Nullable enable IDE.

src/Analyzers/CSharp/Analyzers/RemoveUnusedParametersAndValues/CSharpRemoveUnusedParametersAndValuesDiagnosticAnalyzer.cs

@@ -35,7 +35,7 @@ protected override bool MethodHasHandlesClause(IMethodSymbol method)
     protected override bool IsIfConditionalDirective(SyntaxNode node)
         => node is IfDirectiveTriviaSyntax;
 
-    protected override bool ReturnsThrow(SyntaxNode node)
+    protected override bool ReturnsThrow(SyntaxNode? node)
     {
         if (node is not BaseMethodDeclarationSyntax methodSyntax)
         {

src/Analyzers/CSharp/Analyzers/UseExpressionBody/Helpers/UseExpressionBodyForIndexersHelper.cs

@@ -14,7 +14,7 @@
 
 namespace Microsoft.CodeAnalysis.CSharp.UseExpressionBody;
 
-internal class UseExpressionBodyForIndexersHelper :
+internal sealed class UseExpressionBodyForIndexersHelper :
     UseExpressionBodyHelper<IndexerDeclarationSyntax>
 {
     public static readonly UseExpressionBodyForIndexersHelper Instance = new();

src/Analyzers/CSharp/CodeFixes/ConvertToAsync/CSharpConvertToAsyncMethodCodeFixProvider.cs

@@ -25,6 +25,8 @@ internal sealed class CSharpConvertToAsyncMethodCodeFixProvider() : AbstractConv
     /// </summary>
     private const string CS4008 = nameof(CS4008);
 
+    public override FixAllProvider? GetFixAllProvider() => base.GetFixAllProvider();
+
     public override ImmutableArray<string> FixableDiagnosticIds => [CS4008];
 
     protected override async Task<string> GetDescriptionAsync(
@@ -40,21 +42,19 @@ protected override async Task<string> GetDescriptionAsync(
         return string.Format(CSharpCodeFixesResources.Make_0_return_Task_instead_of_void, methodNode!.WithBody(null));
     }
 
-    protected override async Task<Tuple<SyntaxTree, SyntaxNode>?> GetRootInOtherSyntaxTreeAsync(
+    protected override async Task<(SyntaxTree syntaxTree, SyntaxNode root)?> GetRootInOtherSyntaxTreeAsync(
         SyntaxNode node,
         SemanticModel semanticModel,
         Diagnostic diagnostic,
         CancellationToken cancellationToken)
     {
         var methodDeclaration = await GetMethodDeclarationAsync(node, semanticModel, cancellationToken).ConfigureAwait(false);
         if (methodDeclaration == null)
-        {
             return null;
-        }
 
         var oldRoot = await methodDeclaration.SyntaxTree.GetRootAsync(cancellationToken).ConfigureAwait(false);
         var newRoot = oldRoot.ReplaceNode(methodDeclaration, ConvertToAsyncFunction(methodDeclaration));
-        return Tuple.Create(oldRoot.SyntaxTree, newRoot);
+        return (oldRoot.SyntaxTree, newRoot);
     }
 
     private static async Task<MethodDeclarationSyntax?> GetMethodDeclarationAsync(

src/Analyzers/CSharp/CodeFixes/GenerateConstructor/CSharpGenerateConstructorService.cs

@@ -2,11 +2,10 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-#nullable disable
-
 using System;
 using System.Collections.Immutable;
 using System.Composition;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Threading;
 using Microsoft.CodeAnalysis.CodeGeneration;
@@ -44,7 +43,7 @@ protected override bool TryInitializeConstructorInitializerGeneration(
         CancellationToken cancellationToken,
         out SyntaxToken token,
         out ImmutableArray<Argument<ExpressionSyntax>> arguments,
-        out INamedTypeSymbol typeToGenerateIn)
+        [NotNullWhen(true)] out INamedTypeSymbol? typeToGenerateIn)
     {
         var constructorInitializer = (ConstructorInitializerSyntax)node;
 
