Offer completion for `#nullable enable|disable` (#31171)

src/Compilers/CSharp/Portable/Syntax/DirectiveTriviaSyntax.cs

@@ -52,6 +52,8 @@ public SyntaxToken DirectiveNameToken
                         return ((LoadDirectiveTriviaSyntax)this).LoadKeyword;
                     case SyntaxKind.ShebangDirectiveTrivia:
                         return ((ShebangDirectiveTriviaSyntax)this).ExclamationToken;
+                    case SyntaxKind.NullableDirectiveTrivia:
+                        return ((NullableDirectiveTriviaSyntax)this).NullableKeyword;
                     default:
                         throw ExceptionUtilities.UnexpectedValue(this.Kind());
                 }

src/Compilers/CSharp/Portable/Syntax/SyntaxKindFacts.cs

@@ -247,6 +247,7 @@ public static bool IsPreprocessorDirective(SyntaxKind kind)
                 case SyntaxKind.LoadDirectiveTrivia:
                 case SyntaxKind.BadDirectiveTrivia:
                 case SyntaxKind.ShebangDirectiveTrivia:
+                case SyntaxKind.NullableDirectiveTrivia:
                     return true;
                 default:
                     return false;

src/Compilers/CSharp/Test/Syntax/LexicalAndXml/PreprocessorTests.cs

@@ -260,6 +260,9 @@ private void VerifyDirectivesSpecial(CSharpSyntaxNode node, params DirectiveInfo
                             Assert.Equal(exp.Text, setting.ValueText);
                             Assert.True(setting.Kind() == SyntaxKind.EnableKeyword || setting.Kind() == SyntaxKind.DisableKeyword);
                         }
+                        Assert.Equal(SyntaxKind.NullableKeyword, nn.DirectiveNameToken.Kind());
+                        Assert.True(SyntaxFacts.IsPreprocessorDirective(SyntaxKind.NullableDirectiveTrivia));
+                        Assert.True(SyntaxFacts.IsPreprocessorKeyword(SyntaxKind.NullableKeyword));
                         break;
                     default:
                         if (null != exp.Text)

src/EditorFeatures/CSharpTest2/Recommendations/DisableKeywordRecommenderTests.cs

@@ -2,12 +2,31 @@
 
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis.Test.Utilities;
+using Roslyn.Test.Utilities;
 using Xunit;
 
 namespace Microsoft.CodeAnalysis.Editor.CSharp.UnitTests.Recommendations
 {
     public class DisableKeywordRecommenderTests : KeywordRecommenderTests
     {
+        [Fact, Trait(Traits.Feature, Traits.Features.KeywordRecommending)]
+        [WorkItem(31130, "https://github.com/dotnet/roslyn/issues/31130")]
+        public async Task TestAfterNullable()
+        {
+            await VerifyKeywordAsync(@"#nullable $$");
+        }
+
+        [Fact]
+        [WorkItem(31130, "https://github.com/dotnet/roslyn/issues/31130")]
+        public async Task TestNotAfterNullableAndNewline()
+        {
+            await VerifyAbsenceAsync(@"
+#nullable 
+$$
+");
+        }
+
+
         [Fact, Trait(Traits.Feature, Traits.Features.KeywordRecommending)]
         public async Task TestNotAtRoot_Interactive()
         {

