Enable nullable reference types for the repo

Directory.Build.props

@@ -11,6 +11,7 @@
   <PropertyGroup>
     <LangVersion Condition="'$(Language)' == 'C#'">8</LangVersion>
     <LangVersion Condition="'$(Language)' == 'VB'">16</LangVersion>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <PropertyGroup>

src/Microsoft.NetCore.Analyzers/Core/Runtime/DisposeObjectsBeforeLosingScope.cs

@@ -77,7 +77,7 @@ public override void Initialize(AnalysisContext context)
             context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None);
             context.RegisterCompilationStartAction(compilationContext =>
             {
-                if (!DisposeAnalysisHelper.TryGetOrCreate(compilationContext.Compilation, out DisposeAnalysisHelper disposeAnalysisHelper))
+                if (!DisposeAnalysisHelper.TryGetOrCreate(compilationContext.Compilation, out var disposeAnalysisHelper))
                 {
                     return;
                 }

src/Utilities/Compiler/Analyzer.Utilities.projitems

@@ -61,7 +61,6 @@
     <Compile Include="$(MSBuildThisFileDirectory)Extensions\IOperationExtensions.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Extensions\ISymbolExtensions.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Extensions\ITypeSymbolExtensions.cs" />
-    <Compile Include="$(MSBuildThisFileDirectory)Extensions\ObjectExtensions.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Extensions\StringExtensions.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Extensions\SymbolVisibility.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Extensions\UriExtensions.cs" />
@@ -70,6 +69,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Options\AnalyzerOptionsExtensions.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Options\CategorizedAnalyzerConfigOptions.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Options\EditorConfigParser.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)NullableAttributes.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)SymbolDisplayFormats.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)FxCopWellKnownDiagnosticTags.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)UnusedValue.cs" />

src/Utilities/Compiler/BoundedCacheWithFactory.cs

@@ -15,13 +15,13 @@ internal class BoundedCacheWithFactory<TKey, TValue>
     {
         // Bounded weak reference cache.
         // Size 5 is an arbitrarily chosen bound, which can be tuned in future as required.
-        private readonly List<WeakReference<Entry>> _weakReferencedEntries
-            = new List<WeakReference<Entry>> {
-                new WeakReference<Entry>(null),
-                new WeakReference<Entry>(null),
-                new WeakReference<Entry>(null),
-                new WeakReference<Entry>(null),
-                new WeakReference<Entry>(null),
+        private readonly List<WeakReference<Entry?>> _weakReferencedEntries
+            = new List<WeakReference<Entry?>> {
+                new WeakReference<Entry?>(null),
+                new WeakReference<Entry?>(null),
+                new WeakReference<Entry?>(null),
+                new WeakReference<Entry?>(null),
+                new WeakReference<Entry?>(null),
             };
 
         public TValue GetOrCreateValue(TKey key, Func<TKey, TValue> valueFactory)

src/Utilities/Compiler/CodeMetrics/CodeAnalysisMetricData.AssemblyMetricData.cs

@@ -44,7 +44,7 @@ internal static async Task<AssemblyMetricData> ComputeAsync(IAssemblySymbol asse
                     MetricsHelper.AddCoupledNamedTypes(coupledTypesBuilder, child.CoupledNamedTypes);
                     linesOfCode += child.SourceLines;
                     cyclomaticComplexity += child.CyclomaticComplexity;
-                    depthOfInheritance = Math.Max(child.DepthOfInheritance.Value, depthOfInheritance);
+                    depthOfInheritance = Math.Max(child.DepthOfInheritance.GetValueOrDefault(), depthOfInheritance);
 
                     // Compat: Maintainability index of an assembly is computed based on the values of types, not namespace children.
                     Debug.Assert(child.Symbol.Kind == SymbolKind.Namespace);

src/Utilities/Compiler/CodeMetrics/CodeAnalysisMetricData.NamedTypeMetricData.cs

@@ -87,7 +87,7 @@ internal static async Task<NamedTypeMetricData> ComputeAsync(INamedTypeSymbol na
 
