LanguageFeatures.fs

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

/// Coordinating compiler operations - configuration, loading initial context, reporting errors etc.
module internal FSharp.Compiler.Features

//------------------------------------------------------------------------------------------------------------------
// Language version command line switch
//------------------------------------------------------------------------------------------------------------------
// Add your features to this List - in code use languageVersion.SupportsFeature(LanguageFeatures.yourFeature)
// a return value of false means your feature is not supported by the user's language selection
// All new language features added from now on must be protected by this.
// Note:
//   *  The fslang design process will require a decision about feature name and whether it is required.
//   *  When a feature is assigned a release language, we will scrub the code of feature references and apply
//      the Release Language version.

[<RequireQualifiedAccess>]
type LanguageFeature =
    | SingleUnderscorePattern
    | WildCardInForLoop
    | RelaxWhitespace
    | RelaxWhitespace2
    | StrictIndentation
    | NameOf
    | ImplicitYield
    | OpenTypeDeclaration
    | DotlessFloat32Literal
    | PackageManagement
    | FromEndSlicing
    | FixedIndexSlice3d4d
    | AndBang
    | ResumableStateMachines
    | NullableOptionalInterop
    | DefaultInterfaceMemberConsumption
    | WitnessPassing
    | AdditionalTypeDirectedConversions
    | InterfacesWithMultipleGenericInstantiation
    | StringInterpolation
    | OverloadsForCustomOperations
    | ExpandedMeasurables
    | NullnessChecking
    | StructActivePattern
    | PrintfBinaryFormat
    | IndexerNotationWithoutDot
    | RefCellNotationInformationals
    | UseBindingValueDiscard
    | UnionIsPropertiesVisible
    | NonVariablePatternsToRightOfAsPatterns
    | AttributesToRightOfModuleKeyword
    | BetterExceptionPrinting
    | DelegateTypeNameResolutionFix
    | ReallyLongLists
    | ErrorOnDeprecatedRequireQualifiedAccess
    | RequiredPropertiesSupport
    | InitPropertiesSupport
    | LowercaseDUWhenRequireQualifiedAccess
    | InterfacesWithAbstractStaticMembers
    | SelfTypeConstraints
    | AccessorFunctionShorthand
    | MatchNotAllowedForUnionCaseWithNoData
    | CSharpExtensionAttributeNotRequired
    | ErrorForNonVirtualMembersOverrides
    | WarningWhenInliningMethodImplNoInlineMarkedFunction
    | EscapeDotnetFormattableStrings
    | ArithmeticInLiterals
    | ErrorReportingOnStaticClasses
    | TryWithInSeqExpression
    | WarningWhenCopyAndUpdateRecordChangesAllFields
    | StaticMembersInInterfaces
    | NonInlineLiteralsAsPrintfFormat
    | NestedCopyAndUpdate
    | ExtendedStringInterpolation
    | WarningWhenMultipleRecdTypeChoice
    | ImprovedImpliedArgumentNames
    | DiagnosticForObjInference
    | ConstraintIntersectionOnFlexibleTypes
    | StaticLetInRecordsDusEmptyTypes
    | WarningWhenTailRecAttributeButNonTailRecUsage
    | UnmanagedConstraintCsharpInterop
    | WhileBang
    | ReuseSameFieldsInStructUnions
    | ExtendedFixedBindings
    | PreferStringGetPinnableReference
    | PreferExtensionMethodOverPlainProperty
    | WarningIndexedPropertiesGetSetSameType
    | WarningWhenTailCallAttrOnNonRec
    | BooleanReturningAndReturnTypeDirectedPartialActivePattern
    | EnforceAttributeTargets
    | LowerInterpolatedStringToConcat
    | LowerIntegralRangesToFastLoops
    | AllowAccessModifiersToAutoPropertiesGettersAndSetters
    | LowerSimpleMappingsInComprehensionsToFastLoops
    | ParsedHashDirectiveArgumentNonQuotes
    | EmptyBodiedComputationExpressions
    | AllowObjectExpressionWithoutOverrides
    | DontWarnOnUppercaseIdentifiersInBindingPatterns
    | UseTypeSubsumptionCache
    | DeprecatePlacesWhereSeqCanBeOmitted
    | SupportValueOptionsAsOptionalParameters
    | WarnWhenUnitPassedToObjArg
    | UseBangBindingValueDiscard
    | BetterAnonymousRecordParsing
    | ScopedNowarn
    | ErrorOnInvalidDeclsInTypeDefinitions
    | AllowTypedLetUseAndBang
    | ReturnFromFinal
    | WarnWhenFunctionValueUsedAsInterpolatedStringArg
    | MethodOverloadsCache
    | ImplicitDIMCoverage
    | PreprocessorElif
    | WarnOnLetInSequenceExpression