src/EditorFeatures/CSharpTest2/Recommendations/EnableKeywordRecommenderTests.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.
+
+using System.Threading.Tasks;
+using Microsoft.CodeAnalysis.Test.Utilities;
+using Roslyn.Test.Utilities;
+using Xunit;
+
+namespace Microsoft.CodeAnalysis.Editor.CSharp.UnitTests.Recommendations
+{
+    [Trait(Traits.Feature, Traits.Features.KeywordRecommending)]
+    public class EnableKeywordRecommenderTests : KeywordRecommenderTests
+    {
+        [Fact]
+        [WorkItem(31130, "https://github.com/dotnet/roslyn/issues/31130")]
+        public async Task TestAfterNullable()
+        {
+            await VerifyKeywordAsync(@"#nullable $$");
+        }
+
+        [Fact]
+        [WorkItem(31130, "https://github.com/dotnet/roslyn/issues/31130")]
+        public async Task TestNotAfterNullableAndNewline()
+        {
+            await VerifyAbsenceAsync(@"
+#nullable 
+$$
+");
+        }
+
+        [Fact]
+        [WorkItem(31130, "https://github.com/dotnet/roslyn/issues/31130")]
+        public async Task TestNotAfterHash()
+        {
+            await VerifyAbsenceAsync(@"#$$");
+        }
+
+        [Fact]
+        public async Task TestNotAtRoot_Interactive()
+        {
+            await VerifyAbsenceAsync(SourceCodeKind.Script, @"$$");
+        }
+
+        [Fact]
+        public async Task TestNotAfterClass_Interactive()
+        {
+            await VerifyAbsenceAsync(SourceCodeKind.Script,
+@"class C { }
+$$");
+        }
+
+        [Fact]
+        public async Task TestNotAfterGlobalStatement_Interactive()
+        {
+            await VerifyAbsenceAsync(SourceCodeKind.Script,
+@"System.Console.WriteLine();
+$$");
+        }
+
+        [Fact]
+        public async Task TestNotAfterGlobalVariableDeclaration_Interactive()
+        {
+            await VerifyAbsenceAsync(SourceCodeKind.Script,
+@"int i = 0;
+$$");
+        }
+
+        [Fact]
+        public async Task TestNotInUsingAlias()
+        {
+            await VerifyAbsenceAsync(@"using Goo = $$");
+        }
+
+        [Fact]
+        public async Task TestNotInEmptyStatement()
+        {
+            await VerifyAbsenceAsync(AddInsideMethod(@"$$"));
+        }
+
+        [Fact]
+        public async Task TestNotAfterPragma()
+        {
+            await VerifyAbsenceAsync(@"#pragma $$");
+        }
+
+        [Fact]
+        public async Task TestNotAfterPragmaWarning()
+        {
+            await VerifyAbsenceAsync(@"#pragma warning $$");
+        }
+    }
+}

src/EditorFeatures/CSharpTest2/Recommendations/NullableKeywordRecommenderTests.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.
+
+using System.Threading.Tasks;
+using Microsoft.CodeAnalysis.Test.Utilities;
+using Xunit;
+
+namespace Microsoft.CodeAnalysis.Editor.CSharp.UnitTests.Recommendations
+{
+    [Trait(Traits.Feature, Traits.Features.KeywordRecommending)]
+    public class NullableKeywordRecommenderTests : KeywordRecommenderTests
+    {
+        [Fact]
+        public async Task TestNotAtRoot_Interactive()
+        {
+            await VerifyAbsenceAsync(SourceCodeKind.Script,
+@"$$");
+        }
+
+        [Fact]
+        public async Task TestNotAfterClass_Interactive()
+        {
+            await VerifyAbsenceAsync(SourceCodeKind.Script,
+@"class C { }
+$$");
+        }
+
+        [Fact]
+        public async Task TestNotAfterGlobalStatement_Interactive()
+        {
+            await VerifyAbsenceAsync(SourceCodeKind.Script,
+@"System.Console.WriteLine();
+$$");
+        }
+
+        [Fact]
+        public async Task TestNotAfterGlobalVariableDeclaration_Interactive()
+        {
+            await VerifyAbsenceAsync(SourceCodeKind.Script,
+@"int i = 0;
+$$");
+        }
+
+        [Fact]
+        public async Task TestNotInUsingAlias()
+        {
+            await VerifyAbsenceAsync(
+@"using Goo = $$");
+        }
+
+        [Fact]
+        public async Task TestNotInEmptyStatement()
+        {
+            await VerifyAbsenceAsync(AddInsideMethod(
+@"$$"));
+        }
+
+        [Fact]
+        public async Task TestAfterHash()
+        {
+            await VerifyKeywordAsync(
+@"#$$");
+        }
+
+        [Fact]
+        public async Task TestAfterHashAndSpace()
+        {
+            await VerifyKeywordAsync(
+@"# $$");
+        }
+
+        [Fact]
+        public async Task TestNotAfterHashAndNullable()
+        {
+            await VerifyAbsenceAsync(
+@"#nullable $$");
+        }
+    }
+}

src/Features/CSharp/Portable/Completion/CompletionProviders/KeywordCompletionProvider.cs

