// Copyright (c) Microsoft Corporation.  All Rights Reserved.  See License.txt in the project root for license information.

namespace FSharp.Compiler.CodeAnalysis

open System
open System.Collections.Generic
open System.Collections.Immutable
open System.Diagnostics
open System.IO
open System.Threading
open Internal.Utilities.Library
open Internal.Utilities.Collections
open FSharp.Compiler
open FSharp.Compiler.AbstractIL.IL
open FSharp.Compiler.AbstractIL.ILBinaryReader
open FSharp.Compiler.CheckBasics
open FSharp.Compiler.CheckDeclarations
open FSharp.Compiler.CompilerConfig
open FSharp.Compiler.CompilerDiagnostics
open FSharp.Compiler.CompilerImports
open FSharp.Compiler.CompilerOptions
open FSharp.Compiler.CreateILModule
open FSharp.Compiler.DependencyManager
open FSharp.Compiler.Diagnostics
open FSharp.Compiler.EditorServices
open FSharp.Compiler.DiagnosticsLogger
open FSharp.Compiler.IO
open FSharp.Compiler.CodeAnalysis
open FSharp.Compiler.NameResolution
open FSharp.Compiler.ParseAndCheckInputs
open FSharp.Compiler.ScriptClosure
open FSharp.Compiler.Syntax
open FSharp.Compiler.TcGlobals
open FSharp.Compiler.Text
open FSharp.Compiler.Text.Range
open FSharp.Compiler.Xml
open FSharp.Compiler.TypedTree
open FSharp.Compiler.TypedTreeOps
open FSharp.Compiler.BuildGraph

[<AutoOpen>]
module internal IncrementalBuild =

    let mutable injectCancellationFault = false
    let LocallyInjectCancellationFault() =
        injectCancellationFault <- true
        { new IDisposable with member _.Dispose() = injectCancellationFault <- false }

// Record the most recent IncrementalBuilder events, so we can more easily unit test/debug the
// 'incremental' behavior of the product.
module IncrementalBuilderEventTesting =

    type internal FixedLengthMRU<'T>() =
        let MAX = 400   // Length of the MRU.  For our current unit tests, 400 is enough.
        let data = Array.create MAX None
        let mutable curIndex = 0
        let mutable numAdds = 0

        // called by the product, to note when a parse/typecheck happens for a file
        member _.Add(fileName:'T) =
            numAdds <- numAdds + 1
            data[curIndex] <- Some fileName
            curIndex <- (curIndex + 1) % MAX

        member _.CurrentEventNum = numAdds
        // called by unit tests, returns 'n' most recent additions.

        member _.MostRecentList(n: int) : 'T list =
            if n < 0 || n > MAX then
                raise <| ArgumentOutOfRangeException("n", sprintf "n must be between 0 and %d, inclusive, but got %d" MAX n)
            let mutable remaining = n
            let mutable s = []
            let mutable i = curIndex - 1
            while remaining <> 0 do
                if i < 0 then
                    i <- MAX - 1
                match data[i] with
                | None -> ()
                | Some x -> s <- x :: s
                i <- i - 1
                remaining <- remaining - 1
            List.rev s

    type IBEvent =
        | IBEParsed of fileName: string
        | IBETypechecked of fileName: string
        | IBECreated

    // ++GLOBAL MUTABLE STATE FOR TESTING++
    let MRU = FixedLengthMRU<IBEvent>()
    let GetMostRecentIncrementalBuildEvents n = MRU.MostRecentList n
    let GetCurrentIncrementalBuildEventNum() = MRU.CurrentEventNum

module Tc = CheckExpressions

type internal FSharpFile = {
        Range: range
        Source: FSharpSource
        Flags: bool * bool
    }
 
// This module is only here to contain the SyntaxTree type as to avoid ambiguity with the module FSharp.Compiler.Syntax.
[<AutoOpen>]
module IncrementalBuildSyntaxTree =

    type ParseResult = ParsedInput * range * string * (PhasedDiagnostic * FSharpDiagnosticSeverity) array

    /// Information needed to lazily parse a file to get a ParsedInput. Internally uses a weak cache.
    [<Sealed>]
    type SyntaxTree (
            tcConfig: TcConfig,
            fileParsed: Event<string>,
            lexResourceManager,
            file: FSharpFile,
            hasSignature
        ) =

        let fileName = file.Source.FilePath
        let sourceRange = file.Range
        let source = file.Source
        let isLastCompiland = file.Flags

        let skippedImplFilePlaceholder sigName =
            ParsedInput.ImplFile(
                ParsedImplFileInput(
                    fileName,
                    false,
                    sigName,
                    [],
                    [],
                    [],
                    isLastCompiland,
                    { ConditionalDirectives = []; CodeComments = [] },
                    Set.empty
                )
            ), sourceRange, fileName, [||]

        let parse (source: FSharpSource) =
            async {
                IncrementalBuilderEventTesting.MRU.Add(IncrementalBuilderEventTesting.IBEParsed fileName)
                use _ =
                    Activity.start "IncrementalBuildSyntaxTree.parse"
                        [|
                            Activity.Tags.fileName, fileName
                            Activity.Tags.buildPhase, !! BuildPhase.Parse.ToString()
                        |]

                try
                    let diagnosticsLogger = CompilationDiagnosticLogger("Parse", tcConfig.diagnosticsOptions)
                    // Return the disposable object that cleans up
                    use _holder = new CompilationGlobalsScope(diagnosticsLogger, BuildPhase.Parse)
                    use! text = source.GetTextContainer()
                    let input =
                        match text with
                        | TextContainer.Stream(stream) ->
                            ParseOneInputStream(tcConfig, lexResourceManager, fileName, isLastCompiland, diagnosticsLogger, false, stream)
                        | TextContainer.SourceText(sourceText) ->
                            ParseOneInputSourceText(tcConfig, lexResourceManager, fileName, isLastCompiland, diagnosticsLogger, sourceText)
                        | TextContainer.OnDisk ->
                            ParseOneInputFile(tcConfig, lexResourceManager, fileName, isLastCompiland, diagnosticsLogger, true)

                    fileParsed.Trigger fileName

                    return input, sourceRange, fileName, diagnosticsLogger.GetDiagnostics()
                with exn ->
                    let msg = sprintf "unexpected failure in SyntaxTree.parse\nerror = %s" (exn.ToString())
                    System.Diagnostics.Debug.Assert(false, msg)
                    failwith msg
                    return Unchecked.defaultof<_>
            }

        /// Parse the given file and return the given input.
        member val ParseNode : GraphNode<ParseResult> = parse source |> GraphNode

        member _.Invalidate() =
            SyntaxTree(tcConfig, fileParsed, lexResourceManager, file, hasSignature)

        member _.Skip = skippedImplFilePlaceholder

        member _.FileName = fileName

        member _.HasSignature  = hasSignature

        member _.SourceRange = sourceRange

/// Accumulated results of type checking. The minimum amount of state in order to continue type-checking following files.
[<NoEquality; NoComparison>]
type TcInfo =
    {
        tcState: TcState
        tcEnvAtEndOfFile: TcEnv

        /// Disambiguation table for module names
        moduleNamesDict: ModuleNamesDict

        topAttribs: TopAttribs option

        latestCcuSigForFile: ModuleOrNamespaceType option

        /// Accumulated diagnostics, last file first
        tcDiagnosticsRev:(PhasedDiagnostic * FSharpDiagnosticSeverity)[] list

        tcDependencyFiles: string list

        sigNameOpt: (string * QualifiedNameOfFile) option
    }

    member x.TcDiagnostics =
        Array.concat (List.rev x.tcDiagnosticsRev)

/// Accumulated results of type checking. Optional data that isn't needed to type-check a file, but needed for more information for in tooling.
[<NoEquality; NoComparison>]
type TcInfoExtras =
    {
      tcResolutions: TcResolutions
      tcSymbolUses: TcSymbolUses
      tcOpenDeclarations: OpenDeclaration[]

      /// Result of checking most recent file, if any
      latestImplFile: CheckedImplFile option

      /// If enabled, stores a linear list of ranges and strings that identify an Item(symbol) in a file. Used for background find all references.
      itemKeyStore: ItemKeyStore option

      /// If enabled, holds semantic classification information for Item(symbol)s in a file.
      semanticClassificationKeyStore: SemanticClassificationKeyStore option
    }

    member x.TcSymbolUses =
        x.tcSymbolUses

module ValueOption =
    let toOption = function
        | ValueSome x -> Some x
        | _ -> None

type private SingleFileDiagnostics = (PhasedDiagnostic * FSharpDiagnosticSeverity) array
type private TypeCheck = TcInfo * TcResultsSinkImpl * CheckedImplFile option * string * SingleFileDiagnostics