@@ -57,7 +56,7 @@ protected override bool TryInitializeConstructorInitializerGeneration(
             var currentType = semanticModel.GetEnclosingNamedType(constructorInitializer.SpanStart, cancellationToken);
             typeToGenerateIn = constructorInitializer.IsKind(SyntaxKind.ThisConstructorInitializer)
                 ? currentType
-                : currentType.BaseType.OriginalDefinition;
+                : currentType?.BaseType?.OriginalDefinition;
             return typeToGenerateIn != null;
         }
 
@@ -82,11 +81,11 @@ protected override bool TryInitializeSimpleNameGenerationState(
         CancellationToken cancellationToken,
         out SyntaxToken token,
         out ImmutableArray<Argument<ExpressionSyntax>> arguments,
-        out INamedTypeSymbol typeToGenerateIn)
+        [NotNullWhen(true)] out INamedTypeSymbol? typeToGenerateIn)
     {
         var simpleName = (SimpleNameSyntax)node;
         var fullName = simpleName.IsRightSideOfQualifiedName()
-            ? (NameSyntax)simpleName.Parent
+            ? (NameSyntax)simpleName.GetRequiredParent()
             : simpleName;
 
         if (fullName.Parent is ObjectCreationExpressionSyntax objectCreationExpression)
@@ -114,11 +113,11 @@ protected override bool TryInitializeSimpleAttributeNameGenerationState(
         CancellationToken cancellationToken,
         out SyntaxToken token,
         out ImmutableArray<Argument<ExpressionSyntax>> arguments,
-        out INamedTypeSymbol typeToGenerateIn)
+        [NotNullWhen(true)] out INamedTypeSymbol? typeToGenerateIn)
     {
         var simpleName = (SimpleNameSyntax)node;
         var fullName = simpleName.IsRightSideOfQualifiedName()
-            ? (NameSyntax)simpleName.Parent
+            ? (NameSyntax)simpleName.GetRequiredParent()
             : simpleName;
 
         if (fullName.Parent is AttributeSyntax attribute)
@@ -132,7 +131,7 @@ protected override bool TryInitializeSimpleAttributeNameGenerationState(
                     token = simpleName.Identifier;
                     arguments = GetArguments(attribute.ArgumentList.Arguments);
 
-                    typeToGenerateIn = symbolInfo.CandidateSymbols.FirstOrDefault().ContainingSymbol as INamedTypeSymbol;
+                    typeToGenerateIn = symbolInfo.CandidateSymbols.FirstOrDefault()?.ContainingSymbol as INamedTypeSymbol;
                     return typeToGenerateIn != null;
                 }
             }
@@ -149,7 +148,7 @@ protected override bool TryInitializeImplicitObjectCreation(SemanticDocument doc
         CancellationToken cancellationToken,
         out SyntaxToken token,
         out ImmutableArray<Argument<ExpressionSyntax>> arguments,
-        out INamedTypeSymbol typeToGenerateIn)
+        [NotNullWhen(true)] out INamedTypeSymbol? typeToGenerateIn)
     {
         var implicitObjectCreation = (ImplicitObjectCreationExpressionSyntax)node;
         if (implicitObjectCreation.ArgumentList != null &&
@@ -175,15 +174,15 @@ protected override string GenerateNameForExpression(SemanticModel semanticModel,
         => semanticModel.GenerateNameForExpression(expression, capitalize: false, cancellationToken: cancellationToken);
 
     protected override ITypeSymbol GetArgumentType(SemanticModel semanticModel, Argument<ExpressionSyntax> argument, CancellationToken cancellationToken)
-        => InternalExtensions.DetermineParameterType(argument.Expression, semanticModel, cancellationToken);
+        => InternalExtensions.DetermineParameterType(argument.Expression!, semanticModel, cancellationToken);
 
     protected override bool IsConversionImplicit(Compilation compilation, ITypeSymbol sourceType, ITypeSymbol targetType)
         => compilation.ClassifyConversion(sourceType, targetType).IsImplicit;
 
-    protected override IMethodSymbol GetCurrentConstructor(SemanticModel semanticModel, SyntaxToken token, CancellationToken cancellationToken)
+    protected override IMethodSymbol? GetCurrentConstructor(SemanticModel semanticModel, SyntaxToken token, CancellationToken cancellationToken)
         => token.GetAncestor<ConstructorDeclarationSyntax>() is { } constructor ? semanticModel.GetDeclaredSymbol(constructor, cancellationToken) : null;
 
