* Make the code do nothing if no listeners are hooked up.

* Cleanup

src/Compiler/Checking/CheckDeclarations.fs

@@ -5173,9 +5173,7 @@ let CheckOneImplFile
     let infoReader = InfoReader(g, amap)
 
     cancellable {
-        use act = Activity.activitySource.StartActivity("CheckOneSigFile")
-        act.AddTag("fileName", fileName) |> ignore
-        act.AddTag("qualifiedNameOfFile", qualNameOfFile.Text) |> ignore
+        use _ = Activity.instance.Start "CheckOneImplFile" [|"fileName", fileName; "qualifiedNameOfFile", qualNameOfFile.Text|]
         let cenv = 
             cenv.Create (g, isScript, niceNameGen, amap, thisCcu, false, Option.isSome rootSigOpt,
                 conditionalDefines, tcSink, (LightweightTcValForUsingInBuildMethodCall g), isInternalTestSpanStackReferring,
@@ -5303,9 +5301,12 @@ let CheckOneImplFile
 /// Check an entire signature file
 let CheckOneSigFile (g, niceNameGen, amap, thisCcu, checkForErrors, conditionalDefines, tcSink, isInternalTestSpanStackReferring) tcEnv (ParsedSigFileInput (fileName = fileName; qualifiedNameOfFile = qualNameOfFile; modules = sigFileFrags)) = 
  cancellable {
-    use act = Activity.activitySource.StartActivity("CheckOneSigFile")
-    act.AddTag("fileName", fileName) |> ignore
-    act.AddTag("qualifiedNameOfFile", qualNameOfFile.Text) |> ignore
+    use _ =
+        Activity.instance.Start "CheckOneSigFile"
+            [|
+                "fileName", fileName
+                "qualifiedNameOfFile", qualNameOfFile.Text
+            |]
 
     let cenv = 
         cenv.Create 

src/Compiler/Driver/ParseAndCheckInputs.fs

@@ -22,7 +22,6 @@ open FSharp.Compiler.CompilerConfig
 open FSharp.Compiler.CompilerDiagnostics
 open FSharp.Compiler.CompilerImports
 open FSharp.Compiler.Diagnostics
-open FSharp.Compiler.Diagnostics.Activity
 open FSharp.Compiler.DiagnosticsLogger
 open FSharp.Compiler.Features
 open FSharp.Compiler.IO
@@ -1140,8 +1139,7 @@ let CheckOneInput
 
     cancellable {
         try
-            use tcOneInputActivity = activitySource.StartActivity("CheckOneInput")
-            tcOneInputActivity.AddTag("inputName", inp.FileName) |> ignore<_>
+            use _ = Activity.instance.Start "CheckOneInput" [|"inputName", inp.FileName|]
 
             CheckSimulateException tcConfig
 
@@ -1344,7 +1342,7 @@ let CheckClosedInputSetFinish (declaredImpls: CheckedImplFile list, tcState) =
     tcState, declaredImpls, ccuContents
 
 let CheckClosedInputSet (ctok, checkForErrors, tcConfig, tcImports, tcGlobals, prefixPathOpt, tcState, inputs) =
-    use tcActivity = activitySource.StartActivity("CheckClosedInputSet")
+    use tcActivity = Activity.instance.StartNoTags("CheckClosedInputSet")
     // tcEnvAtEndOfLastFile is the environment required by fsi.exe when incrementally adding definitions
     let results, tcState =
         (tcState, inputs)

src/Compiler/Driver/fsc.fs

@@ -39,7 +39,6 @@ open FSharp.Compiler.CompilerGlobalState
 open FSharp.Compiler.CreateILModule
 open FSharp.Compiler.DependencyManager
 open FSharp.Compiler.Diagnostics
-open FSharp.Compiler.Diagnostics.Activity
 open FSharp.Compiler.DiagnosticsLogger
 open FSharp.Compiler.IlxGen
 open FSharp.Compiler.InfoReader
@@ -167,8 +166,7 @@ let TypeCheck
         inputs,
         exiter: Exiter
     ) =
-    use typecheckActivity = activitySource.StartActivity("typecheck_inputs")
-    typecheckActivity.AddTag("assemblyName", assemblyName) |> ignore
+    use _ = Activity.instance.Start "typecheck_inputs" [|"assemblyName", assemblyName|]
 
     try
         if isNil inputs then
@@ -535,7 +533,7 @@ let main1
 
     // Process command line, flags and collect filenames
     let sourceFiles =
-        use parseActivity = activitySource.StartActivity("determine_source_files")
+        use parseActivity = Activity.instance.StartNoTags("determine_source_files")
 
