Proposal to add roslyn 'tags' to diagnostic response

src/OmniSharp.Abstractions/Models/v1/Diagnostics/DiagnosticLocation.cs

@@ -6,6 +6,7 @@ public class DiagnosticLocation : QuickFix
     {
         public string LogLevel { get; set; }
         public string Id { get; set; }
+        public string[] Tags { get; set; }
 
         public override bool Equals(object obj)
         {

src/OmniSharp.Roslyn.CSharp/Helpers/DiagnosticExtensions.cs

@@ -1,13 +1,17 @@
 using Microsoft.CodeAnalysis;
 using OmniSharp.Models.Diagnostics;
 using System.Collections.Generic;
+using System.Collections.Immutable;
 using System.Linq;
 using System.Threading.Tasks;
 
 namespace OmniSharp.Helpers
 {
     internal static class DiagnosticExtensions
     {
+        private static readonly ImmutableHashSet<string> _tagFilter =
+            ImmutableHashSet.Create<string>("Unnecessary");
+
         internal static DiagnosticLocation ToDiagnosticLocation(this Diagnostic diagnostic)
         {
             var span = diagnostic.Location.GetMappedLineSpan();
@@ -20,6 +24,10 @@ internal static DiagnosticLocation ToDiagnosticLocation(this Diagnostic diagnost
                 EndColumn = span.EndLinePosition.Character,
                 Text = $"{diagnostic.GetMessage()} ({diagnostic.Id})",
                 LogLevel = diagnostic.Severity.ToString(),
+                Tags = diagnostic
+                    .Descriptor.CustomTags
+                    .Where(x => _tagFilter.Contains(x))
+                    .ToArray(),
                 Id = diagnostic.Id
             };
         }

tests/OmniSharp.Roslyn.CSharp.Tests/DiagnosticsFacts.cs

@@ -3,6 +3,7 @@
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis;
 using OmniSharp.Models.CodeCheck;
+using OmniSharp.Models.Diagnostics;
 using OmniSharp.Roslyn.CSharp.Services.Diagnostics;
 using TestUtility;
 using Xunit;
@@ -45,7 +46,7 @@ private OmniSharpTestHost GetHost(bool roslynAnalyzersEnabled)
         [InlineData(false)]
         public async Task CheckAllFiles(bool roslynAnalyzersEnabled)
         {
-            using(var host = GetHost(roslynAnalyzersEnabled))
+            using (var host = GetHost(roslynAnalyzersEnabled))
             {
                 host.AddFilesToWorkspace(
                     new TestFile("a.cs", "class C1 { int n = true; }"),
@@ -63,7 +64,7 @@ public async Task CheckAllFiles(bool roslynAnalyzersEnabled)
         [InlineData(false)]
         public async Task WhenFileIsDeletedFromWorkSpaceThenResultsAreNotReturnedAnyMore(bool roslynAnalyzersEnabled)
         {
-            using(var host = GetHost(roslynAnalyzersEnabled))
+            using (var host = GetHost(roslynAnalyzersEnabled))
             {
                 host.AddFilesToWorkspace(new TestFile("a.cs", "class C1 { int n = true; }"));
                 await host.RequestCodeCheckAsync();
@@ -83,7 +84,7 @@ public async Task WhenFileIsDeletedFromWorkSpaceThenResultsAreNotReturnedAnyMore
         [Fact]
         public async Task AnalysisSupportBuiltInIDEAnalysers()
         {
-            using(var host = GetHost(roslynAnalyzersEnabled: true))
+            using (var host = GetHost(roslynAnalyzersEnabled: true))
             {
                 host.AddFilesToWorkspace(
                     new TestFile("a.cs", "class C1 { int n = true; }"));
@@ -92,5 +93,39 @@ public async Task AnalysisSupportBuiltInIDEAnalysers()
                 Assert.Contains(quickFixes.QuickFixes, x => x.Text.Contains("IDE0044"));
             }
         }
+
+        [Fact]
+        public async Task WhenUnusedImportExistsWithoutAnalyzersEnabled_ThenReturnEmptyTags()
+        {
+            using (var host = GetHost(roslynAnalyzersEnabled: false))
+            {
+                host.AddFilesToWorkspace(
+                    new TestFile("returnemptytags.cs", @"using System.IO;"));
+
+                var quickFixResponse = await host.RequestCodeCheckAsync("returnemptytags.cs");
+
+                var allDiagnostics = quickFixResponse.QuickFixes.OfType<DiagnosticLocation>();
+
+                Assert.Empty(allDiagnostics.SelectMany(x => x.Tags));
+            }
+        }
+
+        [Fact]
+        public async Task WhenUnusedImportIsFoundAndAnalyzersEnabled_ThenReturnUnnecessaryTag()
+        {
+            using (var host = GetHost(roslynAnalyzersEnabled: true))
+            {
+                host.AddFilesToWorkspace(
+                    new TestFile("returnidetags.cs", @"using System.IO;"));
+
+                var quickFixResponse = await host.RequestCodeCheckAsync("returnidetags.cs");
+
+                Assert.Contains("Unnecessary", quickFixResponse
+                    .QuickFixes
+                    .OfType<DiagnosticLocation>()
+                    .Single(x => x.Id == "IDE0005")
+                    .Tags);
+            }
+        }
     }
 }