Merge pull request #5340 from hvitved/csharp/null-checks

C#: Use `is [not] null` throughout in the extractor

csharp/autobuilder/Semmle.Autobuild.CSharp/CSharpAutobuilder.cs

@@ -97,21 +97,21 @@ namespace Semmle.Autobuild.CSharp
         /// </summary>
         private CSharpBuildStrategy GetCSharpBuildStrategy()
         {
-            if (Options.BuildCommand != null)
+            if (Options.BuildCommand is not null)
                 return CSharpBuildStrategy.CustomBuildCommand;
 
             if (Options.Buildless)
                 return CSharpBuildStrategy.Buildless;
 
-            if (Options.MsBuildArguments != null
-                || Options.MsBuildConfiguration != null
-                || Options.MsBuildPlatform != null
-                || Options.MsBuildTarget != null)
+            if (Options.MsBuildArguments is not null
+                || Options.MsBuildConfiguration is not null
+                || Options.MsBuildPlatform is not null
+                || Options.MsBuildTarget is not null)
             {
                 return CSharpBuildStrategy.MSBuild;
             }
 
-            if (Options.DotNetArguments != null || Options.DotNetVersion != null)
+            if (Options.DotNetArguments is not null || Options.DotNetVersion is not null)
                 return CSharpBuildStrategy.DotNet;
 
             return CSharpBuildStrategy.Auto;

csharp/autobuilder/Semmle.Autobuild.CSharp/DotNetRule.cs

@@ -27,7 +27,7 @@ namespace Semmle.Autobuild.CSharp
                     .SelectMany(p => Enumerators.Singleton(p).Concat(p.IncludedProjects))
                     .OfType<Project>()
                     .FirstOrDefault(p => !p.DotNetProject);
-                if (notDotNetProject != null)
+                if (notDotNetProject is not null)
                 {
                     builder.Log(Severity.Info, "Not using .NET Core because of incompatible project {0}", notDotNetProject);
                     return BuildScript.Failure;
@@ -103,7 +103,7 @@ namespace Semmle.Autobuild.CSharp
 
                     if (!compatibleClr)
                     {
-                        if (env == null)
+                        if (env is null)
                             env = new Dictionary<string, string>();
                         env.Add("UseSharedCompilation", "false");
                     }
@@ -266,7 +266,7 @@ Invoke-Command -ScriptBlock $ScriptBlock";
         }
 
         private static string DotNetCommand(IBuildActions actions, string? dotNetPath) =>
-            dotNetPath != null ? actions.PathCombine(dotNetPath, "dotnet") : "dotnet";
+            dotNetPath is not null ? actions.PathCombine(dotNetPath, "dotnet") : "dotnet";
 
         private static BuildScript GetInfoCommand(IBuildActions actions, string? dotNetPath, IDictionary<string, string>? environment)
         {

csharp/autobuilder/Semmle.Autobuild.CSharp/StandaloneBuildRule.cs

@@ -13,11 +13,11 @@ namespace Semmle.Autobuild.CSharp
             BuildScript GetCommand(string? solution)
             {
                 string standalone;
-                if (builder.CodeQLExtractorLangRoot is object && builder.CodeQlPlatform is object)
+                if (builder.CodeQLExtractorLangRoot is not null && builder.CodeQlPlatform is not null)
                 {
                     standalone = builder.Actions.PathCombine(builder.CodeQLExtractorLangRoot, "tools", builder.CodeQlPlatform, "Semmle.Extraction.CSharp.Standalone");
                 }
-                else if (builder.SemmlePlatformTools is object)
+                else if (builder.SemmlePlatformTools is not null)
                 {
                     standalone = builder.Actions.PathCombine(builder.SemmlePlatformTools, "csharp", "Semmle.Extraction.CSharp.Standalone");
                 }
@@ -29,7 +29,7 @@ namespace Semmle.Autobuild.CSharp
                 var cmd = new CommandBuilder(builder.Actions);
                 cmd.RunCommand(standalone);
 
-                if (solution != null)
+                if (solution is not null)
                     cmd.QuoteArgument(solution);
 
                 cmd.Argument("--references:.");

csharp/autobuilder/Semmle.Autobuild.Shared/AutobuildOptions.cs

@@ -59,7 +59,7 @@ namespace Semmle.Autobuild.Shared
     {
         public static bool AsBool(this string? value, string param, bool defaultValue)
         {
-            if (value == null)
+            if (value is null)
                 return defaultValue;
 
             switch (value.ToLower())
@@ -81,7 +81,7 @@ namespace Semmle.Autobuild.Shared
 
         public static string[] AsListWithExpandedEnvVars(this string? value, IBuildActions actions, string[] defaultValue)
         {
-            if (value == null)
+            if (value is null)
                 return defaultValue;
 
             return value.

csharp/autobuilder/Semmle.Autobuild.Shared/Autobuilder.cs

@@ -176,12 +176,12 @@ namespace Semmle.Autobuild.Shared
 
                 // First look for `.proj` files
                 ret = FindFiles(".proj", f => new Project(this, f))?.ToList();
-                if (ret != null)
+                if (ret is not null)
                     return ret;
 
                 // Then look for `.sln` files
                 ret = FindFiles(".sln", f => new Solution(this, f, false))?.ToList();
-                if (ret != null)
+                if (ret is not null)
                     return ret;
 
                 // Finally look for language specific project files, e.g. `.csproj` files

csharp/autobuilder/Semmle.Autobuild.Shared/BuildActions.cs

@@ -157,11 +157,11 @@ namespace Semmle.Autobuild.Shared
                 UseShellExecute = false,
                 RedirectStandardOutput = redirectStandardOutput
             };
-            if (workingDirectory != null)
+            if (workingDirectory is not null)
                 pi.WorkingDirectory = workingDirectory;
 
             // Environment variables can only be used when not redirecting stdout
-            if (!redirectStandardOutput && environment != null)
+            if (!redirectStandardOutput && environment is not null)
                 environment.ForEach(kvp => pi.Environment[kvp.Key] = kvp.Value);
             return pi;
         }

csharp/autobuilder/Semmle.Autobuild.Shared/BuildCommandAutoRule.cs

@@ -39,7 +39,7 @@ namespace Semmle.Autobuild.Shared
             var scripts = buildScripts.SelectMany(s => extensions.Select(e => s + e));
             var scriptPath = builder.Paths.Where(p => scripts.Any(p.Item1.ToLower().EndsWith)).OrderBy(p => p.Item2).Select(p => p.Item1).FirstOrDefault();
 
-            if (scriptPath == null)
+            if (scriptPath is null)
                 return BuildScript.Failure;
 
             var chmod = new CommandBuilder(builder.Actions);
@@ -55,7 +55,7 @@ namespace Semmle.Autobuild.Shared
 
                 // A specific Visual Studio version may be required
                 var vsTools = MsBuildRule.GetVcVarsBatFile(builder);
-                if (vsTools != null)
+                if (vsTools is not null)
                     command.CallBatFile(vsTools.Path);
 
                 builder.MaybeIndex(command, scriptPath);

csharp/autobuilder/Semmle.Autobuild.Shared/BuildCommandRule.cs

@@ -14,7 +14,7 @@
 
         public BuildScript Analyse(Autobuilder builder, bool auto)
         {
-            if (builder.Options.BuildCommand == null)
+            if (builder.Options.BuildCommand is null)
                 return BuildScript.Failure;
 
             // Custom build commands may require a specific .NET Core version
@@ -24,7 +24,7 @@
 
                     // Custom build commands may require a specific Visual Studio version
                     var vsTools = MsBuildRule.GetVcVarsBatFile(builder);
-                    if (vsTools != null)
+                    if (vsTools is not null)
                         command.CallBatFile(vsTools.Path);
                     builder.MaybeIndex(command, builder.Options.BuildCommand);
 

csharp/autobuilder/Semmle.Autobuild.Shared/BuildScript.cs

@@ -150,13 +150,13 @@ namespace Semmle.Autobuild.Shared
             public override int Run(IBuildActions actions, Action<string, bool> startCallback, Action<int, string, bool> exitCallBack)
             {
                 int ret1;
-                if (s2a != null)
+                if (s2a is not null)
                 {
                     ret1 = s1.Run(actions, startCallback, exitCallBack, out var stdout1);
                     return s2a(stdout1, ret1).Run(actions, startCallback, exitCallBack);
                 }
 
-                if (s2b != null)
+                if (s2b is not null)
                 {
                     ret1 = s1.Run(actions, startCallback, exitCallBack);
                     return s2b(ret1).Run(actions, startCallback, exitCallBack);
@@ -168,7 +168,7 @@ namespace Semmle.Autobuild.Shared
             public override int Run(IBuildActions actions, Action<string, bool> startCallback, Action<int, string, bool> exitCallBack, out IList<string> stdout)
             {
                 var ret1 = s1.Run(actions, startCallback, exitCallBack, out var stdout1);
-                var ret2 = (s2a != null ? s2a(stdout1, ret1) : s2b!(ret1)).Run(actions, startCallback, exitCallBack, out var stdout2);
+                var ret2 = (s2a is not null ? s2a(stdout1, ret1) : s2b!(ret1)).Run(actions, startCallback, exitCallBack, out var stdout2);
                 var @out = new List<string>();
                 @out.AddRange(stdout1);
                 @out.AddRange(stdout2);

csharp/autobuilder/Semmle.Autobuild.Shared/BuildTools.cs

@@ -27,7 +27,7 @@ namespace Semmle.Autobuild.Shared
         public static IEnumerable<VcVarsBatFile> GetCandidateVcVarsFiles(IBuildActions actions)
         {
             var programFilesx86 = actions.GetEnvironmentVariable("ProgramFiles(x86)");
-            if (programFilesx86 == null)
+            if (programFilesx86 is null)
                 yield break;
 
             // Attempt to use vswhere to find installations of Visual Studio

csharp/autobuilder/Semmle.Autobuild.Shared/CommandBuilder.cs

@@ -145,7 +145,7 @@ namespace Semmle.Autobuild.Shared
 
         public CommandBuilder QuoteArgument(string argumentsOpt)
         {
-            if (argumentsOpt != null)
+            if (argumentsOpt is not null)
             {
                 NextArgument();
                 ArgvQuote(argumentsOpt, false);
@@ -161,7 +161,7 @@ namespace Semmle.Autobuild.Shared
 
         public CommandBuilder Argument(string? argumentsOpt)
         {
-            if (argumentsOpt != null)
+            if (argumentsOpt is not null)
             {
                 NextArgument();
                 arguments.Append(argumentsOpt);
@@ -185,7 +185,7 @@ namespace Semmle.Autobuild.Shared
                                           : (exe, null);
 
             NextCommand();
-            if (executable == null)
+            if (executable is null)
             {
                 executable = exe0;
             }

csharp/autobuilder/Semmle.Autobuild.Shared/MsBuildRule.cs

@@ -23,15 +23,15 @@ namespace Semmle.Autobuild.Shared
 
             var vsTools = GetVcVarsBatFile(builder);
 
-            if (vsTools == null && builder.ProjectsOrSolutionsToBuild.Any())
+            if (vsTools is null && builder.ProjectsOrSolutionsToBuild.Any())
             {
                 var firstSolution = builder.ProjectsOrSolutionsToBuild.OfType<ISolution>().FirstOrDefault();
-                vsTools = firstSolution != null
+                vsTools = firstSolution is not null
                                 ? BuildTools.FindCompatibleVcVars(builder.Actions, firstSolution)
                                 : BuildTools.VcVarsAllBatFiles(builder.Actions).OrderByDescending(b => b.ToolsVersion).FirstOrDefault();
             }
 
-            if (vsTools == null && builder.Actions.IsWindows())
+            if (vsTools is null && builder.Actions.IsWindows())
             {
                 builder.Log(Severity.Warning, "Could not find a suitable version of VsDevCmd.bat/vcvarsall.bat");
             }
@@ -85,7 +85,7 @@ namespace Semmle.Autobuild.Shared
 
                 var command = new CommandBuilder(builder.Actions);
 
-                if (vsTools != null)
+                if (vsTools is not null)
                 {
                     command.CallBatFile(vsTools.Path);
                     // `vcvarsall.bat` sets a default Platform environment variable,
@@ -105,9 +105,9 @@ namespace Semmle.Autobuild.Shared
                 var configuration = builder.Options.MsBuildConfiguration ?? (projectOrSolution is ISolution s2 ? s2.DefaultConfigurationName : null);
 
                 command.Argument("/t:" + target);
-                if (platform != null)
+                if (platform is not null)
                     command.Argument(string.Format("/p:Platform=\"{0}\"", platform));
-                if (configuration != null)
+                if (configuration is not null)
                     command.Argument(string.Format("/p:Configuration=\"{0}\"", configuration));
                 command.Argument("/p:MvcBuildViews=true");
 