         // The ParseCompilerOptions function calls imperative function to process "real" args
         // Rather than start processing, just collect names, then process them.
@@ -569,7 +567,7 @@ let main1
 
     // If there's a problem building TcConfig, abort
     let tcConfig =
-        use createConfigActivity = activitySource.StartActivity("create_tc_config")
+        use createConfigActivity = Activity.instance.StartNoTags("create_tc_config")
 
         try
             TcConfig.Create(tcConfigB, validate = false)
@@ -595,12 +593,12 @@ let main1
     let foundationalTcConfigP = TcConfigProvider.Constant tcConfig
 
     let sysRes, otherRes, knownUnresolved =
-        use splitResolutionsActivity = activitySource.StartActivity("split_resolutions")
+        use splitResolutionsActivity = Activity.instance.StartNoTags("split_resolutions")
         TcAssemblyResolutions.SplitNonFoundationalResolutions(tcConfig)
 
     // Import basic assemblies
     let tcGlobals, frameworkTcImports =
-        use frameworkImportsActivity = activitySource.StartActivity("import_framework_references")
+        use frameworkImportsActivity = Activity.instance.StartNoTags("import_framework_references")
         TcImports.BuildFrameworkTcImports(foundationalTcConfigP, sysRes, otherRes)
         |> NodeCode.RunImmediateWithoutCancellation
 
@@ -653,7 +651,7 @@ let main1
     ReportTime tcConfig "Import non-system references"
 
     let tcImports =
-        use nonFrameworkImportsActivity = activitySource.StartActivity("import_non_framework_references")
+        use nonFrameworkImportsActivity = Activity.instance.StartNoTags("import_non_framework_references")
         TcImports.BuildNonFrameworkTcImports(tcConfigP, frameworkTcImports, otherRes, knownUnresolved, dependencyProvider)
         |> NodeCode.RunImmediateWithoutCancellation
 
@@ -672,7 +670,7 @@ let main1
     use unwindParsePhase = PushThreadBuildPhaseUntilUnwind BuildPhase.TypeCheck
 
     let tcEnv0, openDecls0 =
-        use initialTcEnvActivity = activitySource.StartActivity("get_initial_tc_env")
+        use initialTcEnvActivity = Activity.instance.StartNoTags("get_initial_tc_env")
         GetInitialTcEnv(assemblyName, rangeStartup, tcConfig, tcImports, tcGlobals)
 
     // Type check the inputs
@@ -733,7 +731,7 @@ let main1OfAst
         inputs: ParsedInput list
     ) =
 
-    use main1AstActivity = activitySource.StartActivity("main1_of_ast")
+    use main1AstActivity = Activity.instance.StartNoTags("main1_of_ast")
 
     let tryGetMetadataSnapshot = (fun _ -> None)
 
@@ -919,8 +917,7 @@ let main2
            exiter: Exiter,
            ilSourceDocs))
     =
-    use main2Activity = activitySource.StartActivity("main2")
-
+    use main2Activity = Activity.instance.StartNoTags("main2")
 
     if tcConfig.typeCheckOnly then
         exiter.Exit 0
@@ -1029,7 +1026,7 @@ let main3
            exiter: Exiter,
            ilSourceDocs))
     =
-    use main3Activity = activitySource.StartActivity("main3")
+    use main3Activity = Activity.instance.StartNoTags("main3")
     // Encode the signature data
     ReportTime tcConfig "Encode Interface Data"
     let exportRemapping = MakeExportRemapping generatedCcu generatedCcu.Contents
@@ -1125,7 +1122,7 @@ let main4
            exiter: Exiter,
            ilSourceDocs))
     =
-    use main4Activity = activitySource.StartActivity("main4")
+    use main4Activity = Activity.instance.StartNoTags("main4")
 
     match tcImportsCapture with
     | None -> ()
@@ -1229,7 +1226,7 @@ let main5
            exiter: Exiter,
            ilSourceDocs))
     =
-    use main5Activity = activitySource.StartActivity("main5")
+    use main5Activity = Activity.instance.StartNoTags("main5")
 
     use unwindBuildPhase = PushThreadBuildPhaseUntilUnwind BuildPhase.Output
 
@@ -1262,7 +1259,7 @@ let main6
            exiter: Exiter,
            ilSourceDocs))
     =
-    use main6Activity = activitySource.StartActivity("main6")
+    use main6Activity = Activity.instance.StartNoTags("main6")
 
