Parallel project analysis behind a feature flag

src/Compiler/Driver/CompilerConfig.fs

@@ -388,6 +388,11 @@ type MetadataAssemblyGeneration =
     | ReferenceOut of outputPath: string
     | ReferenceOnly
 
+[<RequireQualifiedAccess>]
+type ParallelReferenceResolution =
+    | On
+    | Off
+
 [<NoEquality; NoComparison>]
 type TcConfigBuilder =
     {
@@ -580,6 +585,8 @@ type TcConfigBuilder =
         mutable xmlDocInfoLoader: IXmlDocumentationInfoLoader option
 
         mutable exiter: Exiter
+
+        mutable parallelReferenceResolution: ParallelReferenceResolution
     }
 
     // Directories to start probing in
@@ -767,6 +774,7 @@ type TcConfigBuilder =
             sdkDirOverride = sdkDirOverride
             xmlDocInfoLoader = None
             exiter = QuitProcessExiter
+            parallelReferenceResolution = ParallelReferenceResolution.Off
         }
 
     member tcConfigB.FxResolver =
@@ -1310,6 +1318,7 @@ type TcConfig private (data: TcConfigBuilder, validate: bool) =
     member _.applyLineDirectives = data.applyLineDirectives
     member _.xmlDocInfoLoader = data.xmlDocInfoLoader
     member _.exiter = data.exiter
+    member _.parallelReferenceResolution = data.parallelReferenceResolution
 
     static member Create(builder, validate) =
         use _ = UseBuildPhase BuildPhase.Parameter

src/Compiler/Driver/CompilerConfig.fsi

@@ -198,6 +198,11 @@ type MetadataAssemblyGeneration =
     /// Only emits the assembly as a reference assembly.
     | ReferenceOnly
 
+[<RequireQualifiedAccess>]
+type ParallelReferenceResolution =
+    | On
+    | Off
+
 [<NoEquality; NoComparison>]
 type TcConfigBuilder =
     {
@@ -482,6 +487,8 @@ type TcConfigBuilder =
         mutable xmlDocInfoLoader: IXmlDocumentationInfoLoader option
 
         mutable exiter: Exiter
+
+        mutable parallelReferenceResolution: ParallelReferenceResolution
     }
 
     static member CreateNew:
@@ -845,6 +852,8 @@ type TcConfig =
 
     member exiter: Exiter
 
+    member parallelReferenceResolution: ParallelReferenceResolution
+
 /// Represents a computation to return a TcConfig. Normally this is just a constant immutable TcConfig,
 /// but for F# Interactive it may be based on an underlying mutable TcConfigBuilder.
 [<Sealed>]

src/Compiler/Driver/CompilerImports.fs

@@ -2141,6 +2141,12 @@ and [<Sealed>] TcImports
         node {
             CheckDisposed()
 
+            let tcConfig = tcConfigP.Get ctok
+            let runMethod =
+                match tcConfig.parallelReferenceResolution with
+                | ParallelReferenceResolution.On -> NodeCode.Parallel
+                | ParallelReferenceResolution.Off -> NodeCode.Sequential
+
             let! results =
                 nms
                 |> List.map (fun nm ->
@@ -2151,7 +2157,7 @@ and [<Sealed>] TcImports
                             errorR (Error(FSComp.SR.buildProblemReadingAssembly (nm.resolvedPath, e.Message), nm.originalReference.Range))
                             return None
                     })
-                |> NodeCode.Sequential
+                |> runMethod
 
             let dllinfos, phase2s = results |> Array.choose id |> List.ofArray |> List.unzip
             fixupOrphanCcus ()

src/Compiler/Driver/CompilerOptions.fs

@@ -1680,6 +1680,14 @@ let internalFlags (tcConfigB: TcConfigBuilder) =
             None
         )
 
+        CompilerOption(
+            "parallelreferenceresolution",
+            tagNone,
+            OptionUnit(fun () -> tcConfigB.parallelReferenceResolution <- ParallelReferenceResolution.On),
+            Some(InternalCommandLineOption("--parallelreferenceresolution", rangeCmdArgs)),
+            None
+        )
+
         testFlag tcConfigB
     ]
     @

src/Compiler/Driver/fsc.fs

@@ -446,6 +446,18 @@ let TryFindVersionAttribute g attrib attribName attribs deterministic =
 [<NoEquality; NoComparison>]
 type Args<'T> = Args of 'T
 