@@ -130,7 +130,7 @@ namespace Semmle.Autobuild.Shared
         {
             VcVarsBatFile? vsTools = null;
 
-            if (builder.Options.VsToolsVersion != null)
+            if (builder.Options.VsToolsVersion is not null)
             {
                 if (int.TryParse(builder.Options.VsToolsVersion, out var msToolsVersion))
                 {
@@ -140,7 +140,7 @@ namespace Semmle.Autobuild.Shared
                     }
 
                     vsTools = BuildTools.FindCompatibleVcVars(builder.Actions, msToolsVersion);
-                    if (vsTools == null)
+                    if (vsTools is null)
                         builder.Log(Severity.Warning, "Could not find build tools matching version {0}", msToolsVersion);
                     else
                         builder.Log(Severity.Info, "Setting Visual Studio tools to {0}", vsTools.Path);

csharp/autobuilder/Semmle.Autobuild.Shared/Solution.cs

@@ -49,13 +49,13 @@ namespace Semmle.Autobuild.Shared
         public override IEnumerable<IProjectOrSolution> IncludedProjects => includedProjects;
 
         public IEnumerable<SolutionConfigurationInSolution> Configurations =>
-            solution == null ? Enumerable.Empty<SolutionConfigurationInSolution>() : solution.SolutionConfigurations;
+            solution is null ? Enumerable.Empty<SolutionConfigurationInSolution>() : solution.SolutionConfigurations;
 
         public string DefaultConfigurationName =>
-            solution == null ? "" : solution.GetDefaultConfigurationName();
+            solution is null ? "" : solution.GetDefaultConfigurationName();
 
         public string DefaultPlatformName =>
-            solution == null ? "" : solution.GetDefaultPlatformName();
+            solution is null ? "" : solution.GetDefaultPlatformName();
 
         public Solution(Autobuilder builder, string path, bool allowProject) : base(builder, path)
         {

csharp/extractor/Semmle.Extraction.CIL/Context.cs

@@ -47,7 +47,7 @@ namespace Semmle.Extraction.CIL
             if (extractPdbs)
             {
                 Pdb = PDB.PdbReader.Create(assemblyPath, PeReader);
-                if (Pdb != null)
+                if (Pdb is not null)
                 {
                     Extractor.Logger.Log(Util.Logging.Severity.Info, string.Format("Found PDB information for {0}", assemblyPath));
                 }
@@ -56,7 +56,7 @@ namespace Semmle.Extraction.CIL
 
         public void Dispose()
         {
-            if (Pdb != null)
+            if (Pdb is not null)
                 Pdb.Dispose();
             PeReader.Dispose();
             stream.Dispose();

csharp/extractor/Semmle.Extraction.CIL/Entities/Assembly.cs

@@ -56,7 +56,7 @@ namespace Semmle.Extraction.CIL.Entities
                 yield return file;
                 yield return Tuples.assemblies(this, file, FullName, assemblyName.Name ?? string.Empty, assemblyName.Version?.ToString() ?? string.Empty);
 
-                if (Context.Pdb != null)
+                if (Context.Pdb is not null)
                 {
                     foreach (var f in Context.Pdb.SourceFiles)
                     {
@@ -77,7 +77,7 @@ namespace Semmle.Extraction.CIL.Entities
                     }
 
                     // Limitation of C#: Cannot yield return inside a try-catch.
-                    if (product != null)
+                    if (product is not null)
                         yield return product;
                 }
 
@@ -93,7 +93,7 @@ namespace Semmle.Extraction.CIL.Entities
                         Context.ExtractionError("Error processing bytecode", e.Message, GeneratedLocation.Create(Context), e.StackTrace);
                     }
 
-                    if (product != null)
+                    if (product is not null)
                         yield return product;
                 }
             }

csharp/extractor/Semmle.Extraction.CIL/Entities/DefinitionMethod.cs

@@ -150,7 +150,7 @@ namespace Semmle.Extraction.CIL.Entities
 
                     yield return Tuples.cil_method_stack_size(Implementation, body.MaxStack);
 
-                    if (methodDebugInformation != null)
+                    if (methodDebugInformation is not null)
                     {
                         var sourceLocation = Context.CreateSourceLocation(methodDebugInformation.Location);
                         yield return sourceLocation;
@@ -205,7 +205,7 @@ namespace Semmle.Extraction.CIL.Entities
             IEnumerator<PDB.SequencePoint>? nextSequencePoint = null;
             PdbSourceLocation? instructionLocation = null;
 
-            if (methodDebugInformation != null)
+            if (methodDebugInformation is not null)
             {
                 nextSequencePoint = methodDebugInformation.SequencePoints.GetEnumerator();
                 if (nextSequencePoint.MoveNext())
@@ -225,7 +225,7 @@ namespace Semmle.Extraction.CIL.Entities
                 var instruction = new Instruction(Context, this, ilbytes!, offset, child++);
                 yield return instruction;
 
-                if (nextSequencePoint != null && offset >= nextSequencePoint.Current.Offset)
+                if (nextSequencePoint is not null && offset >= nextSequencePoint.Current.Offset)
                 {
                     instructionLocation = Context.CreateSourceLocation(nextSequencePoint.Current.Location);
                     yield return instructionLocation;
@@ -233,7 +233,7 @@ namespace Semmle.Extraction.CIL.Entities
                         nextSequencePoint = null;
                 }
 
-                if (instructionLocation != null)
+                if (instructionLocation is not null)
                     yield return Tuples.cil_instruction_location(instruction, instructionLocation);
 
                 jump_table.Add(instruction.Offset, instruction);

csharp/extractor/Semmle.Extraction.CIL/Entities/GenericsHelper.cs

@@ -45,7 +45,7 @@ namespace Semmle.Extraction.CIL.Entities
 
         public static IEnumerable<Type> GetAllTypeParameters(Type? container, IEnumerable<TypeTypeParameter> thisTypeParameters)
         {
-            if (container != null)
+            if (container is not null)
             {
                 foreach (var t in container.TypeParameters)
                     yield return t;

csharp/extractor/Semmle.Extraction.CIL/Entities/Instruction.cs

@@ -390,7 +390,7 @@ namespace Semmle.Extraction.CIL.Entities
                             var handle = MetadataTokens.EntityHandle(payloadValue);
                             var target = Context.CreateGeneric(Method, handle);
                             yield return target;
-                            if (target != null)
+                            if (target is not null)
                             {
                                 yield return Tuples.cil_access(this, target);
                             }
@@ -402,14 +402,14 @@ namespace Semmle.Extraction.CIL.Entities
                         }
                     case Payload.Arg8:
                     case Payload.Arg16:
-                        if (Method.Parameters is object)
+                        if (Method.Parameters is not null)
                         {
                             yield return Tuples.cil_access(this, Method.Parameters[(int)unsignedPayloadValue]);
                         }
                         break;
                     case Payload.Local8:
                     case Payload.Local16:
-                        if (Method.LocalVariables is object)
+                        if (Method.LocalVariables is not null)
                         {
                             yield return Tuples.cil_access(this, Method.LocalVariables[(int)unsignedPayloadValue]);
                         }
@@ -435,7 +435,7 @@ namespace Semmle.Extraction.CIL.Entities
                                 Context.Extractor.Logger.Log(Util.Logging.Severity.Warning, $"Couldn't interpret payload of payload type {PayloadType} as a function pointer type. {exc.Message} {exc.StackTrace}");
                             }
 
-                            if (target != null)
+                            if (target is not null)
                             {
                                 yield return target;
                                 yield return Tuples.cil_access(this, target);

csharp/extractor/Semmle.Extraction.CIL/Entities/MemberReferenceMethod.cs

@@ -87,7 +87,7 @@ namespace Semmle.Extraction.CIL.Entities
                     yield return m;
                 }
 
-                if (SourceDeclaration != null)
+                if (SourceDeclaration is not null)
                     yield return Tuples.cil_method_source_declaration(this, SourceDeclaration);
             }
         }

csharp/extractor/Semmle.Extraction.CIL/Entities/Method.cs

@@ -25,7 +25,7 @@ namespace Semmle.Extraction.CIL.Entities
         public override IEnumerable<Type> TypeParameters => gc.TypeParameters.Concat(DeclaringType.TypeParameters);
 
         public override IEnumerable<Type> MethodParameters =>
-            genericParams == null ? gc.MethodParameters : gc.MethodParameters.Concat(genericParams);
+            genericParams is null ? gc.MethodParameters : gc.MethodParameters.Concat(genericParams);
 
         public int GenericParameterCount => signature.GenericParameterCount;
 

csharp/extractor/Semmle.Extraction.CIL/Entities/NamedTypeIdWriter.cs

@@ -21,7 +21,7 @@ namespace Semmle.Extraction.CIL.Entities
             }
 
             var ct = type.ContainingType;
-            if (ct != null)
+            if (ct is not null)
             {
                 ct.WriteId(trapFile, inContext);
                 trapFile.Write('.');
@@ -41,7 +41,7 @@ namespace Semmle.Extraction.CIL.Entities
             trapFile.Write(type.Name);
 
             var thisTypeArguments = type.ThisTypeArguments;
-            if (thisTypeArguments != null && thisTypeArguments.Any())
+            if (thisTypeArguments is not null && thisTypeArguments.Any())
             {
                 trapFile.Write('<');
                 var index = 0;

csharp/extractor/Semmle.Extraction.CIL/Entities/Namespace.cs

@@ -16,7 +16,7 @@ namespace Semmle.Extraction.CIL.Entities
 
         public override void WriteId(TextWriter trapFile)
         {
-            if (ParentNamespace != null && !ParentNamespace.IsGlobalNamespace)
+            if (ParentNamespace is not null && !ParentNamespace.IsGlobalNamespace)
             {
                 ParentNamespace.WriteId(trapFile);
                 trapFile.Write('.');
@@ -77,7 +77,7 @@ namespace Semmle.Extraction.CIL.Entities
             get
             {
                 yield return Tuples.namespaces(this, Name);
-                if (ParentNamespace is object)
+                if (ParentNamespace is not null)
                     yield return Tuples.parent_namespace(this, ParentNamespace);
             }
         }

csharp/extractor/Semmle.Extraction.CIL/Entities/NoMetadataHandleType.cs

@@ -36,11 +36,11 @@ namespace Semmle.Extraction.CIL.Entities
             isContainerNamespace = nameParser.IsContainerNamespace;
             containerName = nameParser.ContainerName;
 
-            unboundGenericType = nameParser.UnboundGenericTypeName == null
+            unboundGenericType = nameParser.UnboundGenericTypeName is null
                 ? this
                 : new NoMetadataHandleType(Context, nameParser.UnboundGenericTypeName);
 
-            if (nameParser.TypeArguments != null)
+            if (nameParser.TypeArguments is not null)
             {
                 thisTypeArguments = nameParser.TypeArguments.Select(t => new NoMetadataHandleType(Context, t)).ToArray();
             }
@@ -66,7 +66,7 @@ namespace Semmle.Extraction.CIL.Entities
 
         private void Populate()
         {
-            if (ContainingNamespace is object)
+            if (ContainingNamespace is not null)
             {
                 Context.Populate(ContainingNamespace);
             }

csharp/extractor/Semmle.Extraction.CIL/Entities/PdbSourceFile.cs

@@ -20,7 +20,7 @@ namespace Semmle.Extraction.CIL.Entities
 
                 var text = file.Contents;
 
-                if (text == null)
+                if (text is null)
                     Context.Extractor.Logger.Log(Util.Logging.Severity.Warning, string.Format("PDB source file {0} could not be found", OriginalPath));
                 else
                     Context.TrapWriter.Archive(TransformedPath, text);

csharp/extractor/Semmle.Extraction.CIL/Entities/Type.cs

@@ -124,7 +124,7 @@ namespace Semmle.Extraction.CIL.Entities
         {
             get
             {
-                if (ContainingType != null)
+                if (ContainingType is not null)
                 {
                     foreach (var t in ContainingType.GenericArguments)
                         yield return t;
@@ -184,7 +184,7 @@ namespace Semmle.Extraction.CIL.Entities
 
         private bool TryGetPrimitiveTypeCode(out PrimitiveTypeCode code)
         {
-            if (ContainingType == null &&
+            if (ContainingType is null &&
                 ContainingNamespace?.Name == Context.SystemNamespace.Name &&
                 primitiveTypeCodeMapping.TryGetValue(Name, out code))
             {

csharp/extractor/Semmle.Extraction.CIL/PDB/MetadataPdbReader.cs

@@ -49,7 +49,7 @@ namespace Semmle.Extraction.PDB
                 .Where(p => !p.Document.IsNil && !p.IsHidden)
                 .Select(p => new SequencePoint(p.Offset, new Location(
                     new SourceFile(reader, p.Document), p.StartLine, p.StartColumn, p.EndLine, p.EndColumn)))
-                .Where(p => p.Location.File.Path != null)
+                .Where(p => p.Location.File.Path is not null)
                 .ToArray();
 
             return sequencePoints.Any() ? new Method(sequencePoints) : null;
@@ -63,7 +63,7 @@ namespace Semmle.Extraction.PDB
                 .Select(dirEntry => peReader.ReadEmbeddedPortablePdbDebugDirectoryData(dirEntry))
                 .FirstOrDefault();
 