     ReportTime tcConfig "Write .NET Binary"
 

src/Compiler/Facilities/BuildGraph.fs

@@ -7,6 +7,7 @@ open System.Threading
 open System.Threading.Tasks
 open System.Diagnostics
 open System.Globalization
+open FSharp.Compiler.Diagnostics.Activity
 open FSharp.Compiler.DiagnosticsLogger
 open Internal.Utilities.Library
 
@@ -93,7 +94,7 @@ type NodeCodeBuilder() =
     member _.Combine(Node (p1): NodeCode<unit>, Node (p2): NodeCode<'T>) : NodeCode<'T> = Node(async.Combine(p1, p2))
 
     [<DebuggerHidden; DebuggerStepThrough>]
-    member _.Using(value: Activity, binder: Activity -> NodeCode<'U>) =
+    member _.Using(value: ActivityFacade, binder: ActivityFacade -> NodeCode<'U>) =
         Node(
             async {
                 try

src/Compiler/Facilities/BuildGraph.fsi

@@ -6,6 +6,7 @@ open System
 open System.Diagnostics
 open System.Threading
 open System.Threading.Tasks
+open FSharp.Compiler.Diagnostics.Activity
 open FSharp.Compiler.DiagnosticsLogger
 open Internal.Utilities.Library
 
@@ -48,7 +49,7 @@ type NodeCodeBuilder =
     /// that a proper generic 'use' could be implemented but has not currently been necessary)
     member Using: CompilationGlobalsScope * (CompilationGlobalsScope -> NodeCode<'T>) -> NodeCode<'T>
     
-    member Using: Activity * (Activity -> NodeCode<'T>) -> NodeCode<'T>
+    member Using: ActivityFacade * (ActivityFacade -> NodeCode<'T>) -> NodeCode<'T>
 
 /// Specifies code that can be run as part of the build graph.
 val node: NodeCodeBuilder

src/Compiler/Facilities/Logger.fs

@@ -7,8 +7,34 @@ open System.Diagnostics
 open System.Diagnostics.Tracing
 
 module Activity =
-    let activitySourceName = "fsc"
-    let activitySource = new ActivitySource(activitySourceName)
+
+    type ActivityFacade(activity : Activity option) =
+        member this.AddTag key (value : #obj) = match activity with | Some activity -> activity.AddTag(key, value) |> ignore | None -> ()
+        member this.Perform action = match activity with | Some activity -> action activity | None -> ()
+        member this.Dispose() = match activity with | Some activity -> activity.Dispose() | None -> ()
+        interface IDisposable with
+            member this.Dispose() = this.Dispose()
+
+    let start (source : ActivitySource) (activityName : string) (tags : (string * #obj) seq) =
+        let activity = source.StartActivity(activityName) |> Option.ofObj
+        let facade = new ActivityFacade(activity)
+        for key, value in tags do
+            facade.AddTag key value
+        facade
+
+    let startNoTags (source : ActivitySource) (activityName : string) = start source activityName []
+
+    type ActivitySourceFacade(source : ActivitySource) =
+        member this.Start (name : string) (tags : (string * #obj) seq) = start source name tags
+        member this.StartNoTags name = startNoTags source name
+        member this.Name = source.Name
+        member this.Dispose() = source.Dispose()
+        interface IDisposable with
+            member this.Dispose() = this.Dispose()
+
+    let private activitySourceName = "fsc"
+    let private activitySource = new ActivitySource(activitySourceName)
+    let instance = new ActivitySourceFacade(activitySource)
 
 type LogCompilerFunctionId =
     | Service_ParseAndCheckFileInProject = 1

src/Compiler/Facilities/Logger.fsi

@@ -5,9 +5,24 @@ namespace FSharp.Compiler.Diagnostics
 open System
 open System.Diagnostics
 
