Merge pull request #40493 from jaredpar/nullable3

Nullable annotations for Compilation

.vscode/tasks.json

@@ -28,8 +28,8 @@
         "type": "shell",
         "args": [
           "msbuild",
-          "src/Compilers/CSharp/csc/csc.csproj",
-          "-p:UseRoslynAnalyzers=false"
+          "-p:UseRoslynAnalyzers=false",
+          "src/Compilers/CSharp/csc/csc.csproj"
         ],
         "problemMatcher": "$msCompile",
         "group": "build"

src/Compilers/Core/Portable/Compilation/CandidateReason.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+#nullable enable
+
 using Microsoft.CodeAnalysis.Text;
 
 namespace Microsoft.CodeAnalysis

src/Compilers/Core/Portable/Compilation/CommonModuleCompilationState.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+#nullable enable
+
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Threading;
 
 namespace Microsoft.CodeAnalysis
@@ -33,7 +36,7 @@ internal class ModuleCompilationState<TNamedTypeSymbol, TMethodSymbol> : CommonM
         /// <summary>
         /// Maps an async/iterator method to the synthesized state machine type that implements the method. 
         /// </summary>
-        private Dictionary<TMethodSymbol, TNamedTypeSymbol> _lazyStateMachineTypes;
+        private Dictionary<TMethodSymbol, TNamedTypeSymbol>? _lazyStateMachineTypes;
 
         internal void SetStateMachineType(TMethodSymbol method, TNamedTypeSymbol stateMachineClass)
         {
@@ -50,7 +53,7 @@ internal void SetStateMachineType(TMethodSymbol method, TNamedTypeSymbol stateMa
             }
         }
 
-        internal bool TryGetStateMachineType(TMethodSymbol method, out TNamedTypeSymbol stateMachineType)
+        internal bool TryGetStateMachineType(TMethodSymbol method, [NotNullWhen(true)] out TNamedTypeSymbol? stateMachineType)
         {
             Debug.Assert(Frozen);
 

src/Compilers/Core/Portable/Compilation/CommonSyntaxAndDeclarationManager.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+#nullable enable
+
 using System.Collections.Immutable;
 
 namespace Microsoft.CodeAnalysis

src/Compilers/Core/Portable/Compilation/CompilationOptions.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+#nullable enable
+
 using System;
 using System.Collections.Generic;
 using System.Collections.Immutable;
@@ -29,7 +31,7 @@ public abstract class CompilationOptions
         /// is derived from the name of the compilation (<see cref="Compilation.AssemblyName"/>)
         /// by appending a default extension for <see cref="OutputKind"/>.
         /// </remarks>
-        public string ModuleName { get; protected set; }
+        public string? ModuleName { get; protected set; }
 
         /// <summary>
         /// The full name of a global implicit class (script class). This class implicitly encapsulates top-level statements, 
@@ -41,7 +43,7 @@ public abstract class CompilationOptions
         /// The full name of a type that declares static Main method. Must be a valid non-generic namespace-qualified name.
         /// Null if any static Main method is a candidate for an entry point.
         /// </summary>
-        public string MainTypeName { get; protected set; }
+        public string? MainTypeName { get; protected set; }
 
         // Note that we avoid using default(ImmutableArray<byte>) for unspecified value since 
         // such value is currently not serializable by JSON serializer.
@@ -70,7 +72,7 @@ public abstract class CompilationOptions
         /// path to key file.
         /// </para>
         /// </remarks>
-        public string CryptoKeyFile { get; protected set; }
+        public string? CryptoKeyFile { get; protected set; }
 
         /// <summary>
         /// The CSP container containing the key with which to sign the output.
@@ -86,7 +88,7 @@ public abstract class CompilationOptions
         /// a signing tool (Microsoft .NET Framework Strong Name Utility (sn.exe) or equivalent) to sign them.
         /// </para>
         /// </remarks>
-        public string CryptoKeyContainer { get; protected set; }
+        public string? CryptoKeyContainer { get; protected set; }
 