-            if (provider is object)
+            if (provider is not null)
             {
                 return new MetadataPdbReader(provider);
             }

csharp/extractor/Semmle.Extraction.CIL/PDB/NativePdbReader.cs

@@ -59,7 +59,7 @@ namespace Semmle.Extraction.PDB
         {
             var methodToken = MetadataTokens.GetToken(h.ToDefinitionHandle());
             var method = reader.GetMethod(methodToken);
-            if (method != null)
+            if (method is not null)
             {
                 if (method.GetSequencePointCount(out var count) != 0 || count == 0)
                     return null;
@@ -100,7 +100,7 @@ namespace Semmle.Extraction.PDB
                 .Select(cv => cv.Path)
                 .FirstOrDefault(File.Exists);
 
-            if (path is object)
+            if (path is not null)
             {
                 return new NativePdbReader(path);
             }

csharp/extractor/Semmle.Extraction.CSharp.Standalone/AssemblyCache.cs

@@ -111,7 +111,7 @@ namespace Semmle.BuildAnalyser
             {
                 var loadedAssembly = System.Reflection.Assembly.ReflectionOnlyLoad(id);
 
-                if (loadedAssembly != null)
+                if (loadedAssembly is not null)
                 {
                     // The assembly was somewhere we haven't indexed before.
                     // Add this assembly to our index so that subsequent lookups are faster.

csharp/extractor/Semmle.Extraction.CSharp.Standalone/AssemblyInfo.cs

@@ -46,11 +46,11 @@ namespace Semmle.BuildAnalyser
             get
             {
                 var result = Name;
-                if (Version != null)
+                if (Version is not null)
                     result = string.Format("{0}, Version={1}", result, Version);
-                if (Culture != null)
+                if (Culture is not null)
                     result = string.Format("{0}, Culture={1}", result, Culture);
-                if (PublicKeyToken != null)
+                if (PublicKeyToken is not null)
                     result = string.Format("{0}, PublicKeyToken={1}", result, PublicKeyToken);
                 return result;
             }
@@ -66,9 +66,9 @@ namespace Semmle.BuildAnalyser
             get
             {
                 yield return Id;
-                if (Version != null)
+                if (Version is not null)
                 {
-                    if (Culture != null)
+                    if (Culture is not null)
                         yield return string.Format("{0}, Version={1}, Culture={2}", Name, Version, Culture);
                     yield return string.Format("{0}, Version={1}", Name, Version);
                 }

csharp/extractor/Semmle.Extraction.CSharp.Standalone/BuildAnalysis.cs

@@ -104,7 +104,7 @@ namespace Semmle.BuildAnalyser
             using (new FileRenamer(sourceDir.GetFiles("global.json", SearchOption.AllDirectories)))
             using (new FileRenamer(sourceDir.GetFiles("Directory.Build.props", SearchOption.AllDirectories)))
             {
-                var solutions = options.SolutionFile != null ?
+                var solutions = options.SolutionFile is not null ?
                         new[] { options.SolutionFile } :
                         sourceDir.GetFiles("*.sln", SearchOption.AllDirectories).Select(d => d.FullName);
 

csharp/extractor/Semmle.Extraction.CSharp.Standalone/Program.cs

@@ -30,7 +30,7 @@ namespace Semmle.Extraction.CSharp.Standalone
             buildAnalysis = new BuildAnalysis(options, progressMonitor);
             References = buildAnalysis.ReferenceFiles;
             Extraction = new Extraction(options.SrcDir);
-            Extraction.Sources.AddRange(options.SolutionFile == null ? buildAnalysis.AllSourceFiles : buildAnalysis.ProjectSourceFiles);
+            Extraction.Sources.AddRange(options.SolutionFile is null ? buildAnalysis.AllSourceFiles : buildAnalysis.ProjectSourceFiles);
         }
 
         public IEnumerable<string> References { get; }

csharp/extractor/Semmle.Extraction.CSharp.Standalone/Runtime.cs

@@ -22,13 +22,13 @@ namespace Semmle.Extraction.CSharp.Standalone
             get
             {
                 var dotnetPath = FileUtils.FindProgramOnPath(Win32.IsWindows() ? "dotnet.exe" : "dotnet");
-                var dotnetDirs = dotnetPath != null
+                var dotnetDirs = dotnetPath is not null
                     ? new[] { dotnetPath }
                     : new[] { "/usr/share/dotnet", @"C:\Program Files\dotnet" };
                 var coreDirs = dotnetDirs.Select(d => Path.Combine(d, "shared", "Microsoft.NETCore.App"));
 
                 var dir = coreDirs.FirstOrDefault(Directory.Exists);
-                if (dir is object)
+                if (dir is not null)
                 {
                     return Directory.EnumerateDirectories(dir).OrderByDescending(Path.GetFileName);
                 }
@@ -46,7 +46,7 @@ namespace Semmle.Extraction.CSharp.Standalone
             get
             {
                 var monoPath = FileUtils.FindProgramOnPath(Win32.IsWindows() ? "mono.exe" : "mono");
-                var monoDirs = monoPath != null
+                var monoDirs = monoPath is not null
                     ? new[] { monoPath }
                     : new[] { "/usr/lib/mono", @"C:\Program Files\Mono\lib\mono" };
 
@@ -58,7 +58,7 @@ namespace Semmle.Extraction.CSharp.Standalone
 
                 var dir = monoDirs.FirstOrDefault(Directory.Exists);
 
-                if (dir is object)
+                if (dir is not null)
                 {
                     return Directory.EnumerateDirectories(dir)
                         .Where(d => Char.IsDigit(Path.GetFileName(d)[0]))

csharp/extractor/Semmle.Extraction.CSharp/Comments/CommentProcessor.cs

@@ -48,9 +48,9 @@ namespace Semmle.Extraction.CSharp
         {
             if (object.ReferenceEquals(l1, l2))
                 return 0;
-            if (l1 == null)
+            if (l1 is null)
                 return -1;
-            if (l2 == null)
+            if (l2 is null)
                 return 1;
 
             var diff = l1.SourceTree == l2.SourceTree ? 0 : l1.SourceTree!.FilePath.CompareTo(l2.SourceTree!.FilePath);
@@ -70,9 +70,9 @@ namespace Semmle.Extraction.CSharp
         /// <param name="loc">The location of the element.</param>
         public void AddElement(Label elementLabel, Key? duplicationGuardKey, Location? loc)
         {
-            if (loc != null && loc.IsInSource)
+            if (loc is not null && loc.IsInSource)
                 elements[loc] = elementLabel;
-            if (duplicationGuardKey != null)
+            if (duplicationGuardKey is not null)
                 duplicationGuardKeys[elementLabel] = duplicationGuardKey;
         }
 
@@ -80,7 +80,7 @@ namespace Semmle.Extraction.CSharp
         // which can happen when processing multiple files.
         private static void EnsureSameFile(Comments.CommentBlock commentBlock, ref KeyValuePair<Location, Label>? element)
         {
-            if (element != null && element.Value.Key.SourceTree != commentBlock.Location.SourceTree)
+            if (element is not null && element.Value.Key.SourceTree != commentBlock.Location.SourceTree)
                 element = null;
         }
 
@@ -106,19 +106,19 @@ namespace Semmle.Extraction.CSharp
             EnsureSameFile(commentBlock, ref nextElement);
             EnsureSameFile(commentBlock, ref parentElement);
 
-            if (previousElement != null)
+            if (previousElement is not null)
             {
                 var key = previousElement.Value.Value;
                 callback(key, GetDuplicationGuardKey(key), commentBlock, CommentBinding.Before);
             }
 
-            if (nextElement != null)
+            if (nextElement is not null)
             {
                 var key = nextElement.Value.Value;
                 callback(key, GetDuplicationGuardKey(key), commentBlock, CommentBinding.After);
             }
 
-            if (parentElement != null)
+            if (parentElement is not null)
             {
                 var key = parentElement.Value.Value;
                 callback(key, GetDuplicationGuardKey(key), commentBlock, CommentBinding.Parent);
@@ -127,17 +127,17 @@ namespace Semmle.Extraction.CSharp
             // Heuristic to decide which is the "best" element associated with the comment.
             KeyValuePair<Location, Label>? bestElement;
 
-            if (previousElement != null && previousElement.Value.Key.EndLine() == commentBlock.Location.StartLine())
+            if (previousElement is not null && previousElement.Value.Key.EndLine() == commentBlock.Location.StartLine())
             {
                 // 1. If the comment is on the same line as the previous element, use that
                 bestElement = previousElement;
             }
-            else if (nextElement != null && nextElement.Value.Key.StartLine() == commentBlock.Location.EndLine())
+            else if (nextElement is not null && nextElement.Value.Key.StartLine() == commentBlock.Location.EndLine())
             {
                 // 2. If the comment is on the same line as the next element, use that
                 bestElement = nextElement;
             }
-            else if (nextElement != null && previousElement != null &&
+            else if (nextElement is not null && previousElement is not null &&
                 previousElement.Value.Key.EndLine() + 1 == commentBlock.Location.StartLine() &&
                 commentBlock.Location.EndLine() + 1 == nextElement.Value.Key.StartLine())
             {
@@ -145,12 +145,12 @@ namespace Semmle.Extraction.CSharp
                 // because it's ambiguous whether the comment refers to the next or previous element
                 bestElement = parentElement;
             }
-            else if (nextElement != null && nextElement.Value.Key.StartLine() == commentBlock.Location.EndLine() + 1)
+            else if (nextElement is not null && nextElement.Value.Key.StartLine() == commentBlock.Location.EndLine() + 1)
             {
                 // 4. If there is no gap after the comment, use "nextElement"
                 bestElement = nextElement;
             }
-            else if (previousElement != null && previousElement.Value.Key.EndLine() + 1 == commentBlock.Location.StartLine())
+            else if (previousElement is not null && previousElement.Value.Key.EndLine() + 1 == commentBlock.Location.StartLine())
             {
                 // 5. If there is no gap before the comment, use previousElement
                 bestElement = previousElement;
@@ -168,7 +168,7 @@ namespace Semmle.Extraction.CSharp
                  */
             }
 
-            if (bestElement != null)
+            if (bestElement is not null)
             {
                 var label = bestElement.Value.Value;
                 callback(label, GetDuplicationGuardKey(label), commentBlock, CommentBinding.Best);
@@ -268,7 +268,7 @@ namespace Semmle.Extraction.CSharp
             Comments.CommentBlock? block = null;
 
             // Iterate comments until the commentEnumerator has gone past nextElement
-            while (nextElement == null || Compare(commentEnumerator.Current.Value.Location, nextElement.Value.Key) < 0)
+            while (nextElement is null || Compare(commentEnumerator.Current.Value.Location, nextElement.Value.Key) < 0)
             {
                 if (block is null)
                     block = new Comments.CommentBlock(commentEnumerator.Current.Value);

csharp/extractor/Semmle.Extraction.CSharp/Entities/Accessor.cs

@@ -40,7 +40,7 @@ namespace Semmle.Extraction.CSharp.Entities
             ContainingType!.PopulateGenerics();
 
             var prop = PropertySymbol;
-            if (prop == null)
+            if (prop is null)
             {
                 Context.ModelError(Symbol, "Unhandled accessor associated symbol");
                 return;
@@ -72,7 +72,7 @@ namespace Semmle.Extraction.CSharp.Entities
 
             Overrides(trapFile);
 
-            if (Symbol.FromSource() && Block == null)
+            if (Symbol.FromSource() && Block is null)
             {
                 trapFile.compiler_generated(this);
             }

csharp/extractor/Semmle.Extraction.CSharp/Entities/Assembly.cs

@@ -14,7 +14,7 @@ namespace Semmle.Extraction.CSharp.Entities
         private Assembly(Context cx, Microsoft.CodeAnalysis.Location? init)
             : base(cx, init)
         {
-            if (init == null)
+            if (init is null)
             {
                 // This is the output assembly
                 assemblyPath = ((TracingExtractor)cx.Extractor).OutputPath;
@@ -31,7 +31,7 @@ namespace Semmle.Extraction.CSharp.Entities
 
         public override void Populate(TextWriter trapFile)
         {
-            if (assemblyPath != null)
+            if (assemblyPath is not null)
             {
                 trapFile.assemblies(this, File.Create(Context, assemblyPath), assembly.ToString() ?? "",
                     assembly.Identity.Name, assembly.Identity.Version.ToString());
@@ -41,7 +41,7 @@ namespace Semmle.Extraction.CSharp.Entities
         public override bool NeedsPopulation => true;
 
         public override int GetHashCode() =>
-            Symbol == null ? 91187354 : Symbol.GetHashCode();
+            Symbol is null ? 91187354 : Symbol.GetHashCode();
 
         public override bool Equals(object? obj)
         {

csharp/extractor/Semmle.Extraction.CSharp/Entities/Attribute.cs

@@ -51,7 +51,7 @@ namespace Semmle.Extraction.CSharp.Entities
             trapFile.attributes(this, type.TypeRef, entity);
             trapFile.attribute_location(this, Location);
 
