Add MergeUsageAnalyzer to detect legacy merge service usage

- Implemented MergeUsageAnalyzer to flag usage of AdvisoryMergeService and AddMergeModule.
- Created AnalyzerReleases.Shipped.md and AnalyzerReleases.Unshipped.md for release documentation.
- Added tests for MergeUsageAnalyzer to ensure correct diagnostics for various scenarios.
- Updated project files for analyzers and tests to include necessary dependencies and configurations.
- Introduced a sample report structure for scanner output.

src/Concelier/__Tests/StellaOps.Concelier.Merge.Analyzers.Tests/MergeUsageAnalyzerTests.cs

@@ -0,0 +1,165 @@
+using System;
+using System.Collections.Generic;
+using System.Collections.Immutable;
+using System.Linq;
+using System.Reflection;
+using System.Threading.Tasks;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.Diagnostics;
+
+namespace StellaOps.Concelier.Merge.Analyzers.Tests;
+
+public sealed class MergeUsageAnalyzerTests
+{
+    [Fact]
+    public async Task ReportsDiagnostic_ForAdvisoryMergeServiceInstantiation()
+    {
+        const string source = """
+            using StellaOps.Concelier.Merge.Services;
+
+            namespace Sample.App;
+
+            public sealed class Demo
+            {
+                public void Run()
+                {
+                    var merge = new AdvisoryMergeService();
+                }
+            }
+            """;
+
+        var diagnostics = await AnalyzeAsync(source, "Sample.App");
+        Assert.Contains(diagnostics, d => d.Id == MergeUsageAnalyzer.DiagnosticId && d.GetMessage().Contains("AdvisoryMergeService", StringComparison.Ordinal));
+    }
+
+    [Fact]
+    public async Task ReportsDiagnostic_ForAddMergeModuleInvocation()
+    {
+        const string source = """
+            using Microsoft.Extensions.Configuration;
+            using Microsoft.Extensions.DependencyInjection;
+            using StellaOps.Concelier.Merge;
+
+            namespace Sample.Services;
+
+            public static class Installer
+            {
+                public static void Configure(IServiceCollection services, IConfiguration configuration)
+                {
+                    services.AddMergeModule(configuration);
+                }
+            }
+            """;
+
+        var diagnostics = await AnalyzeAsync(source, "Sample.Services");
+        Assert.Contains(diagnostics, d => d.Id == MergeUsageAnalyzer.DiagnosticId && d.GetMessage().Contains("AddMergeModule", StringComparison.Ordinal));
+    }
+
+    [Fact]
+    public async Task ReportsDiagnostic_ForFieldDeclaration()
+    {
+        const string source = """
+            using StellaOps.Concelier.Merge.Services;
+
+            namespace Sample.Library;
+
+            public sealed class Demo
+            {
+                private AdvisoryMergeService? _mergeService;
+            }
+            """;
+
+        var diagnostics = await AnalyzeAsync(source, "Sample.Library");
+        Assert.Contains(diagnostics, d => d.Id == MergeUsageAnalyzer.DiagnosticId);
+    }
+
+    [Fact]
+    public async Task DoesNotReportDiagnostic_InsideMergeAssembly()
+    {
+        const string source = """
+            using StellaOps.Concelier.Merge.Services;
+
+            namespace StellaOps.Concelier.Merge.Internal;
+
+            internal static class MergeDiagnostics
+            {
+                public static AdvisoryMergeService Create() => new AdvisoryMergeService();
+            }
+            """;
+
+        var diagnostics = await AnalyzeAsync(source, "StellaOps.Concelier.Merge");
+        Assert.DoesNotContain(diagnostics, d => d.Id == MergeUsageAnalyzer.DiagnosticId);
+    }
+
+    [Fact]
+    public async Task ReportsDiagnostic_ForTypeOfUsage()
+    {
+        const string source = """
+            using System;
+            using StellaOps.Concelier.Merge.Services;
+
+            namespace Sample.TypeOf;
+
+            public static class Demo
+            {
+                public static Type TargetType => typeof(AdvisoryMergeService);
+            }
+            """;
+
+        var diagnostics = await AnalyzeAsync(source, "Sample.TypeOf");
+        Assert.Contains(diagnostics, d => d.Id == MergeUsageAnalyzer.DiagnosticId);
+    }
+
+    private static async Task<ImmutableArray<Diagnostic>> AnalyzeAsync(string source, string assemblyName)
+    {
+        var compilation = CSharpCompilation.Create(
+            assemblyName,
+            new[]
+            {
+                CSharpSyntaxTree.ParseText(source),
+                CSharpSyntaxTree.ParseText(Stubs)
+            },
+            CreateMetadataReferences(),
+            new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary));
+
+        var analyzer = new MergeUsageAnalyzer();
+        var compilationWithAnalyzers = compilation.WithAnalyzers(ImmutableArray.Create<DiagnosticAnalyzer>(analyzer));
+        return await compilationWithAnalyzers.GetAnalyzerDiagnosticsAsync();
+    }
+
+    private static IEnumerable<MetadataReference> CreateMetadataReferences()
+    {
+        yield return MetadataReference.CreateFromFile(typeof(object).GetTypeInfo().Assembly.Location);
+        yield return MetadataReference.CreateFromFile(typeof(Enumerable).GetTypeInfo().Assembly.Location);
+    }
+
+    private const string Stubs = """
+        namespace Microsoft.Extensions.DependencyInjection
+        {
+            public interface IServiceCollection { }
+        }
+
+        namespace Microsoft.Extensions.Configuration
+        {
+            public interface IConfiguration { }
+        }
+
+        namespace StellaOps.Concelier.Merge.Services
+        {
+            public sealed class AdvisoryMergeService { }
+        }
+
+        namespace StellaOps.Concelier.Merge
+        {
+            public static class MergeServiceCollectionExtensions
+            {
+                public static void AddMergeModule(
+                    this Microsoft.Extensions.DependencyInjection.IServiceCollection services,
+                    Microsoft.Extensions.Configuration.IConfiguration configuration)
+                {
+                }
+            }
+        }
+        """;
+}