         /// <summary>
         /// Mark the compilation assembly as delay-signed.
@@ -207,25 +209,25 @@ public abstract class CompilationOptions
         /// Resolves paths to metadata references specified in source via #r directives.
         /// Null if the compilation can't contain references to metadata other than those explicitly passed to its factory (such as #r directives in sources). 
         /// </summary>
-        public MetadataReferenceResolver MetadataReferenceResolver { get; protected set; }
+        public MetadataReferenceResolver? MetadataReferenceResolver { get; protected set; }
 
         /// <summary>
         /// Gets the resolver for resolving XML document references for the compilation.
         /// Null if the compilation is not allowed to contain XML file references, such as XML doc comment include tags and permission sets stored in an XML file.
         /// </summary>
-        public XmlReferenceResolver XmlReferenceResolver { get; protected set; }
+        public XmlReferenceResolver? XmlReferenceResolver { get; protected set; }
 
         /// <summary>
         /// Gets the resolver for resolving source document references for the compilation.
         /// Null if the compilation is not allowed to contain source file references, such as #line pragmas and #load directives.
         /// </summary>
-        public SourceReferenceResolver SourceReferenceResolver { get; protected set; }
+        public SourceReferenceResolver? SourceReferenceResolver { get; protected set; }
 
         /// <summary>
         /// Provides strong name and signature the source assembly.
         /// Null if assembly signing is not supported.
         /// </summary>
-        public StrongNameProvider StrongNameProvider { get; protected set; }
+        public StrongNameProvider? StrongNameProvider { get; protected set; }
 
         /// <summary>
         /// Used to compare assembly identities. May implement unification and portability policies specific to the target platform.
@@ -264,11 +266,11 @@ protected set
         internal CompilationOptions(
             OutputKind outputKind,
             bool reportSuppressedDiagnostics,
-            string moduleName,
-            string mainTypeName,
-            string scriptClassName,
-            string cryptoKeyContainer,
-            string cryptoKeyFile,
+            string? moduleName,
+            string? mainTypeName,
+            string? scriptClassName,
+            string? cryptoKeyContainer,
+            string? cryptoKeyFile,
             ImmutableArray<byte> cryptoPublicKey,
             bool? delaySign,
             bool publicSign,
@@ -282,11 +284,11 @@ protected set
             bool deterministic,
             DateTime currentLocalTime,
             bool debugPlusMode,
-            XmlReferenceResolver xmlReferenceResolver,
-            SourceReferenceResolver sourceReferenceResolver,
-            MetadataReferenceResolver metadataReferenceResolver,
+            XmlReferenceResolver? xmlReferenceResolver,
+            SourceReferenceResolver? sourceReferenceResolver,
+            MetadataReferenceResolver? metadataReferenceResolver,
             AssemblyIdentityComparer assemblyIdentityComparer,
-            StrongNameProvider strongNameProvider,
+            StrongNameProvider? strongNameProvider,
             MetadataImportOptions metadataImportOptions,
             bool referencesSupersedeLowerVersions)
         {
@@ -448,17 +450,17 @@ public CompilationOptions WithOptimizationLevel(OptimizationLevel value)
             return CommonWithOptimizationLevel(value);
         }
 
-        public CompilationOptions WithXmlReferenceResolver(XmlReferenceResolver resolver)
+        public CompilationOptions WithXmlReferenceResolver(XmlReferenceResolver? resolver)
         {
             return CommonWithXmlReferenceResolver(resolver);
         }
 
-        public CompilationOptions WithSourceReferenceResolver(SourceReferenceResolver resolver)
+        public CompilationOptions WithSourceReferenceResolver(SourceReferenceResolver? resolver)
         {
             return CommonWithSourceReferenceResolver(resolver);
         }
 
-        public CompilationOptions WithMetadataReferenceResolver(MetadataReferenceResolver resolver)
+        public CompilationOptions WithMetadataReferenceResolver(MetadataReferenceResolver? resolver)
         {
             return CommonWithMetadataReferenceResolver(resolver);
         }
@@ -468,17 +470,17 @@ public CompilationOptions WithAssemblyIdentityComparer(AssemblyIdentityComparer
             return CommonWithAssemblyIdentityComparer(comparer);
         }
 
-        public CompilationOptions WithStrongNameProvider(StrongNameProvider provider)
+        public CompilationOptions WithStrongNameProvider(StrongNameProvider? provider)
         {
             return CommonWithStrongNameProvider(provider);
         }
 