/// LanguageVersion management
type LanguageVersion(versionText, ?disabledFeaturesArray: LanguageFeature array) =

    // When we increment language versions here preview is higher than current RTM version
    static let languageVersion46 = 4.6m
    static let languageVersion47 = 4.7m
    static let languageVersion50 = 5.0m
    static let languageVersion60 = 6.0m
    static let languageVersion70 = 7.0m
    static let languageVersion80 = 8.0m
    static let languageVersion90 = 9.0m
    static let languageVersion100 = 10.0m
    static let languageVersion110 = 11.0m
    static let previewVersion = 9999m // Language version when preview specified
    static let defaultVersion = languageVersion100 // Language version when default specified
    static let latestVersion = defaultVersion // Language version when latest specified
    static let latestMajorVersion = defaultVersion // Language version when latestmajor specified

    static let validOptions = [| "preview"; "default"; "latest"; "latestmajor" |]

    static let languageVersions =
        set
            [|
                languageVersion46
                languageVersion47
                languageVersion50
                languageVersion60
                languageVersion70
                languageVersion80
                languageVersion90
                languageVersion100
                languageVersion110
            |]

    static let features =
        dict
            [
                // F# 4.7
                LanguageFeature.SingleUnderscorePattern, languageVersion47
                LanguageFeature.WildCardInForLoop, languageVersion47
                LanguageFeature.RelaxWhitespace, languageVersion47
                LanguageFeature.ImplicitYield, languageVersion47

                // F# 5.0
                LanguageFeature.FixedIndexSlice3d4d, languageVersion50
                LanguageFeature.DotlessFloat32Literal, languageVersion50
                LanguageFeature.AndBang, languageVersion50
                LanguageFeature.NullableOptionalInterop, languageVersion50
                LanguageFeature.DefaultInterfaceMemberConsumption, languageVersion50
                LanguageFeature.OpenTypeDeclaration, languageVersion50
                LanguageFeature.PackageManagement, languageVersion50
                LanguageFeature.WitnessPassing, languageVersion50
                LanguageFeature.InterfacesWithMultipleGenericInstantiation, languageVersion50
                LanguageFeature.NameOf, languageVersion50
                LanguageFeature.StringInterpolation, languageVersion50

                // F# 6.0
                LanguageFeature.AdditionalTypeDirectedConversions, languageVersion60
                LanguageFeature.RelaxWhitespace2, languageVersion60
                LanguageFeature.OverloadsForCustomOperations, languageVersion60
                LanguageFeature.ExpandedMeasurables, languageVersion60
                LanguageFeature.ResumableStateMachines, languageVersion60
                LanguageFeature.StructActivePattern, languageVersion60
                LanguageFeature.PrintfBinaryFormat, languageVersion60
                LanguageFeature.IndexerNotationWithoutDot, languageVersion60
                LanguageFeature.RefCellNotationInformationals, languageVersion60
                LanguageFeature.UseBindingValueDiscard, languageVersion60
                LanguageFeature.NonVariablePatternsToRightOfAsPatterns, languageVersion60
                LanguageFeature.AttributesToRightOfModuleKeyword, languageVersion60
                LanguageFeature.DelegateTypeNameResolutionFix, languageVersion60