                 ImmutableHashSet<IFieldSymbol> getFilteredFieldsForComplexity()
                 {
-                    ImmutableHashSet<IFieldSymbol>.Builder builderOpt = null;
+                    ImmutableHashSet<IFieldSymbol>.Builder? builderOpt = null;
                     var orderedFieldDatas = children.Where(c => c.Symbol.Kind == SymbolKind.Field).OrderBy(c => c.MaintainabilityIndex);
                     var indexThreshold = 99;
                     foreach (CodeAnalysisMetricData fieldData in orderedFieldDatas)

src/Utilities/Compiler/CodeMetrics/CodeAnalysisMetricData.NamespaceMetricData.cs

@@ -42,7 +42,7 @@ internal static async Task<NamespaceMetricData> ComputeAsync(INamespaceSymbol @n
                     MetricsHelper.AddCoupledNamedTypes(coupledTypesBuilder, child.CoupledNamedTypes);
                     maintainabilityIndexTotal += child.MaintainabilityIndex;
                     cyclomaticComplexity += child.CyclomaticComplexity;
-                    depthOfInheritance = Math.Max(child.DepthOfInheritance.Value, depthOfInheritance);
+                    depthOfInheritance = Math.Max(child.DepthOfInheritance.GetValueOrDefault(), depthOfInheritance);
 
                     // Avoid double counting lines for nested types.
                     if (child.Symbol.ContainingType == null)

src/Utilities/Compiler/CodeMetrics/CodeAnalysisMetricData.cs

@@ -32,7 +32,6 @@ internal CodeAnalysisMetricData(
             int? depthOfInheritance,
             ImmutableArray<CodeAnalysisMetricData> children)
         {
-            Debug.Assert(symbol != null);
             Debug.Assert(
                 symbol.Kind == SymbolKind.Assembly ||
                 symbol.Kind == SymbolKind.Namespace ||

src/Utilities/Compiler/CodeMetrics/ComputationalComplexityMetrics.cs

@@ -89,19 +89,17 @@ private static ComputationalComplexityMetrics Create(
 
         public static ComputationalComplexityMetrics Compute(IOperation operationBlock)
         {
-            Debug.Assert(operationBlock != null);
-
             bool hasSymbolInitializer = false;
             long executableLinesOfCode = 0;
             long operatorUsageCounts = 0;
             long symbolUsageCounts = 0;
             long constantUsageCounts = 0;
-            ImmutableHashSet<OperationKind>.Builder distinctOperatorKindsBuilder = null;
-            ImmutableHashSet<BinaryOperatorKind>.Builder distinctBinaryOperatorKindsBuilder = null;
-            ImmutableHashSet<UnaryOperatorKind>.Builder distinctUnaryOperatorKindsBuilder = null;
-            ImmutableHashSet<CaseKind>.Builder distinctCaseKindsBuilder = null;
-            ImmutableHashSet<ISymbol>.Builder distinctReferencedSymbolsBuilder = null;
-            ImmutableHashSet<object>.Builder distinctReferencedConstantsBuilder = null;
+            ImmutableHashSet<OperationKind>.Builder? distinctOperatorKindsBuilder = null;
+            ImmutableHashSet<BinaryOperatorKind>.Builder? distinctBinaryOperatorKindsBuilder = null;
+            ImmutableHashSet<UnaryOperatorKind>.Builder? distinctUnaryOperatorKindsBuilder = null;
+            ImmutableHashSet<CaseKind>.Builder? distinctCaseKindsBuilder = null;
+            ImmutableHashSet<ISymbol>.Builder? distinctReferencedSymbolsBuilder = null;
+            ImmutableHashSet<object>.Builder? distinctReferencedConstantsBuilder = null;
 
             // Explicit user applied attribute.
             if (operationBlock.Kind == OperationKind.None &&

src/Utilities/Compiler/DiagnosticHelpers.cs

@@ -87,7 +87,6 @@ public static bool TryConvertToUInt64(object value, SpecialType specialType, out
 
         internal static bool TryGetEnumMemberValues(INamedTypeSymbol enumType, out IList<ulong> values)
         {
-            Debug.Assert(enumType != null);
             Debug.Assert(enumType.TypeKind == TypeKind.Enum);
 
             values = new List<ulong>();
@@ -115,12 +114,10 @@ internal static bool TryGetEnumMemberValues(INamedTypeSymbol enumType, out IList
         public static string GetMemberName(ISymbol symbol)
         {
             // For Types
-            if (symbol.Kind == SymbolKind.NamedType)
+            if (symbol is INamedTypeSymbol namedType &&
+                namedType.IsGenericType)
             {
-                if ((symbol as INamedTypeSymbol).IsGenericType)
-                {
-                    return symbol.MetadataName;
-                }
+                return symbol.MetadataName;
             }
 