-        public CompilationOptions WithModuleName(string moduleName)
+        public CompilationOptions WithModuleName(string? moduleName)
         {
             return CommonWithModuleName(moduleName);
         }
 
-        public CompilationOptions WithMainTypeName(string mainTypeName)
+        public CompilationOptions WithMainTypeName(string? mainTypeName)
         {
             return CommonWithMainTypeName(mainTypeName);
         }
@@ -488,7 +490,7 @@ public CompilationOptions WithScriptClassName(string scriptClassName)
             return CommonWithScriptClassName(scriptClassName);
         }
 
-        public CompilationOptions WithCryptoKeyContainer(string cryptoKeyContainer)
+        public CompilationOptions WithCryptoKeyContainer(string? cryptoKeyContainer)
         {
             return CommonWithCryptoKeyContainer(cryptoKeyContainer);
         }
@@ -521,19 +523,19 @@ public CompilationOptions WithOverflowChecks(bool checkOverflow)
         protected abstract CompilationOptions CommonWithPlatform(Platform platform);
         protected abstract CompilationOptions CommonWithPublicSign(bool publicSign);
         protected abstract CompilationOptions CommonWithOptimizationLevel(OptimizationLevel value);
-        protected abstract CompilationOptions CommonWithXmlReferenceResolver(XmlReferenceResolver resolver);
-        protected abstract CompilationOptions CommonWithSourceReferenceResolver(SourceReferenceResolver resolver);
-        protected abstract CompilationOptions CommonWithMetadataReferenceResolver(MetadataReferenceResolver resolver);
+        protected abstract CompilationOptions CommonWithXmlReferenceResolver(XmlReferenceResolver? resolver);
+        protected abstract CompilationOptions CommonWithSourceReferenceResolver(SourceReferenceResolver? resolver);
+        protected abstract CompilationOptions CommonWithMetadataReferenceResolver(MetadataReferenceResolver? resolver);
         protected abstract CompilationOptions CommonWithAssemblyIdentityComparer(AssemblyIdentityComparer comparer);
-        protected abstract CompilationOptions CommonWithStrongNameProvider(StrongNameProvider provider);
+        protected abstract CompilationOptions CommonWithStrongNameProvider(StrongNameProvider? provider);
         protected abstract CompilationOptions CommonWithGeneralDiagnosticOption(ReportDiagnostic generalDiagnosticOption);
         protected abstract CompilationOptions CommonWithSpecificDiagnosticOptions(ImmutableDictionary<string, ReportDiagnostic> specificDiagnosticOptions);
         protected abstract CompilationOptions CommonWithSpecificDiagnosticOptions(IEnumerable<KeyValuePair<string, ReportDiagnostic>> specificDiagnosticOptions);
         protected abstract CompilationOptions CommonWithReportSuppressedDiagnostics(bool reportSuppressedDiagnostics);
-        protected abstract CompilationOptions CommonWithModuleName(string moduleName);
-        protected abstract CompilationOptions CommonWithMainTypeName(string mainTypeName);
+        protected abstract CompilationOptions CommonWithModuleName(string? moduleName);
+        protected abstract CompilationOptions CommonWithMainTypeName(string? mainTypeName);
         protected abstract CompilationOptions CommonWithScriptClassName(string scriptClassName);
-        protected abstract CompilationOptions CommonWithCryptoKeyContainer(string cryptoKeyContainer);
+        protected abstract CompilationOptions CommonWithCryptoKeyContainer(string? cryptoKeyContainer);
         protected abstract CompilationOptions CommonWithCryptoKeyFile(string cryptoKeyFile);
         protected abstract CompilationOptions CommonWithCryptoPublicKey(ImmutableArray<byte> cryptoPublicKey);
         protected abstract CompilationOptions CommonWithDelaySign(bool? delaySign);
@@ -672,12 +674,12 @@ protected int GetHashCodeHelper()
                    Hash.Combine((int)this.NullableContextOptions, 0)))))))))))))))))))))))))));
         }
 
-        public static bool operator ==(CompilationOptions left, CompilationOptions right)
+        public static bool operator ==(CompilationOptions? left, CompilationOptions? right)
         {
             return object.Equals(left, right);
         }
 