+let getParallelReferenceResolutionFromEnvironment () =
+    Environment.GetEnvironmentVariable("FCS_ParallelReferenceResolution")
+    |> Option.ofObj
+    |> Option.bind (fun flag ->
+        match bool.TryParse flag with
+        | true, runInParallel ->
+            if runInParallel then
+                Some ParallelReferenceResolution.On
+            else
+                Some ParallelReferenceResolution.Off
+        | false, _ -> None)
+
 /// First phase of compilation.
 ///   - Set up console encoding and code page settings
 ///   - Process command line, flags and collect filenames
@@ -533,6 +545,11 @@ let main1
 
     tcConfigB.conditionalDefines <- "COMPILED" :: tcConfigB.conditionalDefines
 
+    // Override ParallelReferenceResolution set on the CLI with an environment setting if present.
+    match getParallelReferenceResolutionFromEnvironment () with
+    | Some parallelReferenceResolution -> tcConfigB.parallelReferenceResolution <- parallelReferenceResolution
+    | None -> ()
+
     // Display the banner text, if necessary
     if not bannerAlreadyPrinted then
         Console.Write(GetBannerText tcConfigB)

src/Compiler/Driver/fsc.fsi

@@ -55,3 +55,6 @@ val CompileFromCommandLineArguments:
     tcImportsCapture: (TcImports -> unit) option *
     dynamicAssemblyCreator: (TcConfig * TcGlobals * string * ILModuleDef -> unit) option ->
         unit
+
+/// Read the parallelReferenceResolution flag from environment variables
+val internal getParallelReferenceResolutionFromEnvironment: unit -> ParallelReferenceResolution option

src/Compiler/Facilities/BuildGraph.fs

@@ -182,6 +182,12 @@ type NodeCode private () =
 
             return results.ToArray()
         }
+
+    static member Parallel (computations: NodeCode<'T> seq) =
+        computations
+        |> Seq.map (fun (Node x) -> x)
+        |> Async.Parallel
+        |> Node
 
 type private AgentMessage<'T> = GetValue of AsyncReplyChannel<Result<'T, Exception>> * callerCancellationToken: CancellationToken
 
@@ -331,7 +337,7 @@ type GraphNode<'T>(retryCompute: bool, computation: NodeCode<'T>) =
                             // occur, making sure we are under the protection of the 'try'.
                             // For example, NodeCode's 'try/finally' (TryFinally) uses async.TryFinally which does
                             // implicit cancellation checks even before the try is entered, as do the
-                            // de-sugaring of 'do!' and other CodeCode constructs.
+                            // de-sugaring of 'do!' and other NodeCode constructs.
                             let mutable taken = false
 
                             try

src/Compiler/Facilities/BuildGraph.fsi

@@ -65,6 +65,8 @@ type NodeCode =
 
     static member Sequential: computations: NodeCode<'T> seq -> NodeCode<'T[]>
 
+    static member Parallel: computations: (NodeCode<'T> seq) -> NodeCode<'T[]>
+
     /// Execute the cancellable computation synchronously using the ambient cancellation token of
     /// the NodeCode.
     static member FromCancellable: computation: Cancellable<'T> -> NodeCode<'T>

src/Compiler/Service/IncrementalBuild.fs

@@ -1432,7 +1432,8 @@ type IncrementalBuilder(initialState: IncrementalBuilderInitialState, state: Inc
             enableBackgroundItemKeyStoreAndSemanticClassification,
             enablePartialTypeChecking: bool,
             enableParallelCheckingWithSignatureFiles: bool,
-            dependencyProvider
+            dependencyProvider,
+            parallelReferenceResolution
         ) =
 
       let useSimpleResolutionSwitch = "--simpleresolution"
@@ -1514,6 +1515,7 @@ type IncrementalBuilder(initialState: IncrementalBuilderInitialState, state: Inc
                     |> Some
 
                 tcConfigB.parallelCheckingWithSignatureFiles <- enableParallelCheckingWithSignatureFiles
+                tcConfigB.parallelReferenceResolution <- parallelReferenceResolution
 
                 tcConfigB, sourceFilesNew
 

src/Compiler/Service/IncrementalBuild.fsi

@@ -264,7 +264,8 @@ type internal IncrementalBuilder =
         enableBackgroundItemKeyStoreAndSemanticClassification: bool *
         enablePartialTypeChecking: bool *
         enableParallelCheckingWithSignatureFiles: bool *
-        dependencyProvider: DependencyProvider option ->
+        dependencyProvider: DependencyProvider option *
+        parallelReferenceResolution: ParallelReferenceResolution ->
             NodeCode<IncrementalBuilder option * FSharpDiagnostic[]>
 
 /// Generalized Incremental Builder. This is exposed only for unit testing purposes.