/// Bound model of an underlying syntax and typed tree.
type BoundModel private (
        tcConfig: TcConfig,
        tcGlobals,
        tcImports: TcImports,
        keepAssemblyContents, keepAllBackgroundResolutions,
        keepAllBackgroundSymbolUses,
        enableBackgroundItemKeyStoreAndSemanticClassification,
        beforeFileChecked: Event<string>,
        fileChecked: Event<string>,
        prevTcInfo: TcInfo,
        syntaxTreeOpt: SyntaxTree option,
        ?tcStateOpt: GraphNode<TcInfo> * GraphNode<TcInfoExtras>
    ) =

    let getTypeCheck (syntaxTree: SyntaxTree) : Async<TypeCheck> =
        async {
            let! input, _sourceRange, fileName, parseErrors = syntaxTree.ParseNode.GetOrComputeValue()
            use _ = Activity.start "BoundModel.TypeCheck" [|Activity.Tags.fileName, fileName|]

            IncrementalBuilderEventTesting.MRU.Add(IncrementalBuilderEventTesting.IBETypechecked fileName)
            let capturingDiagnosticsLogger = CapturingDiagnosticsLogger("TypeCheck")
            let diagnosticsLogger = GetDiagnosticsLoggerFilteringByScopedPragmas(tcConfig.langVersion, input.ScopedPragmas, tcConfig.diagnosticsOptions, capturingDiagnosticsLogger)
            use _ = new CompilationGlobalsScope(diagnosticsLogger, BuildPhase.TypeCheck)

            beforeFileChecked.Trigger fileName
                    
            ApplyMetaCommandsFromInputToTcConfig (tcConfig, input, !! Path.GetDirectoryName(fileName), tcImports.DependencyProvider) |> ignore
            let sink = TcResultsSinkImpl(tcGlobals)
            let hadParseErrors = not (Array.isEmpty parseErrors)
            let input, moduleNamesDict = DeduplicateParsedInputModuleName prevTcInfo.moduleNamesDict input

            let! (tcEnvAtEndOfFile, topAttribs, implFile, ccuSigForFile), tcState =
                CheckOneInput (
                        (fun () -> hadParseErrors || diagnosticsLogger.ErrorCount > 0),
                        tcConfig, tcImports,
                        tcGlobals,
                        None,
                        TcResultsSink.WithSink sink,
                        prevTcInfo.tcState, input )
                |> Cancellable.toAsync

            fileChecked.Trigger fileName

            let newErrors = Array.append parseErrors (capturingDiagnosticsLogger.Diagnostics |> List.toArray)
            let tcEnvAtEndOfFile = if keepAllBackgroundResolutions then tcEnvAtEndOfFile else tcState.TcEnvFromImpls

            let tcInfo =
                {
                    tcState = tcState
                    tcEnvAtEndOfFile = tcEnvAtEndOfFile
                    moduleNamesDict = moduleNamesDict
                    latestCcuSigForFile = Some ccuSigForFile
                    tcDiagnosticsRev = newErrors :: prevTcInfo.tcDiagnosticsRev
                    topAttribs = Some topAttribs
                    tcDependencyFiles = fileName :: prevTcInfo.tcDependencyFiles
                    sigNameOpt =
                        match input with
                        | ParsedInput.SigFile sigFile ->
                            Some(sigFile.FileName, sigFile.QualifiedName)
                        | _ ->
                            None
                }
            return tcInfo, sink, implFile, fileName, newErrors
        }

    let skippedImplementationTypeCheck =
        match syntaxTreeOpt, prevTcInfo.sigNameOpt with
        | Some syntaxTree, Some (_, qualifiedName) when syntaxTree.HasSignature ->
            let input, _, fileName, _ = syntaxTree.Skip qualifiedName
            SkippedImplFilePlaceholder(tcConfig, tcImports, tcGlobals, prevTcInfo.tcState, input)
            |> Option.map (fun ((_, topAttribs, _, ccuSigForFile), tcState) ->
                    {
                        tcState = tcState
                        tcEnvAtEndOfFile = tcState.TcEnvFromImpls
                        moduleNamesDict = prevTcInfo.moduleNamesDict
                        latestCcuSigForFile = Some ccuSigForFile
                        tcDiagnosticsRev = prevTcInfo.tcDiagnosticsRev
                        topAttribs = Some topAttribs
                        tcDependencyFiles = fileName :: prevTcInfo.tcDependencyFiles
                        sigNameOpt = Some(fileName, qualifiedName)
                    })
        | _ -> None

    let getTcInfo (typeCheck: GraphNode<TypeCheck>) =
        async {
            let! tcInfo , _, _, _, _ = typeCheck.GetOrComputeValue()
            return tcInfo
        } |> GraphNode

    let getTcInfoExtras (typeCheck: GraphNode<TypeCheck>) =
        async {
            let! _ , sink, implFile, fileName, _ = typeCheck.GetOrComputeValue()
            // Build symbol keys
            let itemKeyStore, semanticClassification =
                if enableBackgroundItemKeyStoreAndSemanticClassification then
                    use _ = Activity.start "IncrementalBuild.CreateItemKeyStoreAndSemanticClassification" [|Activity.Tags.fileName, fileName|]
                    let sResolutions = sink.GetResolutions()
                    let builder = ItemKeyStoreBuilder(tcGlobals)
                    let preventDuplicates = HashSet({ new IEqualityComparer<struct(pos * pos)> with
                                                        member _.Equals((s1, e1): struct(pos * pos), (s2, e2): struct(pos * pos)) = Position.posEq s1 s2 && Position.posEq e1 e2
                                                        member _.GetHashCode o = o.GetHashCode() })
                    sResolutions.CapturedNameResolutions
                    |> Seq.iter (fun cnr ->
                        let r = cnr.Range
                        if preventDuplicates.Add struct(r.Start, r.End) then
                            builder.Write(cnr.Range, cnr.Item))
                    
                    let semanticClassification = sResolutions.GetSemanticClassification(tcGlobals, tcImports.GetImportMap(), sink.GetFormatSpecifierLocations(), None)
                    
                    let sckBuilder = SemanticClassificationKeyStoreBuilder()
                    sckBuilder.WriteAll semanticClassification
                    
                    let res = builder.TryBuildAndReset(), sckBuilder.TryBuildAndReset()
                    res
                else
                    None, None
            return
                {
                    // Only keep the typed interface files when doing a "full" build for fsc.exe, otherwise just throw them away
                    latestImplFile = if keepAssemblyContents then implFile else None
                    tcResolutions = (if keepAllBackgroundResolutions then sink.GetResolutions() else TcResolutions.Empty)
                    tcSymbolUses = (if keepAllBackgroundSymbolUses then sink.GetSymbolUses() else TcSymbolUses.Empty)
                    tcOpenDeclarations = sink.GetOpenDeclarations()
                    itemKeyStore = itemKeyStore
                    semanticClassificationKeyStore = semanticClassification
                }
        } |> GraphNode

    let defaultTypeCheck = async { return prevTcInfo, TcResultsSinkImpl(tcGlobals), None, "default typecheck - no syntaxTree", [||] }
    let typeCheckNode = syntaxTreeOpt |> Option.map getTypeCheck |> Option.defaultValue defaultTypeCheck |> GraphNode
    let tcInfoExtras = getTcInfoExtras typeCheckNode
    let diagnostics  =
        async {
            let! _, _, _, _, diags = typeCheckNode.GetOrComputeValue()
            return diags
        } |> GraphNode

    let startComputingFullTypeCheck =
        async {
            let! _ = tcInfoExtras.GetOrComputeValue()
            return! diagnostics.GetOrComputeValue()
        }

    let tcInfo, tcInfoExtras =
        match tcStateOpt with
        | Some tcState -> tcState
        | _ ->
            match skippedImplementationTypeCheck with
            | Some tcInfo ->
                // For skipped implementation sources do full type check only when requested.
                GraphNode.FromResult tcInfo, tcInfoExtras
            | _ ->
                // start computing extras, so that typeCheckNode can be GC'd quickly 
                startComputingFullTypeCheck |> Async.Catch |> Async.Ignore |> Async.Start
                getTcInfo typeCheckNode, tcInfoExtras

    member val Diagnostics = diagnostics

    member val TcInfo = tcInfo

    member val TcInfoExtras = tcInfoExtras

    member _.TcConfig = tcConfig

    member _.TcGlobals = tcGlobals

    member _.TcImports = tcImports

    member this.TryPeekTcInfo() = this.TcInfo.TryPeekValue() |> ValueOption.toOption
    
    member this.TryPeekTcInfoWithExtras() = 
        (this.TcInfo.TryPeekValue(), this.TcInfoExtras.TryPeekValue())
        ||> ValueOption.map2 (fun a b -> a, b)
        |> ValueOption.toOption
    
    member this.GetOrComputeTcInfo = this.TcInfo.GetOrComputeValue
    
    member this.GetOrComputeTcInfoExtras = this.TcInfoExtras.GetOrComputeValue
    
    member this.GetOrComputeTcInfoWithExtras() = async {
        let! tcInfo = this.TcInfo.GetOrComputeValue()
        let! tcInfoExtras = this.TcInfoExtras.GetOrComputeValue()
        return tcInfo, tcInfoExtras
    }