             // For other language constructs

src/Utilities/Compiler/DoNotCatchGeneralUnlessRethrown.cs

@@ -17,11 +17,11 @@ namespace Analyzer.Utilities
     internal abstract class DoNotCatchGeneralUnlessRethrownAnalyzer : DiagnosticAnalyzer
     {
         private readonly bool _shouldCheckLambdas;
-        private readonly string _enablingMethodAttributeFullyQualifiedName;
+        private readonly string? _enablingMethodAttributeFullyQualifiedName;
 
         private bool RequiresAttributeOnMethod => !string.IsNullOrEmpty(_enablingMethodAttributeFullyQualifiedName);
 
-        protected DoNotCatchGeneralUnlessRethrownAnalyzer(bool shouldCheckLambdas, string enablingMethodAttributeFullyQualifiedName = null)
+        protected DoNotCatchGeneralUnlessRethrownAnalyzer(bool shouldCheckLambdas, string? enablingMethodAttributeFullyQualifiedName = null)
         {
             _shouldCheckLambdas = shouldCheckLambdas;
             _enablingMethodAttributeFullyQualifiedName = enablingMethodAttributeFullyQualifiedName;
@@ -40,7 +40,7 @@ public override void Initialize(AnalysisContext analysisContext)
 
             analysisContext.RegisterCompilationStartAction(compilationStartAnalysisContext =>
             {
-                INamedTypeSymbol requiredAttributeType = null;
+                INamedTypeSymbol? requiredAttributeType = null;
                 if (RequiresAttributeOnMethod && (requiredAttributeType = GetRequiredAttributeType(compilationStartAnalysisContext.Compilation)) == null)
                 {
                     return;
@@ -61,7 +61,7 @@ bool IsDisallowedCatchType(INamedTypeSymbol type) =>
 
                     var method = (IMethodSymbol)operationBlockAnalysisContext.OwningSymbol;
 
-                    if (RequiresAttributeOnMethod && !MethodHasAttribute(method, requiredAttributeType))
+                    if (RequiresAttributeOnMethod && !MethodHasAttribute(method, requiredAttributeType!))
                     {
                         return;
                     }
@@ -80,9 +80,9 @@ bool IsDisallowedCatchType(INamedTypeSymbol type) =>
             });
         }
 
-        private INamedTypeSymbol GetRequiredAttributeType(Compilation compilation)
+        private INamedTypeSymbol? GetRequiredAttributeType(Compilation compilation)
         {
-            return compilation.GetOrCreateTypeByMetadataName(_enablingMethodAttributeFullyQualifiedName);
+            return compilation.GetOrCreateTypeByMetadataName(_enablingMethodAttributeFullyQualifiedName!);
         }
 
         private bool MethodHasAttribute(IMethodSymbol method, INamedTypeSymbol attributeType)
@@ -97,7 +97,7 @@ private static IReadOnlyCollection<INamedTypeSymbol> GetDisallowedCatchTypes(Com
                     compilation.GetSpecialType(SpecialType.System_Object),
                     compilation.GetOrCreateTypeByMetadataName(WellKnownTypeNames.SystemException),
                     compilation.GetOrCreateTypeByMetadataName(WellKnownTypeNames.SystemSystemException)
-                }.Where(x => x != null));
+                }.WhereNotNull());
         }
 
         /// <summary>

src/Utilities/Compiler/Extensions/CompilationExtensions.cs

@@ -1,4 +1,5 @@
-using System.Linq;
+using System.Diagnostics.CodeAnalysis;
+using System.Linq;
 using Microsoft.CodeAnalysis;
 
 namespace Analyzer.Utilities.Extensions
@@ -14,7 +15,7 @@ internal static class CompilationExtensions
         /// <param name="compilation">The compilation.</param>
         /// <param name="fullTypeName">Namespace + type name, e.g. "System.Exception".</param>
         /// <returns>The <see cref="INamedTypeSymbol"/> if found, null otherwise.</returns>
-        internal static INamedTypeSymbol GetOrCreateTypeByMetadataName(this Compilation compilation, string fullTypeName) =>
+        internal static INamedTypeSymbol? GetOrCreateTypeByMetadataName(this Compilation compilation, string fullTypeName) =>
             WellKnownTypeProvider.GetOrCreate(compilation).GetOrCreateTypeByMetadataName(fullTypeName);
 