-        public static bool operator !=(CompilationOptions left, CompilationOptions right)
+        public static bool operator !=(CompilationOptions? left, CompilationOptions? right)
         {
             return !object.Equals(left, right);
         }

src/Compilers/Core/Portable/Compilation/CompilationStage.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+#nullable enable
+
 using Microsoft.CodeAnalysis.Text;
 
 namespace Microsoft.CodeAnalysis

src/Compilers/Core/Portable/Compilation/ControlFlowAnalysis.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+#nullable enable
+
 using System.Collections.Immutable;
 
 namespace Microsoft.CodeAnalysis

src/Compilers/Core/Portable/Compilation/DataFlowAnalysis.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+#nullable enable
+
 using System.Collections.Immutable;
 
 namespace Microsoft.CodeAnalysis

src/Compilers/Core/Portable/Compilation/EmitResult.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+#nullable enable
+
 using System.Collections.Immutable;
 using System.Diagnostics;
 

src/Compilers/Core/Portable/Compilation/Expression.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+#nullable enable
+
 namespace Microsoft.CodeAnalysis.Operations
 {
     internal class Expression
@@ -38,7 +40,7 @@ public static ConstantValue SynthesizeNumeric(ITypeSymbol type, int value)
 
             if (type.TypeKind == TypeKind.Enum)
             {
-                return SynthesizeNumeric(((INamedTypeSymbol)type).EnumUnderlyingType, value);
+                return SynthesizeNumeric(((INamedTypeSymbol)type).EnumUnderlyingType!, value);
             }
 
             return ConstantValue.Bad;

src/Compilers/Core/Portable/Compilation/Extensions.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+#nullable enable
+
 using System;
 using System.Collections.Generic;
 using System.Collections.Immutable;

src/Compilers/Core/Portable/Compilation/LoadDirective.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+#nullable enable
+
 using System;
 using System.Collections.Immutable;
 using System.Diagnostics;
@@ -8,16 +10,16 @@
 
 namespace Microsoft.CodeAnalysis
 {
-    internal struct LoadDirective : IEquatable<LoadDirective>
+    internal readonly struct LoadDirective : IEquatable<LoadDirective>
     {
-        public readonly string ResolvedPath;
+        public readonly string? ResolvedPath;
         public readonly ImmutableArray<Diagnostic> Diagnostics;
 
-        public LoadDirective(string resolvedPath, ImmutableArray<Diagnostic> diagnostics)
+        public LoadDirective(string? resolvedPath, ImmutableArray<Diagnostic> diagnostics)
         {
-            Debug.Assert((resolvedPath != null) || !diagnostics.IsEmpty);
-            Debug.Assert(!diagnostics.IsDefault);
-            Debug.Assert(diagnostics.IsEmpty || diagnostics.All(d => d.Severity == DiagnosticSeverity.Error));
+            RoslynDebug.Assert((resolvedPath != null) || !diagnostics.IsEmpty);
+            RoslynDebug.Assert(!diagnostics.IsDefault);
+            RoslynDebug.Assert(diagnostics.IsEmpty || diagnostics.All(d => d.Severity == DiagnosticSeverity.Error));
 
             ResolvedPath = resolvedPath;
             Diagnostics = diagnostics;
@@ -36,7 +38,7 @@ public override bool Equals(object obj)
 
         public override int GetHashCode()
         {
-            return Hash.Combine(this.Diagnostics.GetHashCode(), this.ResolvedPath.GetHashCode());
+            return Hash.Combine(this.Diagnostics.GetHashCode(), this.ResolvedPath?.GetHashCode() ?? 0);
         }
     }
 }

src/Compilers/Core/Portable/Compilation/OptimizationLevel.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+#nullable enable
+
 using System.Diagnostics;
 
 namespace Microsoft.CodeAnalysis

src/Compilers/Core/Portable/Compilation/ParseOptions.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+#nullable enable
+
 using System;
 using System.Collections.Generic;
 using System.Collections.Immutable;
@@ -127,9 +129,9 @@ public ParseOptions WithFeatures(IEnumerable<KeyValuePair<string, string>> featu
         /// </summary>
         public abstract IEnumerable<string> PreprocessorSymbolNames { get; }
 