                // F# 7.0
                LanguageFeature.BetterExceptionPrinting, languageVersion70
                LanguageFeature.ReallyLongLists, languageVersion70
                LanguageFeature.ErrorOnDeprecatedRequireQualifiedAccess, languageVersion70
                LanguageFeature.RequiredPropertiesSupport, languageVersion70
                LanguageFeature.InitPropertiesSupport, languageVersion70
                LanguageFeature.LowercaseDUWhenRequireQualifiedAccess, languageVersion70
                LanguageFeature.InterfacesWithAbstractStaticMembers, languageVersion70
                LanguageFeature.SelfTypeConstraints, languageVersion70

                // F# 8.0
                LanguageFeature.AccessorFunctionShorthand, languageVersion80
                LanguageFeature.MatchNotAllowedForUnionCaseWithNoData, languageVersion80
                LanguageFeature.CSharpExtensionAttributeNotRequired, languageVersion80
                LanguageFeature.ErrorForNonVirtualMembersOverrides, languageVersion80
                LanguageFeature.WarningWhenInliningMethodImplNoInlineMarkedFunction, languageVersion80
                LanguageFeature.EscapeDotnetFormattableStrings, languageVersion80
                LanguageFeature.ArithmeticInLiterals, languageVersion80
                LanguageFeature.ErrorReportingOnStaticClasses, languageVersion80
                LanguageFeature.TryWithInSeqExpression, languageVersion80
                LanguageFeature.WarningWhenCopyAndUpdateRecordChangesAllFields, languageVersion80
                LanguageFeature.StaticMembersInInterfaces, languageVersion80
                LanguageFeature.NonInlineLiteralsAsPrintfFormat, languageVersion80
                LanguageFeature.NestedCopyAndUpdate, languageVersion80
                LanguageFeature.ExtendedStringInterpolation, languageVersion80
                LanguageFeature.WarningWhenMultipleRecdTypeChoice, languageVersion80
                LanguageFeature.ImprovedImpliedArgumentNames, languageVersion80
                LanguageFeature.DiagnosticForObjInference, languageVersion80
                LanguageFeature.WarningWhenTailRecAttributeButNonTailRecUsage, languageVersion80
                LanguageFeature.StaticLetInRecordsDusEmptyTypes, languageVersion80
                LanguageFeature.StrictIndentation, languageVersion80
                LanguageFeature.ConstraintIntersectionOnFlexibleTypes, languageVersion80
                LanguageFeature.WhileBang, languageVersion80
                LanguageFeature.ExtendedFixedBindings, languageVersion80
                LanguageFeature.PreferStringGetPinnableReference, languageVersion80

                // F# 9.0
                LanguageFeature.NullnessChecking, languageVersion90
                LanguageFeature.ReuseSameFieldsInStructUnions, languageVersion90
                LanguageFeature.PreferExtensionMethodOverPlainProperty, languageVersion90
                LanguageFeature.WarningIndexedPropertiesGetSetSameType, languageVersion90
                LanguageFeature.WarningWhenTailCallAttrOnNonRec, languageVersion90
                LanguageFeature.UnionIsPropertiesVisible, languageVersion90
                LanguageFeature.BooleanReturningAndReturnTypeDirectedPartialActivePattern, languageVersion90
                LanguageFeature.LowerInterpolatedStringToConcat, languageVersion90
                LanguageFeature.LowerIntegralRangesToFastLoops, languageVersion90
                LanguageFeature.LowerSimpleMappingsInComprehensionsToFastLoops, languageVersion90
                LanguageFeature.ParsedHashDirectiveArgumentNonQuotes, languageVersion90
                LanguageFeature.EmptyBodiedComputationExpressions, languageVersion90