-    protected override IMethodSymbol GetDelegatedConstructor(SemanticModel semanticModel, IMethodSymbol constructor, CancellationToken cancellationToken)
+    protected override IMethodSymbol? GetDelegatedConstructor(SemanticModel semanticModel, IMethodSymbol constructor, CancellationToken cancellationToken)
     {
         if (constructor.DeclaringSyntaxReferences[0].GetSyntax(cancellationToken) is ConstructorDeclarationSyntax constructorDeclarationSyntax &&
             constructorDeclarationSyntax.Initializer.IsKind(SyntaxKind.ThisConstructorInitializer))

src/Analyzers/CSharp/CodeFixes/GenerateConstructor/GenerateConstructorCodeFixProvider.cs

@@ -2,8 +2,6 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-#nullable disable
-
 using System.Collections.Immutable;
 using System.Composition;
 using System.Diagnostics.CodeAnalysis;
@@ -42,27 +40,18 @@ internal sealed class GenerateConstructorCodeFixProvider() : AbstractGenerateMem
     protected override Task<ImmutableArray<CodeAction>> GetCodeActionsAsync(
         Document document, SyntaxNode node, CancellationToken cancellationToken)
     {
-        var service = document.GetLanguageService<IGenerateConstructorService>();
+        var service = document.GetRequiredLanguageService<IGenerateConstructorService>();
         return service.GenerateConstructorAsync(document, node, cancellationToken);
     }
 
     protected override bool IsCandidate(SyntaxNode node, SyntaxToken token, Diagnostic diagnostic)
-    {
-        return node is BaseObjectCreationExpressionSyntax or
-               ConstructorInitializerSyntax or
-               AttributeSyntax;
-    }
+        => node is BaseObjectCreationExpressionSyntax or ConstructorInitializerSyntax or AttributeSyntax;
 
-    protected override SyntaxNode GetTargetNode(SyntaxNode node)
-    {
-        switch (node)
+    protected override SyntaxNode? GetTargetNode(SyntaxNode node)
+        => node switch
         {
-            case ObjectCreationExpressionSyntax objectCreationNode:
-                return objectCreationNode.Type.GetRightmostName();
-            case AttributeSyntax attributeNode:
-                return attributeNode.Name;
-        }
-
-        return node;
-    }
+            ObjectCreationExpressionSyntax objectCreationNode => objectCreationNode.Type.GetRightmostName(),
+            AttributeSyntax attributeNode => attributeNode.Name,
+            _ => node,
+        };
 }

src/Analyzers/CSharp/CodeFixes/GenerateEnumMember/CSharpGenerateEnumMemberService.cs

@@ -2,14 +2,14 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-#nullable disable
-
 using System;
 using System.Composition;
+using System.Diagnostics.CodeAnalysis;
 using System.Threading;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.CodeAnalysis.GenerateMember.GenerateEnumMember;
 using Microsoft.CodeAnalysis.Host.Mef;
+using Microsoft.CodeAnalysis.Shared.Extensions;
 
 namespace Microsoft.CodeAnalysis.CSharp.GenerateMember.GenerateEnumMember;
 
@@ -24,7 +24,8 @@ protected override bool IsIdentifierNameGeneration(SyntaxNode node)
 
     protected override bool TryInitializeIdentifierNameState(
         SemanticDocument document, SimpleNameSyntax identifierName, CancellationToken cancellationToken,
-        out SyntaxToken identifierToken, out ExpressionSyntax simpleNameOrMemberAccessExpression)
+        out SyntaxToken identifierToken,
+        [NotNullWhen(true)] out ExpressionSyntax? simpleNameOrMemberAccessExpression)
     {
         identifierToken = identifierName.Identifier;
         if (identifierToken.ValueText != string.Empty &&
@@ -37,7 +38,7 @@ protected override bool TryInitializeIdentifierNameState(
             // If we're being invoked, then don't offer this, offer generate method instead.
             // Note: we could offer to generate a field with a delegate type.  However, that's
             // very esoteric and probably not what most users want.
-            if (simpleNameOrMemberAccessExpression.Parent.Kind()
+            if (simpleNameOrMemberAccessExpression.GetRequiredParent().Kind()
                     is SyntaxKind.InvocationExpression
                     or SyntaxKind.ObjectCreationExpression
                     or SyntaxKind.GotoStatement

src/Analyzers/CSharp/CodeFixes/GenerateMethod/GenerateDeconstructMethodCodeFixProvider.cs

