Fill in IRunnerUtilityContext, and add support for v3 runner utility

src/xunit.analyzers/Utility/EmptyRunnerUtilityContext.cs

@@ -0,0 +1,15 @@
+using System;
+
+namespace Xunit.Analyzers;
+
+public class EmptyRunnerUtilityContext : IRunnerUtilityContext
+{
+	EmptyRunnerUtilityContext()
+	{ }
+
+	public static EmptyRunnerUtilityContext Instance { get; } = new();
+
+	public string Platform => "N/A";
+
+	public Version Version { get; } = new();
+}

src/xunit.analyzers/Utility/IRunnerUtilityContext.cs

@@ -1,5 +1,17 @@
+using System;
+
 namespace Xunit.Analyzers;
 
 public interface IRunnerUtilityContext
 {
+	/// <summary>
+	/// Gets a description of the target platform for the runner utility (i.e., "net452"). This is
+	/// typically extracted from the assembly name (i.e., "xunit.runner.utility.net452").
+	/// </summary>
+	string Platform { get; }
+
+	/// <summary>
+	/// Gets the version number of the runner utility assembly.
+	/// </summary>
+	Version Version { get; }
 }

src/xunit.analyzers/Utility/V2RunnerUtilityContext.cs

@@ -25,7 +25,7 @@ public class V2RunnerUtilityContext : IRunnerUtilityContext
 
 	public string Platform { get; }
 
-	public Version Version { get; set; }
+	public Version Version { get; }
 
 	public static V2RunnerUtilityContext? Get(
 		Compilation compilation,

src/xunit.analyzers/Utility/V3RunnerUtilityContext.cs

@@ -0,0 +1,42 @@
+using System;
+using System.Linq;
+using Microsoft.CodeAnalysis;
+
+namespace Xunit.Analyzers;
+
+public class V3RunnerUtilityContext : IRunnerUtilityContext
+{
+	const string assemblyPrefix = "xunit.v3.runner.utility.";
+
+	V3RunnerUtilityContext(
+		string platform,
+		Version version)
+	{
+		Platform = platform;
+		Version = version;
+	}
+
+	/// <inheritdoc/>
+	public string Platform { get; }
+
+	/// <inheritdoc/>
+	public Version Version { get; }
+
+	public static V3RunnerUtilityContext? Get(
+		Compilation compilation,
+		Version? versionOverride = null)
+	{
+		var assembly =
+			compilation
+				.ReferencedAssemblyNames
+				.FirstOrDefault(a => a.Name.StartsWith(assemblyPrefix, StringComparison.OrdinalIgnoreCase));
+
+		if (assembly is null)
+			return null;
+
+		var version = versionOverride ?? assembly.Version;
+		var platform = assembly.Name.Substring(assemblyPrefix.Length);
+
+		return version is null ? null : new(platform, version);
+	}
+}

src/xunit.analyzers/Utility/XunitContext.cs

@@ -10,6 +10,7 @@ public class XunitContext
 {
 	IAssertContext? assert;
 	ICoreContext? core;
+	IRunnerUtilityContext? runnerUtility;
 	static readonly Version v2AbstractionsVersion = new(2, 0, 3);
 
 	XunitContext()
@@ -72,6 +73,19 @@ public ICoreContext Core
 	public bool HasV3References =>
 		V3Assert is not null || V3Core is not null;
 
+	/// <summary>
+	/// Gets a combined view of features available to either v2 runners (linked against xunit.runner.utility.*)
+	/// or v3 runners (linked against xunit.v3.runner.utility.*).
+	/// </summary>
+	public IRunnerUtilityContext RunnerUtility
+	{
+		get
+		{
+			runnerUtility ??= V3RunnerUtility ?? (IRunnerUtilityContext?)V2RunnerUtility ?? EmptyRunnerUtilityContext.Instance;
+			return runnerUtility;
+		}
+	}
+
 	/// <summary>
 	/// Gets information about the reference to xunit.abstractions (v2). If the project does
 	/// not reference v2 Abstractions, then returns <c>null</c>.
@@ -114,6 +128,12 @@ public ICoreContext Core
 	/// </summary>
 	public V3CoreContext? V3Core { get; private set; }
 
+	/// <summary>
+	/// Gets information about the reference to xunit.v3.runner.utility.* (v3). If the project does
+	/// not reference v3 Runner Utility, then returns <c>null</c>.
+	/// </summary>
+	public V3RunnerUtilityContext? V3RunnerUtility { get; private set; }
+
 	/// <summary>
 	/// Used to create a context object for test purposes, which only contains a reference to
 	/// xunit.abstraction (which is always set to version 2.0.3, since it did not float version).