-module Activity = 
-    val activitySourceName: string
-    val activitySource: ActivitySource
+module Activity =
+
+    type ActivityFacade =
+        interface IDisposable
+        new : Activity option -> ActivityFacade
+        member AddTag : string -> #obj -> unit
+        member Perform : (Activity -> unit) -> unit
+        member Dispose : unit -> unit
+
+    type ActivitySourceFacade =
+        interface IDisposable
+        new : ActivitySource -> ActivitySourceFacade
+        member Start : string -> (string * #obj) seq -> ActivityFacade
+        member StartNoTags : string -> ActivityFacade
+        member Name : string
+        member Dispose : unit -> unit
+
+    val instance: ActivitySourceFacade
 
 type internal LogCompilerFunctionId =
     | Service_ParseAndCheckFileInProject = 1

src/Compiler/Service/FSharpCheckerResults.fs

@@ -2347,9 +2347,8 @@ module internal ParseAndCheckFile =
 
     let parseFile (sourceText: ISourceText, fileName, options: FSharpParsingOptions, userOpName: string, suggestNamesForErrors: bool) =
         Trace.TraceInformation("FCS: {0}.{1} ({2})", userOpName, "parseFile", fileName)
-        use act = Activity.activitySource.StartActivity("parseFile")
-        act.AddTag("fileName", fileName) |> ignore
-
+        use act = Activity.instance.Start "parseFile" [|"fileName", fileName|]
+
         let errHandler =
             ErrorHandler(true, fileName, options.DiagnosticOptions, sourceText, suggestNamesForErrors)
 

src/Compiler/Service/IncrementalBuild.fs

@@ -116,17 +116,20 @@ module IncrementalBuildSyntaxTree =
         let mutable weakCache: WeakReference<_> option = None
 
         let parse(sigNameOpt: QualifiedNameOfFile option) =
-            use act = Activity.activitySource.StartActivity("SyntaxTree.parse")
-            act.AddTag("fileName", source.FilePath) |> ignore
-            act.AddTag("buildPhase", BuildPhase.Parse) |> ignore
+            use act =
+                Activity.instance.Start "SyntaxTree.parse"
+                    [|
+                        "fileName", source.FilePath
+                        "buildPhase", BuildPhase.Parse.ToString()
+                    |]
             let diagnosticsLogger = CompilationDiagnosticLogger("Parse", tcConfig.diagnosticsOptions)
             // Return the disposable object that cleans up
             use _holder = new CompilationGlobalsScope(diagnosticsLogger, BuildPhase.Parse)
 
             try
                 IncrementalBuilderEventTesting.MRU.Add(IncrementalBuilderEventTesting.IBEParsed fileName)
                 let canSkip = sigNameOpt.IsSome && FSharpImplFileSuffixes |> List.exists (FileSystemUtils.checkSuffix fileName)
-                act.AddTag("canSkip", canSkip) |> ignore
+                act.AddTag "canSkip" canSkip
                 let input =
                     if canSkip then
                         ParsedInput.ImplFile(
@@ -469,8 +472,7 @@ type BoundModel private (tcConfig: TcConfig,
                 let! res = defaultTypeCheck ()
                 return res
             | Some syntaxTree ->
-                use act = Activity.activitySource.StartActivity("TypeCheck")
-                act.AddTag("fileName", syntaxTree.FileName) |> ignore
+                use _ = Activity.instance.Start "TypeCheck" [|"fileName", syntaxTree.FileName|]
                 let sigNameOpt =
                     if partialCheck then
                         this.BackingSignature
@@ -508,7 +510,7 @@ type BoundModel private (tcConfig: TcConfig,
                                 partialCheck)
                         |> NodeCode.FromCancellable
 
-                    use _ = Activity.activitySource.StartActivity("TypeCheck_BuildState")
+                    use _ = Activity.instance.StartNoTags("TypeCheck_BuildState")
                     Logger.LogBlockMessageStop fileName LogCompilerFunctionId.IncrementalBuild_TypeCheck
 
                     fileChecked.Trigger fileName
@@ -1045,8 +1047,7 @@ module IncrementalBuilderStateHelpers =
 
     let rec createFinalizeBoundModelGraphNode (initialState: IncrementalBuilderInitialState) (boundModels: ImmutableArray<GraphNode<BoundModel>>.Builder) =
         GraphNode(node {
-            use act = Activity.activitySource.StartActivity("GetCheckResultsAndImplementationsForProject")
-            act.AddTag("projectOutFile", initialState.outfile) |> ignore
+            use _ = Activity.instance.Start "GetCheckResultsAndImplementationsForProject" [|"projectOutFile", initialState.outfile|]
             // Compute last bound model then get all the evaluated models.
             let! _ = boundModels[boundModels.Count - 1].GetOrComputeValue()
             let boundModels =