-            if (attributeSyntax is object)
+            if (attributeSyntax is not null)
             {
                 if (!Context.Extractor.Standalone)
                 {
@@ -66,18 +66,18 @@ namespace Semmle.Extraction.CSharp.Entities
 
         private void ExtractArguments(TextWriter trapFile)
         {
-            var ctorArguments = attributeSyntax?.ArgumentList?.Arguments.Where(a => a.NameEquals == null).ToList();
+            var ctorArguments = attributeSyntax?.ArgumentList?.Arguments.Where(a => a.NameEquals is null).ToList();
 
             var childIndex = 0;
             for (var i = 0; i < Symbol.ConstructorArguments.Length; i++)
             {
                 var constructorArgument = Symbol.ConstructorArguments[i];
                 var paramName = Symbol.AttributeConstructor?.Parameters[i].Name;
-                var argSyntax = ctorArguments?.SingleOrDefault(a => a.NameColon != null && a.NameColon.Name.Identifier.Text == paramName);
+                var argSyntax = ctorArguments?.SingleOrDefault(a => a.NameColon is not null && a.NameColon.Name.Identifier.Text == paramName);
 
-                if (argSyntax == null &&                            // couldn't find named argument
+                if (argSyntax is null &&                            // couldn't find named argument
                     ctorArguments?.Count > childIndex &&            // there're more arguments
-                    ctorArguments[childIndex].NameColon == null)    // the argument is positional
+                    ctorArguments[childIndex].NameColon is null)    // the argument is positional
                 {
                     argSyntax = ctorArguments[childIndex];
                 }
@@ -97,7 +97,7 @@ namespace Semmle.Extraction.CSharp.Entities
                     this,
                     childIndex++);
 
-                if (expr is object)
+                if (expr is not null)
                 {
                     trapFile.expr_argument_name(expr, namedArgument.Key);
                 }

csharp/extractor/Semmle.Extraction.CSharp/Entities/CachedSymbol.cs

@@ -16,7 +16,7 @@ namespace Semmle.Extraction.CSharp.Entities
         {
         }
 
-        public virtual Type? ContainingType => Symbol.ContainingType != null ? Type.Create(Context, Symbol.ContainingType) : null;
+        public virtual Type? ContainingType => Symbol.ContainingType is not null ? Type.Create(Context, Symbol.ContainingType) : null;
 
         public void PopulateModifiers(TextWriter trapFile)
         {
@@ -77,7 +77,7 @@ namespace Semmle.Extraction.CSharp.Entities
             get
             {
                 var loc = ReportingLocation;
-                if (loc != null)
+                if (loc is not null)
                 {
                     // Some built in operators lack locations, so loc is null.
                     yield return Context.CreateLocation(ReportingLocation);
@@ -151,7 +151,7 @@ namespace Semmle.Extraction.CSharp.Entities
                 if (handleProp is null)
                 {
                     var underlyingSymbolProp = GetPropertyInfo(Symbol, "UnderlyingSymbol");
-                    if (underlyingSymbolProp is object)
+                    if (underlyingSymbolProp is not null)
                     {
                         if (underlyingSymbolProp.GetValue(Symbol) is object underlying)
                         {
@@ -161,7 +161,7 @@ namespace Semmle.Extraction.CSharp.Entities
                     }
                 }
 
-                if (handleProp is object)
+                if (handleProp is not null)
                 {
                     switch (handleProp.GetValue(handleObj))
                     {

csharp/extractor/Semmle.Extraction.CSharp/Entities/Compilations/Compilation.cs

@@ -56,7 +56,7 @@ namespace Semmle.Extraction.CSharp.Entities
             index = 0;
             foreach (var file in Context.Compilation.References
                 .OfType<PortableExecutableReference>()
-                .Where(r => r.FilePath is object)
+                .Where(r => r.FilePath is not null)
                 .Select(r => File.Create(Context, r.FilePath!)))
             {
                 trapFile.compilation_referencing_files(this, index++, file);

csharp/extractor/Semmle.Extraction.CSharp/Entities/Constructor.cs

@@ -40,7 +40,7 @@ namespace Semmle.Extraction.CSharp.Entities
             var syntax = Syntax;
             var initializer = syntax?.Initializer;
 
-            if (initializer == null)
+            if (initializer is null)
                 return;
 
             ITypeSymbol initializerType;
@@ -71,7 +71,7 @@ namespace Semmle.Extraction.CSharp.Entities
             var init = new Expression(initInfo);
 
             var target = Constructor.Create(Context, (IMethodSymbol?)symbolInfo.Symbol);
-            if (target == null)
+            if (target is null)
             {
                 Context.ModelError(Symbol, "Unable to resolve call");
                 return;
@@ -100,7 +100,7 @@ namespace Semmle.Extraction.CSharp.Entities
         [return: NotNullIfNotNull("constructor")]
         public static new Constructor? Create(Context cx, IMethodSymbol? constructor)
         {
-            if (constructor == null)
+            if (constructor is null)
                 return null;
 
             switch (constructor.MethodKind)
@@ -132,7 +132,7 @@ namespace Semmle.Extraction.CSharp.Entities
             get
             {
                 var syn = GetSyntax();
-                if (syn != null)
+                if (syn is not null)
                 {
                     return syn.Identifier.GetLocation();
                 }

csharp/extractor/Semmle.Extraction.CSharp/Entities/Destructor.cs

@@ -20,7 +20,7 @@ namespace Semmle.Extraction.CSharp.Entities
 
         private static new Destructor OriginalDefinition(Context cx, Destructor original, IMethodSymbol symbol)
         {
-            return symbol.OriginalDefinition == null || SymbolEqualityComparer.Default.Equals(symbol.OriginalDefinition, symbol) ? original : Create(cx, symbol.OriginalDefinition);
+            return symbol.OriginalDefinition is null || SymbolEqualityComparer.Default.Equals(symbol.OriginalDefinition, symbol) ? original : Create(cx, symbol.OriginalDefinition);
         }
 
         public static new Destructor Create(Context cx, IMethodSymbol symbol) =>

csharp/extractor/Semmle.Extraction.CSharp/Entities/EventAccessor.cs

@@ -19,7 +19,7 @@ namespace Semmle.Extraction.CSharp.Entities
             ContainingType!.PopulateGenerics();
 
             var @event = EventSymbol;
-            if (@event == null)
+            if (@event is null)
             {
                 Context.ModelError(Symbol, "Unhandled event accessor associated symbol");
                 return;

csharp/extractor/Semmle.Extraction.CSharp/Entities/Expression.cs

@@ -68,7 +68,7 @@ namespace Semmle.Extraction.CSharp.Entities
         /// <returns>The string representation.</returns>
         public static string ValueAsString(object? value)
         {
-            return value == null
+            return value is null
                 ? "null"
                 : value is bool b
                     ? b
@@ -215,7 +215,7 @@ namespace Semmle.Extraction.CSharp.Entities
                 switch (method.MethodKind)
                 {
                     case MethodKind.BuiltinOperator:
-                        if (method.ContainingType != null && method.ContainingType.TypeKind == Microsoft.CodeAnalysis.TypeKind.Delegate)
+                        if (method.ContainingType is not null && method.ContainingType.TypeKind == Microsoft.CodeAnalysis.TypeKind.Delegate)
                             return CallType.UserOperator;
                         return CallType.BuiltInOperator;
                     case MethodKind.Constructor:
@@ -234,7 +234,7 @@ namespace Semmle.Extraction.CSharp.Entities
         public static bool IsDynamic(Context cx, ExpressionSyntax node)
         {
             var ti = cx.GetTypeInfo(node).ConvertedType;
-            return ti != null && ti.TypeKind == Microsoft.CodeAnalysis.TypeKind.Dynamic;
+            return ti is not null && ti.TypeKind == Microsoft.CodeAnalysis.TypeKind.Dynamic;
         }
 
         /// <summary>
@@ -244,7 +244,7 @@ namespace Semmle.Extraction.CSharp.Entities
         /// <returns>The qualifier of the conditional access.</returns>
         protected static ExpressionSyntax FindConditionalQualifier(ExpressionSyntax node)
         {
-            for (SyntaxNode? n = node; n != null; n = n.Parent)
+            for (SyntaxNode? n = node; n is not null; n = n.Parent)
             {
                 if (n.Parent is ConditionalAccessExpressionSyntax conditionalAccess &&
                     conditionalAccess.WhenNotNull == n)
@@ -290,7 +290,7 @@ namespace Semmle.Extraction.CSharp.Entities
             }
             trapFile.expr_argument(expr, mode);
 
-            if (arg.NameColon != null)
+            if (arg.NameColon is not null)
             {
                 trapFile.expr_argument_name(expr, arg.NameColon.Name.Identifier.Text);
             }

csharp/extractor/Semmle.Extraction.CSharp/Entities/ExpressionNodeInfo.cs

@@ -48,7 +48,7 @@ namespace Semmle.Extraction.CSharp.Entities
 
                 var type = ResolvedType;
 
-                if (type.Symbol == null)
+                if (type.Symbol is null)
                     type.Symbol = (TypeInfo.Type ?? TypeInfo.ConvertedType).DisambiguateType();
 
                 // Roslyn workaround: It can't work out the type of "new object[0]"
@@ -59,7 +59,7 @@ namespace Semmle.Extraction.CSharp.Entities
                     {
                         var elementType = Context.GetType(arrayCreation.Type.ElementType);
 
-                        if (elementType.Symbol != null)
+                        if (elementType.Symbol is not null)
                             // There seems to be no way to create an array with a nullable element at present.
                             return new AnnotatedTypeSymbol(Context.Compilation.CreateArrayTypeSymbol(elementType.Symbol, arrayCreation.Type.RankSpecifiers.Count), NullableAnnotation.NotAnnotated);
                     }
@@ -80,7 +80,7 @@ namespace Semmle.Extraction.CSharp.Entities
         {
             get
             {
-                if (location == null)
+                if (location is null)
                     location = Node.FixedLocation();
                 return location;
             }
@@ -117,7 +117,7 @@ namespace Semmle.Extraction.CSharp.Entities
         {
             get
             {
-                if (cachedLocation == null)
+                if (cachedLocation is null)
                     cachedLocation = Context.CreateLocation(CodeAnalysisLocation);
                 return cachedLocation;
             }
@@ -164,7 +164,7 @@ namespace Semmle.Extraction.CSharp.Entities
         {
             get
             {
-                if (cachedSymbolInfo.Symbol == null && cachedSymbolInfo.CandidateReason == CandidateReason.None)
+                if (cachedSymbolInfo.Symbol is null && cachedSymbolInfo.CandidateReason == CandidateReason.None)
                     cachedSymbolInfo = Model.GetSymbolInfo(Node);
                 return cachedSymbolInfo;
             }

csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/ArrayCreation.cs

@@ -158,7 +158,7 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
 
         protected override void PopulateExpression(TextWriter trapFile)
         {
-            if (Syntax.Initializer != null)
+            if (Syntax.Initializer is not null)
             {
                 ArrayInitializer.Create(new ExpressionNodeInfo(Context, Syntax.Initializer, this, InitializerIndex));
             }

csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/Assignment.cs

@@ -84,7 +84,7 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
             var kind = GetAssignmentOperation(cx, syntax);
             var leftType = cx.GetType(syntax.Left);
 
-            if (leftType.Symbol != null && leftType.Symbol.SpecialType != SpecialType.None)
+            if (leftType.Symbol is not null && leftType.Symbol.SpecialType != SpecialType.None)
             {
                 // In Mono, the builtin types did not specify their operator invocation
                 // even though EVERY operator has an invocation in C#. (This is a flaw in the dbscheme and should be fixed).

csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/ElementAccess.cs

@@ -49,7 +49,7 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
             var qualifierType = cx.GetType(qualifier);
 