src/Compiler/Service/service.fs

@@ -175,7 +175,8 @@ type BackgroundCompiler
         keepAllBackgroundSymbolUses,
         enableBackgroundItemKeyStoreAndSemanticClassification,
         enablePartialTypeChecking,
-        enableParallelCheckingWithSignatureFiles
+        enableParallelCheckingWithSignatureFiles,
+        parallelReferenceResolution
     ) as self =
 
     let beforeFileChecked = Event<string * FSharpProjectOptions>()
@@ -303,7 +304,8 @@ type BackgroundCompiler
                     enableBackgroundItemKeyStoreAndSemanticClassification,
                     enablePartialTypeChecking,
                     enableParallelCheckingWithSignatureFiles,
-                    dependencyProvider
+                    dependencyProvider,
+                    parallelReferenceResolution
                 )
 
             match builderOpt with
@@ -1096,7 +1098,8 @@ type FSharpChecker
         keepAllBackgroundSymbolUses,
         enableBackgroundItemKeyStoreAndSemanticClassification,
         enablePartialTypeChecking,
-        enableParallelCheckingWithSignatureFiles
+        enableParallelCheckingWithSignatureFiles,
+        parallelReferenceResolution
     ) =
 
     let backgroundCompiler =
@@ -1110,7 +1113,8 @@ type FSharpChecker
             keepAllBackgroundSymbolUses,
             enableBackgroundItemKeyStoreAndSemanticClassification,
             enablePartialTypeChecking,
-            enableParallelCheckingWithSignatureFiles
+            enableParallelCheckingWithSignatureFiles,
+            parallelReferenceResolution
         )
 
     static let globalInstance = lazy FSharpChecker.Create()
@@ -1122,6 +1126,24 @@ type FSharpChecker
     let braceMatchCache =
         MruCache<AnyCallerThreadToken, _, _>(braceMatchCacheSize, areSimilar = AreSimilarForParsing, areSame = AreSameForParsing)
 
+    static let inferParallelReferenceResolution (parallelReferenceResolution: bool option) =
+        let explicitValue =
+            parallelReferenceResolution
+            |> Option.defaultValue false
+            |> function
+                | true -> ParallelReferenceResolution.On
+                | false -> ParallelReferenceResolution.Off
+
+        let withEnvOverride =
+            // Override ParallelReferenceResolution set on the constructor with an environment setting if present.
+            getParallelReferenceResolutionFromEnvironment ()
+            |> Option.defaultValue explicitValue
+
+        withEnvOverride
+
+    static member getParallelReferenceResolutionFromEnvironment() =
+        getParallelReferenceResolutionFromEnvironment ()
+
     /// Instantiate an interactive checker.
     static member Create
         (
@@ -1134,7 +1156,8 @@ type FSharpChecker
             ?keepAllBackgroundSymbolUses,
             ?enableBackgroundItemKeyStoreAndSemanticClassification,
             ?enablePartialTypeChecking,
-            ?enableParallelCheckingWithSignatureFiles
+            ?enableParallelCheckingWithSignatureFiles,
+            ?parallelReferenceResolution
         ) =
 
         let legacyReferenceResolver =
@@ -1158,6 +1181,8 @@ type FSharpChecker
         if keepAssemblyContents && enablePartialTypeChecking then
             invalidArg "enablePartialTypeChecking" "'keepAssemblyContents' and 'enablePartialTypeChecking' cannot be both enabled."
 
+        let parallelReferenceResolution = inferParallelReferenceResolution parallelReferenceResolution
+
         FSharpChecker(
             legacyReferenceResolver,
             projectCacheSizeReal,
@@ -1168,7 +1193,8 @@ type FSharpChecker
             keepAllBackgroundSymbolUses,
             enableBackgroundItemKeyStoreAndSemanticClassification,
             enablePartialTypeChecking,
-            enableParallelCheckingWithSignatureFiles
+            enableParallelCheckingWithSignatureFiles,
+            parallelReferenceResolution
         )
 