    member this.Next(syntaxTree) = async {
        let! tcInfo = this.TcInfo.GetOrComputeValue()
        return
            BoundModel(
                tcConfig,
                tcGlobals,
                tcImports,
                keepAssemblyContents,
                keepAllBackgroundResolutions,
                keepAllBackgroundSymbolUses,
                enableBackgroundItemKeyStoreAndSemanticClassification,
                beforeFileChecked,
                fileChecked,
                tcInfo,
                Some syntaxTree
            )
    }

    member this.Finish(finalTcDiagnosticsRev, finalTopAttribs) =
        async {
            let! tcInfo = this.TcInfo.GetOrComputeValue()
            let finishState = { tcInfo with tcDiagnosticsRev = finalTcDiagnosticsRev; topAttribs = finalTopAttribs }
            return
                BoundModel(
                    tcConfig,
                    tcGlobals,
                    tcImports,
                    keepAssemblyContents,
                    keepAllBackgroundResolutions,
                    keepAllBackgroundSymbolUses,
                    enableBackgroundItemKeyStoreAndSemanticClassification,
                    beforeFileChecked,
                    fileChecked,
                    prevTcInfo,
                    syntaxTreeOpt,
                    (GraphNode.FromResult finishState, this.TcInfoExtras)
                )
        }

    static member Create(
        tcConfig: TcConfig,
        tcGlobals: TcGlobals,
        tcImports: TcImports,
        keepAssemblyContents, keepAllBackgroundResolutions,
        keepAllBackgroundSymbolUses,
        enableBackgroundItemKeyStoreAndSemanticClassification,
        beforeFileChecked: Event<string>,
        fileChecked: Event<string>,
        prevTcInfo: TcInfo,
        syntaxTreeOpt: SyntaxTree option
    ) =
        BoundModel(
            tcConfig, tcGlobals, tcImports,
            keepAssemblyContents, keepAllBackgroundResolutions,
            keepAllBackgroundSymbolUses,
            enableBackgroundItemKeyStoreAndSemanticClassification,
            beforeFileChecked,
            fileChecked,
            prevTcInfo,
            syntaxTreeOpt
        )

/// Global service state
type FrameworkImportsCacheKey = 
    | FrameworkImportsCacheKey of resolvedpath: string list * assemblyName: string * targetFrameworkDirectories: string list * fsharpBinaries: string * langVersion: decimal * checkNulls: bool

    interface ICacheKey<string, FrameworkImportsCacheKey> with
        member this.GetKey() =
            this |> function FrameworkImportsCacheKey(assemblyName=a;checkNulls=c) -> if c then a + "CheckNulls" else a

        member this.GetLabel() = 
            this |> function FrameworkImportsCacheKey(assemblyName=a;checkNulls=c) -> if c then a + "CheckNulls" else a

        member this.GetVersion() = this
        
/// Represents a cache of 'framework' references that can be shared between multiple incremental builds
type FrameworkImportsCache(size) =

    let gate = obj()

    // Mutable collection protected via CompilationThreadToken
    let frameworkTcImportsCache = AgedLookup<AnyCallerThreadToken, FrameworkImportsCacheKey, GraphNode<TcGlobals * TcImports>>(size, areSimilar=(fun (x, y) -> x = y))

    /// Reduce the size of the cache in low-memory scenarios
    member _.Downsize() = frameworkTcImportsCache.Resize(AnyCallerThread, newKeepStrongly=0)

    /// Clear the cache
    member _.Clear() = frameworkTcImportsCache.Clear AnyCallerThread

    /// This function strips the "System" assemblies from the tcConfig and returns a age-cached TcImports for them.
    member _.GetNode(tcConfig: TcConfig, frameworkDLLs: AssemblyResolution list, nonFrameworkResolutions: AssemblyResolution list) =
        let frameworkDLLsKey =
            frameworkDLLs
            |> List.map (fun ar->ar.resolvedPath) // The cache key. Just the minimal data.
            |> List.sort  // Sort to promote cache hits.

        // Prepare the frameworkTcImportsCache
        //
        // The data elements in this key are very important. There should be nothing else in the TcConfig that logically affects
        // the import of a set of framework DLLs into F# CCUs. That is, the F# CCUs that result from a set of DLLs (including
        // FSharp.Core.dll and mscorlib.dll) must be logically invariant of all the other compiler configuration parameters.
        let key =
            FrameworkImportsCacheKey(frameworkDLLsKey,
                    tcConfig.primaryAssembly.Name,
                    tcConfig.GetTargetFrameworkDirectories(),
                    tcConfig.fsharpBinariesDir,
                    tcConfig.langVersion.SpecifiedVersion,
                    tcConfig.checkNullness)

        let node =
            lock gate (fun () ->
                match frameworkTcImportsCache.TryGet (AnyCallerThread, key) with
                | Some lazyWork -> lazyWork
                | None ->
                    let lazyWork = GraphNode(async {
                        let tcConfigP = TcConfigProvider.Constant tcConfig
                        return! TcImports.BuildFrameworkTcImports (tcConfigP, frameworkDLLs, nonFrameworkResolutions)
                    })
                    frameworkTcImportsCache.Put(AnyCallerThread, key, lazyWork)
                    lazyWork
            )
        node
                

    /// This function strips the "System" assemblies from the tcConfig and returns a age-cached TcImports for them.
    member this.Get(tcConfig: TcConfig) =
      async {
        // Split into installed and not installed.
        let frameworkDLLs, nonFrameworkResolutions, unresolved = TcAssemblyResolutions.SplitNonFoundationalResolutions(tcConfig)
        let node = this.GetNode(tcConfig, frameworkDLLs, nonFrameworkResolutions)
        let! tcGlobals, frameworkTcImports = node.GetOrComputeValue()

        // If the tcGlobals was loaded from a different project, langVersion and realsig may be different 
        // for each cached project.  So here we create a new tcGlobals, with the existing framework values
        // and updated realsig and langversion
        let tcGlobals =
            if tcGlobals.langVersion.SpecifiedVersion <> tcConfig.langVersion.SpecifiedVersion
                || tcGlobals.realsig <> tcConfig.realsig then
                    TcGlobals(
                        tcGlobals.compilingFSharpCore,
                        tcGlobals.ilg,
                        tcGlobals.fslibCcu,
                        tcGlobals.directoryToResolveRelativePaths,
                        tcGlobals.mlCompatibility,
                        tcGlobals.isInteractive,
                        tcGlobals.checkNullness,
                        tcGlobals.useReflectionFreeCodeGen,
                        tcGlobals.tryFindSysTypeCcuHelper,
                        tcGlobals.emitDebugInfoInQuotations,
                        tcGlobals.noDebugAttributes,
                        tcGlobals.pathMap,
                        tcConfig.langVersion,
                        tcConfig.realsig
                    )

            else
                tcGlobals

        return tcGlobals, frameworkTcImports, nonFrameworkResolutions, unresolved
      }

/// Represents the interim state of checking an assembly
[<Sealed>]
type PartialCheckResults (boundModel: BoundModel, timeStamp: DateTime, projectTimeStamp: DateTime) =

    member _.TcImports = boundModel.TcImports

    member _.TcGlobals = boundModel.TcGlobals

    member _.TcConfig = boundModel.TcConfig

    member _.TimeStamp = timeStamp

    member _.ProjectTimeStamp = projectTimeStamp

    member _.TryPeekTcInfo() = boundModel.TryPeekTcInfo()

    member _.TryPeekTcInfoWithExtras() = boundModel.TryPeekTcInfoWithExtras()

    member _.GetOrComputeTcInfo() = boundModel.GetOrComputeTcInfo()

    member _.GetOrComputeTcInfoWithExtras() = boundModel.GetOrComputeTcInfoWithExtras()

    member _.GetOrComputeItemKeyStoreIfEnabled() =
        async {
            let! info = boundModel.GetOrComputeTcInfoExtras()
            return info.itemKeyStore
        }

    member _.GetOrComputeSemanticClassificationIfEnabled() =
        async {
            let! info = boundModel.GetOrComputeTcInfoExtras()
            return info.semanticClassificationKeyStore
        }

[<AutoOpen>]
module Utilities =
    let TryFindFSharpStringAttribute tcGlobals attribSpec attribs =
        match TryFindFSharpAttribute tcGlobals attribSpec attribs with
        | Some (Attrib(_, _, [ AttribStringArg s ], _, _, _, _))  -> Some s
        | _ -> None

