Add code-folding/structure-guides/sticky-scroll support for extension blocks

src/EditorFeatures/CSharpTest/Structure/AbstractCSharpSyntaxNodeStructureTests.cs

@@ -2,6 +2,8 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System.Diagnostics.CodeAnalysis;
+using System.Threading.Tasks;
 using Microsoft.CodeAnalysis.Editor.UnitTests.Structure;
 
 namespace Microsoft.CodeAnalysis.Editor.CSharp.UnitTests.Structure;
@@ -11,4 +13,9 @@ public abstract class AbstractCSharpSyntaxNodeStructureTests<TSyntaxNode> :
     where TSyntaxNode : SyntaxNode
 {
     protected sealed override string LanguageName => LanguageNames.CSharp;
+
+    private protected new Task VerifyBlockSpansAsync(
+        [StringSyntax(PredefinedEmbeddedLanguageNames.CSharpTest)] string markupCode,
+        params RegionData[] expectedRegionData)
+        => base.VerifyBlockSpansAsync(markupCode, expectedRegionData);
 }

src/EditorFeatures/CSharpTest/Structure/TypeDeclarationStructureTests.cs

@@ -249,4 +249,22 @@ public Task TestTypeDeclarationNoBraces2()
                 """,
             Region("comment", "// comment ...", autoCollapse: true),
             Region("textspan1", "hint1", CSharpStructureHelpers.Ellipsis, autoCollapse: false));
+
+    [Fact, WorkItem("https://github.com/dotnet/roslyn/issues/81662")]
+    public Task TestExtension1()
+        => VerifyBlockSpansAsync("""
+                {|hint:$$extension{|textspan:(string s)
+                {
+                }|}|}
+                """,
+            Region("textspan", "hint", CSharpStructureHelpers.Ellipsis, autoCollapse: false));
+
+    [Fact, WorkItem("https://github.com/dotnet/roslyn/issues/81662")]
+    public Task TestExtension2()
+        => VerifyBlockSpansAsync("""
+                {|hint:$$extension<T>{|textspan:(string s)
+                {
+                }|}|}
+                """,
+            Region("textspan", "hint", CSharpStructureHelpers.Ellipsis, autoCollapse: false));
 }

src/Features/CSharp/Portable/Structure/CSharpBlockStructureProvider.cs

@@ -2,16 +2,15 @@
 // 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 Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.CodeAnalysis.Structure;
 
 namespace Microsoft.CodeAnalysis.CSharp.Structure;
 
-internal sealed class CSharpBlockStructureProvider : AbstractBlockStructureProvider
+internal sealed class CSharpBlockStructureProvider()
+    : AbstractBlockStructureProvider(CreateDefaultNodeProviderMap(), CreateDefaultTriviaProviderMap())
 {
     private static ImmutableDictionary<Type, ImmutableArray<AbstractSyntaxStructureProvider>> CreateDefaultNodeProviderMap()
     {
@@ -32,6 +31,7 @@ private static ImmutableDictionary<Type, ImmutableArray<AbstractSyntaxStructureP
         builder.Add<EnumMemberDeclarationSyntax, EnumMemberDeclarationStructureProvider>();
         builder.Add<EventDeclarationSyntax, EventDeclarationStructureProvider>();
         builder.Add<EventFieldDeclarationSyntax, EventFieldDeclarationStructureProvider>();
+        builder.Add<ExtensionBlockDeclarationSyntax, TypeDeclarationStructureProvider>();
         builder.Add<FieldDeclarationSyntax, FieldDeclarationStructureProvider>();
         builder.Add<FileScopedNamespaceDeclarationSyntax, FileScopedNamespaceDeclarationStructureProvider>();
         builder.Add<IndexerDeclarationSyntax, IndexerDeclarationStructureProvider>();
@@ -68,9 +68,4 @@ private static ImmutableDictionary<int, ImmutableArray<AbstractSyntaxStructurePr
 
         return builder.ToImmutable();
     }
-
-    internal CSharpBlockStructureProvider()
-        : base(CreateDefaultNodeProviderMap(), CreateDefaultTriviaProviderMap())
-    {
-    }
 }

src/Features/CSharp/Portable/Structure/Providers/TypeDeclarationStructureProvider.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.Threading;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.CodeAnalysis.PooledObjects;
@@ -25,9 +23,11 @@ protected override void CollectBlockSpans(
         if (!typeDeclaration.OpenBraceToken.IsMissing &&
             !typeDeclaration.CloseBraceToken.IsMissing)
         {
-            var lastToken = typeDeclaration.TypeParameterList == null
-                ? typeDeclaration.Identifier
-                : typeDeclaration.TypeParameterList.GetLastToken(includeZeroWidth: true);
+            var lastToken = typeDeclaration.TypeParameterList != null
+                ? typeDeclaration.TypeParameterList.GetLastToken(includeZeroWidth: true)
+                : typeDeclaration is ExtensionBlockDeclarationSyntax extensionBlock
+                    ? extensionBlock.Keyword
+                    : typeDeclaration.Identifier;
 
             SyntaxNodeOrToken current = typeDeclaration;
             var nextSibling = current.GetNextSibling();