             // This is a compilation error, so make a guess and continue.
-            if (qualifierType.Symbol == null)
+            if (qualifierType.Symbol is null)
                 return ExprKind.ARRAY_ACCESS;
 
             if (qualifierType.Symbol.TypeKind == Microsoft.CodeAnalysis.TypeKind.Pointer)

csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/Factory.cs

@@ -12,7 +12,7 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
             // to the extent that the stack has been known to overflow.
             using (info.Context.StackGuard)
             {
-                if (info.Node == null)
+                if (info.Node is null)
                 {
                     info.Context.ModelError("Attempt to create a null expression");
                     return new Unknown(info);

csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/ImplicitCast.cs

@@ -23,7 +23,7 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
             Expr = Factory.Create(info.SetParent(this, 0));
 
             var target = Method.Create(Context, method);
-            if (target != null)
+            if (target is not null)
                 Context.TrapWriter.Writer.expr_call(this, target);
             else
                 Context.ModelError(info.Node, "Failed to resolve target for operator invocation");
@@ -44,7 +44,7 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
             var convertedType = info.ConvertedType;
             var conversion = info.Conversion;
 
-            if (conversion.MethodSymbol != null)
+            if (conversion.MethodSymbol is not null)
             {
                 var convertedToDelegate = Entities.Type.IsDelegate(convertedType.Symbol);
 
@@ -65,15 +65,15 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
                     return Factory.Create(info);
                 }
 
-                if (resolvedType.Symbol != null)
+                if (resolvedType.Symbol is not null)
                     return new ImplicitCast(info, conversion.MethodSymbol);
             }
 
             var implicitUpcast = conversion.IsImplicit &&
-                convertedType.Symbol != null &&
+                convertedType.Symbol is not null &&
                 !conversion.IsBoxing &&
                 (
-                    resolvedType.Symbol == null ||
+                    resolvedType.Symbol is null ||
                     conversion.IsReference ||
                     convertedType.Symbol.SpecialType == SpecialType.System_Object)
                 ;

csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/Initializer.cs

@@ -139,7 +139,7 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
 
                 var invocation = new Expression(new ExpressionInfo(Context, voidType, Context.CreateLocation(i.GetLocation()), ExprKind.METHOD_INVOCATION, this, child++, false, null));
 
-                if (addMethod != null)
+                if (addMethod is not null)
                     trapFile.expr_call(invocation, addMethod);
                 else
                     Context.ModelError(Syntax, "Unable to find an Add() method for collection initializer");

csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/Invocation.cs

@@ -51,10 +51,10 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
                 case SimpleNameSyntax simpleName when (Kind == ExprKind.METHOD_INVOCATION):
                     // Unqualified method call; `M()`
                     memberName = simpleName.Identifier.Text;
-                    if (target != null && !target.IsStatic)
+                    if (target is not null && !target.IsStatic)
                     {
                         // Implicit `this` qualifier; add explicitly
-                        if (Location.Symbol is object &&
+                        if (Location.Symbol is not null &&
                             Context.GetModel(Syntax).GetEnclosingSymbol(Location.Symbol.SourceSpan.Start) is IMethodSymbol callingMethod)
                         {
                             This.CreateImplicit(Context, callingMethod.ContainingType, Location, this, child++);
@@ -79,7 +79,7 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
             var isDynamicCall = IsDynamicCall(info);
             if (isDynamicCall)
             {
-                if (memberName != null)
+                if (memberName is not null)
                     trapFile.dynamic_member_name(this, memberName);
                 else
                     Context.ModelError(Syntax, "Unable to get name for dynamic call.");
@@ -87,7 +87,7 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
 
             PopulateArguments(trapFile, Syntax.ArgumentList, child);
 
-            if (target == null)
+            if (target is null)
             {
                 if (!isDynamicCall && !IsDelegateLikeCall(info))
                     Context.ModelError(Syntax, "Unable to resolve target for call. (Compilation error?)");
@@ -115,7 +115,7 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
             {
                 var si = SymbolInfo;
 
-                if (si.Symbol != null)
+                if (si.Symbol is not null)
                     return si.Symbol as IMethodSymbol;
 
                 if (si.CandidateReason == CandidateReason.OverloadResolutionFailure)
@@ -163,7 +163,7 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
             if (si.CandidateReason == CandidateReason.LateBound &&
                 node.Expression is IdentifierNameSyntax &&
                 IsDynamic(info.Context, node.Expression) &&
-                si.Symbol == null)
+                si.Symbol is null)
             {
                 return true;
             }
@@ -173,13 +173,13 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
 
         private static bool IsFunctionPointer(ISymbol? symbol)
         {
-            return symbol != null &&
+            return symbol is not null &&
                 symbol.Kind == SymbolKind.FunctionPointerType;
         }
 
         private static bool IsDelegateInvoke(ISymbol? symbol)
         {
-            return symbol != null &&
+            return symbol is not null &&
                 symbol.Kind == SymbolKind.Method &&
                 ((IMethodSymbol)symbol).MethodKind == MethodKind.DelegateInvoke;
         }

csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/Lambda.cs

@@ -59,7 +59,7 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
         public static Lambda Create(ExpressionNodeInfo info, SimpleLambdaExpressionSyntax node) => new Lambda(info, node);
 
         private Lambda(ExpressionNodeInfo info, AnonymousMethodExpressionSyntax node) :
-            this(info.SetKind(ExprKind.ANONYMOUS_METHOD), node.Body, node.ParameterList == null ? Enumerable.Empty<ParameterSyntax>() : node.ParameterList.Parameters)
+            this(info.SetKind(ExprKind.ANONYMOUS_METHOD), node.Body, node.ParameterList is null ? Enumerable.Empty<ParameterSyntax>() : node.ParameterList.Parameters)
         { }
 
         public static Lambda Create(ExpressionNodeInfo info, AnonymousMethodExpressionSyntax node) => new Lambda(info, node);

csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/Literal.cs

@@ -75,7 +75,7 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
 
                 case null:
                 default:
-                    if (expr is object)
+                    if (expr is not null)
                         context.ModelError(expr, "Unhandled literal type");
                     else
                         context.ModelError("Unhandled literal type");

csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/MemberAccess.cs

@@ -11,7 +11,7 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
             var trapFile = info.Context.TrapWriter.Writer;
             Qualifier = Create(Context, qualifier, this, -1);
 
-            if (target == null)
+            if (target is null)
             {
                 if (info.Kind != ExprKind.DYNAMIC_MEMBER_ACCESS)
                     Context.ModelError(info.Node, "Could not determine target for member access");
@@ -59,14 +59,14 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
 
             var symbol = target.Symbol ?? info.Context.GetSymbolInfo(name).Symbol;
 
-            if (symbol == null && target.CandidateSymbols.Length >= 1)
+            if (symbol is null && target.CandidateSymbols.Length >= 1)
             {
                 // Pick the first symbol. This could occur for something like `nameof(Foo.Bar)`
                 // where `Bar` is a method group. Technically, we don't know which symbol is accessed.
                 symbol = target.CandidateSymbols[0];
             }
 
-            if (symbol == null)
+            if (symbol is null)
             {
                 info.Context.ModelError(info.Node, "Failed to determine symbol for member access");
                 // Default to property access - this can still give useful results but

csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/Name.cs

@@ -13,26 +13,26 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
 
             var target = symbolInfo.Symbol;
 
-            if (target == null &&
+            if (target is null &&
                 symbolInfo.CandidateReason == CandidateReason.OverloadResolutionFailure &&
                 info.Node.Parent.IsKind(SyntaxKind.SuppressNullableWarningExpression))
             {
                 target = symbolInfo.CandidateSymbols.FirstOrDefault();
             }
 
-            if (target == null && symbolInfo.CandidateReason == CandidateReason.OverloadResolutionFailure)
+            if (target is null && symbolInfo.CandidateReason == CandidateReason.OverloadResolutionFailure)
             {
                 // The expression is probably a cast
                 target = info.Context.GetSymbolInfo((CSharpSyntaxNode)info.Node.Parent!).Symbol;
             }
 
-            if (target == null && (symbolInfo.CandidateReason == CandidateReason.Ambiguous || symbolInfo.CandidateReason == CandidateReason.MemberGroup))
+            if (target is null && (symbolInfo.CandidateReason == CandidateReason.Ambiguous || symbolInfo.CandidateReason == CandidateReason.MemberGroup))
             {
                 // Pick one at random - they probably resolve to the same ID
                 target = symbolInfo.CandidateSymbols.First();
             }
 
-            if (target == null)
+            if (target is null)
             {
                 if (IsInsideIfDirective(info.Node))
                 {

csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/ObjectCreation/AnonymousObjectCreation.cs

@@ -19,7 +19,7 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
         {
             var target = Context.GetSymbolInfo(Syntax);
             var method = (IMethodSymbol?)target.Symbol;
-            if (method != null)
+            if (method is not null)
             {
                 trapFile.expr_call(this, Method.Create(Context, method));
             }

csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/ObjectCreation/BaseObjectCreation.cs

@@ -17,7 +17,7 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
 
         protected override void PopulateExpression(TextWriter trapFile)
         {
-            if (Syntax.ArgumentList != null)
+            if (Syntax.ArgumentList is not null)
             {
                 PopulateArguments(trapFile, Syntax.ArgumentList, 0);
             }
@@ -41,7 +41,7 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
                 }
             }
 
-            if (Syntax.Initializer != null)
+            if (Syntax.Initializer is not null)
             {
                 switch (Syntax.Initializer.Kind())
                 {
@@ -68,7 +68,7 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
 
         private static bool IsDynamicObjectCreation(Context cx, BaseObjectCreationExpressionSyntax node)
         {
-            return node.ArgumentList != null &&
+            return node.ArgumentList is not null &&
                 node.ArgumentList.Arguments.Any(arg => IsDynamic(cx, arg.Expression));
         }
     }

csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/Query.cs

@@ -26,7 +26,7 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
                         cx.CreateLocation(clause.GetLocation()),
                         ExprKind.METHOD_INVOCATION, parent, child, false, null))
             {
-                if (method != null)
+                if (method is not null)
                     cx.TrapWriter.Writer.expr_call(this, Method.Create(cx, method));
             }
         }
@@ -56,7 +56,7 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
 
             public Clause AddArgument(ExpressionSyntax arg)
             {
-                if (arg != null)
+                if (arg is not null)
                     arguments.Add(arg);
                 return this;
             }
@@ -69,7 +69,7 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
                 TypeSyntax? declTypeSyntax = null;
                 if (getElement)
                 {
-                    if (node is FromClauseSyntax from && from.Type != null)
+                    if (node is FromClauseSyntax from && from.Type is not null)
                     {
                         declTypeSyntax = from.Type;
                         declType = cx.GetType(from.Type);
@@ -116,7 +116,7 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
             private static AnnotatedTypeSymbol? GetEnumerableElementType(Context cx, INamedTypeSymbol type)
             {
                 var et = GetEnumerableType(cx, type);
-                if (et != null)
+                if (et is not null)
                     return et;
 
                 return type.AllInterfaces
@@ -182,13 +182,13 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
 
             private void DeclareIntoVariable(Context cx, IExpressionParentEntity parent, int intoChild, bool getElement)
             {
-                if (intoDeclaration != null)
+                if (intoDeclaration is not null)
                     DeclareRangeVariable(cx, parent, intoChild, getElement, intoDeclaration, name);
             }
 
             public override Expression Populate(Context cx, IExpressionParentEntity parent, int child)
             {
-                if (method == null)
+                if (method is null)
                     cx.ModelError(node, "Unable to determine target of query expression");
 
                 var callExpr = new QueryCall(cx, method, node, parent, child);
@@ -248,7 +248,7 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
 
                             clauseExpr = clauseExpr.WithCallClause(method, orderByClause).AddArgument(ordering.Expression);
 
-                            if (method == null)
+                            if (method is null)
                                 cx.ModelError(ordering, "Could not determine method call for orderby clause");
                         }
                         break;
@@ -275,7 +275,7 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
                             AddArgument(joinClause.LeftExpression).
                             AddArgument(joinClause.RightExpression);
 
-                        if (joinClause.Into != null)
+                        if (joinClause.Into is not null)
                         {
                             var into = cx.GetModel(node).GetDeclaredSymbol(joinClause.Into)!;
                             ((LetClause)clauseExpr).WithInto(into);

csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/VariableDeclaration.cs

@@ -18,7 +18,7 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
             {
                 var l = LocalVariable.Create(cx, symbol);
                 l.PopulateManual(ret, isVar);
-                if (optionalSyntax != null)
+                if (optionalSyntax is not null)
                     TypeMention.Create(cx, optionalSyntax, ret, type);
             });
             return ret;
@@ -27,7 +27,7 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
         private static VariableDeclaration CreateSingle(Context cx, DeclarationExpressionSyntax node, SingleVariableDesignationSyntax designation, IExpressionParentEntity parent, int child)
         {
             var variableSymbol = cx.GetModel(designation).GetDeclaredSymbol(designation) as ILocalSymbol;
-            if (variableSymbol == null)
+            if (variableSymbol is null)
             {
                 cx.ModelError(node, "Failed to determine local variable");
                 return Create(cx, node, (AnnotatedTypeSymbol?)null, parent, child);
@@ -149,7 +149,7 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
                 var localVar = LocalVariable.Create(cx, declSymbol);
                 localVar.PopulateManual(ret, isVar);
 