/// The implementation of the information needed by TcImports in CompileOps.fs for an F# assembly reference.
///
/// Constructs the build data (IRawFSharpAssemblyData) representing the assembly when used
/// as a cross-assembly reference.  Note the assembly has not been generated on disk, so this is
/// a virtualized view of the assembly contents as computed by background checking.
[<Sealed>]
type RawFSharpAssemblyDataBackedByLanguageService (tcConfig, tcGlobals, generatedCcu: CcuThunk, outfile, topAttrs, assemblyName, ilAssemRef) =

    let exportRemapping = MakeExportRemapping generatedCcu generatedCcu.Contents

    let sigData =
        let _sigDataAttributes, sigDataResources = EncodeSignatureData(tcConfig, tcGlobals, exportRemapping, generatedCcu, outfile, true)
        GetResourceNameAndSignatureDataFuncs sigDataResources

    let autoOpenAttrs = topAttrs.assemblyAttrs |> List.choose (List.singleton >> TryFindFSharpStringAttribute tcGlobals tcGlobals.attrib_AutoOpenAttribute)

    let ivtAttrs = topAttrs.assemblyAttrs |> List.choose (List.singleton >> TryFindFSharpStringAttribute tcGlobals tcGlobals.attrib_InternalsVisibleToAttribute)

    interface IRawFSharpAssemblyData with
        member _.GetAutoOpenAttributes() = autoOpenAttrs
        member _.GetInternalsVisibleToAttributes() =  ivtAttrs
        member _.TryGetILModuleDef() = None
        member _.GetRawFSharpSignatureData(_m, _ilShortAssemName, _filename) = sigData
        member _.GetRawFSharpOptimizationData(_m, _ilShortAssemName, _filename) = [ ]
        member _.GetRawTypeForwarders() = mkILExportedTypes []  // TODO: cross-project references with type forwarders
        member _.ShortAssemblyName = assemblyName
        member _.ILScopeRef = ILScopeRef.Assembly ilAssemRef
        member _.ILAssemblyRefs = [] // These are not significant for service scenarios
        member _.HasAnyFSharpSignatureDataAttribute =  true
        member _.HasMatchingFSharpSignatureDataAttribute = true

[<AutoOpen>]
module IncrementalBuilderHelpers =

    /// Timestamps of referenced assemblies are taken from the file's timestamp.
    let StampReferencedAssemblyTask (cache: TimeStampCache) (_ref, timeStamper) =
        timeStamper cache

    // Link all the assemblies together and produce the input typecheck accumulator
    let CombineImportedAssembliesTask (
        assemblyName, 
        tcConfig: TcConfig, 
        tcConfigP, 
        tcGlobals, 
        frameworkTcImports, 
        nonFrameworkResolutions, 
        unresolvedReferences, 
        dependencyProvider, 
        loadClosureOpt: LoadClosure option, 
        basicDependencies,
        keepAssemblyContents,
        keepAllBackgroundResolutions,
        keepAllBackgroundSymbolUses,
        enableBackgroundItemKeyStoreAndSemanticClassification,
        beforeFileChecked,
        fileChecked
#if !NO_TYPEPROVIDERS
        ,importsInvalidatedByTypeProvider: Event<unit>
#endif
        ) : Async<BoundModel * SingleFileDiagnostics> =

      async {
        let diagnosticsLogger = CompilationDiagnosticLogger("CombineImportedAssembliesTask", tcConfig.diagnosticsOptions)
        use _ = new CompilationGlobalsScope(diagnosticsLogger, BuildPhase.Parameter)

        let! tcImports =
          async {
            try
                let! tcImports = TcImports.BuildNonFrameworkTcImports(tcConfigP, frameworkTcImports, nonFrameworkResolutions, unresolvedReferences, dependencyProvider)
#if !NO_TYPEPROVIDERS
                tcImports.GetCcusExcludingBase() |> Seq.iter (fun ccu ->
                    // When a CCU reports an invalidation, merge them together and just report a
                    // general "imports invalidated". This triggers a rebuild.
                    //
                    // We are explicit about what the handler closure captures to help reason about the
                    // lifetime of captured objects, especially in case the type provider instance gets leaked
                    // or keeps itself alive mistakenly, e.g. via some global state in the type provider instance.
                    //
                    // The handler only captures
                    //    1. a weak reference to the importsInvalidated event.
                    //
                    // The IncrementalBuilder holds the strong reference the importsInvalidated event.
                    //
                    // In the invalidation handler we use a weak reference to allow the IncrementalBuilder to
                    // be collected if, for some reason, a TP instance is not disposed or not GC'd.
                    let capturedImportsInvalidated = WeakReference<_>(importsInvalidatedByTypeProvider)
                    ccu.Deref.InvalidateEvent.Add(fun _ ->
                        match capturedImportsInvalidated.TryGetTarget() with
                        | true, tg -> tg.Trigger()
                        | _ -> ()))
#endif
                return tcImports
            with exn ->
                Debug.Assert(false, sprintf "Could not BuildAllReferencedDllTcImports %A" exn)
                diagnosticsLogger.Warning exn
                return frameworkTcImports
          }

        let tcInitial, openDecls0 = GetInitialTcEnv (assemblyName, rangeStartup, tcConfig, tcImports, tcGlobals)
        let tcState = GetInitialTcState (rangeStartup, assemblyName, tcConfig, tcGlobals, tcImports, tcInitial, openDecls0)
        let loadClosureErrors =
           [ match loadClosureOpt with
             | None -> ()
             | Some loadClosure ->
                for inp in loadClosure.Inputs do
                    yield! inp.MetaCommandDiagnostics ]

        let initialErrors = Array.append (Array.ofList loadClosureErrors) (diagnosticsLogger.GetDiagnostics())
        let tcInfo =
            {
              tcState=tcState
              tcEnvAtEndOfFile=tcInitial
              topAttribs=None
              latestCcuSigForFile=None
              tcDiagnosticsRev = [ initialErrors ]
              moduleNamesDict = Map.empty
              tcDependencyFiles = basicDependencies
              sigNameOpt = None
            }
        return
            BoundModel.Create(
                tcConfig,
                tcGlobals,
                tcImports,
                keepAssemblyContents,
                keepAllBackgroundResolutions,
                keepAllBackgroundSymbolUses,
                enableBackgroundItemKeyStoreAndSemanticClassification,
                beforeFileChecked,
                fileChecked,
                tcInfo,
                None
            ), initialErrors
      }

    /// Finish up the typechecking to produce outputs for the rest of the compilation process
    let FinalizeTypeCheckTask (tcConfig: TcConfig) tcGlobals partialCheck assemblyName outfile (boundModels: GraphNode<BoundModel> seq) =
      async {
        let diagnosticsLogger = CompilationDiagnosticLogger("FinalizeTypeCheckTask", tcConfig.diagnosticsOptions)
        use _ = new CompilationGlobalsScope(diagnosticsLogger, BuildPhase.TypeCheck)

        let! computedBoundModels = boundModels |> Seq.map (fun g -> g.GetOrComputeValue()) |> MultipleDiagnosticsLoggers.Sequential

        let! tcInfos =
            computedBoundModels
            |> Seq.map (fun boundModel -> async { return! boundModel.GetOrComputeTcInfo() })
            |> MultipleDiagnosticsLoggers.Sequential

        // tcInfoExtras can be computed in parallel. This will check any previously skipped implementation files in parallel, too.
        let! latestImplFiles =
            computedBoundModels
            |> Seq.map (fun boundModel -> async {
                    if partialCheck then
                        return None
                    else
                        let! tcInfoExtras = boundModel.GetOrComputeTcInfoExtras()
                        return tcInfoExtras.latestImplFile
                })
            |> MultipleDiagnosticsLoggers.Parallel

        let results = [
            for tcInfo, latestImplFile in Seq.zip tcInfos latestImplFiles ->
                tcInfo.tcEnvAtEndOfFile, defaultArg tcInfo.topAttribs EmptyTopAttrs, latestImplFile, tcInfo.latestCcuSigForFile
        ]

        // Get the state at the end of the type-checking of the last file
        let finalInfo = Array.last tcInfos

        // Finish the checking
        let (_tcEnvAtEndOfLastFile, topAttrs, mimpls, _), tcState =
            CheckMultipleInputsFinish (results, finalInfo.tcState)

        let ilAssemRef, tcAssemblyDataOpt, tcAssemblyExprOpt =
            try
                let tcState, tcAssemblyExpr, ccuContents = CheckClosedInputSetFinish (mimpls, tcState)

                let generatedCcu = tcState.Ccu.CloneWithFinalizedContents(ccuContents)

                // Compute the identity of the generated assembly based on attributes, options etc.
                // Some of this is duplicated from fsc.fs
                let ilAssemRef =
                    let publicKey =
                        try
                            let signingInfo = ValidateKeySigningAttributes (tcConfig, tcGlobals, topAttrs)
                            match GetStrongNameSigner signingInfo with
                            | None -> None
                            | Some s -> Some (PublicKey.KeyAsToken(s.PublicKey))
                        with exn ->
                            errorRecoveryNoRange exn
                            None
                    let locale = TryFindFSharpStringAttribute tcGlobals (tcGlobals.FindSysAttrib "System.Reflection.AssemblyCultureAttribute") topAttrs.assemblyAttrs
                    let assemVerFromAttrib =
                        TryFindFSharpStringAttribute tcGlobals (tcGlobals.FindSysAttrib "System.Reflection.AssemblyVersionAttribute") topAttrs.assemblyAttrs
                        |> Option.bind  (fun v -> try Some (parseILVersion v) with _ -> None)
                    let ver =
                        match assemVerFromAttrib with
                        | None -> tcConfig.version.GetVersionInfo(tcConfig.implicitIncludeDir)
                        | Some v -> v
                    ILAssemblyRef.Create(assemblyName, None, publicKey, false, Some ver, locale)

                let tcAssemblyDataOpt =
                    try
                        // Assemblies containing type provider components cannot successfully be used via cross-assembly references.
                        // We return 'None' for the assembly portion of the cross-assembly reference
                        let hasTypeProviderAssemblyAttrib =
                            topAttrs.assemblyAttrs |> List.exists (fun (Attrib(tcref, _, _, _, _, _, _)) ->
                                let nm = tcref.CompiledRepresentationForNamedType.BasicQualifiedName
                                nm = !! typeof<Microsoft.FSharp.Core.CompilerServices.TypeProviderAssemblyAttribute>.FullName)