                // F# 10.0
                LanguageFeature.EnforceAttributeTargets, languageVersion100
                LanguageFeature.UseTypeSubsumptionCache, languageVersion100
                LanguageFeature.AllowObjectExpressionWithoutOverrides, languageVersion100
                LanguageFeature.DontWarnOnUppercaseIdentifiersInBindingPatterns, languageVersion100
                LanguageFeature.DeprecatePlacesWhereSeqCanBeOmitted, languageVersion100
                LanguageFeature.SupportValueOptionsAsOptionalParameters, languageVersion100
                LanguageFeature.WarnWhenUnitPassedToObjArg, languageVersion100
                LanguageFeature.UseBangBindingValueDiscard, languageVersion100
                LanguageFeature.BetterAnonymousRecordParsing, languageVersion100
                LanguageFeature.ScopedNowarn, languageVersion100
                LanguageFeature.AllowTypedLetUseAndBang, languageVersion100
                LanguageFeature.UnmanagedConstraintCsharpInterop, languageVersion100
                LanguageFeature.AllowAccessModifiersToAutoPropertiesGettersAndSetters, languageVersion100
                LanguageFeature.ReturnFromFinal, languageVersion100
                LanguageFeature.ErrorOnInvalidDeclsInTypeDefinitions, languageVersion100

                // F# 11.0
                // Put stabilized features here for F# 11.0 previews via .NET SDK preview channels
                LanguageFeature.WarnWhenFunctionValueUsedAsInterpolatedStringArg, languageVersion110
                LanguageFeature.PreprocessorElif, languageVersion110
                LanguageFeature.WarnOnLetInSequenceExpression, languageVersion110

                // Difference between languageVersion110 and preview - 11.0 gets turned on automatically by picking a preview .NET 11 SDK
                // previewVersion is only when "preview" is specified explicitly in project files  and users also need a preview SDK

                // F# preview (still preview in 10.0)
                LanguageFeature.FromEndSlicing, previewVersion // Unfinished features --- needs work
                LanguageFeature.MethodOverloadsCache, previewVersion // Performance optimization for overload resolution
                LanguageFeature.ImplicitDIMCoverage, languageVersion110
            ]

    static let defaultLanguageVersion = LanguageVersion("default")

    static let getVersionFromString (version: string) =
        match version.ToUpperInvariant() with
        | "?" -> 0m
        | "PREVIEW" -> previewVersion
        | "DEFAULT" -> defaultVersion
        | "LATEST" -> latestVersion
        | "LATESTMAJOR" -> latestMajorVersion
        | "4.6" -> languageVersion46
        | "4.7" -> languageVersion47
        | "5.0"
        | "5" -> languageVersion50
        | "6.0"
        | "6" -> languageVersion60
        | "7.0"
        | "7" -> languageVersion70
        | "8.0"
        | "8" -> languageVersion80
        | "9.0"
        | "9" -> languageVersion90
        | "10.0"
        | "10" -> languageVersion100
        | "11.0"
        | "11" -> languageVersion110
        | _ -> 0m

    let specified = getVersionFromString versionText

    static let versionToString v =
        if v = previewVersion then "'PREVIEW'" else string v

    let specifiedString = versionToString specified

    let disabledFeatures: LanguageFeature array = defaultArg disabledFeaturesArray [||]

    /// Get the disabled features
    member _.DisabledFeatures = disabledFeatures

    /// Check if this feature is supported by the selected langversion
    member _.SupportsFeature featureId =
        if Array.contains featureId disabledFeatures then
            false
        else
            match features.TryGetValue featureId with
            | true, v -> v <= specified
            | false, _ -> false

    /// Create a new LanguageVersion with updated disabled features
    member _.WithDisabledFeatures(disabled: LanguageFeature array) = LanguageVersion(versionText, disabled)

