Add regression tests for https://github.com/dotnet/roslyn/issues/4055

src/Compilers/CSharp/Test/Semantic/Diagnostics/DiagnosticAnalyzerTests.cs

@@ -1105,6 +1105,20 @@ void Method()
             TestGenericNameCore(source, new AnalyzerWithNoActions(), new CSharpGenericNameAnalyzer());
         }
 
+        [Fact, WorkItem(4055, "https://github.com/dotnet/roslyn/issues/4055")]
+        public void TestAnalyzerWithNoSupportedDiagnostics()
+        {
+            var source = @"
+class MyClass
+{
+}";
+            // Ensure that adding a dummy analyzer with no supported diagnostics doesn't bring down entire analysis.
+            var analyzers = new DiagnosticAnalyzer[] { new AnalyzerWithNoSupportedDiagnostics() };
+            CreateCompilationWithMscorlib45(source)
+                .VerifyDiagnostics()
+                .VerifyAnalyzerDiagnostics(analyzers);
+        }
+
         private static void TestEffectiveSeverity(
             DiagnosticSeverity defaultSeverity,
             ReportDiagnostic expectedEffectiveSeverity,

src/EditorFeatures/Test2/Diagnostics/DiagnosticServiceTests.vb

@@ -1685,5 +1685,43 @@ namespace ConsoleApplication1
             ' See https//github.com/dotnet/roslyn/issues/2980 for details.
             TestGenericNameCore(test, CSharpGenericNameAnalyzer.Message, CSharpGenericNameAnalyzer.DiagnosticId, New AnalyzerWithNoActions, New CSharpGenericNameAnalyzer)
         End Sub
+
+        <Fact, WorkItem(4055, "https://github.com/dotnet/roslyn/issues/4055")>
+        Public Sub TestAnalyzerWithNoSupportedDiagnostics()
+            Dim test = <Workspace>
+                           <Project Language="C#" CommonReferences="true">
+                               <Document><![CDATA[
+class MyClass
+{
+}]]>
+                               </Document>
+                           </Project>
+                       </Workspace>
+
+            ' Ensure that adding a dummy analyzer with no supported diagnostics doesn't bring down entire analysis.
+            Using workspace = TestWorkspaceFactory.CreateWorkspace(test)
+                Dim project = workspace.CurrentSolution.Projects.Single()
+
+                ' Add analyzer
+                Dim analyzer = New AnalyzerWithNoSupportedDiagnostics()
+                Dim analyzerReference = New AnalyzerImageReference(ImmutableArray.Create(Of DiagnosticAnalyzer)(analyzer))
+                project = project.AddAnalyzerReference(analyzerReference)
+
+                Dim diagnosticService = New TestDiagnosticAnalyzerService()
+                Dim incrementalAnalyzer = diagnosticService.CreateIncrementalAnalyzer(workspace)
+
+                ' Verify available diagnostic descriptors/analyzers
+                Dim descriptorsMap = diagnosticService.GetDiagnosticDescriptors(project)
+                Assert.Equal(1, descriptorsMap.Count)
+                Assert.Equal(0, descriptorsMap.First().Value.Length)
+
+                Dim document = project.Documents.Single()
+                Dim diagnostics = diagnosticService.GetDiagnosticsForSpanAsync(document,
+                    document.GetSyntaxRootAsync().WaitAndGetResult(CancellationToken.None).FullSpan,
+                    CancellationToken.None).WaitAndGetResult(CancellationToken.None)
+
+                Assert.Equal(0, diagnostics.Count())
+            End Using
+        End Sub
     End Class
 End Namespace

src/Test/Utilities/CommonDiagnosticAnalyzers.cs

@@ -291,6 +291,13 @@ public sealed class AnalyzerWithNoActions : DiagnosticAnalyzer
             public override void Initialize(AnalysisContext context) { }
         }
 
+        [DiagnosticAnalyzer(LanguageNames.CSharp, LanguageNames.VisualBasic)]
+        public sealed class AnalyzerWithNoSupportedDiagnostics : DiagnosticAnalyzer
+        {
+            public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics { get; }
+            public override void Initialize(AnalysisContext context) { }
+        }
+
         [DiagnosticAnalyzer(LanguageNames.CSharp, LanguageNames.VisualBasic)]
         public sealed class AnalyzerThatThrowsInGetMessage : DiagnosticAnalyzer
         {