Add using directive support.

src/Compiler/Microsoft.CodeAnalysis.Razor.Compiler/src/Language/Legacy/CSharpCodeParser.cs

@@ -30,6 +30,14 @@ internal class CSharpCodeParser : TokenizerBackedParser<CSharpTokenizer>
             builder.Description = Resources.AddTagHelperDirective_Description;
         });
 
+    internal static readonly DirectiveDescriptor UsingDirectiveDescriptor = DirectiveDescriptor.CreateDirective(
+        SyntaxConstants.CSharp.UsingKeyword,
+        DirectiveKind.SingleLine,
+        builder =>
+        {
+            builder.Description = Resources.UsingDirective_Description;
+        });
+
     internal static readonly DirectiveDescriptor RemoveTagHelperDirectiveDescriptor = DirectiveDescriptor.CreateDirective(
         SyntaxConstants.CSharp.RemoveTagHelperKeyword,
         DirectiveKind.SingleLine,

src/Compiler/Microsoft.CodeAnalysis.Razor.Compiler/src/Language/Legacy/SyntaxConstants.cs

@@ -17,6 +17,7 @@ internal static class SyntaxConstants
     public static class CSharp
     {
         public const int UsingKeywordLength = 5;
+        public const string UsingKeyword = "using";
         public const string TagHelperPrefixKeyword = "tagHelperPrefix";
         public const string AddTagHelperKeyword = "addTagHelper";
         public const string RemoveTagHelperKeyword = "removeTagHelper";

src/Compiler/Microsoft.CodeAnalysis.Razor.Compiler/src/Language/Resources.resx

@@ -1,4 +1,4 @@
-<?xml version="1.0" encoding="utf-8"?>
+<?xml version="1.0" encoding="utf-8"?>
 <root>
   <!-- 
     Microsoft ResX Schema 
@@ -595,4 +595,7 @@
   <data name="DirectiveExpectsIdentifierOrExpression" xml:space="preserve">
     <value>The '{0}' directive expects an identifier or explicit razor expression ("@()").</value>
   </data>
-</root>
+  <data name="UsingDirective_Description" xml:space="preserve">
+    <value>Adds the C# using directive to the generated view.</value>
+  </data>
+</root>

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

@@ -0,0 +1,54 @@
+// 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.Frozen;
+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 FrozenDictionary<string, (string Label, string SortText)> s_snippetToCompletionData = new Dictionary<string, (string Label, string SortText)>()
+    {
+        // Modifying label of the C# using snippet to "using statement" to disambiguate from
+        // Razor @using directive, and also appending a space to sort text to make sure it's sorted
+        // after Razor "using" keyword and "using directive ..." entries (which use "using" as sort text)
+        ["using"] = (Label:$"using {SR.Statement}", SortText:"using ")
+    }
+    .ToFrozenDictionary();
+
+    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_snippetToCompletionData.TryGetValue(item.Label, out var completionData))
+                {
+                    item.Label = completionData.Label;
+                    item.SortText = completionData.SortText;
+                }
+            }
+        }
+
+        return Task.FromResult(completionList);
+    }
+}

src/Razor/src/Microsoft.AspNetCore.Razor.LanguageServer/Completion/RazorCompletionItemResolver.cs

@@ -39,7 +39,29 @@ public RazorCompletionItemResolver(
             return null;
         }
 
-        var associatedRazorCompletion = razorCompletionResolveContext.CompletionItems.FirstOrDefault(completion => string.Equals(completion.DisplayText, completionItem.Label, StringComparison.Ordinal));
+        var associatedRazorCompletion = razorCompletionResolveContext.CompletionItems.FirstOrDefault(completion =>
+        {
+            if (completion.DisplayText != completionItem.Label)
+            {
+                return false;
+            }
+
+            // We may have items of different types with the same label (e.g. snippet and keyword)
+            if (clientCapabilities is not null)
+            {
+                // CompletionItem.Kind and RazorCompletionItem.Kind are not compatible/comparable, so we need to convert
+                // Razor completion item to VS completion item (as logic to convert just the kind is not easy to separate from
+                // the rest of the conversion logic) prior to comparing them
+                if (RazorCompletionListProvider.TryConvert(completion, clientCapabilities, out var convertedRazorCompletionItem))
+                {
+                    return completionItem.Kind == convertedRazorCompletionItem.Kind;
+                }
+            }
+
+            // If display text matches but we couldn't convert razor completion item to VS completion item for some reason,
+            // do what previous version of the code did and return true.
+            return true;
+        });
         if (associatedRazorCompletion is null)
         {
             return null;

src/Razor/src/Microsoft.AspNetCore.Razor.LanguageServer/Completion/RazorCompletionResolveEndpoint.cs

@@ -1,7 +1,6 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the MIT license. See License.txt in the project root for license information.
 