    /// Has preview been explicitly specified
    member _.IsExplicitlySpecifiedAs50OrBefore() =
        let v = getVersionFromString versionText
        v <> 0.0m && v <= 5.0m

    /// Has preview been explicitly specified
    member _.IsPreviewEnabled = specified = previewVersion

    /// Is the selected LanguageVersion valid
    static member ContainsVersion version =
        let langVersion = getVersionFromString version
        langVersion <> 0m && languageVersions.Contains langVersion

    /// Is the selected LanguageVersion currently supported
    static member IsVersionSupported version =
        let langVersion = getVersionFromString version

        langVersion >= languageVersion80
        || System.Environment.GetEnvironmentVariable("SKIP_VERSION_SUPPORTED_CHECK") = "1"

    /// Get a list of valid strings for help text
    static member ValidOptions = validOptions

    /// Get a list of valid versions for help text
    static member ValidVersions =
        [|
            for v in languageVersions |> Seq.sort -> sprintf "%M%s" v (if v = defaultVersion then " (Default)" else "")
        |]

    /// Get the text used to specify the version
    member _.VersionText = versionText

    /// Get the specified LanguageVersion
    member _.SpecifiedVersion = specified

    /// Get the specified LanguageVersion as a string
    member _.SpecifiedVersionString = specifiedString

