F# VS editor: reduce background CPU load by gating expensive analyzers to the active document only

vsintegration/src/FSharp.Editor/Diagnostics/ActiveDocumentDetection.fs

@@ -0,0 +1,63 @@
+// Copyright (c) Microsoft Corporation.  All Rights Reserved.  See License.txt in the project root for license information.
+
+namespace Microsoft.VisualStudio.FSharp.Editor
+
+open System
+open Microsoft.CodeAnalysis
+open Microsoft.VisualStudio
+open Microsoft.VisualStudio.Shell
+open Microsoft.VisualStudio.Shell.Interop
+
+/// Helpers for determining whether a Roslyn Document corresponds to the document
+/// currently active (focused) in the Visual Studio shell.
+///
+/// Background expensive analyzers (UnusedOpens, UnusedDeclarations, SimplifyName,
+/// InlayHints) should run only for the active document, mirroring how C# restricts
+/// "remove unnecessary usings" and similar live analyzers.
+///
+/// Roslyn's BackgroundAnalysisScope lets a host choose "open documents" or
+/// "entire solution" but has no built-in "active document only" tier, so we
+/// determine the truly active document ourselves via the VS shell.
+[<RequireQualifiedAccess>]
+module internal ActiveDocumentDetection =
+
+    /// Returns the document moniker (full file path) of the currently focused
+    /// editor window, or ValueNone if it cannot be determined.
+    let tryGetActiveDocumentMoniker (serviceProvider: IServiceProvider) : string voption =
+        match serviceProvider.GetService(typeof<SVsShellMonitorSelection>) with
+        | :? IVsMonitorSelection as monitorSelection ->
+            let mutable frameObj = null
+
+            if
+                ErrorHandler.Succeeded(
+                    monitorSelection.GetCurrentElementValue(uint32 VSConstants.VSSELELEMID.SEID_DocumentFrame, &frameObj)
+                )
+            then
+                match frameObj with
+                | :? IVsWindowFrame as frame ->
+                    let mutable monikerObj = null
+
+                    if
+                        ErrorHandler.Succeeded(frame.GetProperty(int32 __VSFPROPID.VSFPROPID_pszMkDocument, &monikerObj))
+                    then
+                        match monikerObj with
+                        | :? string as moniker -> ValueSome moniker
+                        | _ -> ValueNone
+                    else
+                        ValueNone
+                | _ -> ValueNone
+            else
+                ValueNone
+        | _ -> ValueNone
+
+    /// Returns true when the given document is the currently active editor document.
+    ///
+    /// Falls back to true (= do not suppress analysis) when the active document
+    /// cannot be determined, so analysis is never silently lost.
+    let isActiveDocument (serviceProvider: IServiceProvider) (document: Document) : bool =
+        match document.FilePath with
+        | null -> true
+        | filePath ->
+            match tryGetActiveDocumentMoniker serviceProvider with
+            | ValueNone -> true // couldn't determine the active document, don't suppress analysis
+            | ValueSome activeMoniker -> String.Equals(activeMoniker, filePath, StringComparison.OrdinalIgnoreCase)

vsintegration/src/FSharp.Editor/Diagnostics/SimplifyNameDiagnosticAnalyzer.fs

@@ -22,7 +22,9 @@ type private PerDocumentSavedData =
     }
 
 [<Export(typeof<IFSharpSimplifyNameDiagnosticAnalyzer>)>]
-type internal SimplifyNameDiagnosticAnalyzer [<ImportingConstructor>] () =
+type internal SimplifyNameDiagnosticAnalyzer
+    [<ImportingConstructor>]
+    ([<Import("Microsoft.VisualStudio.Shell.SVsServiceProvider")>] serviceProvider: IServiceProvider) =
 
     static let userOpName = "SimplifyNameDiagnosticAnalyzer"
     static let cache = new MemoryCache("FSharp.Editor." + userOpName)
@@ -37,6 +39,7 @@ type internal SimplifyNameDiagnosticAnalyzer [<ImportingConstructor>] () =
 
             asyncMaybe {
                 do! Option.guard document.Project.IsFSharpCodeFixesSimplifyNameEnabled
+                do! Option.guard (ActiveDocumentDetection.isActiveDocument serviceProvider document)
                 do Trace.TraceInformation("{0:n3} (start) SimplifyName", DateTime.Now.TimeOfDay.TotalSeconds)
                 let! textVersion = document.GetTextVersionAsync(cancellationToken)
                 let textVersionHash = textVersion.GetHashCode()

vsintegration/src/FSharp.Editor/Diagnostics/UnusedDeclarationsAnalyzer.fs

@@ -13,14 +13,17 @@ open Microsoft.CodeAnalysis.ExternalAccess.FSharp.Diagnostics
 open CancellableTasks
 
