Prefer 'is null' over '== null'

Author: manfred-brands

.editorconfig

@@ -13,4 +13,18 @@ indent_size = 4
 
 [*.{proj,csproj,vcxproj,xproj,json,config,nuspec,xml,yml}]
 indent_style = space
-indent_size = 2
+indent_size = 2
+
+##########################################################################################
+# Analysis settings
+
+[*.cs]
+# CSharpIsNull Analyzers
+
+dotnet_style_prefer_is_null_check_over_reference_equality_method = true:warning
+
+# CSIsNull001: Use `is null` for null checks
+dotnet_diagnostic.CSIsNull001.severity = warning
+
+# CSIsNull002: Use `is object` for non-null checks
+dotnet_diagnostic.CSIsNull002.severity = warning

src/Directory.Build.props

@@ -43,6 +43,7 @@
     <ItemGroup>
         <PackageReference Include="StyleCop.Analyzers.Unstable" Version="1.2.0.556" PrivateAssets="all" />
         <GlobalAnalyzerConfigFiles Include="$(MSBuildThisFileDirectory)/StyleCop.Analyzers.globalconfig" />
+        <PackageReference Include="CSharpIsNullAnalyzer" Version="0.1.593" PrivateAssets="all" />
     </ItemGroup>
 
 </Project>

src/NUnitCommon/nunit.agent.core.tests/Drivers/NotRunnableFrameworkDriverTests.cs

@@ -100,7 +100,7 @@ private IFrameworkDriver GetDriver(string filePath)
         private static string? GetSkipReason(XmlNode result)
         {
             var propNode = result.SelectSingleNode(string.Format("properties/property[@name='{0}']", PropertyNames.SkipReason));
-            return propNode == null ? null : propNode.GetAttribute("value");
+            return propNode is null ? null : propNode.GetAttribute("value");
         }
 
         private class NullListener : ITestEventListener

src/NUnitCommon/nunit.agent.core.tests/Runners/DomainManagerStaticTests.cs

@@ -93,7 +93,7 @@ public static void ApplicationBaseTests(string filePath, string? appBase, string
             expected = TestPath(expected);
 
             var package = new TestPackage(filePath);
-            if (appBase != null)
+            if (appBase is not null)
                 package.Settings["BasePath"] = appBase;
 
             Assert.That(DomainManager.GetApplicationBase(package), Is.SamePath(expected));
@@ -124,7 +124,7 @@ public static void ConfigFileTests(string filePath, string appBase, string? conf
             expected = TestPath(expected);
 
             var package = new TestPackage(filePath);
-            if (configSetting != null)
+            if (configSetting is not null)
                 package.Settings["ConfigurationFile"] = configSetting;
 
             Assert.That(DomainManager.GetConfigFile(appBase, package), Is.EqualTo(expected));
@@ -138,7 +138,7 @@ public static void ConfigFileTests(string filePath, string appBase, string? conf
         [return: NotNullIfNotNull(nameof(path))]
         private static string? TestPath(string? path)
         {
-            if (path != null && Path.DirectorySeparatorChar != '/')
+            if (path is not null && Path.DirectorySeparatorChar != '/')
             {
                 path = path.Replace('/', Path.DirectorySeparatorChar);
                 if (path[0] == Path.DirectorySeparatorChar)

src/NUnitCommon/nunit.agent.core.tests/Runners/TestAgentRunnerTests.cs

@@ -35,7 +35,7 @@ public void Initialize()
         [TearDown]
         public void Cleanup()
         {
-            if (_runner != null)
+            if (_runner is not null)
                 _runner.Dispose();
         }
 

src/NUnitCommon/nunit.agent.core/AgentOptions.cs

@@ -55,10 +55,10 @@ public AgentOptions(params string[] args)
 
                     if (optionTakesValue)
                     {
-                        if (val == null && index + 1 < args.Length)
+                        if (val is null && index + 1 < args.Length)
                             val = args[++index];
 
-                        if (val == null)
+                        if (val is null)
                             throw new Exception($"Option requires a value: {arg}");
                     }
                     else if (delim > 0)

src/NUnitCommon/nunit.agent.core/Agents/RemoteTestAgent.cs

@@ -32,13 +32,13 @@ public RemoteTestAgent(Guid agentId) : base(agentId)
 
         public override bool Start()
         {
-            Guard.OperationValid(Transport != null, "Transport must be set before calling Start().");
+            Guard.OperationValid(Transport is not null, "Transport must be set before calling Start().");
             return Transport.Start();
         }
 
         public override void Stop()
         {
-            Guard.OperationValid(Transport != null, "Transport must be set before calling Stop().");
+            Guard.OperationValid(Transport is not null, "Transport must be set before calling Stop().");
             Transport.Stop();
         }
 

src/NUnitCommon/nunit.agent.core/Communication/Transports/Remoting/TestAgentRemotingTransport.cs

