Partial fix for https://github.com/dotnet/vscode-csharp/issues/7678

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Completion/CompletionListMerger.cs

@@ -22,7 +22,9 @@ internal static class CompletionListMerger
     [return: NotNullIfNotNull(nameof(delegatedCompletionList))]
     public static VSInternalCompletionList? Merge(VSInternalCompletionList? razorCompletionList, VSInternalCompletionList? delegatedCompletionList)
     {
-        if (razorCompletionList is null)
+        // In VSCode case we always think completion was invoked explicitly and create empty Razor completion list,
+        // so check for empty Items collection as well. 
+        if (razorCompletionList is null || razorCompletionList.Items.Length == 0)
         {
             return delegatedCompletionList;
         }
@@ -38,7 +40,8 @@ internal static class CompletionListMerger
         var mergedIsIncomplete = razorCompletionList.IsIncomplete || delegatedCompletionList.IsIncomplete;
         var mergedItems = razorCompletionList.Items.Concat(delegatedCompletionList.Items).ToArray();
         var mergedData = MergeData(razorCompletionList.Data, delegatedCompletionList.Data);
-        var mergedCommitCharacters = razorCompletionList.CommitCharacters ?? delegatedCompletionList.CommitCharacters;
+        var mergedCommitCharacters = razorCompletionList.CommitCharacters
+            ?? delegatedCompletionList.CommitCharacters;
         var mergedSuggestionMode = razorCompletionList.SuggestionMode || delegatedCompletionList.SuggestionMode;
 
         // We don't fully support merging continue characters currently. Razor doesn't currently use them so delegated completion lists always win.
@@ -58,6 +61,8 @@ internal static class CompletionListMerger
             ItemDefaults = new CompletionListItemDefaults()
             {
                 EditRange = mergedItemDefaultsEditRange,
+                // VSCode won't use VSInternalCompletionList.CommitCharacters, make sure we don't lose item defaults
+                CommitCharacters = razorCompletionList.ItemDefaults?.CommitCharacters ?? delegatedCompletionList.ItemDefaults?.CommitCharacters
             }
         };
 

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Completion/CompletionTriggerAndCommitCharacters.cs

@@ -19,7 +19,7 @@ internal class CompletionTriggerAndCommitCharacters
     private static readonly char[] s_vsCodeHtmlTriggerCharacters = ['#', '.', '!', ',', '-', '<'];
     private static readonly char[] s_razorTriggerCharacters = ['<', ':', ' '];
     private static readonly char[] s_csharpTriggerCharacters = [' ', '(', '=', '#', '.', '<', '[', '{', '"', '/', ':', '~'];
-    private static readonly char[] s_commitCharacters = [' ', '>', ';', '='];
+    private static readonly ImmutableArray<string> s_commitCharacters = [" ", ">", ";", "="];
 
     private readonly HashSet<char> _csharpTriggerCharacters;
     private readonly HashSet<char> _delegationTriggerCharacters;
@@ -68,15 +68,16 @@ public CompletionTriggerAndCommitCharacters(LanguageServerFeatureOptions languag
         allTriggerCharacters.UnionWith(razorTriggerCharacters);
         allTriggerCharacters.UnionWith(delegationTriggerCharacters);
 
-        var commitCharacters = new HashSet<char>();
-        commitCharacters.UnionWith(s_commitCharacters);
-
         _csharpTriggerCharacters = csharpTriggerCharacters;
         _htmlTriggerCharacters = htmlTriggerCharacters;
         _razorTriggerCharacters = razorTriggerCharacters;
         _delegationTriggerCharacters = delegationTriggerCharacters;
+
+        // We shouldn't specify commit characters for VSCode.
+        // It doesn't appear to need them and they interfere with normal item commit.
+        // E.g. see https://github.com/dotnet/vscode-csharp/issues/7678
+        AllCommitCharacters = languageServerFeatureOptions.UseVsCodeCompletionTriggerCharacters ? [] : s_commitCharacters;
         AllTriggerCharacters = allTriggerCharacters.SelectAsArray(static c => c.ToString());
-        AllCommitCharacters = commitCharacters.SelectAsArray(static c => c.ToString());
     }
 
     public bool IsValidCSharpTrigger(CompletionContext completionContext)

src/Razor/test/Microsoft.AspNetCore.Razor.LanguageServer.Test/Completion/CompletionListProviderTest.cs

