src/Lucene.Net.CodeAnalysis.Dev/LuceneDev1004_ArrayMethodReturnValueCSCodeAnalyzer.cs

using Lucene.Net.CodeAnalysis.Dev.Helpers;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Diagnostics;
using System;
using System.Collections.Generic;
using System.Collections.Immutable;
using System.Linq;
using System.Reflection.Metadata;
using System.Threading;

namespace Lucene.Net.CodeAnalysis.Dev
{
    [DiagnosticAnalyzer(LanguageNames.CSharp)]
    public class LuceneDev1004_ArrayMethodReturnValueCSCodeAnalyzer : DiagnosticAnalyzer
    {
        public const string DiagnosticId = "LuceneDev1004";

        // You can change these strings in the Resources.resx file. If you do not want your analyzer to be localize-able, you can use regular strings for Title and MessageFormat.
        // See https://github.com/dotnet/roslyn/blob/main/docs/analyzers/Localizing%20Analyzers.md for more on localization
        private static readonly LocalizableString Title = new LocalizableResourceString(nameof(Resources.LuceneDev1004_AnalyzerTitle), Resources.ResourceManager, typeof(Resources));
        private static readonly LocalizableString MessageFormat = new LocalizableResourceString(nameof(Resources.LuceneDev1004_AnalyzerMessageFormat), Resources.ResourceManager, typeof(Resources));
        private static readonly LocalizableString Description = new LocalizableResourceString(nameof(Resources.LuceneDev1004_AnalyzerDescription), Resources.ResourceManager, typeof(Resources));
        private const string Category = "Design";

        private static readonly DiagnosticDescriptor Rule = new DiagnosticDescriptor(DiagnosticId, Title, MessageFormat, Category, DiagnosticSeverity.Warning, isEnabledByDefault: true, description: Description);

        public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics { get { return ImmutableArray.Create(Rule); } }

        public override void Initialize(AnalysisContext context)
        {
            context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.Analyze);
            context.EnableConcurrentExecution();

            // TODO: Consider registering other actions that act on syntax instead of or in addition to symbols
            // See https://github.com/dotnet/roslyn/blob/main/docs/analyzers/Analyzer%20Actions%20Semantics.md for more information
            context.RegisterSyntaxNodeAction(AnalyzeNodeCS, SyntaxKind.MethodDeclaration, SyntaxKind.ReturnKeyword);
        }

        private static void AnalyzeNodeCS(SyntaxNodeAnalysisContext context)
        {
            if (context.Node is Microsoft.CodeAnalysis.CSharp.Syntax.MethodDeclarationSyntax methodDeclaration)
            {
                if (methodDeclaration.ReturnType is ArrayTypeSyntax arrayTypeSyntax)
                {
                    if (arrayTypeSyntax.ElementType is PredefinedTypeSyntax predefinedTypeSyntax)
                    {
                        if (predefinedTypeSyntax.Keyword.ValueText != "char")
                            context.ReportDiagnostic(Diagnostic.Create(Rule, arrayTypeSyntax.GetLocation(), arrayTypeSyntax.ToString()));
                    }
                }
            }
        }
    }
}