@@ -70,7 +70,7 @@ public bool Start()
 
         public void Stop()
         {
-            Guard.OperationValid(_channel != null, "Channel is not open");
+            Guard.OperationValid(_channel is not null, "Channel is not open");
 
             log.Info("Stopping");
 

src/NUnitCommon/nunit.agent.core/Drivers/DriverService.cs

@@ -56,7 +56,7 @@ public IFrameworkDriver GetDriver(AppDomain domain, TestPackage package, string
             if (!PathUtils.IsAssemblyFileType(assemblyPath))
                 return new InvalidAssemblyFrameworkDriver(assemblyPath, package.ID, "File type is not supported");
 
-            if (targetFramework != null)
+            if (targetFramework is not null)
             {
                 // This takes care of an issue with Roslyn. It may get fixed, but we still
                 // have to deal with assemblies having this setting. I'm assuming that

src/NUnitCommon/nunit.agent.core/Drivers/NUnitFrameworkApi2009.cs

@@ -72,7 +72,7 @@ public string Load(string testAssemblyPath, IDictionary<string, object> settings
                         null,
                         null).ShouldNotBeNull();
                 }
-                catch (BadImageFormatException ex) when (requestedRuntime != null)
+                catch (BadImageFormatException ex) when (requestedRuntime is not null)
                 {
                     throw new NUnitEngineException($"Requested runtime {requestedRuntime} is not suitable for use with test assembly {_testAssemblyPath}", ex);
                 }
@@ -113,7 +113,7 @@ public string Explore(string filter)
 
             private void CheckLoadWasCalled()
             {
-                if (_frameworkController == null)
+                if (_frameworkController is null)
                     throw new InvalidOperationException(LOAD_MESSAGE);
             }
 

src/NUnitCommon/nunit.agent.core/Drivers/NUnitFrameworkApi2018.cs

@@ -96,7 +96,7 @@ public string Load(string testAssemblyPath, IDictionary<string, object> settings
             _frameworkAssembly = LoadAssembly(_nunitRef);
 
             _frameworkController = CreateInstance(CONTROLLER_TYPE, testAssembly, idPrefix, settings);
-            if (_frameworkController == null)
+            if (_frameworkController is null)
             {
                 log.Error(INVALID_FRAMEWORK_MESSAGE);
                 throw new NUnitEngineException(INVALID_FRAMEWORK_MESSAGE);
@@ -114,14 +114,14 @@ public int CountTestCases(string filter)
         {
             CheckLoadWasCalled();
             object? count = ExecuteMethod(COUNT_METHOD, filter);
-            return count != null ? (int)count : 0;
+            return count is not null ? (int)count : 0;
         }
 
         public string Run(ITestEventListener? listener, string filter)
         {
             CheckLoadWasCalled();
             log.Info("Running {0} - see separate log file", Path.GetFileName(_testAssemblyPath.ShouldNotBeNull()));
-            Action<string>? callback = listener != null ? listener.OnTestEvent : null;
+            Action<string>? callback = listener is not null ? listener.OnTestEvent : null;
             return (string)ExecuteMethod(RUN_METHOD, [typeof(Action<string>), typeof(string)], callback, filter);
         }
 
@@ -146,7 +146,7 @@ public string Explore(string filter)
 
         private void CheckLoadWasCalled()
         {
-            if (_frameworkController == null)
+            if (_frameworkController is null)
                 throw new InvalidOperationException(LOAD_MESSAGE);
         }
 
@@ -164,7 +164,7 @@ private Assembly LoadAssembly(string assemblyPath)
             try
             {
                 assembly = _assemblyLoadContext?.LoadFromAssemblyPath(assemblyPath)!;
-                if (assembly == null)
+                if (assembly is null)
                     throw new Exception("LoadFromAssemblyPath returned null");
             }
             catch (Exception e)
@@ -185,7 +185,7 @@ private Assembly LoadAssembly(AssemblyName assemblyName)
             try
             {
                 assembly = _assemblyLoadContext?.LoadFromAssemblyName(assemblyName)!;
-                if (assembly == null)
+                if (assembly is null)
                     throw new Exception("LoadFromAssemblyName returned null");
             }
             catch (Exception e)
@@ -227,7 +227,7 @@ private object ExecuteMethod(string methodName, Type[] ptypes, params object?[]
 
