Add snippet completion item re-writer so we can change C# "using" sni…

…ppet to say "using statement"

src/Razor/src/Microsoft.AspNetCore.Razor.LanguageServer/Completion/Delegation/SnippetResponseRewriter.cs

@@ -0,0 +1,48 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the MIT license. See License.txt in the project root for license information.
+
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Razor.LanguageServer.Protocol;
+using Microsoft.VisualStudio.LanguageServer.Protocol;
+
+namespace Microsoft.AspNetCore.Razor.LanguageServer.Completion.Delegation;
+
+/// <summary>
+/// Modifies delegated snippet completion items
+/// </summary>
+/// <remarks>
+/// At the moment primarily used to modify C# "using" snippet to "using statement" snippet
+/// in order to disambiguate it from Razor "using directive" snippet
+/// </remarks>
+internal class SnippetResponseRewriter : DelegatedCompletionResponseRewriter
+{
+    private static readonly IReadOnlyDictionary<string, string> s_snippetToLabel = new Dictionary<string, string>()
+    {
+        ["using"] = $"using {SR.Statement}"
+    };
+
+    public override int Order => ExecutionBehaviorOrder.ChangesCompletionItems;
+
+    public override Task<VSInternalCompletionList> RewriteAsync(VSInternalCompletionList completionList, int hostDocumentIndex, DocumentContext hostDocumentContext, DelegatedCompletionParams delegatedParameters, CancellationToken cancellationToken)
+    {
+        foreach (var item in completionList.Items)
+        {
+            if (item.Kind == CompletionItemKind.Snippet)
+            {
+                if (item.Label is null)
+                {
+                    continue;
+                }
+
+                if (s_snippetToLabel.TryGetValue(item.Label, out var newLabel))
+                {
+                    item.Label = newLabel;
+                }
+            }
+        }
+
+        return Task.FromResult(completionList);
+    }
+}

src/Razor/src/Microsoft.AspNetCore.Razor.LanguageServer/Extensions/IServiceCollectionExtensions.cs

@@ -90,6 +90,7 @@ public static void AddCompletionServices(this IServiceCollection services, Langu
         services.AddSingleton<DelegatedCompletionResponseRewriter, TextEditResponseRewriter>();
         services.AddSingleton<DelegatedCompletionResponseRewriter, DesignTimeHelperResponseRewriter>();
         services.AddSingleton<DelegatedCompletionResponseRewriter, HtmlCommitCharacterResponseRewriter>();
+        services.AddSingleton<DelegatedCompletionResponseRewriter, SnippetResponseRewriter>();
 
         services.AddSingleton<AggregateCompletionItemResolver>();
         services.AddSingleton<CompletionItemResolver, RazorCompletionItemResolver>();

src/Razor/src/Microsoft.AspNetCore.Razor.LanguageServer/Resources/SR.resx

@@ -195,4 +195,7 @@
   <data name="Version_Should_Not_Be_Null" xml:space="preserve">
     <value>Provided version should not be null.</value>
   </data>
+  <data name="Statement" xml:space="preserve">
+    <value>statement</value>
+  </data>
 </root>

src/Razor/test/Microsoft.AspNetCore.Razor.LanguageServer.Test/Completion/Delegation/SnippetResponseRewriterTest.cs