    /// Get a string name for the given feature.
    static member GetFeatureString feature =
        match feature with
        | LanguageFeature.SingleUnderscorePattern -> FSComp.SR.featureSingleUnderscorePattern ()
        | LanguageFeature.WildCardInForLoop -> FSComp.SR.featureWildCardInForLoop ()
        | LanguageFeature.RelaxWhitespace -> FSComp.SR.featureRelaxWhitespace ()
        | LanguageFeature.RelaxWhitespace2 -> FSComp.SR.featureRelaxWhitespace2 ()
        | LanguageFeature.NameOf -> FSComp.SR.featureNameOf ()
        | LanguageFeature.ImplicitYield -> FSComp.SR.featureImplicitYield ()
        | LanguageFeature.OpenTypeDeclaration -> FSComp.SR.featureOpenTypeDeclaration ()
        | LanguageFeature.DotlessFloat32Literal -> FSComp.SR.featureDotlessFloat32Literal ()
        | LanguageFeature.PackageManagement -> FSComp.SR.featurePackageManagement ()
        | LanguageFeature.FromEndSlicing -> FSComp.SR.featureFromEndSlicing ()
        | LanguageFeature.FixedIndexSlice3d4d -> FSComp.SR.featureFixedIndexSlice3d4d ()
        | LanguageFeature.AndBang -> FSComp.SR.featureAndBang ()
        | LanguageFeature.NullnessChecking -> FSComp.SR.featureNullnessChecking ()
        | LanguageFeature.ResumableStateMachines -> FSComp.SR.featureResumableStateMachines ()
        | LanguageFeature.NullableOptionalInterop -> FSComp.SR.featureNullableOptionalInterop ()
        | LanguageFeature.DefaultInterfaceMemberConsumption -> FSComp.SR.featureDefaultInterfaceMemberConsumption ()
        | LanguageFeature.WitnessPassing -> FSComp.SR.featureWitnessPassing ()
        | LanguageFeature.AdditionalTypeDirectedConversions -> FSComp.SR.featureAdditionalImplicitConversions ()
        | LanguageFeature.InterfacesWithMultipleGenericInstantiation -> FSComp.SR.featureInterfacesWithMultipleGenericInstantiation ()
        | LanguageFeature.StringInterpolation -> FSComp.SR.featureStringInterpolation ()
        | LanguageFeature.OverloadsForCustomOperations -> FSComp.SR.featureOverloadsForCustomOperations ()
        | LanguageFeature.ExpandedMeasurables -> FSComp.SR.featureExpandedMeasurables ()
        | LanguageFeature.StructActivePattern -> FSComp.SR.featureStructActivePattern ()
        | LanguageFeature.PrintfBinaryFormat -> FSComp.SR.featurePrintfBinaryFormat ()
        | LanguageFeature.IndexerNotationWithoutDot -> FSComp.SR.featureIndexerNotationWithoutDot ()
        | LanguageFeature.RefCellNotationInformationals -> FSComp.SR.featureRefCellNotationInformationals ()
        | LanguageFeature.UseBindingValueDiscard -> FSComp.SR.featureDiscardUseValue ()
        | LanguageFeature.UnionIsPropertiesVisible -> FSComp.SR.featureUnionIsPropertiesVisible ()
        | LanguageFeature.NonVariablePatternsToRightOfAsPatterns -> FSComp.SR.featureNonVariablePatternsToRightOfAsPatterns ()
        | LanguageFeature.AttributesToRightOfModuleKeyword -> FSComp.SR.featureAttributesToRightOfModuleKeyword ()
        | LanguageFeature.BetterExceptionPrinting -> FSComp.SR.featureBetterExceptionPrinting ()
        | LanguageFeature.DelegateTypeNameResolutionFix -> FSComp.SR.featureDelegateTypeNameResolutionFix ()
        | LanguageFeature.ReallyLongLists -> FSComp.SR.featureReallyLongList ()
        | LanguageFeature.ErrorOnDeprecatedRequireQualifiedAccess -> FSComp.SR.featureErrorOnDeprecatedRequireQualifiedAccess ()
        | LanguageFeature.RequiredPropertiesSupport -> FSComp.SR.featureRequiredProperties ()
        | LanguageFeature.InitPropertiesSupport -> FSComp.SR.featureInitProperties ()
        | LanguageFeature.LowercaseDUWhenRequireQualifiedAccess -> FSComp.SR.featureLowercaseDUWhenRequireQualifiedAccess ()
        | LanguageFeature.InterfacesWithAbstractStaticMembers -> FSComp.SR.featureInterfacesWithAbstractStaticMembers ()
        | LanguageFeature.SelfTypeConstraints -> FSComp.SR.featureSelfTypeConstraints ()
        | LanguageFeature.AccessorFunctionShorthand -> FSComp.SR.featureAccessorFunctionShorthand ()
        | LanguageFeature.MatchNotAllowedForUnionCaseWithNoData -> FSComp.SR.featureMatchNotAllowedForUnionCaseWithNoData ()
        | LanguageFeature.CSharpExtensionAttributeNotRequired -> FSComp.SR.featureCSharpExtensionAttributeNotRequired ()
        | LanguageFeature.ErrorForNonVirtualMembersOverrides -> FSComp.SR.featureErrorForNonVirtualMembersOverrides ()
        | LanguageFeature.WarningWhenInliningMethodImplNoInlineMarkedFunction ->
            FSComp.SR.featureWarningWhenInliningMethodImplNoInlineMarkedFunction ()
        | LanguageFeature.EscapeDotnetFormattableStrings -> FSComp.SR.featureEscapeBracesInFormattableString ()
        | LanguageFeature.ArithmeticInLiterals -> FSComp.SR.featureArithmeticInLiterals ()
        | LanguageFeature.ErrorReportingOnStaticClasses -> FSComp.SR.featureErrorReportingOnStaticClasses ()
        | LanguageFeature.TryWithInSeqExpression -> FSComp.SR.featureTryWithInSeqExpressions ()
        | LanguageFeature.WarningWhenCopyAndUpdateRecordChangesAllFields ->
            FSComp.SR.featureWarningWhenCopyAndUpdateRecordChangesAllFields ()
        | LanguageFeature.StaticMembersInInterfaces -> FSComp.SR.featureStaticMembersInInterfaces ()
        | LanguageFeature.NonInlineLiteralsAsPrintfFormat -> FSComp.SR.featureNonInlineLiteralsAsPrintfFormat ()
        | LanguageFeature.NestedCopyAndUpdate -> FSComp.SR.featureNestedCopyAndUpdate ()
        | LanguageFeature.ExtendedStringInterpolation -> FSComp.SR.featureExtendedStringInterpolation ()
        | LanguageFeature.WarningWhenMultipleRecdTypeChoice -> FSComp.SR.featureWarningWhenMultipleRecdTypeChoice ()
        | LanguageFeature.ImprovedImpliedArgumentNames -> FSComp.SR.featureImprovedImpliedArgumentNames ()
        | LanguageFeature.DiagnosticForObjInference -> FSComp.SR.featureInformationalObjInferenceDiagnostic ()