-        public abstract override bool Equals(object obj);
+        public abstract override bool Equals(object? obj);
 
-        protected bool EqualsHelper(ParseOptions other)
+        protected bool EqualsHelper(ParseOptions? other)
         {
             if (object.ReferenceEquals(other, null))
             {
@@ -166,12 +168,12 @@ private static int HashFeatures(IReadOnlyDictionary<string, string> features)
             return value;
         }
 
-        public static bool operator ==(ParseOptions left, ParseOptions right)
+        public static bool operator ==(ParseOptions? left, ParseOptions? right)
         {
             return object.Equals(left, right);
         }
 
-        public static bool operator !=(ParseOptions left, ParseOptions right)
+        public static bool operator !=(ParseOptions? left, ParseOptions? right)
         {
             return !object.Equals(left, right);
         }

src/Compilers/Core/Portable/Compilation/Platform.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+#nullable enable
+
 namespace Microsoft.CodeAnalysis
 {
     public enum Platform

src/Compilers/Core/Portable/Compilation/PreprocessingSymbolInfo.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+#nullable enable
+
 using Roslyn.Utilities;
 using System;
 
@@ -12,14 +14,14 @@ public struct PreprocessingSymbolInfo : IEquatable<PreprocessingSymbolInfo>
         /// <summary>
         /// The symbol that was referred to by the identifier, if any. 
         /// </summary>
-        public IPreprocessingSymbol Symbol { get; }
+        public IPreprocessingSymbol? Symbol { get; }
 
         /// <summary>
         /// Returns true if this preprocessing symbol is defined at the identifier position.
         /// </summary>
         public bool IsDefined { get; }
 
-        internal PreprocessingSymbolInfo(IPreprocessingSymbol symbol, bool isDefined)
+        internal PreprocessingSymbolInfo(IPreprocessingSymbol? symbol, bool isDefined)
             : this()
         {
             this.Symbol = symbol;
@@ -34,7 +36,7 @@ public bool Equals(PreprocessingSymbolInfo other)
 
         public override bool Equals(object obj)
         {
-            return obj is PreprocessingSymbolInfo && this.Equals((PreprocessingSymbolInfo)obj);
+            return obj is PreprocessingSymbolInfo p && this.Equals(p);
         }
 
         public override int GetHashCode()

src/Compilers/Core/Portable/Compilation/ScriptCompilationInfo.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+#nullable enable
+
 using System;
 
 namespace Microsoft.CodeAnalysis
 {
     public abstract class ScriptCompilationInfo
     {
-        internal Type ReturnTypeOpt { get; }
+        internal Type? ReturnTypeOpt { get; }
         public Type ReturnType => ReturnTypeOpt ?? typeof(object);
         public Type GlobalsType { get; }
 

src/Compilers/Core/Portable/Compilation/SemanticModel.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+#nullable enable
+
 using System;
 using System.Collections.Generic;
 using System.Collections.Immutable;
@@ -72,7 +74,7 @@ public SyntaxTree SyntaxTree
         /// <param name="node">The expression or statement syntax node.</param>
         /// <param name="cancellationToken">An optional cancellation token.</param>
         /// <returns></returns>
-        public IOperation GetOperation(SyntaxNode node, CancellationToken cancellationToken = default(CancellationToken))
+        public IOperation? GetOperation(SyntaxNode node, CancellationToken cancellationToken = default(CancellationToken))
         {
             try
             {
@@ -457,8 +459,8 @@ internal ImmutableArray<ISymbol> GetDeclaredSymbolsForNode(SyntaxNode declaratio
         /// </remarks>
         public ImmutableArray<ISymbol> LookupSymbols(
             int position,
-            INamespaceOrTypeSymbol container = null,
-            string name = null,
+            INamespaceOrTypeSymbol? container = null,
+            string? name = null,
             bool includeReducedExtensionMethods = false)
         {
             return LookupSymbolsCore(position, container, name, includeReducedExtensionMethods);
@@ -469,8 +471,8 @@ internal ImmutableArray<ISymbol> GetDeclaredSymbolsForNode(SyntaxNode declaratio
         /// </summary>
         protected abstract ImmutableArray<ISymbol> LookupSymbolsCore(
             int position,
-            INamespaceOrTypeSymbol container,
-            string name,
+            INamespaceOrTypeSymbol? container,
+            string? name,
             bool includeReducedExtensionMethods);
 