-                if (d.Initializer != null)
+                if (d.Initializer is not null)
                 {
                     Create(cx, d.Initializer.Value, ret, 0);
 

csharp/extractor/Semmle.Extraction.CSharp/Entities/Field.cs

@@ -61,7 +61,7 @@ namespace Semmle.Extraction.CSharp.Entities
             foreach (var initializer in Symbol.DeclaringSyntaxReferences
                 .Select(n => n.GetSyntax())
                 .OfType<VariableDeclaratorSyntax>()
-                .Where(n => n.Initializer != null))
+                .Where(n => n.Initializer is not null))
             {
                 Context.PopulateLater(() =>
                 {
@@ -79,7 +79,7 @@ namespace Semmle.Extraction.CSharp.Entities
             foreach (var initializer in Symbol.DeclaringSyntaxReferences
                 .Select(n => n.GetSyntax())
                 .OfType<EnumMemberDeclarationSyntax>()
-                .Where(n => n.EqualsValue != null))
+                .Where(n => n.EqualsValue is not null))
             {
                 // Mark fields that have explicit initializers.
                 var constValue = Symbol.HasConstantValue

csharp/extractor/Semmle.Extraction.CSharp/Entities/File.cs

@@ -45,7 +45,7 @@ namespace Semmle.Extraction.CSharp.Entities
                     var lineCount = 0;
                     using (var sr = new StreamReader(originalPath, detectEncodingFromByteOrderMarks: true))
                     {
-                        while (sr.ReadLine() != null)
+                        while (sr.ReadLine() is not null)
                         {
                             lineCount++;
                         }

csharp/extractor/Semmle.Extraction.CSharp/Entities/Indexer.cs

@@ -42,7 +42,7 @@ namespace Semmle.Extraction.CSharp.Entities
             if (IsSourceDeclaration)
             {
                 var expressionBody = ExpressionBody;
-                if (expressionBody != null)
+                if (expressionBody is not null)
                 {
                     // The expression may need to reference parameters in the getter.
                     // So we need to arrange that the expression is populated after the getter.

csharp/extractor/Semmle.Extraction.CSharp/Entities/Method.cs

@@ -74,13 +74,13 @@ namespace Semmle.Extraction.CSharp.Entities
             var block = Block;
             var expr = ExpressionBody;
 
-            if (block != null || expr != null)
+            if (block is not null || expr is not null)
             {
                 Context.PopulateLater(
                    () =>
                    {
                        ExtractInitializers(trapFile);
-                       if (block != null)
+                       if (block is not null)
                            Statements.Block.Create(Context, block, this, 0);
                        else
                            Expression.Create(Context, expr!, this, 0);
@@ -96,7 +96,7 @@ namespace Semmle.Extraction.CSharp.Entities
             {
                 var node = (CSharpSyntaxNode)decl.GetSyntax();
                 var lineCounts = node.Accept(new AstLineCounter());
-                if (lineCounts is object)
+                if (lineCounts is not null)
                 {
                     trapFile.numlines(callable, lineCounts);
                 }
@@ -118,7 +118,7 @@ namespace Semmle.Extraction.CSharp.Entities
                 }
             }
 
-            if (Symbol.OverriddenMethod != null)
+            if (Symbol.OverriddenMethod is not null)
             {
                 trapFile.overrides(this, Method.Create(Context, Symbol.OverriddenMethod));
             }
@@ -239,7 +239,7 @@ namespace Semmle.Extraction.CSharp.Entities
         [return: NotNullIfNotNull("methodDecl")]
         public static Method? Create(Context cx, IMethodSymbol? methodDecl)
         {
-            if (methodDecl == null)
+            if (methodDecl is null)
                 return null;
 
             var methodKind = methodDecl.MethodKind;

csharp/extractor/Semmle.Extraction.CSharp/Entities/Modifier.cs

@@ -72,7 +72,7 @@ namespace Semmle.Extraction.CSharp.Entities
 
         public static void ExtractModifiers(Context cx, TextWriter trapFile, IEntity key, ISymbol symbol)
         {
-            var interfaceDefinition = symbol.ContainingType != null
+            var interfaceDefinition = symbol.ContainingType is not null
                 && symbol.ContainingType.Kind == SymbolKind.NamedType
                 && symbol.ContainingType.TypeKind == TypeKind.Interface;
 

csharp/extractor/Semmle.Extraction.CSharp/Entities/Namespace.cs

@@ -14,7 +14,7 @@ namespace Semmle.Extraction.CSharp.Entities
         {
             trapFile.namespaces(this, Symbol.Name);
 
-            if (Symbol.ContainingNamespace != null)
+            if (Symbol.ContainingNamespace is not null)
             {
                 var parent = Create(Context, Symbol.ContainingNamespace);
                 trapFile.parent_namespace(this, parent);

csharp/extractor/Semmle.Extraction.CSharp/Entities/NamespaceDeclaration.cs

@@ -40,7 +40,7 @@ namespace Semmle.Extraction.CSharp.Entities
                 member.Accept(visitor);
             }
 
-            if (parent != null)
+            if (parent is not null)
             {
                 trapFile.parent_namespace_declaration(this, parent);
             }

csharp/extractor/Semmle.Extraction.CSharp/Entities/Parameter.cs

@@ -75,10 +75,10 @@ namespace Semmle.Extraction.CSharp.Entities
 
         public override void WriteId(TextWriter trapFile)
         {
-            if (Parent == null)
+            if (Parent is null)
                 Parent = Method.Create(Context, Symbol.ContainingSymbol as IMethodSymbol);
 
-            if (Parent == null)
+            if (Parent is null)
                 throw new InternalError(Symbol, "Couldn't get parent of symbol.");
 
             trapFile.WriteSubId(Parent);
@@ -134,7 +134,7 @@ namespace Semmle.Extraction.CSharp.Entities
                 foreach (var syntax in Symbol.DeclaringSyntaxReferences
                     .Select(d => d.GetSyntax())
                     .OfType<ParameterSyntax>()
-                    .Where(s => s.Type != null))
+                    .Where(s => s.Type is not null))
                 {
                     TypeMention.Create(Context, syntax.Type!, this, type);
                 }
@@ -146,22 +146,22 @@ namespace Semmle.Extraction.CSharp.Entities
                 // We should really define param_default(param, string)
                 // And use parameter child #0 to encode the default expression.
                 var defaultValue = GetParameterDefaultValue(Symbol);
-                if (defaultValue == null)
+                if (defaultValue is null)
                 {
                     // In case this parameter belongs to an accessor of an indexer, we need
                     // to get the default value from the corresponding parameter belonging
                     // to the indexer itself
                     var method = (IMethodSymbol)Symbol.ContainingSymbol;
-                    if (method != null)
+                    if (method is not null)
                     {
                         var i = method.Parameters.IndexOf(Symbol);
                         var indexer = (IPropertySymbol?)method.AssociatedSymbol;
-                        if (indexer != null)
+                        if (indexer is not null)
                             defaultValue = GetParameterDefaultValue(indexer.Parameters[i]);
                     }
                 }
 
-                if (defaultValue != null)
+                if (defaultValue is not null)
                 {
                     Context.PopulateLater(() =>
                     {
@@ -217,7 +217,7 @@ namespace Semmle.Extraction.CSharp.Entities
 
         public override bool Equals(object? obj)
         {
-            return obj != null && obj.GetType() == typeof(VarargsType);
+            return obj is not null && obj.GetType() == typeof(VarargsType);
         }
 
         public static VarargsType Create(Context cx) => VarargsTypeFactory.Instance.CreateEntity(cx, typeof(VarargsType), null);
@@ -254,7 +254,7 @@ namespace Semmle.Extraction.CSharp.Entities
 
         public override bool Equals(object? obj)
         {
-            return obj != null && obj.GetType() == typeof(VarargsParam);
+            return obj is not null && obj.GetType() == typeof(VarargsParam);
         }
 
         public static VarargsParam Create(Context cx, Method method) => VarargsParamFactory.Instance.CreateEntity(cx, typeof(VarargsParam), method);

csharp/extractor/Semmle.Extraction.CSharp/Entities/Property.cs

@@ -72,7 +72,7 @@ namespace Semmle.Extraction.CSharp.Entities
             if (IsSourceDeclaration && Symbol.FromSource())
             {
                 var expressionBody = ExpressionBody;
-                if (expressionBody != null)
+                if (expressionBody is not null)
                 {
                     Context.PopulateLater(() => Expression.Create(Context, expressionBody, this, 0));
                 }
@@ -80,7 +80,7 @@ namespace Semmle.Extraction.CSharp.Entities
                 var child = 1;
                 foreach (var initializer in declSyntaxReferences
                     .Select(n => n.Initializer)
-                    .Where(i => i != null))
+                    .Where(i => i is not null))
                 {
                     Context.PopulateLater(() =>
                     {

csharp/extractor/Semmle.Extraction.CSharp/Entities/Statements/Case.cs

@@ -72,7 +72,7 @@ namespace Semmle.Extraction.CSharp.Entities.Statements
         {
             Expressions.Pattern.Create(Context, Stmt.Pattern, this, 0);
 
-            if (Stmt.WhenClause != null)
+            if (Stmt.WhenClause is not null)
             {
                 Expression.Create(Context, Stmt.WhenClause.Condition, this, 1);
             }

csharp/extractor/Semmle.Extraction.CSharp/Entities/Statements/Catch.cs

@@ -14,7 +14,7 @@ namespace Semmle.Extraction.CSharp.Entities.Statements
 
         protected override void PopulateStatement(TextWriter trapFile)
         {
-            var isSpecificCatchClause = Stmt.Declaration != null;
+            var isSpecificCatchClause = Stmt.Declaration is not null;
             var hasVariableDeclaration = isSpecificCatchClause && Stmt.Declaration!.Identifier.RawKind != 0;
 
             if (hasVariableDeclaration) // A catch clause of the form 'catch(Ex ex) { ... }'
@@ -32,7 +32,7 @@ namespace Semmle.Extraction.CSharp.Entities.Statements
                 trapFile.catch_type(this, exception, false);
             }
 
-            if (Stmt.Filter != null)
+            if (Stmt.Filter is not null)
             {
                 // For backward compatibility, the catch filter clause is child number 2.
                 Expression.Create(Context, Stmt.Filter.FilterExpression, this, 2);

csharp/extractor/Semmle.Extraction.CSharp/Entities/Statements/ExpressionStatement.cs

@@ -17,7 +17,7 @@ namespace Semmle.Extraction.CSharp.Entities.Statements
 
         protected override void PopulateStatement(TextWriter trapFile)
         {
-            if (Stmt.Expression != null)
+            if (Stmt.Expression is not null)
                 Expression.Create(Context, Stmt.Expression, this, 0);
             else
                 Context.ModelError(Stmt, "Invalid expression statement");

csharp/extractor/Semmle.Extraction.CSharp/Entities/Statements/For.cs

@@ -21,7 +21,7 @@ namespace Semmle.Extraction.CSharp.Entities.Statements
         {
             var child = -1;
 
-            if (Stmt.Declaration != null)
+            if (Stmt.Declaration is not null)
                 VariableDeclarations.Populate(Context, Stmt.Declaration, this, child, childIncrement: -1);
 
             foreach (var init in Stmt.Initializers)
@@ -29,7 +29,7 @@ namespace Semmle.Extraction.CSharp.Entities.Statements
                 Expression.Create(Context, init, this, child--);
             }
 
-            if (Stmt.Condition != null)
+            if (Stmt.Condition is not null)
             {
                 Expression.Create(Context, Stmt.Condition, this, 0);
             }

csharp/extractor/Semmle.Extraction.CSharp/Entities/Statements/ForEach.cs

@@ -51,31 +51,31 @@ namespace Semmle.Extraction.CSharp.Entities.Statements
 
             trapFile.foreach_stmt_info(this, info.IsAsynchronous);
 
-            if (info.GetEnumeratorMethod != null)
+            if (info.GetEnumeratorMethod is not null)
             {
                 var m = Method.Create(Context, info.GetEnumeratorMethod);
                 trapFile.foreach_stmt_desugar(this, m, ForeachSymbolType.GetEnumeratorMethod);
             }
 
-            if (info.MoveNextMethod != null)
+            if (info.MoveNextMethod is not null)
             {
                 var m = Method.Create(Context, info.MoveNextMethod);
                 trapFile.foreach_stmt_desugar(this, m, ForeachSymbolType.MoveNextMethod);
             }
 