@@ -56,6 +56,7 @@ private static ImmutableArray<IKeywordRecommender<CSharpSyntaxContext>> GetKeywo
                 new DynamicKeywordRecommender(),
                 new ElifKeywordRecommender(),
                 new ElseKeywordRecommender(),
+                new EnableKeywordRecommender(),
                 new EndIfKeywordRecommender(),
                 new EndRegionKeywordRecommender(),
                 new EnumKeywordRecommender(),
@@ -96,6 +97,7 @@ private static ImmutableArray<IKeywordRecommender<CSharpSyntaxContext>> GetKeywo
                 new NameOfKeywordRecommender(),
                 new NamespaceKeywordRecommender(),
                 new NewKeywordRecommender(),
+                new NullableKeywordRecommender(),
                 new NullKeywordRecommender(),
                 new ObjectKeywordRecommender(),
                 new OnKeywordRecommender(),

src/Features/CSharp/Portable/Completion/KeywordRecommenders/DisableKeywordRecommender.cs

@@ -14,12 +14,20 @@ public DisableKeywordRecommender()
 
         protected override bool IsValidContext(int position, CSharpSyntaxContext context, CancellationToken cancellationToken)
         {
-            // # pragma warning |
-            // # pragma warning d|
             var previousToken1 = context.TargetToken;
             var previousToken2 = previousToken1.GetPreviousToken(includeSkipped: true);
             var previousToken3 = previousToken2.GetPreviousToken(includeSkipped: true);
 
+            if (previousToken1.Kind() == SyntaxKind.NullableKeyword &&
+                previousToken2.Kind() == SyntaxKind.HashToken)
+            {
+                // # nullable |
+                // # nullable d|
+                return true;
+            }
+            
+            // # pragma warning |
+            // # pragma warning d|
             return
                 previousToken1.Kind() == SyntaxKind.WarningKeyword &&
                 previousToken2.Kind() == SyntaxKind.PragmaKeyword &&

src/Features/CSharp/Portable/Completion/KeywordRecommenders/EnableKeywordRecommender.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.
+
+using System.Threading;
+using Microsoft.CodeAnalysis.CSharp.Extensions.ContextQuery;
+
+namespace Microsoft.CodeAnalysis.CSharp.Completion.KeywordRecommenders
+{
+    internal class EnableKeywordRecommender : AbstractSyntacticSingleKeywordRecommender
+    {
+        public EnableKeywordRecommender()
+            : base(SyntaxKind.EnableKeyword, isValidInPreprocessorContext: true)
+        {
+        }
+
+        protected override bool IsValidContext(int position, CSharpSyntaxContext context, CancellationToken cancellationToken)
+        {
+            var previousToken1 = context.TargetToken;
+            var previousToken2 = previousToken1.GetPreviousToken(includeSkipped: true);
+
+            // # nullable |
+            // # nullable e|
+            return previousToken1.Kind() == SyntaxKind.NullableKeyword &&
+                previousToken2.Kind() == SyntaxKind.HashToken;
+        }
+    }
+}

src/Features/CSharp/Portable/Completion/KeywordRecommenders/NullableKeywordRecommender.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.
+
+using System.Threading;
+using Microsoft.CodeAnalysis.CSharp.Extensions.ContextQuery;
+
+namespace Microsoft.CodeAnalysis.CSharp.Completion.KeywordRecommenders
+{
+    internal class NullableKeywordRecommender : AbstractSyntacticSingleKeywordRecommender
+    {
+        public NullableKeywordRecommender()
+            : base(SyntaxKind.NullableKeyword, isValidInPreprocessorContext: true)
+        {
+        }
+
+        protected override bool IsValidContext(int position, CSharpSyntaxContext context, CancellationToken cancellationToken)
+            => context.IsPreProcessorKeywordContext;
+    }
+}