                        if tcState.CreatesGeneratedProvidedTypes || hasTypeProviderAssemblyAttrib then
                            ProjectAssemblyDataResult.Unavailable true
                        else
                            ProjectAssemblyDataResult.Available (RawFSharpAssemblyDataBackedByLanguageService (tcConfig, tcGlobals, generatedCcu, outfile, topAttrs, assemblyName, ilAssemRef) :> IRawFSharpAssemblyData)
                    with exn ->
                        errorRecoveryNoRange exn
                        ProjectAssemblyDataResult.Unavailable true
                ilAssemRef, tcAssemblyDataOpt, Some tcAssemblyExpr
            with exn ->
                errorRecoveryNoRange exn
                mkSimpleAssemblyRef assemblyName, ProjectAssemblyDataResult.Unavailable true, None

        let finalBoundModel = Array.last computedBoundModels

        // Collect diagnostics. This will type check in parallel any implementation files skipped so far.
        let! partialDiagnostics =
            computedBoundModels
            |> Seq.map (fun m -> m.Diagnostics.GetOrComputeValue())
            |> MultipleDiagnosticsLoggers.Parallel
        let diagnostics = [
            diagnosticsLogger.GetDiagnostics()
            yield! partialDiagnostics |> Seq.rev
        ]

        let! finalBoundModelWithErrors = finalBoundModel.Finish(diagnostics, Some topAttrs)
        return ilAssemRef, tcAssemblyDataOpt, tcAssemblyExprOpt, finalBoundModelWithErrors
    }

[<NoComparison;NoEquality>]
type IncrementalBuilderInitialState =
    {
        initialBoundModel: BoundModel
        initialErrors: SingleFileDiagnostics
        tcGlobals: TcGlobals
        referencedAssemblies: ImmutableArray<Choice<string, IProjectReference> * (TimeStampCache -> DateTime)>
        tcConfig: TcConfig
        outfile: string
        assemblyName: string
        lexResourceManager: Lexhelp.LexResourceManager
        fileNames: FSharpFile list
        enablePartialTypeChecking: bool
        beforeFileChecked: Event<string>
        fileChecked: Event<string>
        fileParsed: Event<string>
        projectChecked: Event<unit>
#if !NO_TYPEPROVIDERS
        importsInvalidatedByTypeProvider: Event<unit>
#endif
        allDependencies: string []
        defaultTimeStamp: DateTime
        mutable isImportsInvalidated: bool
        useChangeNotifications: bool
        useSyntaxTreeCache: bool
    }

    static member Create
        (
            initialBoundModel: BoundModel,
            initialErrors: SingleFileDiagnostics,
            tcGlobals,
            nonFrameworkAssemblyInputs,
            tcConfig: TcConfig,
            outfile,
            assemblyName,
            lexResourceManager,
            sourceFiles,
            enablePartialTypeChecking,
            beforeFileChecked: Event<string>,
            fileChecked: Event<string>,
#if !NO_TYPEPROVIDERS
            importsInvalidatedByTypeProvider: Event<unit>,
#endif
            allDependencies,
            defaultTimeStamp: DateTime,
            useChangeNotifications: bool,
            useSyntaxTreeCache
        ) =

        let initialState =
            {
                initialBoundModel = initialBoundModel
                initialErrors = initialErrors
                tcGlobals = tcGlobals
                referencedAssemblies = nonFrameworkAssemblyInputs |> ImmutableArray.ofSeq
                tcConfig = tcConfig
                outfile = outfile
                assemblyName = assemblyName
                lexResourceManager = lexResourceManager
                fileNames = sourceFiles
                enablePartialTypeChecking = enablePartialTypeChecking
                beforeFileChecked = beforeFileChecked
                fileChecked = fileChecked
                fileParsed = Event<string>()
                projectChecked = Event<unit>()
#if !NO_TYPEPROVIDERS
                importsInvalidatedByTypeProvider = importsInvalidatedByTypeProvider
#endif
                allDependencies = allDependencies
                defaultTimeStamp = defaultTimeStamp
                isImportsInvalidated = false
                useChangeNotifications = useChangeNotifications
                useSyntaxTreeCache = useSyntaxTreeCache
            }
#if !NO_TYPEPROVIDERS
        importsInvalidatedByTypeProvider.Publish.Add(fun () -> initialState.isImportsInvalidated <- true)
#endif
        initialState

// Stamp represent the real stamp of the file.
// Notified indicates that there is pending file change.
// LogicalStamp represent the stamp of the file that is used to calculate the project's logical timestamp.
type Slot =
    {
        HasSignature: bool
        Stamp: DateTime
        LogicalStamp: DateTime
        SyntaxTree: SyntaxTree
        Notified: bool
        BoundModel: GraphNode<BoundModel>
    }
    member this.Notify timeStamp =
        if this.Stamp <> timeStamp then { this with Stamp = timeStamp; Notified = true } else this

[<NoComparison;NoEquality>]
type IncrementalBuilderState =
    {
        slots: Slot list
        stampedReferencedAssemblies: ImmutableArray<DateTime>
        finalizedBoundModel: GraphNode<(ILAssemblyRef * ProjectAssemblyDataResult * CheckedImplFile list option * BoundModel) * DateTime>
    }
    member this.stampedFileNames = this.slots |> List.map (fun s -> s.Stamp)
    member this.logicalStampedFileNames = this.slots |> List.map (fun s -> s.LogicalStamp)
    member this.boundModels = this.slots |> List.map (fun s -> s.BoundModel)

[<AutoOpen>]
module IncrementalBuilderStateHelpers =

    // Used to thread the status of the build in computeStampedFileNames mapFold.
    type BuildStatus = Invalidated | Good

    let createBoundModelGraphNode (prevBoundModel: GraphNode<BoundModel>) syntaxTree =
        GraphNode(async {
            let! prevBoundModel = prevBoundModel.GetOrComputeValue()
            return! prevBoundModel.Next(syntaxTree)
        })

    let createFinalizeBoundModelGraphNode (initialState: IncrementalBuilderInitialState) (boundModels: GraphNode<BoundModel> seq) =
        GraphNode(async {
            use _ = Activity.start "GetCheckResultsAndImplementationsForProject" [|Activity.Tags.project, initialState.outfile|]
            let! result = 
                FinalizeTypeCheckTask 
                    initialState.tcConfig 
                    initialState.tcGlobals
                    initialState.enablePartialTypeChecking
                    initialState.assemblyName 
                    initialState.outfile 
                    boundModels
            return result, DateTime.UtcNow
        })

    let computeStampedFileNames (initialState: IncrementalBuilderInitialState) (state: IncrementalBuilderState) (cache: TimeStampCache) =
        let slots = 
            if initialState.useChangeNotifications then
                state.slots
            else
               [ for slot in state.slots -> cache.GetFileTimeStamp slot.SyntaxTree.FileName |> slot.Notify ]

        let slots =
            [ for slot in slots do
                if slot.Notified then { slot with SyntaxTree = slot.SyntaxTree.Invalidate() } else slot ]

        let mapping (status, prevNode) slot =
            let update newStatus =
                let boundModel = createBoundModelGraphNode prevNode slot.SyntaxTree
                { slot with
                    LogicalStamp = slot.Stamp
                    Notified = false
                    BoundModel = boundModel },
                (newStatus, boundModel)

            let noChange = slot, (Good, slot.BoundModel)

            match status with
            // Modifying implementation file that has signature file does not invalidate the build.
            // So we just pass along previous status.
            | status when slot.Notified && slot.HasSignature -> update status
            | Invalidated -> update Invalidated
            | Good when slot.Notified -> update Invalidated
            | _ -> noChange

        if slots |> List.exists (fun s -> s.Notified) then
            let slots, _ = slots |> List.mapFold mapping (Good, GraphNode.FromResult initialState.initialBoundModel)
            let boundModels = slots |> Seq.map (fun s -> s.BoundModel)
            { state with
                slots = slots
                finalizedBoundModel = createFinalizeBoundModelGraphNode initialState boundModels }
        else
            state

    let computeStampedReferencedAssemblies (initialState: IncrementalBuilderInitialState) state canTriggerInvalidation (cache: TimeStampCache) =
        let stampedReferencedAssemblies = state.stampedReferencedAssemblies.ToBuilder()

        let mutable referencesUpdated = false
        initialState.referencedAssemblies
        |> ImmutableArray.iteri (fun i asmInfo ->

            let currentStamp = state.stampedReferencedAssemblies[i]
            let stamp = StampReferencedAssemblyTask cache asmInfo

            if currentStamp <> stamp then
                referencesUpdated <- true
                stampedReferencedAssemblies[i] <- stamp
        )

        if referencesUpdated then
            // Build is invalidated. The build must be rebuilt with the newly updated references.
            if not initialState.isImportsInvalidated && canTriggerInvalidation then
                initialState.isImportsInvalidated <- true
            { state with
                stampedReferencedAssemblies = stampedReferencedAssemblies.ToImmutable()
            }
        else
            state

type IncrementalBuilderState with

    (*
        The data below represents a dependency graph.