-            if (info.DisposeMethod != null)
+            if (info.DisposeMethod is not null)
             {
                 var m = Method.Create(Context, info.DisposeMethod);
                 trapFile.foreach_stmt_desugar(this, m, ForeachSymbolType.DisposeMethod);
             }
 
-            if (info.CurrentProperty != null)
+            if (info.CurrentProperty is not null)
             {
                 var p = Property.Create(Context, info.CurrentProperty);
                 trapFile.foreach_stmt_desugar(this, p, ForeachSymbolType.CurrentProperty);
             }
 
-            if (info.ElementType != null)
+            if (info.ElementType is not null)
             {
                 var t = Type.Create(Context, info.ElementType);
                 trapFile.foreach_stmt_desugar(this, t, ForeachSymbolType.ElementType);

csharp/extractor/Semmle.Extraction.CSharp/Entities/Statements/If.cs

@@ -22,7 +22,7 @@ namespace Semmle.Extraction.CSharp.Entities.Statements
 
             Create(Context, Stmt.Statement, this, 1);
 
-            if (Stmt.Else != null)
+            if (Stmt.Else is not null)
                 Create(Context, Stmt.Else.Statement, this, 2);
         }
     }

csharp/extractor/Semmle.Extraction.CSharp/Entities/Statements/Return.cs

@@ -18,7 +18,7 @@ namespace Semmle.Extraction.CSharp.Entities.Statements
 
         protected override void PopulateStatement(TextWriter trapFile)
         {
-            if (Stmt.Expression != null)
+            if (Stmt.Expression is not null)
                 Expression.Create(Context, Stmt.Expression, this, 0);
         }
     }

csharp/extractor/Semmle.Extraction.CSharp/Entities/Statements/Throw.cs

@@ -18,7 +18,7 @@ namespace Semmle.Extraction.CSharp.Entities.Statements
 
         protected override void PopulateStatement(TextWriter trapFile)
         {
-            if (Stmt.Expression != null)
+            if (Stmt.Expression is not null)
                 Expression.Create(Context, Stmt.Expression, this, 0);
         }
     }

csharp/extractor/Semmle.Extraction.CSharp/Entities/Statements/Try.cs

@@ -27,7 +27,7 @@ namespace Semmle.Extraction.CSharp.Entities.Statements
 
             Create(Context, Stmt.Block, this, 0);
 
-            if (Stmt.Finally != null)
+            if (Stmt.Finally is not null)
             {
                 Create(Context, Stmt.Finally.Block, this, -1);
             }

csharp/extractor/Semmle.Extraction.CSharp/Entities/Statements/Using.cs

@@ -19,13 +19,13 @@ namespace Semmle.Extraction.CSharp.Entities.Statements
 
         protected override void PopulateStatement(TextWriter trapFile)
         {
-            if (Stmt.Declaration != null)
+            if (Stmt.Declaration is not null)
                 VariableDeclarations.Populate(Context, Stmt.Declaration, this, -1, childIncrement: -1);
 
-            if (Stmt.Expression != null)
+            if (Stmt.Expression is not null)
                 Expression.Create(Context, Stmt.Expression, this, 0);
 
-            if (Stmt.Statement != null)
+            if (Stmt.Statement is not null)
                 Statement.Create(Context, Stmt.Statement, this, 1);
         }
     }

csharp/extractor/Semmle.Extraction.CSharp/Entities/Statements/Yield.cs

@@ -18,7 +18,7 @@ namespace Semmle.Extraction.CSharp.Entities.Statements
 
         protected override void PopulateStatement(TextWriter trapFile)
         {
-            if (Stmt.Expression != null)
+            if (Stmt.Expression is not null)
             {
                 Expression.Create(Context, Stmt.Expression, this, 0);
             }

csharp/extractor/Semmle.Extraction.CSharp/Entities/TypeMention.cs

@@ -103,7 +103,7 @@ namespace Semmle.Extraction.CSharp.Entities
                 case SyntaxKind.QualifiedName:
                     var qns = (QualifiedNameSyntax)syntax;
                     var right = Create(Context, qns.Right, parent, type);
-                    if (type.ContainingType is object)
+                    if (type.ContainingType is not null)
                     {
                         // Type qualifier
                         Create(Context, qns.Left, right, type.ContainingType);

csharp/extractor/Semmle.Extraction.CSharp/Entities/Types/NamedType.cs

@@ -76,7 +76,7 @@ namespace Semmle.Extraction.CSharp.Entities
 
             PopulateType(trapFile, constructUnderlyingTupleType);
 
-            if (Symbol.EnumUnderlyingType != null)
+            if (Symbol.EnumUnderlyingType is not null)
             {
                 trapFile.enum_underlying_type(this, Type.Create(Context, Symbol.EnumUnderlyingType).TypeRef);
             }

csharp/extractor/Semmle.Extraction.CSharp/Entities/Types/NullType.cs

@@ -24,7 +24,7 @@ namespace Semmle.Extraction.CSharp.Entities
 
         public override bool Equals(object? obj)
         {
-            return obj != null && obj.GetType() == typeof(NullType);
+            return obj is not null && obj.GetType() == typeof(NullType);
         }
 
         public static Type Create(Context cx) => NullTypeFactory.Instance.CreateEntity(cx, typeof(NullType), null);

csharp/extractor/Semmle.Extraction.CSharp/Entities/Types/Type.cs

@@ -21,7 +21,7 @@ namespace Semmle.Extraction.CSharp.Entities
         public static bool ConstructedOrParentIsConstructed(INamedTypeSymbol symbol)
         {
             return !SymbolEqualityComparer.Default.Equals(symbol, symbol.OriginalDefinition) ||
-                symbol.ContainingType != null && ConstructedOrParentIsConstructed(symbol.ContainingType);
+                symbol.ContainingType is not null && ConstructedOrParentIsConstructed(symbol.ContainingType);
         }
 
         private static Kinds.TypeKind GetClassType(Context cx, ITypeSymbol t, bool constructUnderlyingTupleType)
@@ -101,12 +101,12 @@ namespace Semmle.Extraction.CSharp.Entities
             }
 
             var containingType = ContainingType;
-            if (containingType != null && Symbol.Kind != SymbolKind.TypeParameter)
+            if (containingType is not null && Symbol.Kind != SymbolKind.TypeParameter)
             {
                 var originalDefinition = Symbol.TypeKind == TypeKind.Error ? this : Create(Context, Symbol.OriginalDefinition);
                 trapFile.nested_types(this, containingType, originalDefinition);
             }
-            else if (Symbol.ContainingNamespace != null)
+            else if (Symbol.ContainingNamespace is not null)
             {
                 trapFile.parent_namespace(this, Namespace.Create(Context, Symbol.ContainingNamespace));
             }
@@ -116,7 +116,7 @@ namespace Semmle.Extraction.CSharp.Entities
                 // They are in the namespace of the original object
                 var elementType = array.ElementType;
                 var ns = elementType.TypeKind == TypeKind.TypeParameter ? Context.Compilation.GlobalNamespace : elementType.ContainingNamespace;
-                if (ns != null)
+                if (ns is not null)
                     trapFile.parent_namespace(this, Namespace.Create(Context, ns));
             }
 
@@ -125,11 +125,11 @@ namespace Semmle.Extraction.CSharp.Entities
                 var elementType = pointer.PointedAtType;
                 var ns = elementType.TypeKind == TypeKind.TypeParameter ? Context.Compilation.GlobalNamespace : elementType.ContainingNamespace;
 
-                if (ns != null)
+                if (ns is not null)
                     trapFile.parent_namespace(this, Namespace.Create(Context, ns));
             }
 
-            if (Symbol.BaseType != null && Symbol.BaseType.SpecialType == SpecialType.System_MulticastDelegate)
+            if (Symbol.BaseType is not null && Symbol.BaseType.SpecialType == SpecialType.System_MulticastDelegate)
             {
                 // This is a delegate.
                 // The method "Invoke" has the return type.
@@ -155,7 +155,7 @@ namespace Semmle.Extraction.CSharp.Entities
                 baseLists = baseLists.Concat(declSyntaxReferences.OfType<StructDeclarationSyntax>().Select(c => c.BaseList));
 
                 baseLists
-                    .Where(bl => bl != null)
+                    .Where(bl => bl is not null)
                     .SelectMany(bl => bl!.Types)
                     .Zip(
                         baseTypes.Where(bt => bt.Symbol.SpecialType != SpecialType.System_Object),
@@ -212,7 +212,7 @@ namespace Semmle.Extraction.CSharp.Entities
         /// </summary>
         public void PopulateGenerics()
         {
-            if (Symbol == null || !NeedsPopulation || !Context.ExtractGenerics(this))
+            if (Symbol is null || !NeedsPopulation || !Context.ExtractGenerics(this))
                 return;
 
             var members = new List<ISymbol>();
@@ -240,7 +240,7 @@ namespace Semmle.Extraction.CSharp.Entities
                 Context.CreateEntity(member);
             }
 
-            if (Symbol.BaseType != null)
+            if (Symbol.BaseType is not null)
                 Create(Context, Symbol.BaseType).PopulateGenerics();
 
             foreach (var i in Symbol.Interfaces)
@@ -262,7 +262,7 @@ namespace Semmle.Extraction.CSharp.Entities
         public static Type Create(Context cx, ITypeSymbol? type)
         {
             type = type.DisambiguateType();
-            return type == null
+            return type is null
                 ? NullType.Create(cx)
                 : (Type)cx.CreateEntity(type);
         }
@@ -273,7 +273,7 @@ namespace Semmle.Extraction.CSharp.Entities
         public virtual int Dimension => 0;
 
         public static bool IsDelegate(ITypeSymbol? symbol) =>
-            symbol != null && symbol.TypeKind == TypeKind.Delegate;
+            symbol is not null && symbol.TypeKind == TypeKind.Delegate;
 
         /// <summary>
         /// A copy of a delegate "Invoke" method or function pointer parameter.

csharp/extractor/Semmle.Extraction.CSharp/Entities/Types/TypeParameter.cs

@@ -62,7 +62,7 @@ namespace Semmle.Extraction.CSharp.Entities
                 var declSyntaxReferences = Symbol.DeclaringSyntaxReferences
                     .Select(d => d.GetSyntax())
                     .Select(s => s.Parent)
-                    .Where(p => p != null)
+                    .Where(p => p is not null)
                     .Select(p => p!.Parent)
                     .ToArray();
                 var clauses = declSyntaxReferences.OfType<MethodDeclarationSyntax>().SelectMany(m => m.ConstraintClauses);

csharp/extractor/Semmle.Extraction.CSharp/Entities/UserOperator.cs

@@ -58,15 +58,15 @@ namespace Semmle.Extraction.CSharp.Entities
         private bool IsImplicitOperator(out ITypeSymbol containingType)
         {
             containingType = Symbol.ContainingType;
-            if (containingType != null)
+            if (containingType is not null)
             {
                 var containingNamedType = containingType as INamedTypeSymbol;
-                return containingNamedType == null ||
+                return containingNamedType is null ||
                     !containingNamedType.GetMembers(Symbol.Name).Contains(Symbol);
             }
 
             var pointerType = Symbol.Parameters.Select(p => p.Type).OfType<IPointerTypeSymbol>().FirstOrDefault();
-            if (pointerType != null)
+            if (pointerType is not null)
             {
                 containingType = pointerType;
                 return true;

csharp/extractor/Semmle.Extraction.CSharp/Entities/UsingDirective.cs

@@ -47,7 +47,7 @@ namespace Semmle.Extraction.CSharp.Entities
                 trapFile.using_directive_location(this, Context.CreateLocation(ReportingLocation));
             }
 
-            if (parent != null)
+            if (parent is not null)
             {
                 trapFile.parent_namespace_declaration(this, parent);
             }

csharp/extractor/Semmle.Extraction.CSharp/Extractor/Analyser.cs

@@ -193,7 +193,7 @@ namespace Semmle.Extraction.CSharp
                 var transformedSourcePath = PathTransformer.Transform(sourcePath);
 
                 var projectLayout = layout.LookupProjectOrNull(transformedSourcePath);
-                var excluded = projectLayout == null;
+                var excluded = projectLayout is null;
                 var trapPath = excluded ? "" : projectLayout!.GetTrapPath(Logger, transformedSourcePath, options.TrapCompression);
                 var upToDate = false;
 

csharp/extractor/Semmle.Extraction.CSharp/Extractor/CompilerVersion.cs

@@ -51,7 +51,7 @@ namespace Semmle.Extraction.CSharp
             SpecifiedCompiler = options.CompilerName;
             specifiedFramework = options.Framework;
 