     member _.ReferenceResolver = legacyReferenceResolver

src/Compiler/Service/service.fsi

@@ -8,6 +8,7 @@ open System
 open System.IO
 open FSharp.Compiler.AbstractIL.ILBinaryReader
 open FSharp.Compiler.CodeAnalysis
+open FSharp.Compiler.CompilerConfig
 open FSharp.Compiler.Diagnostics
 open FSharp.Compiler.EditorServices
 open FSharp.Compiler.Symbols
@@ -32,6 +33,7 @@ type public FSharpChecker =
     /// <param name="enableBackgroundItemKeyStoreAndSemanticClassification">Indicates whether a table of symbol keys should be kept for background compilation</param>
     /// <param name="enablePartialTypeChecking">Indicates whether to perform partial type checking. Cannot be set to true if keepAssmeblyContents is true. If set to true, can cause duplicate type-checks when richer information on a file is needed, but can skip background type-checking entirely on implementation files with signature files.</param>
     /// <param name="enableParallelCheckingWithSignatureFiles">Type check implementation files that are backed by a signature file in parallel.</param>
+    /// <param name="parallelReferenceResolution">Indicates whether to resolve references in parallel.</param>
     static member Create:
         ?projectCacheSize: int *
         ?keepAssemblyContents: bool *
@@ -42,7 +44,8 @@ type public FSharpChecker =
         ?keepAllBackgroundSymbolUses: bool *
         ?enableBackgroundItemKeyStoreAndSemanticClassification: bool *
         ?enablePartialTypeChecking: bool *
-        ?enableParallelCheckingWithSignatureFiles: bool ->
+        ?enableParallelCheckingWithSignatureFiles: bool *
+        ?parallelReferenceResolution: bool ->
             FSharpChecker
 
     /// <summary>

tests/FSharp.Compiler.Service.Tests/FSharp.CompilerService.SurfaceArea.netstandard.expected

@@ -2009,7 +2009,7 @@ FSharp.Compiler.CodeAnalysis.FSharpCheckProjectResults: System.String ToString()
 FSharp.Compiler.CodeAnalysis.FSharpCheckProjectResults: System.String[] DependencyFiles
 FSharp.Compiler.CodeAnalysis.FSharpCheckProjectResults: System.String[] get_DependencyFiles()
 FSharp.Compiler.CodeAnalysis.FSharpChecker
-FSharp.Compiler.CodeAnalysis.FSharpChecker: FSharp.Compiler.CodeAnalysis.FSharpChecker Create(Microsoft.FSharp.Core.FSharpOption`1[System.Int32], Microsoft.FSharp.Core.FSharpOption`1[System.Boolean], Microsoft.FSharp.Core.FSharpOption`1[System.Boolean], Microsoft.FSharp.Core.FSharpOption`1[FSharp.Compiler.CodeAnalysis.LegacyReferenceResolver], Microsoft.FSharp.Core.FSharpOption`1[Microsoft.FSharp.Core.FSharpFunc`2[System.Tuple`2[System.String,System.DateTime],Microsoft.FSharp.Core.FSharpOption`1[System.Tuple`3[System.Object,System.IntPtr,System.Int32]]]], Microsoft.FSharp.Core.FSharpOption`1[System.Boolean], Microsoft.FSharp.Core.FSharpOption`1[System.Boolean], Microsoft.FSharp.Core.FSharpOption`1[System.Boolean], Microsoft.FSharp.Core.FSharpOption`1[System.Boolean], Microsoft.FSharp.Core.FSharpOption`1[System.Boolean])
+FSharp.Compiler.CodeAnalysis.FSharpChecker: FSharp.Compiler.CodeAnalysis.FSharpChecker Create(Microsoft.FSharp.Core.FSharpOption`1[System.Int32], Microsoft.FSharp.Core.FSharpOption`1[System.Boolean], Microsoft.FSharp.Core.FSharpOption`1[System.Boolean], Microsoft.FSharp.Core.FSharpOption`1[FSharp.Compiler.CodeAnalysis.LegacyReferenceResolver], Microsoft.FSharp.Core.FSharpOption`1[Microsoft.FSharp.Core.FSharpFunc`2[System.Tuple`2[System.String,System.DateTime],Microsoft.FSharp.Core.FSharpOption`1[System.Tuple`3[System.Object,System.IntPtr,System.Int32]]]], Microsoft.FSharp.Core.FSharpOption`1[System.Boolean], Microsoft.FSharp.Core.FSharpOption`1[System.Boolean], Microsoft.FSharp.Core.FSharpOption`1[System.Boolean], Microsoft.FSharp.Core.FSharpOption`1[System.Boolean], Microsoft.FSharp.Core.FSharpOption`1[System.Boolean], Microsoft.FSharp.Core.FSharpOption`1[System.Boolean])
 FSharp.Compiler.CodeAnalysis.FSharpChecker: FSharp.Compiler.CodeAnalysis.FSharpChecker Instance
 FSharp.Compiler.CodeAnalysis.FSharpChecker: FSharp.Compiler.CodeAnalysis.FSharpChecker get_Instance()
 FSharp.Compiler.CodeAnalysis.FSharpChecker: FSharp.Compiler.CodeAnalysis.FSharpProjectOptions GetProjectOptionsFromCommandLineArgs(System.String, System.String[], Microsoft.FSharp.Core.FSharpOption`1[System.DateTime], Microsoft.FSharp.Core.FSharpOption`1[System.Boolean], Microsoft.FSharp.Core.FSharpOption`1[System.Boolean])