blob/main/Philips.CodeAnalysis.MaintainabilityAnalyzers/Maintainability/LockObjectsMustBeReadonlyAnalyzer.cs)
-| CodeFix  | No |
+| CodeFix  | Yes |
 | Severity | Error |
 | Enabled By Default | Yes |
 

Philips.CodeAnalysis.MaintainabilityAnalyzers/Maintainability/LockObjectsMustBeReadonlyCodeFixProvider.cs

@@ -0,0 +1,75 @@
+// © 2025 Koninklijke Philips N.V. See License.md in the project root for license information.
+
+using System.Collections.Immutable;
+using System.Composition;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CodeFixes;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Formatting;
+using Philips.CodeAnalysis.Common;
+
+namespace Philips.CodeAnalysis.MaintainabilityAnalyzers.Maintainability
+{
+	[ExportCodeFixProvider(LanguageNames.CSharp, Name = nameof(LockObjectsMustBeReadonlyCodeFixProvider)), Shared]
+	public class LockObjectsMustBeReadonlyCodeFixProvider : SingleDiagnosticCodeFixProvider<IdentifierNameSyntax>
+	{
+		protected override string Title => "Add readonly modifier to field";
+
+		protected override DiagnosticId DiagnosticId => DiagnosticId.LocksShouldBeReadonly;
+
+		protected override async Task<Document> ApplyFix(Document document, IdentifierNameSyntax node, ImmutableDictionary<string, string> properties, CancellationToken cancellationToken)
+		{
+			SyntaxNode rootNode = await document.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
+			SemanticModel semanticModel = await document.GetSemanticModelAsync(cancellationToken).ConfigureAwait(false);
+
+			// Get the symbol referenced by the identifier
+			SymbolInfo symbolInfo = semanticModel.GetSymbolInfo(node, cancellationToken);
+			if (symbolInfo.Symbol is not IFieldSymbol fieldSymbol)
+			{
+				return document;
+			}
+
+			// Use the field symbol's declaration reference to find the actual syntax node
+			SyntaxReference declaringSyntaxReference = fieldSymbol.DeclaringSyntaxReferences.FirstOrDefault();
+			if (declaringSyntaxReference == null)
+			{
+				return document;
+			}
+
+			SyntaxNode declaringSyntax = await declaringSyntaxReference.GetSyntaxAsync(cancellationToken).ConfigureAwait(false);
+			FieldDeclarationSyntax fieldDeclaration = declaringSyntax.FirstAncestorOrSelf<FieldDeclarationSyntax>();
+
+			if (fieldDeclaration == null)
+			{
+				return document;
+			}
+
+			// Add readonly modifier if not already present
+			SyntaxTokenList modifiers = fieldDeclaration.Modifiers;
+			if (!modifiers.Any(m => m.IsKind(SyntaxKind.ReadOnlyKeyword)))
+			{
+				// Don't offer a fix for volatile fields since volatile and readonly are mutually exclusive
+				if (modifiers.Any(m => m.IsKind(SyntaxKind.VolatileKeyword)))
+				{
+					return document;
+				}
+
+				SyntaxToken readonlyModifier = SyntaxFactory.Token(SyntaxKind.ReadOnlyKeyword);
+
+				// Simply add readonly to the modifiers list and let Roslyn's formatter handle positioning
+				SyntaxTokenList newModifiers = modifiers.Add(readonlyModifier);
+				FieldDeclarationSyntax newFieldDeclaration = fieldDeclaration.WithModifiers(newModifiers)
+					.WithAdditionalAnnotations(Formatter.Annotation);
+
+				SyntaxNode newRoot = rootNode.ReplaceNode(fieldDeclaration, newFieldDeclaration);
+				return document.WithSyntaxRoot(newRoot);
+			}
+
+			return document;
+		}
+	}
+}