        ReferencedAssembliesStamps => FileStamps => BoundModels => FinalizedBoundModel
    *)
    static member Create(initialState: IncrementalBuilderInitialState) =
        let defaultTimeStamp = initialState.defaultTimeStamp
        let referencedAssemblies = initialState.referencedAssemblies
        let cache = TimeStampCache(defaultTimeStamp)
        let initialBoundModel = GraphNode.FromResult initialState.initialBoundModel

        let hasSignature =
            let isImplFile fileName = FSharpImplFileSuffixes |> List.exists (FileSystemUtils.checkSuffix fileName)
            let isSigFile fileName = FSharpSigFileSuffixes |> List.exists (FileSystemUtils.checkSuffix fileName)
            let isBackingSignature fileName sigName =
                isImplFile fileName && isSigFile sigName &&
                    FileSystemUtils.fileNameWithoutExtension sigName = FileSystemUtils.fileNameWithoutExtension fileName
            [
                false
                for prev, file in initialState.fileNames |> List.pairwise do
                    isBackingSignature file.Source.FilePath prev.Source.FilePath
            ]

        let syntaxTrees =
            [
                for sourceFile, hasSignature in Seq.zip initialState.fileNames hasSignature ->
                    SyntaxTree(initialState.tcConfig, initialState.fileParsed, initialState.lexResourceManager, sourceFile, hasSignature)
            ]

        let boundModels = 
            syntaxTrees
            |> Seq.scan createBoundModelGraphNode initialBoundModel

        let slots =
            [
                for model, syntaxTree, hasSignature in Seq.zip3 (boundModels |> Seq.skip 1) syntaxTrees hasSignature do
                    {
                        HasSignature = hasSignature
                        Stamp = DateTime.MinValue
                        LogicalStamp = DateTime.MinValue
                        Notified = true
                        SyntaxTree = syntaxTree
                        BoundModel = model
                    }
            ]

        let state =
            {
                slots = slots
                stampedReferencedAssemblies = ImmutableArray.init referencedAssemblies.Length (fun _ -> DateTime.MinValue)
                finalizedBoundModel = createFinalizeBoundModelGraphNode initialState boundModels
            }
        let state = computeStampedReferencedAssemblies initialState state false cache
        let state = computeStampedFileNames initialState state cache
        state

/// Manages an incremental build graph for the build of a single F# project
type IncrementalBuilder(initialState: IncrementalBuilderInitialState, state: IncrementalBuilderState) =

    let initialBoundModel = initialState.initialBoundModel
    let tcConfig = initialState.tcConfig
    let fileNames = initialState.fileNames
    let beforeFileChecked = initialState.beforeFileChecked
    let fileChecked = initialState.fileChecked
#if !NO_TYPEPROVIDERS
    let importsInvalidatedByTypeProvider = initialState.importsInvalidatedByTypeProvider
#endif
    let allDependencies = initialState.allDependencies
    let defaultTimeStamp = initialState.defaultTimeStamp
    let fileParsed = initialState.fileParsed
    let projectChecked = initialState.projectChecked

    let tryGetSlot (state: IncrementalBuilderState) slot =
        match state.boundModels[slot].TryPeekValue() with
        | ValueSome boundModel ->
            (boundModel, state.stampedFileNames[slot])
            |> Some
        | _ ->
            None

    let tryGetBeforeSlot (state: IncrementalBuilderState) slot =
        match slot with
        | 0 (* first file *) ->
            (initialBoundModel, defaultTimeStamp)
            |> Some
        | _ ->
            tryGetSlot state (slot - 1)

    let evalUpToTargetSlot (state: IncrementalBuilderState) targetSlot =
        async {
            if targetSlot < 0 then
                return Some(initialBoundModel, defaultTimeStamp)
            else
                let! boundModel = state.boundModels[targetSlot].GetOrComputeValue()
                return Some(boundModel, state.stampedFileNames[targetSlot])
        }

    let MaxTimeStampInDependencies stamps fileSlot =
        if Seq.isEmpty stamps then
            defaultTimeStamp
        else
            let stamps =
                match fileSlot with
                | -1 -> stamps
                | fileSlot -> stamps |> Seq.take fileSlot

            stamps |> Seq.max

    let computeProjectTimeStamp (state: IncrementalBuilderState) fileSlot =
        if fileSlot = 0 then
            MaxTimeStampInDependencies state.stampedReferencedAssemblies -1
        else
            let t1 = MaxTimeStampInDependencies state.stampedReferencedAssemblies -1
            let t2 = MaxTimeStampInDependencies state.logicalStampedFileNames fileSlot
            max t1 t2

    let semaphore = new SemaphoreSlim(1,1)

    let mutable currentState = state 

    let setCurrentState state cache (ct: CancellationToken) =
        async {
            do! semaphore.WaitAsync(ct) |> Async.AwaitTask
            try
                ct.ThrowIfCancellationRequested()
                currentState <- computeStampedFileNames initialState state cache
            finally
                semaphore.Release() |> ignore
        }

    let checkFileTimeStamps (cache: TimeStampCache) =
        async {
            let! ct = Async.CancellationToken
            do! setCurrentState currentState cache ct
        }

    do IncrementalBuilderEventTesting.MRU.Add(IncrementalBuilderEventTesting.IBECreated)

    member _.TcConfig = tcConfig

    member _.FileParsed = fileParsed.Publish

    member _.BeforeFileChecked = beforeFileChecked.Publish

    member _.FileChecked = fileChecked.Publish

    member _.ProjectChecked = projectChecked.Publish

#if !NO_TYPEPROVIDERS
    member _.ImportsInvalidatedByTypeProvider = importsInvalidatedByTypeProvider.Publish
#endif

    member _.IsReferencesInvalidated = 
        // fast path
        if initialState.isImportsInvalidated then true
        else 
            computeStampedReferencedAssemblies initialState currentState true (TimeStampCache(defaultTimeStamp)) |> ignore
            initialState.isImportsInvalidated

    member _.AllDependenciesDeprecated = allDependencies

    member _.PopulatePartialCheckingResults () =
      async {
        let cache = TimeStampCache defaultTimeStamp // One per step
        do! checkFileTimeStamps cache
        let! _ = currentState.finalizedBoundModel.GetOrComputeValue()
        projectChecked.Trigger()
      }

    member builder.GetCheckResultsBeforeFileInProjectEvenIfStale fileName: PartialCheckResults option  =
        let slotOfFile = builder.GetSlotOfFileName fileName
        let result = tryGetBeforeSlot currentState slotOfFile

        match result with
        | Some (boundModel, timestamp) ->
            let projectTimeStamp = builder.GetLogicalTimeStampForFileInProject(fileName)
            Some (PartialCheckResults (boundModel, timestamp, projectTimeStamp))
        | _ -> None

    member builder.GetCheckResultsForFileInProjectEvenIfStale fileName: PartialCheckResults option  =
        let slotOfFile = builder.GetSlotOfFileName fileName
        let result = tryGetSlot currentState slotOfFile

        match result with
        | Some (boundModel, timestamp) ->
            let projectTimeStamp = builder.GetLogicalTimeStampForFileInProject(fileName)
            Some (PartialCheckResults (boundModel, timestamp, projectTimeStamp))
        | _ -> None

    member builder.TryGetCheckResultsBeforeFileInProject fileName =
        let cache = TimeStampCache defaultTimeStamp
        let tmpState = computeStampedFileNames initialState currentState cache

        let slotOfFile = builder.GetSlotOfFileName fileName
        match tryGetBeforeSlot tmpState slotOfFile with
        | Some(boundModel, timestamp) ->
            let projectTimeStamp = builder.GetLogicalTimeStampForFileInProject(fileName)
            Some (PartialCheckResults (boundModel, timestamp, projectTimeStamp))
        | _ -> None

    member builder.AreCheckResultsBeforeFileInProjectReady fileName =
        (builder.TryGetCheckResultsBeforeFileInProject fileName).IsSome