@@ -22,8 +22,8 @@ namespace Microsoft.AspNetCore.Razor.LanguageServer.Completion;
 
 public class CompletionListProviderTest : LanguageServerTestBase
 {
-    private readonly VSInternalCompletionList _completionList1;
-    private readonly VSInternalCompletionList _completionList2;
+    private readonly VSInternalCompletionList _razorCompletionList;
+    private readonly VSInternalCompletionList _delegatedCompletionList;
     private readonly RazorCompletionListProvider _razorCompletionProvider;
     private readonly DelegatedCompletionListProvider _delegatedCompletionProvider;
     private readonly VSInternalCompletionContext _completionContext;
@@ -35,10 +35,10 @@ public class CompletionListProviderTest : LanguageServerTestBase
     public CompletionListProviderTest(ITestOutputHelper testOutput)
         : base(testOutput)
     {
-        _completionList1 = new VSInternalCompletionList() { Items = [] };
-        _completionList2 = new VSInternalCompletionList() { Items = [] };
-        _razorCompletionProvider = new TestRazorCompletionListProvider(_completionList1, LoggerFactory);
-        _delegatedCompletionProvider = new TestDelegatedCompletionListProvider(_completionList2);
+        _razorCompletionList = new VSInternalCompletionList() { Items = [] };
+        _delegatedCompletionList = new VSInternalCompletionList() { Items = [] };
+        _razorCompletionProvider = new TestRazorCompletionListProvider(_razorCompletionList, LoggerFactory);
+        _delegatedCompletionProvider = new TestDelegatedCompletionListProvider(_delegatedCompletionList);
         _completionContext = new VSInternalCompletionContext();
         _documentContext = TestDocumentContext.Create("C:/path/to/file.cshtml");
         _clientCapabilities = new VSInternalClientCapabilities();
@@ -53,12 +53,13 @@ public async Task MultipleCompletionLists_Merges()
         var provider = new CompletionListProvider(_razorCompletionProvider, _delegatedCompletionProvider, _triggerAndCommitCharacters);
 
         // Act
-        var completionList = await provider.GetCompletionListAsync(
+        var mergedCompletionList = await provider.GetCompletionListAsync(
             absoluteIndex: 0, _completionContext, _documentContext, _clientCapabilities, _razorCompletionOptions, correlationId: Guid.Empty, cancellationToken: DisposalToken);
 
         // Assert
-        Assert.NotSame(_completionList1, completionList);
-        Assert.NotSame(_completionList2, completionList);
+        Assert.Empty(mergedCompletionList.Items);
+        Assert.NotSame(_razorCompletionList, mergedCompletionList);
+        Assert.Same(_delegatedCompletionList, mergedCompletionList);
     }
 
     [Fact]
@@ -76,7 +77,7 @@ public async Task MultipleCompletionLists_DifferentCommitCharacters_OnlyCallsApp
             absoluteIndex: 0, _completionContext, _documentContext, _clientCapabilities, _razorCompletionOptions, correlationId: Guid.Empty, cancellationToken: DisposalToken);
 
         // Assert
-        Assert.Same(_completionList2, completionList);
+        Assert.Same(_delegatedCompletionList, completionList);
     }
 
     private class TestDelegatedCompletionListProvider : DelegatedCompletionListProvider

src/Razor/test/Microsoft.VisualStudio.LanguageServices.Razor.Test/Cohost/CohostDocumentCompletionEndpointTest.cs

@@ -565,7 +565,7 @@ private async Task VerifyCompletionListAsync(
         delegatedItemLabels ??= [InvalidLabel];
         var response = new VSInternalCompletionList()
         {
-            Items = delegatedItemLabels.Select((label) => new VSInternalCompletionItem()
+            Items = delegatedItemLabels.Select((label) => new CompletionItem()
             {
                 Label = label,
                 CommitCharacters = delegatedItemCommitCharacters,