-            if (SpecifiedCompiler != null)
+            if (SpecifiedCompiler is not null)
             {
                 if (!File.Exists(SpecifiedCompiler))
                 {
@@ -69,7 +69,7 @@ namespace Semmle.Extraction.CSharp
 
                 var mscorlibExists = File.Exists(Path.Combine(compilerDir, "mscorlib.dll"));
 
-                if (specifiedFramework == null && mscorlibExists)
+                if (specifiedFramework is null && mscorlibExists)
                 {
                     specifiedFramework = compilerDir;
                 }
@@ -81,7 +81,7 @@ namespace Semmle.Extraction.CSharp
                     return;
                 }
 
-                if (versionInfo.LegalCopyright == null || !versionInfo.LegalCopyright.Contains(vendor))
+                if (versionInfo.LegalCopyright is null || !versionInfo.LegalCopyright.Contains(vendor))
                 {
                     SkipExtractionBecause($"the compiler isn't copyright {vendor}, but instead {versionInfo.LegalCopyright ?? "<null>"}");
                     return;
@@ -120,7 +120,7 @@ namespace Semmle.Extraction.CSharp
         /// <summary>
         /// Gets additional reference directories - the compiler directory.
         /// </summary>
-        public string? AdditionalReferenceDirectories => SpecifiedCompiler != null ? Path.GetDirectoryName(SpecifiedCompiler) : null;
+        public string? AdditionalReferenceDirectories => SpecifiedCompiler is not null ? Path.GetDirectoryName(SpecifiedCompiler) : null;
 
         /// <summary>
         /// Adds @csc.rsp to the argument list to mimic csc.exe.

csharp/extractor/Semmle.Extraction.CSharp/Extractor/Context.cs

@@ -21,7 +21,7 @@ namespace Semmle.Extraction.CSharp
             // todo: when this context belongs to a SourceScope, the syntax tree can be retrieved from the scope, and
             // the node parameter could be removed. Is there any case when we pass in a node that's not from the current
             // tree?
-            if (cachedModel == null || node.SyntaxTree != cachedModel.SyntaxTree)
+            if (cachedModel is null || node.SyntaxTree != cachedModel.SyntaxTree)
             {
                 cachedModel = Compilation.GetSemanticModel(node.SyntaxTree);
             }
@@ -80,14 +80,14 @@ namespace Semmle.Extraction.CSharp
 
         public override Extraction.Entities.Location CreateLocation()
         {
-            return SourceTree == null
+            return SourceTree is null
                 ? GeneratedLocation.Create(this)
                 : CreateLocation(Microsoft.CodeAnalysis.Location.Create(SourceTree, Microsoft.CodeAnalysis.Text.TextSpan.FromBounds(0, 0)));
         }
 
         public override Extraction.Entities.Location CreateLocation(Microsoft.CodeAnalysis.Location? location)
         {
-            return (location == null || location.Kind == LocationKind.None)
+            return (location is null || location.Kind == LocationKind.None)
                 ? GeneratedLocation.Create(this)
                 : location.IsInSource
                     ? Entities.NonGeneratedSourceLocation.Create(this, location)

csharp/extractor/Semmle.Extraction.CSharp/Extractor/Extractor.cs

@@ -105,7 +105,7 @@ namespace Semmle.Extraction.CSharp
                     compilerVersion.AdditionalReferenceDirectories
                     );
 
-                if (compilerArguments == null)
+                if (compilerArguments is null)
                 {
                     var sb = new StringBuilder();
                     sb.Append("  Failed to parse command line: ").AppendList(" ", Entities.Compilation.Settings.Args);
@@ -143,7 +143,7 @@ namespace Semmle.Extraction.CSharp
             // 3) Directories specified by / lib.
             // 4) Directories specified by the LIB environment variable.
 
-            if (args.BaseDirectory is object)
+            if (args.BaseDirectory is not null)
             {
                 yield return args.BaseDirectory;
             }
@@ -152,7 +152,7 @@ namespace Semmle.Extraction.CSharp
                 yield return r;
 
             var lib = System.Environment.GetEnvironmentVariable("LIB");
-            if (lib != null)
+            if (lib is not null)
                 yield return lib;
         }
 
@@ -196,7 +196,7 @@ namespace Semmle.Extraction.CSharp
                         .Select(path => canonicalPathCache.GetCanonicalPath(path))
                         .FirstOrDefault();
 
-                    if (composed is object)
+                    if (composed is not null)
                     {
                         var reference = MakeReference(clref, composed);
                         ret.Add(reference);

csharp/extractor/Semmle.Extraction.CSharp/Extractor/TracingAnalyser.cs

@@ -133,11 +133,11 @@ namespace Semmle.Extraction.CSharp
             // There's no apparent way to access the output filename from the compilation,
             // so we need to re-parse the command line arguments.
 
-            if (commandLineArguments.OutputFileName == null)
+            if (commandLineArguments.OutputFileName is null)
             {
                 // No output specified: Use name based on first filename
                 var entry = compilation.GetEntryPoint(System.Threading.CancellationToken.None);
-                if (entry == null)
+                if (entry is null)
                 {
                     if (compilation.SyntaxTrees.Length == 0)
                         throw new InvalidOperationException("No source files seen");
@@ -188,7 +188,7 @@ namespace Semmle.Extraction.CSharp
         {
             get
             {
-                return extractor == null || extractor.Standalone || compilation == null ? Enumerable.Empty<Diagnostic>() :
+                return extractor is null || extractor.Standalone || compilation is null ? Enumerable.Empty<Diagnostic>() :
                     compilation.
                     GetDiagnostics().
                     Where(e => e.Severity >= DiagnosticSeverity.Error && !errorsToIgnore.Contains(e.Id));

csharp/extractor/Semmle.Extraction.CSharp/Populators/CommentPopulator.cs

@@ -24,7 +24,7 @@ namespace Semmle.Extraction.CSharp.Populators
                     // When the duplication guard key exists, it means that the entity is guarded against
                     // trap duplication (<see cref = "Context.BindComments(IEntity, Location)" />).
                     // We must therefore also guard comment construction.
-                    if (duplicationGuardKey != null)
+                    if (duplicationGuardKey is not null)
                         cx.WithDuplicationGuard(duplicationGuardKey, a);
                     else
                         a();

csharp/extractor/Semmle.Extraction.CSharp/Populators/CompilationUnitVisitor.cs

@@ -65,7 +65,7 @@ namespace Semmle.Extraction.CSharp.Populators
 
             for (var i = 0; i < globalStatements.Count; i++)
             {
-                if (globalStatements[i].Statement is object)
+                if (globalStatements[i].Statement is not null)
                 {
                     Statement.Create(Cx, globalStatements[i].Statement, block, i);
                 }

csharp/extractor/Semmle.Extraction.CSharp/Populators/Locations.cs

@@ -15,7 +15,7 @@ namespace Semmle.Extraction.CSharp.Populators
         /// <returns>Extended location.</returns>
         public static Location ExtendLocation(this Location l1, SyntaxNode n2)
         {
-            if (n2 == null)
+            if (n2 is null)
             {
                 return l1;
             }

csharp/extractor/Semmle.Extraction.CSharp/Populators/TypeOrNamespaceVisitor.cs

@@ -12,7 +12,7 @@ namespace Semmle.Extraction.CSharp.Populators
         public override void VisitUsingDirective(UsingDirectiveSyntax usingDirective)
         {
             // Only deal with "using namespace" not "using X = Y"
-            if (usingDirective.Alias == null)
+            if (usingDirective.Alias is null)
                 new UsingDirective(Cx, usingDirective, (NamespaceDeclaration)Parent);
         }
 

csharp/extractor/Semmle.Extraction.CSharp/SymbolExtensions.cs

@@ -117,7 +117,7 @@ namespace Semmle.Extraction.CSharp
                         case TypeKind.Delegate:
                         case TypeKind.Error:
                             var named = (INamedTypeSymbol)type;
-                            if (named.IsTupleType && named.TupleUnderlyingType is object)
+                            if (named.IsTupleType && named.TupleUnderlyingType is not null)
                                 named = named.TupleUnderlyingType;
                             if (IdDependsOnImpl(named.ContainingType))
                                 return true;
@@ -306,14 +306,14 @@ namespace Semmle.Extraction.CSharp
 
             void AddContaining()
             {
-                if (named.ContainingType != null)
+                if (named.ContainingType is not null)
                 {
                     named.ContainingType.BuildOrWriteId(cx, trapFile, symbolBeingDefined, addBaseClass);
                     trapFile.Write('.');
                 }
-                else if (named.ContainingNamespace != null)
+                else if (named.ContainingNamespace is not null)
                 {
-                    if (cx.ShouldAddAssemblyTrapPrefix && named.ContainingAssembly is object)
+                    if (cx.ShouldAddAssemblyTrapPrefix && named.ContainingAssembly is not null)
                         BuildAssembly(named.ContainingAssembly, trapFile);
                     named.ContainingNamespace.BuildNamespace(cx, trapFile);
                 }
@@ -594,7 +594,7 @@ namespace Semmle.Extraction.CSharp
         /// Holds if this method is a source declaration.
         /// </summary>
         public static bool IsSourceDeclaration(this IMethodSymbol method) =>
-            IsSourceDeclaration((ISymbol)method) && SymbolEqualityComparer.Default.Equals(method, method.ConstructedFrom) && method.ReducedFrom == null;
+            IsSourceDeclaration((ISymbol)method) && SymbolEqualityComparer.Default.Equals(method, method.ConstructedFrom) && method.ReducedFrom is null;
 
         /// <summary>
         /// Holds if this parameter is a source declaration.
@@ -618,7 +618,7 @@ namespace Semmle.Extraction.CSharp
         [return: NotNullIfNotNull("symbol")]
         public static IEntity? CreateEntity(this Context cx, ISymbol symbol)
         {
-            if (symbol == null)
+            if (symbol is null)
                 return null;
 
             using (cx.StackGuard)

csharp/extractor/Semmle.Extraction/Context.cs

@@ -148,7 +148,7 @@ namespace Semmle.Extraction
         public void PopulateLater(Action a)
         {
             var key = GetCurrentTagStackKey();
-            if (key is object)
+            if (key is not null)
             {
                 // If we are currently executing with a duplication guard, then the same
                 // guard must be used for the deferred action
@@ -425,11 +425,11 @@ namespace Semmle.Extraction
             {
                 Message message;
 
-                if (node != null)
+                if (node is not null)
                 {
                     message = Message.Create(this, ex.Message, node, ex.StackTrace);
                 }
-                else if (symbol != null)
+                else if (symbol is not null)
                 {
                     message = Message.Create(this, ex.Message, symbol, ex.StackTrace);
                 }

csharp/extractor/Semmle.Extraction/Entities/GeneratedLocation.cs

@@ -26,7 +26,7 @@ namespace Semmle.Extraction.Entities
 
         public override int GetHashCode() => 98732567;
 
-        public override bool Equals(object? obj) => obj != null && obj.GetType() == typeof(GeneratedLocation);
+        public override bool Equals(object? obj) => obj is not null && obj.GetType() == typeof(GeneratedLocation);
 
         public static GeneratedLocation Create(Context cx) => GeneratedLocationFactory.Instance.CreateEntity(cx, typeof(GeneratedLocation), null);
 

csharp/extractor/Semmle.Extraction/Layout.cs

@@ -136,7 +136,7 @@ namespace Semmle.Extraction
         /// </summary>
         /// <param name="path">The absolute path of the file to query.</param>
         /// <returns>True iff there is no layout file or the layout file specifies the file.</returns>
-        public bool FileInLayout(PathTransformer.ITransformedPath path) => LookupProjectOrNull(path) != null;
+        public bool FileInLayout(PathTransformer.ITransformedPath path) => LookupProjectOrNull(path) is not null;
 
         private void ReadLayoutFile(string layout)
         {

csharp/extractor/Semmle.Util/CanonicalPathCache.cs

@@ -42,7 +42,7 @@ namespace Semmle.Util
         {
             var parent = Directory.GetParent(path);
 
-            return parent != null ?
+            return parent is not null ?
                 Path.Combine(cache.GetCanonicalPath(parent.FullName), Path.GetFileName(path)) :
                 path.ToUpperInvariant();
         }
@@ -122,7 +122,7 @@ namespace Semmle.Util
         {
             var parent = Directory.GetParent(path);
 
-            if (parent == null)
+            if (parent is null)
             {
                 // We are at a root of the filesystem.
                 // Convert drive letters, UNC paths etc. to uppercase.

csharp/extractor/Semmle.Util/CommandLineExtensions.cs

@@ -20,7 +20,7 @@ namespace Semmle.Util
             {
                 string? line;
                 using var file = new StreamReader(arg);
-                while ((line = file.ReadLine()) != null)
+                while ((line = file.ReadLine()) is not null)
                     textWriter.WriteLine(line);
                 found = true;
             }