Search each file of a multi-targeted F# project once in Find All References and Rename

docs/release-notes/.VisualStudio/18.vNext.md

@@ -14,6 +14,9 @@
 * Make Alt+F1 (momentary toggle) work for inlay hints. ([PR #19421](https://github.com/dotnet/fsharp/pull/19421))
 * Fix doubled F# diagnostics in tooltips. ([Issue #16360](https://github.com/dotnet/fsharp/issues/16360))
 * Fix `NotSupportedException` in the memory-mapped-file optimization when copying `ReadOnlyMemory` into `MemoryMappedFileViewStream`. ([Issue #20263](https://github.com/dotnet/fsharp/issues/20263))
+* Find All References and Rename search each file of a multi-targeted F# project once instead of once per target framework, revisiting a file in another instance only when it is compiled there alone or under conditional compilation; searches start as each project's snapshot is ready and type checks are bounded across the solution. ([PR #20464](https://github.com/dotnet/fsharp/pull/20464))
+* Find Implementations no longer searches the whole solution for uses it then discards; it reports the declarations alone.
+* Find All References reports the uses of a document in one go instead of starting a task per reference, stops when the request is cancelled, and searches the documents of a project through a fixed set of workers under one solution-wide budget that leaves a core to the editor.
 
 ### Changed
 

vsintegration/src/FSharp.Editor/Common/CancellableTasks.fs

@@ -1130,6 +1130,31 @@ module CancellableTasks =
                 return! allTask
             }
 
+        /// Runs the work over the items with at most maxDegreeOfParallelism of them in flight. A worker
+        /// takes the next item when it frees up, so cancellation cancels the workers rather than a
+        /// pending task per item.
+        let forEachThrottled maxDegreeOfParallelism (work: 'T -> CancellableTask<unit>) (items: 'T seq) =
+            cancellableTask {
+                let! ct = getCancellationToken ()
+                let items = Seq.toArray items
+                let mutable next = -1
+
+                let worker () =
+                    backgroundTask {
+                        let mutable index = Interlocked.Increment &next
+
+                        while index < items.Length do
+                            ct.ThrowIfCancellationRequested()
+                            do! work items[index] ct
+                            index <- Interlocked.Increment &next
+                    }
+
+                let workers =
+                    Array.init (min (max 1 maxDegreeOfParallelism) items.Length) (fun _ -> worker ())
+
+                do! (Task.WhenAll workers :> Task)
+            }
+
         let inline whenAllTasks (tasks: CancellableTask seq) =
             cancellableTask {
                 let! ct = getCancellationToken ()

vsintegration/src/FSharp.Editor/LanguageService/SymbolHelpers.fs

@@ -7,6 +7,7 @@ open System.Collections.Concurrent
 open System.Collections.Generic
 open System.Collections.Immutable
 open System.IO
+open System.Threading
 open System.Threading.Tasks
 
 open Microsoft.CodeAnalysis
@@ -70,34 +71,103 @@ module internal SymbolHelpers =
             return symbolUses
         }
 
-    let getSymbolUsesInProjects (symbol: FSharpSymbol, projects: Project list, onFound: Document -> range -> CancellableTask<unit>) =
-        match projects with
+    /// Ranks the target-framework instances of a project file: the one the current document lives in,
+    /// then those in its dependency closure, whose references resolve the symbol the same way.
+    let private rankInstances (currentProject: Project) =
+        let graph = currentProject.Solution.GetProjectDependencyGraph()
+
+        let related =
+            HashSet
+                [
+                    yield! graph.GetProjectsThatThisProjectTransitivelyDependsOn currentProject.Id
+                    yield! graph.GetProjectsThatTransitivelyDependOnThisProject currentProject.Id
+                ]
+
+        fun (project: Project) ->
+            if project.Id = currentProject.Id then 0
+            elif related.Contains project.Id then 1
+            else 2
+
+    /// One search per project file: the best-ranked target-framework instance is searched in full,
+    /// the others only where their sources can differ from it.
+    let private groupInstances (currentProject: Project) (projects: Project list) =
+        let rank = rankInstances currentProject
+
+        projects
+        |> List.groupBy _.FilePath
+        |> List.map (fun (_, instances) ->
+            let ordered = List.sortBy rank instances
+            struct (ordered.Head, ordered.Tail))
+
+    /// One core is left to the thread that has to stay responsive, and every search in the editor
+    /// shares what remains.
+    let searchThrottle = new SemaphoreSlim(max 1 (Environment.ProcessorCount - 1))
+
+    let getSymbolUsesInProjects
+        (symbol: FSharpSymbol, currentProject: Project, projects: Project list, onFound: Document -> range seq -> CancellableTask<unit>)
+        =
+        match projects |> List.filter _.IsFSharp with
         | [] -> CancellableTask.singleton ()
-        | firstProject :: _ ->
+        | firstProject :: _ as projects ->
             let isFastFindReferencesEnabled = firstProject.IsFastFindReferencesEnabled
 