         /// <summary>
@@ -23,7 +24,7 @@ internal static INamedTypeSymbol GetOrCreateTypeByMetadataName(this Compilation
         /// <param name="compilation">The compilation.</param>
         /// <param name="fullTypeName">Namespace + type name, e.g. "System.Exception".</param>
         /// <returns>The <see cref="INamedTypeSymbol"/> if found, null otherwise.</returns>
-        internal static bool TryGetOrCreateTypeByMetadataName(this Compilation compilation, string fullTypeName, out INamedTypeSymbol namedTypeSymbol) =>
+        internal static bool TryGetOrCreateTypeByMetadataName(this Compilation compilation, string fullTypeName, [NotNullWhen(returnValue: true)] out INamedTypeSymbol? namedTypeSymbol) =>
             WellKnownTypeProvider.GetOrCreate(compilation).TryGetOrCreateTypeByMetadataName(fullTypeName, out namedTypeSymbol);
     }
 }

src/Utilities/Compiler/Extensions/DiagnosticExtensions.cs

@@ -126,7 +126,7 @@ public static Diagnostic CreateDiagnostic(
         {
             if (!location.IsInSource)
             {
-                location = null;
+                location = Location.None;
             }
 
             return Diagnostic.Create(
@@ -158,7 +158,7 @@ public static Diagnostic CreateDiagnostic(
         public static Diagnostic CreateDiagnostic(
             this IEnumerable<Location> locations,
             DiagnosticDescriptor rule,
-            ImmutableDictionary<string, string> properties,
+            ImmutableDictionary<string, string>? properties,
             params object[] args)
         {
             IEnumerable<Location> inSource = locations.Where(l => l.IsInSource);
@@ -197,7 +197,7 @@ public static void ReportNoLocationDiagnostic(
             this Compilation compilation,
             DiagnosticDescriptor rule,
             Action<Diagnostic> addDiagnostic,
-            ImmutableDictionary<string, string> properties,
+            ImmutableDictionary<string, string>? properties,
             params object[] args)
         {
             var effectiveSeverity = GetEffectiveSeverity();

src/Utilities/Compiler/Extensions/IEnumerableExtensions.cs

@@ -60,16 +60,16 @@ public static IEnumerable<T> Order<T>(this IEnumerable<T> source) where T : ICom
             return source.OrderBy((t1, t2) => t1.CompareTo(t2));
         }
 
-        private static readonly Func<object, bool> s_notNullTest = x => x != null;
+        private static readonly Func<object?, bool> s_notNullTest = x => x != null;
 
-        public static IEnumerable<T> WhereNotNull<T>(this IEnumerable<T> source) where T : class
+        public static IEnumerable<T> WhereNotNull<T>(this IEnumerable<T?> source) where T : class
         {
             if (source == null)
             {
                 return ImmutableArray<T>.Empty;
             }
 
-            return source.Where((Func<T, bool>)s_notNullTest);
+            return source.Where((Func<T?, bool>)s_notNullTest)!;
         }
 
         public static ImmutableArray<TSource> WhereAsArray<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> selector)
@@ -95,8 +95,8 @@ public static ImmutableArray<TSource> WhereAsArray<TSource>(this IEnumerable<TSo
             }
         }
 
-        public static void Dispose<T>(this IEnumerable<T> collection)
-            where T : IDisposable
+        public static void Dispose<T>(this IEnumerable<T?> collection)
+            where T : class, IDisposable
         {
             foreach (var item in collection)
             {

src/Utilities/Compiler/Extensions/IEnumerableOfIMethodSymbolExtensions.cs

@@ -100,7 +100,7 @@ public static IEnumerable<IMethodSymbol> GetMethodOverloadsWithDesiredParameterA
         /// <param name="members"></param>
         /// <param name="expectedParameterTypesInOrder"></param>
         /// <returns></returns>
-        public static IMethodSymbol GetFirstOrDefaultMemberWithParameterInfos(this IEnumerable<IMethodSymbol> members, params ParameterInfo[] expectedParameterTypesInOrder)
+        public static IMethodSymbol? GetFirstOrDefaultMemberWithParameterInfos(this IEnumerable<IMethodSymbol> members, params ParameterInfo[] expectedParameterTypesInOrder)
         {
             var expectedParameterCount = expectedParameterTypesInOrder.Length;
             return members?.FirstOrDefault(member =>