Don't offer to remove directives when not on a single line directive (#12862)

Noticed today while demoing at the showcase. I always forget that
`@code` is a directive :(

Author: davidwengier

src/Compiler/Microsoft.CodeAnalysis.Razor.Compiler/src/Language/RazorCodeDocumentExtensions.cs

@@ -6,6 +6,7 @@
 using System.Diagnostics.CodeAnalysis;
 using System.IO;
 using Microsoft.AspNetCore.Mvc.Razor.Extensions;
+using Microsoft.AspNetCore.Razor.Language.Legacy;
 using Microsoft.AspNetCore.Razor.Language.Syntax;
 
 namespace Microsoft.AspNetCore.Razor.Language;
@@ -51,7 +52,7 @@ internal static bool IsImportsFile(this RazorCodeDocument codeDocument)
     /// </remarks>
     internal static bool IsDirectiveUsed(this RazorCodeDocument codeDocument, BaseRazorDirectiveSyntax directive)
     {
-        Debug.Assert(directive is RazorUsingDirectiveSyntax || directive.DirectiveBody.Keyword.GetContent() == "addTagHelper");
+        Debug.Assert(directive is RazorUsingDirectiveSyntax || directive.DirectiveBody.Keyword.GetContent() == SyntaxConstants.CSharp.AddTagHelperKeyword);
 
         // In imports files, all directives are considered used as usage tracking is only for source documents.
         if (codeDocument.IsImportsFile())

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/CodeActions/Razor/RemoveUnnecessaryDirectivesCodeActionProvider.cs

@@ -5,6 +5,7 @@
 using System.Collections.Immutable;
 using System.Threading;
 using System.Threading.Tasks;
+using Microsoft.AspNetCore.Razor.Language.Legacy;
 using Microsoft.AspNetCore.Razor.Language.Syntax;
 using Microsoft.AspNetCore.Razor.Threading;
 using Microsoft.CodeAnalysis.Razor.CodeActions.Models;
@@ -30,7 +31,7 @@ public Task<ImmutableArray<RazorVSInternalCodeAction>> ProvideAsync(RazorCodeAct
             return SpecializedTasks.EmptyImmutableArray<RazorVSInternalCodeAction>();
         }
 
-        // Trigger if the selection start or end is inside any directive
+        // Trigger if the selection start or end is inside any single line directive
         var root = tree.Root;
         var startToken = root.FindToken(context.StartAbsoluteIndex);
         var endToken = context.StartAbsoluteIndex != context.EndAbsoluteIndex
@@ -40,7 +41,7 @@ public Task<ImmutableArray<RazorVSInternalCodeAction>> ProvideAsync(RazorCodeAct
         var startDirective = startToken.Parent?.FirstAncestorOrSelf<BaseRazorDirectiveSyntax>();
         var endDirective = endToken.Parent?.FirstAncestorOrSelf<BaseRazorDirectiveSyntax>();
 
-        if (startDirective is null && endDirective is null)
+        if (!ShouldOffer(startDirective) && !ShouldOffer(endDirective))
         {
             return SpecializedTasks.EmptyImmutableArray<RazorVSInternalCodeAction>();
         }
@@ -62,4 +63,21 @@ public Task<ImmutableArray<RazorVSInternalCodeAction>> ProvideAsync(RazorCodeAct
         var action = RazorCodeActionFactory.CreateRemoveUnnecessaryDirectives(resolutionParams);
         return Task.FromResult<ImmutableArray<RazorVSInternalCodeAction>>([action]);
     }
+
+    private static bool ShouldOffer(BaseRazorDirectiveSyntax? directive)
+    {
+        if (directive is null)
+        {
+            return false;
+        }
+
+        if (directive is RazorUsingDirectiveSyntax)
+        {
+            return true;
+        }
+
+        // We offer for any single line directive on the assumption that the user has a block of directives
+        // at the top of their file that they want to clear up.
+        return directive.DirectiveBody.Keyword.GetContent() == SyntaxConstants.CSharp.AddTagHelperKeyword;
+    }
 }

src/Razor/test/Microsoft.VisualStudioCode.RazorExtension.Test/Endpoints/Shared/CodeActions/RemoveUnnecessaryDirectiveTests.cs

@@ -67,6 +67,26 @@ Hello [||]World
             makeDiagnosticsRequest: true);
     }
 
+    [Fact]
+    public async Task NotOfferedWhenCursorIsInCodeBlock()
+    {
+        await VerifyCodeActionAsync(
+            input: """
+                @using System.Text
+
+                <div>
+                    Hello World
+                </div>
+
+                @code {
+                    private [||]int _x;
+                }
+                """,
+            expected: null,
+            codeActionName: LanguageServerConstants.CodeActions.RemoveUnnecessaryDirectives,
+            makeDiagnosticsRequest: true);
+    }
+
     [Fact]
     public async Task MultipleUnusedDirectives_RemovesAll()
     {