             // TODO: this needs to use already boxed boolean instead of boxing it every time.
             let props =
                 [| nameof isFastFindReferencesEnabled, isFastFindReferencesEnabled :> obj |]
 
+            let groups =
+                if isFastFindReferencesEnabled then
+                    groupInstances currentProject projects
+                else
+                    [ for project in projects -> struct (project, []) ]
+
             cancellableTask {
                 // TODO: this needs to be a single event with a duration
                 TelemetryReporter.ReportSingleEvent(TelemetryEvents.GetSymbolUsesInProjectsStarted, props)
 
+                let! ct = CancellableTask.getCancellationToken ()
+
+                // A file that several projects compile - the target-framework instances of one project
+                // file, or two project files sharing a source file - is searched in each of them and
+                // reports the same range every time. The range carries its file, so the first project
+                // to report a use keeps it and the rest are dropped.
+                let reported = ConcurrentDictionary<range, unit>()
+
+                let onFound document ranges =
+                    let fresh =
+                        ranges |> Seq.filter (fun range -> reported.TryAdd(range, ())) |> Seq.toArray
+
+                    if fresh.Length = 0 then
+                        CancellableTask.singleton ()
+                    else
+                        onFound document fresh
+                // Mutated by the checker while a snapshot is built, so snapshots are built one at a time.
                 let snapshotAccumulator = Dictionary()
+                let searches = ResizeArray<Task>()
+
+                let snapshotFor (project: Project) =
+                    if project.UseTransparentCompiler then
+                        project.GetFSharpProjectSnapshot snapshotAccumulator
+                        |> CancellableTask.map ValueSome
+                    else
+                        CancellableTask.singleton ValueNone
 
-                let! projects =
-                    projects
-                    |> Seq.map (fun project ->
-                        project.GetFSharpProjectSnapshot(snapshotAccumulator)
-                        |> CancellableTask.map (fun s -> project, s))
-                    |> CancellableTask.sequential
+                let start (project: Project) snapshot searchedInstance =
+                    searches.Add(
+                        project.FindFSharpReferencesAsync
+                            (symbol, snapshot, searchedInstance, searchThrottle, onFound, "getSymbolUsesInProjects")
+                            ct
+                    )
 
-                do!
-                    projects
-                    |> Seq.map (fun (project, snapshot) ->
-                        project.FindFSharpReferencesAsync(symbol, snapshot, onFound, "getSymbolUsesInProjects"))
-                    |> CancellableTask.whenAll
+                for struct (primary, secondaries) in groups do
+                    let! snapshot = snapshotFor primary
+                    start primary snapshot ValueNone
+
+                    for secondary in secondaries do
+                        let! snapshot = snapshotFor secondary
+                        start secondary snapshot (ValueSome primary)
+
+                do! Task.WhenAll searches
 
                 TelemetryReporter.ReportSingleEvent(TelemetryEvents.GetSymbolUsesInProjectsFinished, props)
             }
@@ -106,7 +176,7 @@ module internal SymbolHelpers =
         (symbolUse: FSharpSymbolUse)
         (currentDocument: Document)
         (checkFileResults: FSharpCheckFileResults)
-        (onFound: Document -> range -> CancellableTask<unit>)
+        (onFound: Document -> range seq -> CancellableTask<unit>)
         =
         cancellableTask {
             match symbolUse.GetSymbolScope currentDocument with
@@ -115,10 +185,7 @@ module internal SymbolHelpers =
                 let symbolUses =
                     checkFileResults.GetUsesOfSymbolInFile(symbolUse.Symbol, relatedSymbolKinds = RelatedSymbolUseKind.All)
 