@@ -2,8 +2,6 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-#nullable disable
-
 using System.Collections.Immutable;
 using System.Composition;
 using System.Diagnostics;
@@ -20,24 +18,16 @@ namespace Microsoft.CodeAnalysis.CSharp.CodeFixes.GenerateDeconstructMethod;
 
 [ExportCodeFixProvider(LanguageNames.CSharp, Name = PredefinedCodeFixProviderNames.GenerateDeconstructMethod), Shared]
 [ExtensionOrder(After = PredefinedCodeFixProviderNames.GenerateEnumMember)]
-internal class GenerateDeconstructMethodCodeFixProvider : CodeFixProvider
+[method: ImportingConstructor]
+[method: SuppressMessage("RoslynDiagnosticsReliability", "RS0033:Importing constructor should be [Obsolete]", Justification = "Used in test code: https://github.com/dotnet/roslyn/issues/42814")]
+internal sealed class GenerateDeconstructMethodCodeFixProvider() : CodeFixProvider
 {
     private const string CS8129 = nameof(CS8129); // No suitable Deconstruct instance or extension method was found...
 
-    [ImportingConstructor]
-    [SuppressMessage("RoslynDiagnosticsReliability", "RS0033:Importing constructor should be [Obsolete]", Justification = "Used in test code: https://github.com/dotnet/roslyn/issues/42814")]
-    public GenerateDeconstructMethodCodeFixProvider()
-    {
-    }
+    public override FixAllProvider? GetFixAllProvider() => base.GetFixAllProvider();
 
     public sealed override ImmutableArray<string> FixableDiagnosticIds => [CS8129];
 
-    public override FixAllProvider GetFixAllProvider()
-    {
-        // Fix All is not supported by this code fix
-        return null;
-    }
-
     public sealed override async Task RegisterCodeFixesAsync(CodeFixContext context)
     {
         // Not supported in REPL
@@ -48,7 +38,7 @@ public sealed override async Task RegisterCodeFixesAsync(CodeFixContext context)
 
         var document = context.Document;
         var cancellationToken = context.CancellationToken;
-        var root = await document.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
+        var root = await document.GetRequiredSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
         var span = context.Span;
         var token = root.FindToken(span.Start);
 
@@ -61,10 +51,10 @@ public sealed override async Task RegisterCodeFixesAsync(CodeFixContext context)
             return;
         }
 
-        var model = await document.GetSemanticModelAsync(cancellationToken).ConfigureAwait(false);
+        var model = await document.GetRequiredSemanticModelAsync(cancellationToken).ConfigureAwait(false);
 
         DeconstructionInfo info;
-        ITypeSymbol type;
+        ITypeSymbol? type;
         SyntaxNode target;
         switch (deconstruction)
         {
@@ -80,7 +70,7 @@ public sealed override async Task RegisterCodeFixesAsync(CodeFixContext context)
                 break;
             case PositionalPatternClauseSyntax positionalPattern:
                 info = default;
-                type = model.GetTypeInfo(deconstruction.Parent).Type;
+                type = model.GetTypeInfo(deconstruction.GetRequiredParent()).Type;
                 target = deconstruction;
                 break;
             default:
@@ -105,7 +95,7 @@ public sealed override async Task RegisterCodeFixesAsync(CodeFixContext context)
             return;
         }
 
-        var service = document.GetLanguageService<IGenerateDeconstructMemberService>();
+        var service = document.GetRequiredLanguageService<IGenerateDeconstructMemberService>();
         var codeActions = await service.GenerateDeconstructMethodAsync(document, target, (INamedTypeSymbol)type, cancellationToken).ConfigureAwait(false);
 