        | LanguageFeature.StaticLetInRecordsDusEmptyTypes -> FSComp.SR.featureStaticLetInRecordsDusEmptyTypes ()
        | LanguageFeature.StrictIndentation -> FSComp.SR.featureStrictIndentation ()
        | LanguageFeature.ConstraintIntersectionOnFlexibleTypes -> FSComp.SR.featureConstraintIntersectionOnFlexibleTypes ()
        | LanguageFeature.WarningWhenTailRecAttributeButNonTailRecUsage -> FSComp.SR.featureChkNotTailRecursive ()
        | LanguageFeature.UnmanagedConstraintCsharpInterop -> FSComp.SR.featureUnmanagedConstraintCsharpInterop ()
        | LanguageFeature.WhileBang -> FSComp.SR.featureWhileBang ()
        | LanguageFeature.ReuseSameFieldsInStructUnions -> FSComp.SR.featureReuseSameFieldsInStructUnions ()
        | LanguageFeature.ExtendedFixedBindings -> FSComp.SR.featureExtendedFixedBindings ()
        | LanguageFeature.PreferStringGetPinnableReference -> FSComp.SR.featurePreferStringGetPinnableReference ()
        | LanguageFeature.PreferExtensionMethodOverPlainProperty -> FSComp.SR.featurePreferExtensionMethodOverPlainProperty ()
        | LanguageFeature.WarningIndexedPropertiesGetSetSameType -> FSComp.SR.featureWarningIndexedPropertiesGetSetSameType ()
        | LanguageFeature.WarningWhenTailCallAttrOnNonRec -> FSComp.SR.featureChkTailCallAttrOnNonRec ()
        | LanguageFeature.BooleanReturningAndReturnTypeDirectedPartialActivePattern ->
            FSComp.SR.featureBooleanReturningAndReturnTypeDirectedPartialActivePattern ()
        | LanguageFeature.EnforceAttributeTargets -> FSComp.SR.featureEnforceAttributeTargets ()
        | LanguageFeature.LowerInterpolatedStringToConcat -> FSComp.SR.featureLowerInterpolatedStringToConcat ()
        | LanguageFeature.LowerIntegralRangesToFastLoops -> FSComp.SR.featureLowerIntegralRangesToFastLoops ()
        | LanguageFeature.AllowAccessModifiersToAutoPropertiesGettersAndSetters ->
            FSComp.SR.featureAllowAccessModifiersToAutoPropertiesGettersAndSetters ()
        | LanguageFeature.LowerSimpleMappingsInComprehensionsToFastLoops ->
            FSComp.SR.featureLowerSimpleMappingsInComprehensionsToFastLoops ()
        | LanguageFeature.ParsedHashDirectiveArgumentNonQuotes -> FSComp.SR.featureParsedHashDirectiveArgumentNonString ()
        | LanguageFeature.EmptyBodiedComputationExpressions -> FSComp.SR.featureEmptyBodiedComputationExpressions ()
        | LanguageFeature.AllowObjectExpressionWithoutOverrides -> FSComp.SR.featureAllowObjectExpressionWithoutOverrides ()
        | LanguageFeature.DontWarnOnUppercaseIdentifiersInBindingPatterns ->
            FSComp.SR.featureDontWarnOnUppercaseIdentifiersInBindingPatterns ()
        | LanguageFeature.UseTypeSubsumptionCache -> FSComp.SR.featureUseTypeSubsumptionCache ()
        | LanguageFeature.DeprecatePlacesWhereSeqCanBeOmitted -> FSComp.SR.featureDeprecatePlacesWhereSeqCanBeOmitted ()
        | LanguageFeature.SupportValueOptionsAsOptionalParameters -> FSComp.SR.featureSupportValueOptionsAsOptionalParameters ()
        | LanguageFeature.WarnWhenUnitPassedToObjArg -> FSComp.SR.featureSupportWarnWhenUnitPassedToObjArg ()
        | LanguageFeature.UseBangBindingValueDiscard -> FSComp.SR.featureUseBangBindingValueDiscard ()
        | LanguageFeature.BetterAnonymousRecordParsing -> FSComp.SR.featureBetterAnonymousRecordParsing ()
        | LanguageFeature.ScopedNowarn -> FSComp.SR.featureScopedNowarn ()
        | LanguageFeature.ErrorOnInvalidDeclsInTypeDefinitions -> FSComp.SR.featureErrorOnInvalidDeclsInTypeDefinitions ()
        | LanguageFeature.AllowTypedLetUseAndBang -> FSComp.SR.featureAllowLetOrUseBangTypeAnnotationWithoutParens ()
        | LanguageFeature.ReturnFromFinal -> FSComp.SR.featureReturnFromFinal ()
        | LanguageFeature.WarnWhenFunctionValueUsedAsInterpolatedStringArg ->
            FSComp.SR.featureWarnWhenFunctionValueUsedAsInterpolatedStringArg ()
        | LanguageFeature.MethodOverloadsCache -> FSComp.SR.featureMethodOverloadsCache ()
        | LanguageFeature.ImplicitDIMCoverage -> FSComp.SR.featureImplicitDIMCoverage ()
        | LanguageFeature.PreprocessorElif -> FSComp.SR.featurePreprocessorElif ()
        | LanguageFeature.WarnOnLetInSequenceExpression -> FSComp.SR.featureWarnOnLetInSequenceExpression ()