@@ -0,0 +1,149 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the MIT license. See License.txt in the project root for license information.
+
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Razor.LanguageServer.Completion.Delegation;
+using Microsoft.CodeAnalysis.Testing;
+using Microsoft.VisualStudio.LanguageServer.Protocol;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace Microsoft.AspNetCore.Razor.LanguageServer.Test.Completion.Delegation;
+public class SnippetResponseRewriterTest(ITestOutputHelper testOutput)
+    : ResponseRewriterTestBase(new SnippetResponseRewriter(), testOutput)
+{
+    [Fact]
+    public async Task RewriteAsync_ChangesUsingSnippetLabel()
+    {
+        // Arrange
+        var documentContent = "@$$";
+        TestFileMarkupParser.GetPosition(documentContent, out documentContent, out var cursorPosition);
+        var delegatedCompletionList = GenerateCompletionList(
+            ("using", CompletionItemKind.Snippet),
+            ("if", CompletionItemKind.Keyword)
+            );
+        var rewriter = new SnippetResponseRewriter();
+
+        // Act
+        var rewrittenCompletionList = await GetRewrittenCompletionListAsync(
+            cursorPosition, documentContent, delegatedCompletionList, rewriter);
+
+        // Assert
+        Assert.Null(rewrittenCompletionList.CommitCharacters);
+        Assert.Collection(
+            rewrittenCompletionList.Items,
+            completion =>
+            {
+                Assert.Equal("using statement", completion.Label);
+            },
+            completion =>
+            {
+                Assert.Equal("if", completion.Label);
+            }
+        );
+    }
+
+    [Fact]
+    public async Task RewriteAsync_DoesNotChangeUsingKeywordLabel()
+    {
+        // Arrange
+        var documentContent = "@$$";
+        TestFileMarkupParser.GetPosition(documentContent, out documentContent, out var cursorPosition);
+        var delegatedCompletionList = GenerateCompletionList(
+            ("using", CompletionItemKind.Keyword),
+            ("if", CompletionItemKind.Keyword)
+            );
+        var rewriter = new SnippetResponseRewriter();
+
+        // Act
+        var rewrittenCompletionList = await GetRewrittenCompletionListAsync(
+            cursorPosition, documentContent, delegatedCompletionList, rewriter);
+
+        // Assert
+        Assert.Null(rewrittenCompletionList.CommitCharacters);
+        Assert.Collection(
+            rewrittenCompletionList.Items,
+            completion =>
+            {
+                Assert.Equal("using", completion.Label);
+            },
+            completion =>
+            {
+                Assert.Equal("if", completion.Label);
+            }
+        );
+    }
+
+    [Fact]
+    public async Task RewriteAsync_DoesNotChangeIfSnippetLabel()
+    {
+        // Arrange
+        var documentContent = "@$$";
+        TestFileMarkupParser.GetPosition(documentContent, out documentContent, out var cursorPosition);
+        var delegatedCompletionList = GenerateCompletionList(
+            ("using", CompletionItemKind.Keyword),
+            ("if", CompletionItemKind.Snippet)
+            );
+        var rewriter = new SnippetResponseRewriter();
+
+        // Act
+        var rewrittenCompletionList = await GetRewrittenCompletionListAsync(
+            cursorPosition, documentContent, delegatedCompletionList, rewriter);
+
+        // Assert
+        Assert.Null(rewrittenCompletionList.CommitCharacters);
+        Assert.Collection(
+            rewrittenCompletionList.Items,
+            completion =>
+            {
+                Assert.Equal("using", completion.Label);
+            },
+            completion =>
+            {
+                Assert.Equal("if", completion.Label);
+            }
+        );
+    }
+
+    [Fact]
+    public async Task RewriteAsync_HandlesNullLabels()
+    {
+        // Arrange
+        var documentContent = "@$$";
+        TestFileMarkupParser.GetPosition(documentContent, out documentContent, out var cursorPosition);
+        var delegatedCompletionList = GenerateCompletionList(
+            (null, CompletionItemKind.Keyword),
+            ("using", CompletionItemKind.Snippet)
+            );
+        var rewriter = new SnippetResponseRewriter();
+
+        // Act
+        var rewrittenCompletionList = await GetRewrittenCompletionListAsync(
+            cursorPosition, documentContent, delegatedCompletionList, rewriter);
+
+        // Assert
+        Assert.Null(rewrittenCompletionList.CommitCharacters);
+        Assert.Collection(
+            rewrittenCompletionList.Items,
+            completion =>
+            {
+                Assert.Null(completion.Label);
+            },
+            completion =>
+            {
+                Assert.Equal("using statement", completion.Label);
+            }
+        );
+    }
+
+    private static VSInternalCompletionList GenerateCompletionList(params (string? Label, CompletionItemKind Kind)[] itemsData)
+    {
+        var items = itemsData.Select(itemData => new VSInternalCompletionItem() { Label = itemData.Label!, Kind = itemData.Kind}).ToArray();
+        return new VSInternalCompletionList()
+        {
+            Items = items
+        };
+    }
+}