         Debug.Assert(!codeActions.IsDefault);

src/Analyzers/CSharp/CodeFixes/GenerateParameterizedMember/CSharpGenerateConversionService.cs

@@ -2,11 +2,10 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-#nullable disable
-
 using System;
 using System.Collections.Generic;
 using System.Composition;
+using System.Diagnostics.CodeAnalysis;
 using System.Threading;
 using Microsoft.CodeAnalysis.CodeGeneration;
 using Microsoft.CodeAnalysis.CSharp.Extensions;
@@ -57,8 +56,8 @@ protected override bool TryInitializeImplicitConversionState(
        ISet<TypeKind> classInterfaceModuleStructTypes,
        CancellationToken cancellationToken,
        out SyntaxToken identifierToken,
-       out IMethodSymbol methodSymbol,
-       out INamedTypeSymbol typeToGenerateIn)
+       [NotNullWhen(true)] out IMethodSymbol? methodSymbol,
+       [NotNullWhen(true)] out INamedTypeSymbol? typeToGenerateIn)
     {
         if (TryGetConversionMethodAndTypeToGenerateIn(document, expression, classInterfaceModuleStructTypes, cancellationToken, out methodSymbol, out typeToGenerateIn))
         {
@@ -83,8 +82,8 @@ protected override bool TryInitializeExplicitConversionState(
         ISet<TypeKind> classInterfaceModuleStructTypes,
         CancellationToken cancellationToken,
         out SyntaxToken identifierToken,
-        out IMethodSymbol methodSymbol,
-        out INamedTypeSymbol typeToGenerateIn)
+        [NotNullWhen(true)] out IMethodSymbol? methodSymbol,
+        [NotNullWhen(true)] out INamedTypeSymbol? typeToGenerateIn)
     {
         if (TryGetConversionMethodAndTypeToGenerateIn(document, expression, classInterfaceModuleStructTypes, cancellationToken, out methodSymbol, out typeToGenerateIn))
         {
@@ -108,8 +107,8 @@ private static bool TryGetConversionMethodAndTypeToGenerateIn(
         SyntaxNode expression,
         ISet<TypeKind> classInterfaceModuleStructTypes,
         CancellationToken cancellationToken,
-        out IMethodSymbol methodSymbol,
-        out INamedTypeSymbol typeToGenerateIn)
+        [NotNullWhen(true)] out IMethodSymbol? methodSymbol,
+        [NotNullWhen(true)] out INamedTypeSymbol? typeToGenerateIn)
     {
         if (expression is CastExpressionSyntax castExpression)
         {
@@ -136,8 +135,8 @@ private static bool TryGetExplicitConversionMethodAndTypeToGenerateIn(
         CastExpressionSyntax castExpression,
         ISet<TypeKind> classInterfaceModuleStructTypes,
         CancellationToken cancellationToken,
-        out IMethodSymbol methodSymbol,
-        out INamedTypeSymbol typeToGenerateIn)
+        [NotNullWhen(true)] out IMethodSymbol? methodSymbol,
+        [NotNullWhen(true)] out INamedTypeSymbol? typeToGenerateIn)
     {
         methodSymbol = null;
         typeToGenerateIn = document.SemanticModel.GetTypeInfo(castExpression.Type, cancellationToken).Type as INamedTypeSymbol;
@@ -167,8 +166,8 @@ private static bool TryGetImplicitConversionMethodAndTypeToGenerateIn(
         SyntaxNode expression,
         ISet<TypeKind> classInterfaceModuleStructTypes,
         CancellationToken cancellationToken,
-        out IMethodSymbol methodSymbol,
-        out INamedTypeSymbol typeToGenerateIn)
+        [NotNullWhen(true)] out IMethodSymbol? methodSymbol,
+        [NotNullWhen(true)] out INamedTypeSymbol? typeToGenerateIn)
     {
         methodSymbol = null;
         typeToGenerateIn = document.SemanticModel.GetTypeInfo(expression, cancellationToken).ConvertedType as INamedTypeSymbol;