         /// <summary>
@@ -510,7 +512,7 @@ internal ImmutableArray<ISymbol> GetDeclaredSymbolsForNode(SyntaxNode declaratio
         /// </remarks>
         public ImmutableArray<ISymbol> LookupBaseMembers(
             int position,
-            string name = null)
+            string? name = null)
         {
             return LookupBaseMembersCore(position, name);
         }
@@ -520,7 +522,7 @@ internal ImmutableArray<ISymbol> GetDeclaredSymbolsForNode(SyntaxNode declaratio
         /// </summary>
         protected abstract ImmutableArray<ISymbol> LookupBaseMembersCore(
             int position,
-            string name);
+            string? name);
 
         /// <summary>
         /// Gets the available named static member symbols in the context of the specified location and optional container.
@@ -544,8 +546,8 @@ internal ImmutableArray<ISymbol> GetDeclaredSymbolsForNode(SyntaxNode declaratio
         /// </remarks>
         public ImmutableArray<ISymbol> LookupStaticMembers(
             int position,
-            INamespaceOrTypeSymbol container = null,
-            string name = null)
+            INamespaceOrTypeSymbol? container = null,
+            string? name = null)
         {
             return LookupStaticMembersCore(position, container, name);
         }
@@ -555,8 +557,8 @@ internal ImmutableArray<ISymbol> GetDeclaredSymbolsForNode(SyntaxNode declaratio
         /// </summary>
         protected abstract ImmutableArray<ISymbol> LookupStaticMembersCore(
             int position,
-            INamespaceOrTypeSymbol container,
-            string name);
+            INamespaceOrTypeSymbol? container,
+            string? name);
 
         /// <summary>
         /// Gets the available named namespace and type symbols in the context of the specified location and optional container.
@@ -578,8 +580,8 @@ internal ImmutableArray<ISymbol> GetDeclaredSymbolsForNode(SyntaxNode declaratio
         /// </remarks>
         public ImmutableArray<ISymbol> LookupNamespacesAndTypes(
             int position,
-            INamespaceOrTypeSymbol container = null,
-            string name = null)
+            INamespaceOrTypeSymbol? container = null,
+            string? name = null)
         {
             return LookupNamespacesAndTypesCore(position, container, name);
         }
@@ -589,8 +591,8 @@ internal ImmutableArray<ISymbol> GetDeclaredSymbolsForNode(SyntaxNode declaratio
         /// </summary>
         protected abstract ImmutableArray<ISymbol> LookupNamespacesAndTypesCore(
             int position,
-            INamespaceOrTypeSymbol container,
-            string name);
+            INamespaceOrTypeSymbol? container,
+            string? name);
 
         /// <summary>
         /// Gets the available named label symbols in the context of the specified location and optional container.
@@ -608,7 +610,7 @@ internal ImmutableArray<ISymbol> GetDeclaredSymbolsForNode(SyntaxNode declaratio
         /// </remarks>
         public ImmutableArray<ISymbol> LookupLabels(
             int position,
-            string name = null)
+            string? name = null)
         {
             return LookupLabelsCore(position, name);
         }
@@ -618,7 +620,7 @@ internal ImmutableArray<ISymbol> GetDeclaredSymbolsForNode(SyntaxNode declaratio
         /// </summary>
         protected abstract ImmutableArray<ISymbol> LookupLabelsCore(
             int position,
-            string name);
+            string? name);
 
         /// <summary>
         /// Analyze control-flow within a part of a method body.

src/Compilers/Core/Portable/Compilation/SourceReferenceResolver.cs

@@ -27,7 +27,7 @@ protected SourceReferenceResolver()
         /// <param name="path">The source path to normalize. May be absolute or relative.</param>
         /// <param name="baseFilePath">Path of the source file that contains the <paramref name="path"/> (may also be relative), or null if not available.</param>
         /// <returns>Normalized path, or null if <paramref name="path"/> can't be normalized. The resulting path doesn't need to exist.</returns>
-        public abstract string? NormalizePath(string path, string baseFilePath);
+        public abstract string? NormalizePath(string path, string? baseFilePath);
 