         private object ExecuteMethod(MethodInfo? method, params object?[] args)
         {
-            if (method == null)
+            if (method is null)
                 throw new NUnitEngineException(INVALID_FRAMEWORK_MESSAGE);
 
             log.Debug($"Executing {method.DeclaringType}.{method.Name}");

src/NUnitCommon/nunit.agent.core/Drivers/NUnitFrameworkDriver.cs

@@ -133,7 +133,7 @@ public string Load(string testAssemblyPath, IDictionary<string, object> settings
         /// <returns>An Xml string representing the result</returns>
         public string Run(ITestEventListener? listener, string filter)
         {
-            return _api.Run(listener != null ? new EventInterceptor(listener) : null, filter);
+            return _api.Run(listener is not null ? new EventInterceptor(listener) : null, filter);
         }
 
         /// <summary>

src/NUnitCommon/nunit.agent.core/Runners/DomainDetailsBuilder.cs

@@ -23,7 +23,7 @@ internal static class DomainDetailsBuilder
         public static string DetailsFor(AppDomain domain, string? errMsg = null)
         {
             var sb = new StringBuilder();
-            if (errMsg != null)
+            if (errMsg is not null)
                 sb.AppendLine(errMsg);
 
             try

src/NUnitCommon/nunit.agent.core/Runners/DomainManager.cs

@@ -34,7 +34,7 @@ public AppDomain CreateDomain(TestPackage package)
             AppDomainSetup setup = CreateAppDomainSetup(package);
 
             string hashCode = string.Empty;
-            if (package.Name != null)
+            if (package.Name is not null)
             {
                 hashCode = package.Name.GetHashCode().ToString("x") + "-";
             }
@@ -80,7 +80,7 @@ private AppDomainSetup CreateAppDomainSetup(TestPackage package)
                 // .NET versions greater than v4.0 report as v4.0, so look at
                 // the TargetFrameworkAttribute on the assembly if it exists
                 // If property is null, .NET 4.5+ is not installed, so there is no need
-                if (TargetFrameworkNameProperty != null)
+                if (TargetFrameworkNameProperty is not null)
                 {
                     var frameworkName = package.GetSetting(EnginePackageSettings.ImageTargetFrameworkName, string.Empty);
                     if (frameworkName != string.Empty)
@@ -133,7 +133,7 @@ public void Unload()
                     throw new NUnitEngineUnloadException(msg);
                 }
 
-                if (_unloadException != null)
+                if (_unloadException is not null)
                     throw new NUnitEngineUnloadException("Exception encountered unloading application domain", _unloadException);
             }
 
@@ -231,7 +231,7 @@ private static bool IsExecutable(string? fileName)
             var assemblies = new List<string>();
 
             // All subpackages have full names, but this is a public method in a public class so we have no control.
-            foreach (var package in packages.Where(p => p.FullName != null))
+            foreach (var package in packages.Where(p => p.FullName is not null))
                 assemblies.Add(package.FullName!);
 
             return GetCommonAppBase(assemblies);
@@ -244,10 +244,10 @@ private static bool IsExecutable(string? fileName)
             foreach (string assembly in assemblies)
             {
                 string? dir = Path.GetDirectoryName(Path.GetFullPath(assembly))!;
-                if (commonBase == null)
+                if (commonBase is null)
                     commonBase = dir;
                 else
-                    while (commonBase != null && !PathUtils.SamePathOrUnder(commonBase, dir))
+                    while (commonBase is not null && !PathUtils.SamePathOrUnder(commonBase, dir))
                         commonBase = Path.GetDirectoryName(commonBase)!;
             }
 
@@ -266,7 +266,7 @@ private static bool IsExecutable(string? fileName)
             if (package.GetSetting(EnginePackageSettings.AutoBinPath, binPath == string.Empty))
                 binPath = package.SubPackages.Count > 0
                     ? GetPrivateBinPath(appBase, package.SubPackages)
-                    : package.FullName != null
+                    : package.FullName is not null
                         ? GetPrivateBinPath(appBase, package.FullName)
                         : null;
 