 [<Export(typeof<IFSharpUnusedDeclarationsDiagnosticAnalyzer>)>]
-type internal UnusedDeclarationsAnalyzer [<ImportingConstructor>] () =
+type internal UnusedDeclarationsAnalyzer
+    [<ImportingConstructor>]
+    ([<Import("Microsoft.VisualStudio.Shell.SVsServiceProvider")>] serviceProvider: IServiceProvider) =
 
     interface IFSharpUnusedDeclarationsDiagnosticAnalyzer with
 
         member _.AnalyzeSemanticsAsync(descriptor, document, cancellationToken) =
             if
                 (document.Project.IsFSharpMiscellaneousOrMetadata && not document.IsFSharpScript)
                 || not document.Project.IsFSharpCodeFixesUnusedDeclarationsEnabled
+                || not (ActiveDocumentDetection.isActiveDocument serviceProvider document)
             then
                 Threading.Tasks.Task.FromResult(ImmutableArray.Empty)
             else

vsintegration/src/FSharp.Editor/Diagnostics/UnusedOpensDiagnosticAnalyzer.fs

@@ -17,7 +17,9 @@ open Microsoft.CodeAnalysis.ExternalAccess.FSharp.Diagnostics
 open CancellableTasks
 
 [<Export(typeof<IFSharpUnusedOpensDiagnosticAnalyzer>)>]
-type internal UnusedOpensDiagnosticAnalyzer [<ImportingConstructor>] () =
+type internal UnusedOpensDiagnosticAnalyzer
+    [<ImportingConstructor>]
+    ([<Import("Microsoft.VisualStudio.Shell.SVsServiceProvider")>] serviceProvider: IServiceProvider) =
 
     static member GetUnusedOpenRanges(document: Document) =
         cancellableTask {
@@ -41,7 +43,10 @@ type internal UnusedOpensDiagnosticAnalyzer [<ImportingConstructor>] () =
     interface IFSharpUnusedOpensDiagnosticAnalyzer with
 
         member _.AnalyzeSemanticsAsync(descriptor, document: Document, cancellationToken: CancellationToken) =
-            if document.Project.IsFSharpMiscellaneousOrMetadata && not document.IsFSharpScript then
+            if
+                (document.Project.IsFSharpMiscellaneousOrMetadata && not document.IsFSharpScript)
+                || not (ActiveDocumentDetection.isActiveDocument serviceProvider document)
+            then
                 Tasks.Task.FromResult(ImmutableArray.Empty)
             else
                 cancellableTask {

vsintegration/src/FSharp.Editor/FSharp.Editor.fsproj

@@ -72,6 +72,7 @@
     <Compile Include="Formatting\EditorFormattingService.fs" />
     <Compile Include="Debugging\BreakpointResolutionService.fs" />
     <Compile Include="Debugging\LanguageDebugInfoService.fs" />
+    <Compile Include="Diagnostics\ActiveDocumentDetection.fs" />
     <Compile Include="Diagnostics\UnnecessaryParenthesesDiagnosticAnalyzer.fs" />
     <Compile Include="Diagnostics\DocumentDiagnosticAnalyzer.fs" />
     <Compile Include="Diagnostics\SimplifyNameDiagnosticAnalyzer.fs" />

vsintegration/src/FSharp.Editor/Hints/FSharpInlayHintsService.fs

@@ -2,6 +2,7 @@
 
 namespace Microsoft.VisualStudio.FSharp.Editor.Hints
 
+open System
 open System.Collections.Immutable
 open System.ComponentModel.Composition
 open System.Threading.Tasks
@@ -15,7 +16,10 @@ open CancellableTasks
 // e.g. signature hints above the line, pipeline hints on the side and so on.
 
 [<Export(typeof<IFSharpInlineHintsService2>)>]
-type internal FSharpInlayHintsService [<ImportingConstructor>] (settings: EditorOptions) =
+type internal FSharpInlayHintsService
+    [<ImportingConstructor>]
+    (settings: EditorOptions,
+     [<Import("Microsoft.VisualStudio.Shell.SVsServiceProvider")>] serviceProvider: IServiceProvider) =
 
     static let userOpName = "Hints"
 
@@ -27,7 +31,7 @@ type internal FSharpInlayHintsService [<ImportingConstructor>] (settings: Editor
                 else
                     OptionParser.getHintKinds settings.Advanced
 
-            if hintKinds.IsEmpty then
+            if hintKinds.IsEmpty || not (ActiveDocumentDetection.isActiveDocument serviceProvider document) then
                 Task.FromResult ImmutableArray.Empty
             else
                 cancellableTask {