         /// <summary>
         /// Resolves specified path with respect to base file path.
@@ -35,7 +35,7 @@ protected SourceReferenceResolver()
         /// <param name="path">The path to resolve. May be absolute or relative.</param>
         /// <param name="baseFilePath">Path of the source file that contains the <paramref name="path"/> (may also be relative), or null if not available.</param>
         /// <returns>Normalized path, or null if the file can't be resolved.</returns>
-        public abstract string? ResolveReference(string path, string baseFilePath);
+        public abstract string? ResolveReference(string path, string? baseFilePath);
 
         /// <summary>
         /// Opens a <see cref="Stream"/> that allows reading the content of the specified file.

src/Compilers/Core/Portable/Compilation/SpeculativeBindingOption.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+#nullable enable
+
 using Microsoft.CodeAnalysis.Text;
 
 namespace Microsoft.CodeAnalysis

src/Compilers/Core/Portable/Compilation/SubsystemVersion.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+#nullable enable
+
 using System;
 using System.Collections.Generic;
 using System.Globalization;
@@ -83,7 +85,7 @@ public static bool TryParse(string str, out SubsystemVersion version)
             if (!string.IsNullOrWhiteSpace(str))
             {
                 string major;
-                string minor;
+                string? minor;
 
                 int index = str.IndexOf('.');
 

src/Compilers/Core/Portable/Compilation/SymbolFilter.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+#nullable enable
+
 using System;
 
 namespace Microsoft.CodeAnalysis

src/Compilers/Core/Portable/Diagnostic/DiagnosticWithInfo.cs

@@ -102,7 +102,7 @@ public override string GetMessage(IFormatProvider? formatProvider = null)
             return this.Info.GetMessage(formatProvider);
         }
 
-        internal override IReadOnlyList<object> Arguments
+        internal override IReadOnlyList<object?> Arguments
         {
             get { return this.Info.Arguments; }
         }

src/Compilers/Core/Portable/InternalUtilities/RoslynLazyInitializer.cs

+// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
+
+#nullable enable
+
+using System;
+using System.Diagnostics.CodeAnalysis;
+using System.Threading;
+
+namespace Roslyn.Utilities
+{
+    internal static class RoslynLazyInitializer
+    {
+        /// <inheritdoc cref="LazyInitializer.EnsureInitialized{T}(ref T)"/>
+        public static T EnsureInitialized<T>([NotNull] ref T? target) where T : class
+            => LazyInitializer.EnsureInitialized<T>(ref target!);
+
+        /// <inheritdoc cref="LazyInitializer.EnsureInitialized{T}(ref T, Func{T})"/>
+        public static T EnsureInitialized<T>([NotNull] ref T? target, Func<T> valueFactory) where T : class
+            => LazyInitializer.EnsureInitialized<T>(ref target!, valueFactory);
+
+        /// <inheritdoc cref="LazyInitializer.EnsureInitialized{T}(ref T, ref bool, ref object)"/>
+        public static T EnsureInitialized<T>([AllowNull] ref T target, ref bool initialized, [NotNull] ref object? syncLock)
+            => LazyInitializer.EnsureInitialized<T>(ref target!, ref initialized, ref syncLock);
+
+        /// <inheritdoc cref="LazyInitializer.EnsureInitialized{T}(ref T, ref bool, ref object, Func{T})"/>
+        public static T EnsureInitialized<T>([AllowNull] ref T target, ref bool initialized, [NotNull] ref object? syncLock, Func<T> valueFactory)
+            => LazyInitializer.EnsureInitialized<T>(ref target!, ref initialized, ref syncLock, valueFactory);
+    }
+}
\ No newline at end of file

src/Compilers/Core/Portable/SourceFileResolver.cs

@@ -94,13 +94,13 @@ public SourceFileResolver(ImmutableArray<string> searchPaths, string? baseDirect
 
         public ImmutableArray<KeyValuePair<string, string>> PathMap => _pathMap;
 