    member builder.GetCheckResultsBeforeSlotInProject slotOfFile =
      async {
        let cache = TimeStampCache defaultTimeStamp
        do! checkFileTimeStamps cache
        let! result = evalUpToTargetSlot currentState (slotOfFile - 1)
        match result with
        | Some (boundModel, timestamp) ->
            let projectTimeStamp = builder.GetLogicalTimeStampForFileInProject(slotOfFile)
            return PartialCheckResults(boundModel, timestamp, projectTimeStamp)
        | None -> return! failwith "Expected results to be ready. (GetCheckResultsBeforeSlotInProject)."
      }

    member builder.GetFullCheckResultsBeforeSlotInProject slotOfFile =
      async {
        let cache = TimeStampCache defaultTimeStamp
        do! checkFileTimeStamps cache
        let! result = evalUpToTargetSlot currentState (slotOfFile - 1)
        match result with
        | Some (boundModel, timestamp) -> 
            let! _ = boundModel.GetOrComputeTcInfoExtras()
            let projectTimeStamp = builder.GetLogicalTimeStampForFileInProject(slotOfFile)
            return PartialCheckResults(boundModel, timestamp, projectTimeStamp)
        | None -> return! failwith "Expected results to be ready. (GetFullCheckResultsBeforeSlotInProject)."
      }

    member builder.GetCheckResultsBeforeFileInProject fileName =
        let slotOfFile = builder.GetSlotOfFileName fileName
        builder.GetCheckResultsBeforeSlotInProject slotOfFile

    member builder.GetCheckResultsAfterFileInProject fileName =
        let slotOfFile = builder.GetSlotOfFileName fileName + 1
        builder.GetCheckResultsBeforeSlotInProject slotOfFile

    member builder.GetFullCheckResultsBeforeFileInProject fileName =
        let slotOfFile = builder.GetSlotOfFileName fileName
        builder.GetFullCheckResultsBeforeSlotInProject slotOfFile

    member builder.GetFullCheckResultsAfterFileInProject fileName =
        async {
            let slotOfFile = builder.GetSlotOfFileName fileName + 1
            let! result = builder.GetFullCheckResultsBeforeSlotInProject(slotOfFile)
            return result
        }

    member builder.GetCheckResultsAfterLastFileInProject () =
        builder.GetCheckResultsBeforeSlotInProject(builder.GetSlotsCount())

    member builder.GetCheckResultsAndImplementationsForProject() =
      async {
        let cache = TimeStampCache(defaultTimeStamp)
        do! checkFileTimeStamps cache
        let! result = currentState.finalizedBoundModel.GetOrComputeValue()
        match result with
        | (ilAssemRef, tcAssemblyDataOpt, tcAssemblyExprOpt, boundModel), timestamp ->
            let cache = TimeStampCache defaultTimeStamp
            let projectTimeStamp = builder.GetLogicalTimeStampForProject(cache)
            return PartialCheckResults (boundModel, timestamp, projectTimeStamp), ilAssemRef, tcAssemblyDataOpt, tcAssemblyExprOpt
      }

    member builder.GetFullCheckResultsAndImplementationsForProject() =
        async {
            let! result = builder.GetCheckResultsAndImplementationsForProject()
            let results, _, _, _ = result
            let! _ = results.GetOrComputeTcInfoWithExtras() // Make sure we forcefully evaluate the info
            return result
        }

    member builder.GetLogicalTimeStampForFileInProject(filename: string) =
        let slot = builder.GetSlotOfFileName(filename)
        builder.GetLogicalTimeStampForFileInProject(slot)

    member _.GetLogicalTimeStampForFileInProject(slotOfFile: int) =
        let cache = TimeStampCache defaultTimeStamp
        let tempState = computeStampedFileNames initialState currentState cache
        computeProjectTimeStamp tempState slotOfFile

    member _.GetLogicalTimeStampForProject(cache) =
        let tempState = computeStampedFileNames initialState currentState cache
        computeProjectTimeStamp tempState -1

    member _.TryGetSlotOfFileName(fileName: string) =
        // Get the slot of the given file and force it to build.
        let CompareFileNames f =
            let result =
                   String.Compare(fileName, f.Source.FilePath, StringComparison.CurrentCultureIgnoreCase)=0
                || String.Compare(FileSystem.GetFullPathShim fileName, FileSystem.GetFullPathShim f.Source.FilePath, StringComparison.CurrentCultureIgnoreCase)=0
            result
        match fileNames |> List.tryFindIndex CompareFileNames with
        | Some slot -> Some slot
        | None -> None

    member builder.GetSlotOfFileName(fileName: string) =
        match builder.TryGetSlotOfFileName(fileName) with
        | Some slot -> slot
        | None -> failwith (sprintf "The file '%s' was not part of the project. Did you call InvalidateConfiguration when the list of files in the project changed?" fileName)

    member _.GetSlotsCount () = fileNames.Length

    member builder.ContainsFile(fileName: string) =
        (builder.TryGetSlotOfFileName fileName).IsSome

    member builder.GetParseResultsForFile fileName =
        let slotOfFile = builder.GetSlotOfFileName fileName
        let syntaxTree = currentState.slots[slotOfFile].SyntaxTree
        syntaxTree.ParseNode.GetOrComputeValue()
        |> Async.RunSynchronously

    member builder.NotifyFileChanged(fileName, timeStamp) =
        async {
            let slotOfFile = builder.GetSlotOfFileName fileName        
            let cache = TimeStampCache defaultTimeStamp
            let! ct = Async.CancellationToken
            do! setCurrentState
                    { currentState with 
                        slots = currentState.slots |> List.updateAt slotOfFile (currentState.slots[slotOfFile].Notify timeStamp) }
                    cache ct
        }

    member _.SourceFiles = fileNames |> Seq.map (fun f -> f.Source.FilePath) |> List.ofSeq

    /// CreateIncrementalBuilder (for background type checking). Note that fsc.fs also
    /// creates an incremental builder used by the command line compiler.
    static member TryCreateIncrementalBuilderForProjectOptions
        (
            legacyReferenceResolver,
            defaultFSharpBinariesDir,
            frameworkTcImportsCache: FrameworkImportsCache,
            loadClosureOpt: LoadClosure option,
            sourceFiles: string list,
            commandLineArgs: string list,
            projectReferences,
            projectDirectory,
            useScriptResolutionRules,
            keepAssemblyContents,
            keepAllBackgroundResolutions,
            tryGetMetadataSnapshot,
            suggestNamesForErrors,
            keepAllBackgroundSymbolUses,
            enableBackgroundItemKeyStoreAndSemanticClassification,
            enablePartialTypeChecking,
            dependencyProvider,
            parallelReferenceResolution,
            captureIdentifiersWhenParsing,
            getSource,
            useChangeNotifications,
            useSyntaxTreeCache
        ) =

      let useSimpleResolutionSwitch = "--simpleresolution"

      async {

        // Trap and report diagnostics from creation.
        let delayedLogger = CapturingDiagnosticsLogger("IncrementalBuilderCreation")
        use _ = new CompilationGlobalsScope(delayedLogger, BuildPhase.Parameter)

        let! builderOpt =
         async {
          try

            // Create the builder.
            // Share intern'd strings across all lexing/parsing
            let resourceManager = Lexhelp.LexResourceManager()

            /// Create a type-check configuration
            let tcConfigB, sourceFiles =

                let getSwitchValue switchString =
                    match commandLineArgs |> List.tryFindIndex(fun s -> s.StartsWithOrdinal switchString) with
                    | Some idx -> Some(commandLineArgs[idx].Substring(switchString.Length))
                    | _ -> None

                let sdkDirOverride =
                    match loadClosureOpt with
                    | None -> None
                    | Some loadClosure -> loadClosure.SdkDirOverride

                // see also fsc.fs: runFromCommandLineToImportingAssemblies(), as there are many similarities to where the PS creates a tcConfigB
                let tcConfigB =
                    TcConfigBuilder.CreateNew(legacyReferenceResolver,
                         defaultFSharpBinariesDir,
                         implicitIncludeDir=projectDirectory,
                         reduceMemoryUsage=ReduceMemoryFlag.Yes,
                         isInteractive=useScriptResolutionRules,
                         isInvalidationSupported=true,
                         defaultCopyFSharpCore=CopyFSharpCoreFlag.No,
                         tryGetMetadataSnapshot=tryGetMetadataSnapshot,
                         sdkDirOverride=sdkDirOverride,
                         rangeForErrors=range0)

                tcConfigB.primaryAssembly <-
                    match loadClosureOpt with
                    | None -> PrimaryAssembly.Mscorlib
                    | Some loadClosure ->
                        if loadClosure.UseDesktopFramework then
                            PrimaryAssembly.Mscorlib
                        else
                            PrimaryAssembly.System_Runtime

                tcConfigB.resolutionEnvironment <- (LegacyResolutionEnvironment.EditingOrCompilation true)

                tcConfigB.conditionalDefines <-
                    let define = if useScriptResolutionRules then "INTERACTIVE" else "COMPILED"
                    define :: tcConfigB.conditionalDefines

                tcConfigB.projectReferences <- projectReferences

                tcConfigB.useSimpleResolution <- (getSwitchValue useSimpleResolutionSwitch) |> Option.isSome

                tcConfigB.realsig <- List.contains "--realsig" commandLineArgs || List.contains "--realsig+" commandLineArgs