-                do!
-                    symbolUses
-                    |> Seq.map (fun symbolUse -> onFound currentDocument symbolUse.Range)
-                    |> CancellableTask.whenAll
+                do! onFound currentDocument (symbolUses |> Seq.map _.Range)
 
             | Some SymbolScope.SignatureAndImplementation ->
                 let otherFile = getOtherFile currentDocument.FilePath
@@ -132,52 +199,50 @@ module internal SymbolHelpers =
                         }
                     | ValueNone -> CancellableTask.singleton []
 
-                let symbolUses =
-                    (checkFileResults, currentDocument) :: otherFileCheckResults
-                    |> Seq.collect (fun (checkFileResults, doc) ->
+                for checkFileResults, doc in (checkFileResults, currentDocument) :: otherFileCheckResults do
+                    let symbolUses =
                         checkFileResults.GetUsesOfSymbolInFile(symbolUse.Symbol, relatedSymbolKinds = RelatedSymbolUseKind.All)
-                        |> Seq.map (fun symbolUse -> (doc, symbolUse.Range)))
 
-                do! symbolUses |> Seq.map ((<||) onFound) |> CancellableTask.whenAll
+                    do! onFound doc (symbolUses |> Seq.map _.Range)
 
-            | scope ->
+            | Some(SymbolScope.Projects(scopeProjects, isLocalForProject)) ->
                 let projectsToCheck =
-                    match scope with
-                    | Some(SymbolScope.CurrentDocument)
-                    | Some(SymbolScope.SignatureAndImplementation) ->
-                        // For current document or signature/implementation, just search current project
-                        [ currentDocument.Project ]
-                    | Some(SymbolScope.Projects(scopeProjects, false)) ->
+                    if isLocalForProject then
+                        scopeProjects
+                    else
                         [
                             for scopeProject in scopeProjects do
                                 yield scopeProject
                                 yield! scopeProject.GetDependentProjects()
                         ]
                         |> List.distinct
-                    | Some(SymbolScope.Projects(scopeProjects, true)) -> scopeProjects
-                    // The symbol is declared in .NET framework, an external assembly or in a C# project within the solution.
-                    // Optimization: Only search projects that reference the specific assembly
-                    | None ->
-                        match symbolUse.Symbol.Assembly.FileName with
-                        | Some assemblyPath ->
-                            let referencingProjects =
-                                ProjectFiltering.getProjectsReferencingAssembly assemblyPath currentDocument.Project.Solution
-
-                            if List.isEmpty referencingProjects then
-                                Seq.toList currentDocument.Project.Solution.Projects
-                            else
-                                referencingProjects
-                        | None -> Seq.toList currentDocument.Project.Solution.Projects
-
-                do! getSymbolUsesInProjects (symbolUse.Symbol, projectsToCheck, onFound)
+
+                do! getSymbolUsesInProjects (symbolUse.Symbol, currentDocument.Project, projectsToCheck, onFound)
+
+            // The symbol is declared in .NET framework, an external assembly or in a C# project within the solution.
+            // Optimization: Only search projects that reference the specific assembly
+            | None ->
+                let projectsToCheck =
+                    match symbolUse.Symbol.Assembly.FileName with
+                    | Some assemblyPath ->
+                        match ProjectFiltering.getProjectsReferencingAssembly assemblyPath currentDocument.Project.Solution with
+                        | [] -> Seq.toList currentDocument.Project.Solution.Projects
+                        | referencingProjects -> referencingProjects
+                    | None -> Seq.toList currentDocument.Project.Solution.Projects
+
+                do! getSymbolUsesInProjects (symbolUse.Symbol, currentDocument.Project, projectsToCheck, onFound)
         }
 
     let getSymbolUses (symbolUse: FSharpSymbolUse) (currentDocument: Document) (checkFileResults: FSharpCheckFileResults) =
         cancellableTask {
             let symbolUses = ConcurrentBag()
 
             let onFound =
-                fun document range -> cancellableTask { symbolUses.Add(document, range) }
+                fun document (ranges: range seq) ->
+                    cancellableTask {
+                        for range in ranges do
+                            symbolUses.Add(document, range)
+                    }
 
             do! findSymbolUses symbolUse currentDocument checkFileResults onFound