-using System;
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
@@ -50,7 +49,9 @@ public async Task<VSInternalCompletionItem> HandleRequestAsync(VSInternalComplet
 
             // See if this is the right completion list for this corresponding completion item. We cross-check this based on label only given that
             // is what users interact with.
-            if (cacheEntry.CompletionList.Items.Any(completion => string.Equals(completionItem.Label, completion.Label, StringComparison.Ordinal)))
+            if (cacheEntry.CompletionList.Items.Any(completion => completionItem.Label == completion.Label &&
+              // Check the Kind as well, e.g. we may have a Razor snippet and a C# keyword with the same label, etc.
+                                                                  completionItem.Kind == completion.Kind))
             {
                 originalRequestContext = cacheEntry.Context;
                 containingCompletionList = cacheEntry.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/src/Microsoft.CodeAnalysis.Razor.Workspaces/Completion/DirectiveCompletionItemProvider.cs

@@ -4,6 +4,7 @@
 #nullable disable
 
 using System;
+using System.Collections.Frozen;
 using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Composition;
@@ -27,11 +28,15 @@ internal class DirectiveCompletionItemProvider : IRazorCompletionItemProvider
         CSharpCodeParser.AddTagHelperDirectiveDescriptor,
         CSharpCodeParser.RemoveTagHelperDirectiveDescriptor,
         CSharpCodeParser.TagHelperPrefixDirectiveDescriptor,
+        CSharpCodeParser.UsingDirectiveDescriptor
     };
 
+    // Test accessor
+    internal static IEnumerable<DirectiveDescriptor> DefaultDirectives => s_defaultDirectives;
+
     // internal for testing
     // Do not forget to update both insert and display text !important
-    internal static readonly IReadOnlyDictionary<string, (string InsertText, string DisplayText)> s_singleLineDirectiveSnippets = new Dictionary<string, (string InsertText, string DisplayText)>(StringComparer.Ordinal)
+    internal static readonly FrozenDictionary<string, (string InsertText, string DisplayText)> s_singleLineDirectiveSnippets = new Dictionary<string, (string InsertText, string DisplayText)>(StringComparer.Ordinal)
     {
         ["addTagHelper"] = ("addTagHelper ${1:*}, ${2:Microsoft.AspNetCore.Mvc.TagHelpers}", "addTagHelper *, Microsoft.AspNetCore.Mvc.TagHelpers"),
         ["attribute"] = ("attribute [${1:Authorize}]$0", "attribute [Authorize]"),
@@ -45,8 +50,10 @@ internal class DirectiveCompletionItemProvider : IRazorCompletionItemProvider
         ["preservewhitespace"] = ("preservewhitespace ${1:true}$0", "preservewhitespace true"),
         ["removeTagHelper"] = ("removeTagHelper ${1:*}, ${2:Microsoft.AspNetCore.Mvc.TagHelpers}", "removeTagHelper *, Microsoft.AspNetCore.Mvc.TagHelpers"),
         ["tagHelperPrefix"] = ("tagHelperPrefix ${1:prefix}$0", "tagHelperPrefix prefix"),
-        ["typeparam"] = ("typeparam ${1:T}$0", "typeparam T")
-    };
+        ["typeparam"] = ("typeparam ${1:T}$0", "typeparam T"),
+        ["using"] = ("using ${1:MyNamespace}$0", "using MyNamespace")
+    }
+    .ToFrozenDictionary();
 
     public ImmutableArray<RazorCompletionItem> GetCompletionItems(RazorCompletionContext context)
     {
@@ -145,6 +152,10 @@ internal static ImmutableArray<RazorCompletionItem> GetDirectiveCompletionItems(
                 completionDisplayText,
                 directive.Directive,
                 RazorCompletionItemKind.Directive,
+                // Make sort text one less than display text so if there are any delegated completion items
+                // with the same display text in the combined completion list, they will be sorted below
+                // our items.
+                sortText: completionDisplayText,
                 commitCharacters: commitCharacters,
                 isSnippet: false);
             var completionDescription = new DirectiveCompletionDescription(directive.Description);
@@ -154,9 +165,11 @@ internal static ImmutableArray<RazorCompletionItem> GetDirectiveCompletionItems(
             if (s_singleLineDirectiveSnippets.TryGetValue(directive.Directive, out var snippetTexts))
             {
                 var snippetCompletionItem = new RazorCompletionItem(
-                    $"{completionDisplayText} ...",
+                    $"{completionDisplayText} {SR.Directive} ...",
                     snippetTexts.InsertText,
                     RazorCompletionItemKind.Directive,
+                    // Use the same sort text here as the directive completion item so both items are grouped together
+                    sortText: completionDisplayText,
                     commitCharacters: commitCharacters,
                     isSnippet: true);
 

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Resources/SR.resx

@@ -120,6 +120,9 @@
   <data name="ArgumentCannotBeNullOrEmpty" xml:space="preserve">
     <value>Value cannot be null or an empty string.</value>
   </data>
+  <data name="Directive" xml:space="preserve">
+    <value>directive</value>
+  </data>
   <data name="DirectiveSnippetDescription" xml:space="preserve">
     <value>Insert a directive code snippet
 [Tab] to navigate between elements, [Enter] to complete</value>