-        public override string? NormalizePath(string path, string baseFilePath)
+        public override string? NormalizePath(string path, string? baseFilePath)
         {
             string normalizedPath = FileUtilities.NormalizeRelativePath(path, baseFilePath, _baseDirectory);
             return (normalizedPath == null || _pathMap.IsDefaultOrEmpty) ? normalizedPath : PathUtilities.NormalizePathPrefix(normalizedPath, _pathMap);
         }
 
-        public override string? ResolveReference(string path, string baseFilePath)
+        public override string? ResolveReference(string path, string? baseFilePath)
         {
             string resolvedPath = FileUtilities.ResolveRelativePath(path, baseFilePath, _baseDirectory, _searchPaths, FileExists);
             if (resolvedPath == null)

src/Features/CSharp/Portable/ImplementInterface/AbstractChangeImplementionCodeRefactoringProvider.cs

@@ -54,7 +54,7 @@ public sealed override async Task ComputeRefactoringsAsync(CodeRefactoringContex
                 return;
 
             var (document, _, cancellationToken) = context;
-            var semanticModel = await document.GetSemanticModelAsync(cancellationToken).ConfigureAwait(false);
+            var semanticModel = await document.GetRequiredSemanticModelAsync(cancellationToken).ConfigureAwait(false);
             var member = semanticModel.GetDeclaredSymbol(container, cancellationToken);
             Contract.ThrowIfNull(member);
 

src/Features/Core/Portable/PopulateSwitch/AbstractPopulateSwitchCodeFixProvider.cs

@@ -146,7 +146,8 @@ public sealed override Task RegisterCodeFixesAsync(CodeFixContext context)
                 return;
 
             var model = await document.RequireSemanticModelAsync(cancellationToken).ConfigureAwait(false);
-            var switchStatement = (TSwitchOperation)model.GetOperation(switchNode, cancellationToken);
+            // https://github.com/dotnet/roslyn/issues/40505
+            var switchStatement = (TSwitchOperation)model.GetOperation(switchNode, cancellationToken)!;
 
             FixOneDiagnostic(
                 document, editor, model, addCases, addDefaultCase, onlyOneDiagnostic,

src/Features/Core/Portable/UseSystemHashCode/Analyzer.cs

@@ -57,7 +57,7 @@ public static bool TryGetAnalyzer(Compilation compilation, [NotNullWhen(true)] o
         /// Analyzes the containing <c>GetHashCode</c> method to determine which fields and
         /// properties were combined to form a hash code for this type.
         /// </summary>
-        public (bool accessesBase, ImmutableArray<ISymbol> members) GetHashedMembers(ISymbol owningSymbol, IOperation operation)
+        public (bool accessesBase, ImmutableArray<ISymbol> members) GetHashedMembers(ISymbol owningSymbol, IOperation? operation)
         {
             if (!(operation is IBlockOperation blockOperation))
             {

src/Workspaces/Core/Portable/Workspace/Solution/Document.cs

@@ -278,7 +278,7 @@ public bool TryGetSemanticModel([NotNullWhen(returnValue: true)] out SemanticMod
                     return semanticModel;
                 }
 
-                var syntaxTree = await this.GetSyntaxTreeAsync(cancellationToken).ConfigureAwait(false);
+                var syntaxTree = await this.GetRequiredSyntaxTreeAsync(cancellationToken).ConfigureAwait(false);
                 var compilation = (await this.Project.GetCompilationAsync(cancellationToken).ConfigureAwait(false))!;
 
                 var result = compilation.GetSemanticModel(syntaxTree);

src/Workspaces/Core/Portable/Workspace/Solution/SolutionState.CompilationTracker.cs

@@ -633,7 +633,7 @@ public CompilationInfo(Compilation compilation, bool hasSuccessfullyLoaded)
                                     await solution.GetCompilationAsync(projectReference.ProjectId, cancellationToken).ConfigureAwait(false);
 
                                 compilation = compilation.WithScriptCompilationInfo(
-                                    compilation.ScriptCompilationInfo.WithPreviousScriptCompilation(previousSubmissionCompilation));
+                                    compilation.ScriptCompilationInfo.WithPreviousScriptCompilation(previousSubmissionCompilation!));
                             }
                             else
                             {