Merge pull request #4363 from mavasani/Issue4068

Don't skip executing analyzer compilation actions in the IDE when ClosedFileDiagnostics flag is turned off OR the analyzer reports only hidden diagnostics. Compilation actions and compilation end actions can report diagnostics on open files, so they must always be executed.

Fixes #4068 

src/EditorFeatures/Test2/Diagnostics/DiagnosticServiceTests.vb

@@ -1779,5 +1779,46 @@ class MyClass
                 Assert.Equal(0, diagnostics.Count())
             End Using
         End Sub
+
+        <Fact, WorkItem(4068, "https://github.com/dotnet/roslyn/issues/4068")>
+        Public Sub TestAnalyzerWithCompilationActionReportingHiddenDiagnostics()
+            Dim test = <Workspace>
+                           <Project Language="C#" CommonReferences="true">
+                               <Document><![CDATA[
+class MyClass
+{
+}]]>
+                               </Document>
+                           </Project>
+                       </Workspace>
+
+            Using workspace = TestWorkspaceFactory.CreateWorkspace(test)
+                Dim project = workspace.CurrentSolution.Projects.Single()
+
+                ' Add analyzer
+                Dim analyzer = New HiddenDiagnosticsCompilationAnalyzer()
+                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
+                Dim descriptorsMap = diagnosticService.GetDiagnosticDescriptors(project)
+                Assert.Equal(1, descriptorsMap.Count)
+                Dim descriptors = descriptorsMap.First().Value
+                Assert.Equal(1, descriptors.Length)
+                Assert.Equal(HiddenDiagnosticsCompilationAnalyzer.Descriptor.Id, descriptors.Single().Id)
+
+                ' Force project analysis
+                incrementalAnalyzer.AnalyzeProjectAsync(project, semanticsChanged:=True, cancellationToken:=CancellationToken.None).Wait()
+
+                ' Get cached project diagnostics.
+                Dim diagnostics = diagnosticService.GetCachedDiagnosticsAsync(workspace, project.Id).WaitAndGetResult(CancellationToken.None)
+
+                Assert.Equal(1, diagnostics.Count())
+                Assert.Equal(HiddenDiagnosticsCompilationAnalyzer.Descriptor.Id, diagnostics.Single().Id)
+            End Using
+        End Sub
     End Class
 End Namespace

src/Features/Core/Diagnostics/EngineV1/DiagnosticIncrementalAnalyzer.cs

@@ -316,7 +316,8 @@ private async Task AnalyzeProjectAsync(Project project, CancellationToken cancel
         {
             try
             {
-                if (!CheckOption(project.Solution.Workspace, project.Language, documentOpened: false))
+                // Compilation actions can report diagnostics on open files, so "documentOpened = true"
+                if (!CheckOption(project.Solution.Workspace, project.Language, documentOpened: true))
                 {
                     return;
                 }
@@ -329,7 +330,8 @@ private async Task AnalyzeProjectAsync(Project project, CancellationToken cancel
                 var versions = new VersionArgument(projectTextVersion, semanticVersion, projectVersion);
                 foreach (var stateSet in _stateManager.GetOrUpdateStateSets(project))
                 {
-                    if (SkipRunningAnalyzer(project.CompilationOptions, analyzerDriver, openedDocument: false, skipClosedFileChecks: false, stateSet: stateSet))
+                    // Compilation actions can report diagnostics on open files, so we skipClosedFileChecks.
+                    if (SkipRunningAnalyzer(project.CompilationOptions, analyzerDriver, openedDocument: true, skipClosedFileChecks: true, stateSet: stateSet))
                     {
                         await ClearExistingDiagnostics(project, stateSet, cancellationToken).ConfigureAwait(false);
                         continue;

src/Test/Utilities/CommonDiagnosticAnalyzers.cs

@@ -336,5 +336,34 @@ protected override string GetText(IFormatProvider formatProvider)
                 }
             }
         }
+
+        [DiagnosticAnalyzer(LanguageNames.CSharp, LanguageNames.VisualBasic)]
+        public class HiddenDiagnosticsCompilationAnalyzer : DiagnosticAnalyzer
+        {
+            public static readonly DiagnosticDescriptor Descriptor = new DiagnosticDescriptor(
+                "ID 1000",
+                "Description1",
+                string.Empty,
+                "Analysis",
+                DiagnosticSeverity.Hidden,
+                true,
+                customTags: WellKnownDiagnosticTags.NotConfigurable);
+
+            public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics => ImmutableArray.Create(Descriptor);
+
+            public override void Initialize(AnalysisContext context)
+            {
+                context.RegisterCompilationAction(this.OnCompilation);
+            }
+
+            private void OnCompilation(CompilationAnalysisContext context)
+            {
+                // Report the hidden diagnostic on all trees in compilation.
+                foreach (var tree in context.Compilation.SyntaxTrees)
+                {
+                    context.ReportDiagnostic(Diagnostic.Create(Descriptor, tree.GetRoot().GetLocation()));
+                }
+            }
+        }
     }
 }
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