    /// Get a version string associated with the given feature.
    static member GetFeatureVersionString feature =
        match features.TryGetValue feature with
        | true, v -> versionToString v
        | _ -> invalidArg "feature" "Internal error: Unable to find feature."

    /// Try to parse a feature name string to a LanguageFeature option using reflection
    static member TryParseFeature(featureName: string) =
        let normalized = featureName.Trim()

        let bindingFlags =
            System.Reflection.BindingFlags.Public
            ||| System.Reflection.BindingFlags.NonPublic

        Microsoft.FSharp.Reflection.FSharpType.GetUnionCases(typeof<LanguageFeature>, bindingFlags)
        |> Array.tryFind (fun case -> System.String.Equals(case.Name, normalized, System.StringComparison.OrdinalIgnoreCase))
        |> Option.bind (fun case ->
            let union =
                Microsoft.FSharp.Reflection.FSharpValue.MakeUnion(case, [||], bindingFlags)

            match box union with
            | null -> None
            | obj -> Some(obj :?> LanguageFeature))

    override x.Equals(yobj: obj) =
        match yobj with
        | :? LanguageVersion as y ->
            x.SpecifiedVersion = y.SpecifiedVersion
            && x.DisabledFeatures.Length = y.DisabledFeatures.Length
            && (x.DisabledFeatures, y.DisabledFeatures) ||> Array.forall2 (=)
        | _ -> false

    override x.GetHashCode() =
        let mutable h = hash x.SpecifiedVersion

        for f in x.DisabledFeatures do
            h <- h ^^^ hash f

        h

    static member Default = defaultLanguageVersion