                // Apply command-line arguments and collect more source files if they are in the arguments
                let sourceFilesNew = ApplyCommandLineArgs(tcConfigB, sourceFiles, commandLineArgs)

                // Never open PDB files for the language service, even if --standalone is specified
                tcConfigB.openDebugInformationForLaterStaticLinking <- false

                tcConfigB.xmlDocInfoLoader <-
                    { new IXmlDocumentationInfoLoader with
                        /// Try to load xml documentation associated with an assembly by the same file path with the extension ".xml".
                        member _.TryLoad(assemblyFileName) =
                            let xmlFileName = !! Path.ChangeExtension(assemblyFileName, ".xml")

                            // REVIEW: File IO - Will eventually need to change this to use a file system interface of some sort.
                            XmlDocumentationInfo.TryCreateFromFile(xmlFileName)
                    }
                    |> Some

                tcConfigB.parallelReferenceResolution <- parallelReferenceResolution
                tcConfigB.captureIdentifiersWhenParsing <- captureIdentifiersWhenParsing

                tcConfigB, sourceFilesNew

            // If this is a builder for a script, re-apply the settings inferred from the
            // script and its load closure to the configuration.
            //
            // NOTE: it would probably be cleaner and more accurate to re-run the load closure at this point.
            let setupConfigFromLoadClosure () =
                match loadClosureOpt with
                | Some loadClosure ->
                    let dllReferences =
                        [for reference in tcConfigB.referencedDLLs do
                            // If there's (one or more) resolutions of closure references then yield them all
                            match loadClosure.References  |> List.tryFind (fun (resolved, _)->resolved=reference.Text) with
                            | Some (resolved, closureReferences) ->
                                for closureReference in closureReferences do
                                    yield AssemblyReference(closureReference.originalReference.Range, resolved, None)
                            | None -> yield reference]
                    tcConfigB.referencedDLLs <- []
                    tcConfigB.primaryAssembly <- (if loadClosure.UseDesktopFramework then PrimaryAssembly.Mscorlib else PrimaryAssembly.System_Runtime)
                    // Add one by one to remove duplicates
                    dllReferences |> List.iter (fun dllReference ->
                        tcConfigB.AddReferencedAssemblyByPath(dllReference.Range, dllReference.Text))
                    tcConfigB.knownUnresolvedReferences <- loadClosure.UnresolvedReferences
                | None -> ()

            setupConfigFromLoadClosure()

            let tcConfig = TcConfig.Create(tcConfigB, validate=true)
            let outfile, _, assemblyName = tcConfigB.DecideNames sourceFiles

            // Resolve assemblies and create the framework TcImports. This is done when constructing the
            // builder itself, rather than as an incremental task. This caches a level of "system" references. No type providers are
            // included in these references.
            let! tcGlobals, frameworkTcImports, nonFrameworkResolutions, unresolvedReferences = frameworkTcImportsCache.Get(tcConfig)

            // Note we are not calling diagnosticsLogger.GetDiagnostics() anywhere for this task.
            // This is ok because not much can actually go wrong here.
            let diagnosticsLogger = CompilationDiagnosticLogger("nonFrameworkAssemblyInputs", tcConfig.diagnosticsOptions)
            use _ = new CompilationGlobalsScope(diagnosticsLogger, BuildPhase.Parameter)

            // Get the names and time stamps of all the non-framework referenced assemblies, which will act
            // as inputs to one of the nodes in the build.
            //
            // This operation is done when constructing the builder itself, rather than as an incremental task.
            let nonFrameworkAssemblyInputs =
                // Note we are not calling diagnosticsLogger.GetDiagnostics() anywhere for this task.
                // This is ok because not much can actually go wrong here.
                let diagnosticsLogger = CompilationDiagnosticLogger("nonFrameworkAssemblyInputs", tcConfig.diagnosticsOptions)
                // Return the disposable object that cleans up
                use _holder = new CompilationGlobalsScope(diagnosticsLogger, BuildPhase.Parameter)

                [ for r in nonFrameworkResolutions do
                    let fileName = r.resolvedPath
                    yield (Choice1Of2 fileName, (fun (cache: TimeStampCache) -> cache.GetFileTimeStamp fileName))

                  for pr in projectReferences  do
                    yield Choice2Of2 pr, (fun (cache: TimeStampCache) -> cache.GetProjectReferenceTimeStamp pr) ]

            // Start importing

            let tcConfigP = TcConfigProvider.Constant tcConfig
            let beforeFileChecked = Event<string>()
            let fileChecked = Event<string>()

#if !NO_TYPEPROVIDERS
            let importsInvalidatedByTypeProvider = Event<unit>()
#endif

            // Check for the existence of loaded sources and prepend them to the sources list if present.
            let sourceFiles = tcConfig.GetAvailableLoadedSources() @ (sourceFiles |>List.map (fun s -> rangeStartup, s))

            // Mark up the source files with an indicator flag indicating if they are the last source file in the project
            let sourceFiles =
                let flags, isExe = tcConfig.ComputeCanContainEntryPoint(sourceFiles |> List.map snd)
                ((sourceFiles, flags) ||> List.map2 (fun (m, nm) flag -> (m, nm, (flag, isExe))))

            let basicDependencies =
                [ for UnresolvedAssemblyReference(referenceText, _)  in unresolvedReferences do
                    // Exclude things that are definitely not a file name
                    if not(FileSystem.IsInvalidPathShim referenceText) then
                        let file = if FileSystem.IsPathRootedShim referenceText then referenceText else Path.Combine(projectDirectory, referenceText)
                        yield file

                  for r in nonFrameworkResolutions do
                        yield  r.resolvedPath  ]

            let allDependencies =
                [| yield! basicDependencies
                   for _, f, _ in sourceFiles do
                        yield f |]

            // For scripts, the dependency provider is already available.
            // For projects create a fresh one for the project.
            let dependencyProvider =
                match dependencyProvider with
                | None -> new DependencyProvider()
                | Some dependencyProvider -> dependencyProvider

            let defaultTimeStamp = DateTime.UtcNow

            let! initialBoundModel, initialErrors = 
                CombineImportedAssembliesTask(
                    assemblyName,
                    tcConfig,
                    tcConfigP,
                    tcGlobals,
                    frameworkTcImports,
                    nonFrameworkResolutions,
                    unresolvedReferences,
                    dependencyProvider,
                    loadClosureOpt,
                    basicDependencies,
                    keepAssemblyContents,
                    keepAllBackgroundResolutions,
                    keepAllBackgroundSymbolUses,
                    enableBackgroundItemKeyStoreAndSemanticClassification,
                    beforeFileChecked,
                    fileChecked
#if !NO_TYPEPROVIDERS
                    ,importsInvalidatedByTypeProvider
#endif
                )

            let getFSharpSource fileName =
                getSource
                |> Option.map(fun getSource ->
                    let timeStamp = DateTime.UtcNow
                    let getTimeStamp = fun () -> timeStamp
                    let getSourceText() = getSource fileName
                    FSharpSource.Create(fileName, getTimeStamp, getSourceText))
                |> Option.defaultWith(fun () -> FSharpSource.CreateFromFile(fileName))

            let sourceFiles =
                sourceFiles
                |> List.map (fun (m, fileName, isLastCompiland) ->
                    { Range = m; Source = getFSharpSource fileName; Flags = isLastCompiland } )

            let initialState =
                IncrementalBuilderInitialState.Create(
                    initialBoundModel,
                    initialErrors,
                    tcGlobals,
                    nonFrameworkAssemblyInputs,
                    tcConfig,
                    outfile,
                    assemblyName,
                    resourceManager,
                    sourceFiles,
                    enablePartialTypeChecking,
                    beforeFileChecked,
                    fileChecked,
#if !NO_TYPEPROVIDERS
                    importsInvalidatedByTypeProvider,
#endif
                    allDependencies,
                    defaultTimeStamp,
                    useChangeNotifications,
                    useSyntaxTreeCache
                )

            let builder = IncrementalBuilder(initialState, IncrementalBuilderState.Create(initialState))
            return Some builder
          with exn ->
            errorRecoveryNoRange exn
            return None
         }

        let diagnostics =
            let diagnostics, flatErrors =
                match builderOpt with
                | Some builder ->
                    let diagnosticsOptions = builder.TcConfig.diagnosticsOptions
                    let diagnosticsLogger = CompilationDiagnosticLogger("IncrementalBuilderCreation", diagnosticsOptions)
                    delayedLogger.CommitDelayedDiagnostics diagnosticsLogger
                    diagnosticsLogger.GetDiagnostics(), builder.TcConfig.flatErrors
                | _ ->
                    Array.ofList delayedLogger.Diagnostics, false
            diagnostics
            |> Array.map (fun (diagnostic, severity) ->
                FSharpDiagnostic.CreateFromException(diagnostic, severity, range.Zero, suggestNamesForErrors, flatErrors, None))

        return builderOpt, diagnostics
      }
