Update config handling for new MTP API and null safety

Refactor to use Microsoft.Testing.Platform.Configurations.IConfiguration instead of Microsoft.Extensions.Configuration.IConfiguration. Make platform configuration nullable throughout, updating diagnostics and test module resolution logic to handle nulls safely. Remove exception on missing configuration in provider registration. Improves compatibility with latest MTP and robustness when coverage is not enabled.

Author: Bertk

src/coverlet.MTP/CoverletExtensionCollector.cs

@@ -13,7 +13,6 @@
 using Microsoft.Testing.Platform.Extensions.TestHostControllers;
 using Coverlet.MTP.CommandLine;
 using Coverlet.Core.Instrumentation;
-using Microsoft.Extensions.Configuration;
 
 namespace coverlet.Extension.Collector
 {
@@ -25,7 +24,7 @@ internal sealed class CoverletExtensionCollector : ITestHostProcessLifetimeHandl
     private readonly CoverletLoggerAdapter _logger;
     private readonly CoverletExtensionConfiguration _configuration;
     private IServiceProvider? _serviceProvider;
-    private readonly Microsoft.Extensions.Configuration.IConfiguration _platformConfiguration;
+    private readonly Microsoft.Testing.Platform.Configurations.IConfiguration? _platformConfiguration;
     private Coverage? _coverage;
     private readonly Microsoft.Testing.Platform.Logging.ILoggerFactory _loggerFactory;
     private readonly Microsoft.Testing.Platform.CommandLine.ICommandLineOptions _commandLineOptions;
@@ -51,15 +50,16 @@ internal sealed class CoverletExtensionCollector : ITestHostProcessLifetimeHandl
     public CoverletExtensionCollector(
       Microsoft.Testing.Platform.Logging.ILoggerFactory loggerFactory,
       Microsoft.Testing.Platform.CommandLine.ICommandLineOptions commandLineOptions,
-      Microsoft.Extensions.Configuration.IConfiguration configuration)
+      Microsoft.Testing.Platform.Configurations.IConfiguration? configuration)
     {
       _loggerFactory = loggerFactory ?? throw new ArgumentNullException(nameof(loggerFactory));
       _commandLineOptions = commandLineOptions ?? throw new ArgumentNullException(nameof(commandLineOptions));
-      _platformConfiguration = configuration ?? throw new ArgumentNullException(nameof(configuration));
+      _platformConfiguration = configuration; // Allow null - coverage flag checked first
       _configuration = new CoverletExtensionConfiguration();
       _logger = new CoverletLoggerAdapter(_loggerFactory);
 
-      // Allow attaching debugger via environment variable
+      // Only run diagnostics if coverage will be enabled
+      // The actual check happens in BeforeTestHostProcessStartAsync
       AttachDebuggerIfRequested();
 
       LogDiagnostic("CoverletExtensionCollector constructor called");
@@ -241,6 +241,11 @@ Task ITestHostProcessLifetimeHandler.BeforeTestHostProcessStartAsync(Cancellatio
     /// </summary>
     private void LogConfigurationDiagnostics()
     {
+      if (_platformConfiguration == null)
+      {
+        LogDiagnostic("Platform Configuration: null (coverage not enabled)");
+        return;
+      }
       LogDiagnostic("Platform Configuration values:");
       try
       {
@@ -260,11 +265,20 @@ private void LogConfigurationDiagnostics()
           LogDiagnostic($"  [{key}] = {value ?? "(null)"}");
         }
 
-        // Log all configuration children if accessible
-        IEnumerable<IConfigurationSection> children = _platformConfiguration.GetChildren();
-        foreach (IConfigurationSection child in children)
+        // Try to enumerate known configuration keys (as a fallback)
+        string[] knownKeys = new[]
+        {
+          "TestModule",
+          "TestHostController:Mode",
+          "TestHost:Path",
+          "TestAssembly",
+          "TargetPath"
+        };
+
+        foreach (string key in knownKeys)
         {
-          LogDiagnostic($"  Config child: {child.Key} = {child.Value ?? "(section)"}");
+          string? value = _platformConfiguration[key];
+          LogDiagnostic($"  Config key: {key} = {value ?? "(null)"}");
         }
       }
       catch (Exception ex)
@@ -353,22 +367,25 @@ private void LogParsedConfigurationDiagnostics()
     {
       LogDiagnostic("Resolving test module path...");
 
-      // Try platform configuration first
-      string? testModule = _platformConfiguration["TestModule"];
-      LogDiagnostic($"  From config 'TestModule': {testModule ?? "(null)"}");
-      if (!string.IsNullOrEmpty(testModule) && File.Exists(testModule))
+      // Only try platform configuration if it exists
+      if (_platformConfiguration != null)
       {
-        LogDiagnostic($"  -> Using TestModule from config");
-        return testModule;
-      }
+        string? testModule = _platformConfiguration["TestModule"];
+        LogDiagnostic($"  From config 'TestModule': {testModule ?? "(null)"}");
+        if (!string.IsNullOrEmpty(testModule) && File.Exists(testModule))
+        {
+          LogDiagnostic($"  -> Using TestModule from config");
+          return testModule;
+        }
 
-      // Try TestHost:Path
-      testModule = _platformConfiguration["TestHost:Path"];
-      LogDiagnostic($"  From config 'TestHost:Path': {testModule ?? "(null)"}");
-      if (!string.IsNullOrEmpty(testModule) && File.Exists(testModule))
-      {
-        LogDiagnostic($"  -> Using TestHost:Path from config");
-        return testModule;
+        // Try TestHost:Path
+        testModule = _platformConfiguration["TestHost:Path"];
+        LogDiagnostic($"  From config 'TestHost:Path': {testModule ?? "(null)"}");
+        if (!string.IsNullOrEmpty(testModule) && File.Exists(testModule))
+        {
+          LogDiagnostic($"  -> Using TestHost:Path from config");
+          return testModule;
+        }
       }
 
       // Try to get from command line arguments

src/coverlet.MTP/CoverletExtensionProvider.cs

@@ -4,10 +4,10 @@
 using coverlet.Extension.Collector;
 using Coverlet.MTP.CommandLine;
 using Microsoft.Testing.Platform.Builder;
+using Microsoft.Testing.Platform.Configurations;
 using Microsoft.Testing.Platform.Extensions.TestHostControllers;
 using Microsoft.Testing.Platform.Services;
 using Microsoft.Testing.Extensions.Diagnostics;
-using Microsoft.Extensions.Configuration;
 
 namespace coverlet.Extension
 {
@@ -26,10 +26,9 @@ public static void AddCoverletExtensionProvider(this ITestApplicationBuilder bui
       builder.TestHostControllers.AddProcessLifetimeHandler(static serviceProvider
           =>
           {
-            if (serviceProvider.GetConfiguration() is not IConfiguration configuration)
-            {
-              throw new ArgumentNullException(nameof(configuration), "Configuration cannot be null.");
-            }
+            // Configuration may be null when coverlet-coverage is not enabled.
+            // The collector checks for --coverlet-coverage flag before using configuration.
+            IConfiguration configuration = serviceProvider.GetConfiguration();
             return new CoverletExtensionCollector(
                 serviceProvider.GetLoggerFactory(),
                 serviceProvider.GetCommandLineOptions(),