@@ -276,7 +276,7 @@ private static bool IsExecutable(string? fileName)
         public static string? GetPrivateBinPath(string basePath, IList<TestPackage> packages)
         {
             var assemblies = new List<string>();
-            foreach (var package in packages.Where(p => p.FullName != null))
+            foreach (var package in packages.Where(p => p.FullName is not null))
                 assemblies.Add(package.FullName!);
 
             return GetPrivateBinPath(basePath, assemblies);
@@ -292,7 +292,7 @@ private static bool IsExecutable(string? fileName)
                 string? dir = PathUtils.RelativePath(
                     Path.GetFullPath(basePath),
                     Path.GetDirectoryName(Path.GetFullPath(assembly))!);
-                if (dir != null && dir != string.Empty && dir != "." && !dirList.Contains(dir))
+                if (dir is not null && dir != string.Empty && dir != "." && !dirList.Contains(dir))
                 {
                     dirList.Add(dir);
                     if (sb.Length > 0)

src/NUnitCommon/nunit.agent.core/Runners/TestAgentRunner.cs

@@ -42,7 +42,7 @@ public abstract class TestAgentRunner : ITestEngineRunner
         /// </summary>
         public bool IsPackageLoaded
         {
-            get { return LoadResult != null; }
+            get { return LoadResult is not null; }
         }
 
         public TestAgentRunner(TestPackage package)
@@ -89,23 +89,23 @@ public TestEngineResult Explore(TestFilter filter)
         /// <returns>A TestEngineResult.</returns>
         public virtual TestEngineResult Load()
         {
-            Guard.OperationValid(TestDomain != null, "TestDomain is not set");
+            Guard.OperationValid(TestDomain is not null, "TestDomain is not set");
 
             var result = new TestEngineResult();
 
             // The TestAgentRunner constructor guarantees that TestPackage has
             // only a single assembly.
             var assemblyPackage = TestPackage.Select(p => !p.HasSubPackages()).First();
 
-            if (DriverService == null)
+            if (DriverService is null)
                 DriverService = new DriverService();
 
             var testFile = assemblyPackage.FullName!; // We know it's an assembly
 
             string? targetFramework = assemblyPackage.GetSetting(EnginePackageSettings.ImageTargetFrameworkName, (string?)null);
             bool skipNonTestAssemblies = assemblyPackage.GetSetting(EnginePackageSettings.SkipNonTestAssemblies, false);
 
-            if (_assemblyResolver != null && !TestDomain.IsDefaultAppDomain()
+            if (_assemblyResolver is not null && !TestDomain.IsDefaultAppDomain()
                 && assemblyPackage.GetSetting(EnginePackageSettings.ImageRequiresDefaultAppDomainAssemblyResolver, false))
             {
                 // It's OK to do this in the loop because the Add method

src/NUnitCommon/nunit.agent.core/Runners/TestDomainRunner.cs

@@ -28,7 +28,7 @@ public override TestEngineResult Load()
         /// </summary>
         public override void Unload()
         {
-            if (this.TestDomain != null)
+            if (this.TestDomain is not null)
             {
                 _domainManager.Unload(this.TestDomain);
                 this.TestDomain = null;

src/NUnitCommon/nunit.agent.core/TestAssemblyLoadContext.cs

@@ -34,7 +34,7 @@ public TestAssemblyLoadContext(string testAssemblyPath)
             log.Debug("Loading {0} assembly", name);
 
             var loadedAssembly = base.Load(name);
-            if (loadedAssembly != null)
+            if (loadedAssembly is not null)
             {
                 log.Info("Assembly {0} ({1}) is loaded using default base.Load()", name, GetAssemblyLocationInfo(loadedAssembly));
                 return loadedAssembly;
@@ -47,14 +47,14 @@ public TestAssemblyLoadContext(string testAssemblyPath)
                 loadedAssembly = LoadFromAssemblyPath(runtimeResolverPath);
             }
 
-            if (loadedAssembly != null)
+            if (loadedAssembly is not null)
             {
                 log.Info("Assembly {0} ({1}) is loaded using the deps.json info", name, GetAssemblyLocationInfo(loadedAssembly));
                 return loadedAssembly;
             }
 
             loadedAssembly = _resolver.Resolve(this, name);
-            if (loadedAssembly != null)
+            if (loadedAssembly is not null)
             {
                 log.Info("Assembly {0} ({1}) is loaded using the TestAssembliesResolver", name, GetAssemblyLocationInfo(loadedAssembly));
 
@@ -71,7 +71,7 @@ public TestAssemblyLoadContext(string testAssemblyPath)
                 loadedAssembly = LoadFromAssemblyPath(assemblyPath);
             }
 
-            if (loadedAssembly != null)
+            if (loadedAssembly is not null)
             {
                 log.Info("Assembly {0} ({1}) is loaded using base path", name, GetAssemblyLocationInfo(loadedAssembly));
                 return loadedAssembly;