Sync with the ultimate 253

ReSharper.FSharp/src/FSharp.Fantomas.Host/PackagesLock.targets

@@ -5,7 +5,7 @@
     <PackageLock Include="Fantomas.FCS" Version="7.0.3" />
     <PackageLock Include="FSharp.Core" Version="9.0.201" />
     <PackageLock Include="JetBrains.Lifetimes" Version="2025.3.1" />
-    <PackageLock Include="JetBrains.NuGet.Versioning" Version="7.0.20251002.162" />
+    <PackageLock Include="JetBrains.NuGet.Versioning" Version="7.0.20251126.165" />
     <PackageLock Include="JetBrains.RdFramework" Version="2025.3.1" />
     <PackageLock Include="Microsoft.NETCore.Platforms" Version="3.1.0" />
     <PackageLock Include="Microsoft.NETCore.Targets" Version="1.1.3" />

ReSharper.FSharp/src/FSharp.TypeProviders.Host/PackagesLock.targets

@@ -3,7 +3,7 @@
   <ItemGroup>
     <PackageLock Include="FSharp.Core" Version="9.0.201" />
     <PackageLock Include="JetBrains.Annotations" Version="2025.2.0" />
-    <PackageLock Include="JetBrains.FSharp.Compiler.Service" Version="2025.3.2" />
+    <PackageLock Include="JetBrains.FSharp.Compiler.Service" Version="2025.3.5.2" />
     <PackageLock Include="JetBrains.Lifetimes" Version="2025.3.1" />
     <PackageLock Include="JetBrains.RdFramework" Version="2025.3.1" />
     <PackageLock Include="Microsoft.NETCore.Platforms" Version="3.1.0" />

ReSharper.FSharp/src/FSharp/FSharp.Common/src/ProjectModel/FSharpLanguageLevelProvider.fs

@@ -63,18 +63,19 @@ type FSharpLanguageLevelProjectProperty(lifetime, locks, projectPropertiesListen
         let languageLevel = getLanguageLevelByToolsetVersion ()
         VersionMapping(languageLevel, FSharpLanguageLevel.Preview)
 
-    // todo: more versions
     let getLanguageLevelByCompilerVersion (fscVersion: Version): VersionMapping =
         match fscVersion with
         | Version (10, 1000, _) -> VersionMapping(FSharpLanguageLevel.FSharp47, FSharpLanguageLevel.FSharp50)
         | Version (11, 0, _) -> VersionMapping(FSharpLanguageLevel.FSharp50, FSharpLanguageLevel.FSharp60)
         | Version (12, minor, build) ->
             if minor < 4 then VersionMapping(FSharpLanguageLevel.FSharp60, FSharpLanguageLevel.FSharp70)
             elif minor >= 4 && minor <= 7 then VersionMapping(FSharpLanguageLevel.FSharp70, FSharpLanguageLevel.FSharp80)
-            elif minor = 8 && build < 200 then VersionMapping(FSharpLanguageLevel.FSharp80, FSharpLanguageLevel.FSharp90)
-            elif minor = 8 then VersionMapping(FSharpLanguageLevel.FSharp81, FSharpLanguageLevel.FSharp90)
-            elif minor >= 9 then VersionMapping(FSharpLanguageLevel.FSharp90, FSharpLanguageLevel.Preview)
-            else null
+            else
+                match minor with
+                | 8 when build < 200 -> VersionMapping(FSharpLanguageLevel.FSharp80, FSharpLanguageLevel.FSharp90)
+                | 8 -> VersionMapping(FSharpLanguageLevel.FSharp81, FSharpLanguageLevel.FSharp90)
+                | 9 -> VersionMapping(FSharpLanguageLevel.FSharp90, FSharpLanguageLevel.FSharp100)
+                | _ -> VersionMapping(FSharpLanguageLevel.FSharp100, FSharpLanguageLevel.Preview)
         | _ -> null
 
     let getCompilerVersion (fscPath: VirtualFileSystemPath) =
@@ -114,6 +115,7 @@ type FSharpLanguageLevelProjectProperty(lifetime, locks, projectPropertiesListen
                 FSharpLanguageLevel.FSharp81
 
         | FSharpLanguageVersion.FSharp90 -> FSharpLanguageLevel.FSharp90
+        | FSharpLanguageVersion.FSharp100 -> FSharpLanguageLevel.FSharp100
         | FSharpLanguageVersion.Default -> (getFscPath configuration |> getLanguageLevelByCompiler).DefaultVersion
         | FSharpLanguageVersion.LatestMajor -> (getFscPath configuration |> getLanguageLevelByCompiler).LatestMajor
         | FSharpLanguageVersion.Latest -> (getFscPath configuration |> getLanguageLevelByCompiler).LatestMinor

ReSharper.FSharp/src/FSharp/FSharp.Common/src/Shim/AssemblyReader/FcsModuleReaderCommonCache.fs

@@ -16,6 +16,7 @@ open JetBrains.Util.DataStructures
 type FcsModuleReaderCommonCache(lifetime: Lifetime, changeManager: ChangeManager) =
     inherit AssemblyReaderShimChangeListenerBase(lifetime, changeManager)
 
+    // todo: is it ever cleared?
     let assemblyTypeRefs = ConcurrentDictionary<IPsiModule, ConcurrentDictionary<IClrTypeName, ILTypeRef>>()
 
     member this.GetOrCreateAssemblyTypeRefCache(targetModule: IPsiModule) =

ReSharper.FSharp/src/FSharp/FSharp.Common/src/Shim/AssemblyReader/ProjectFcsModuleReader.fs

@@ -1342,6 +1342,9 @@ type ProjectFcsModuleReader(psiModule: IPsiModule, cache: FcsModuleReaderCommonC
         timestamp <- DateTime.UtcNow
         shim.Logger.Trace("New timestamp: {0}: {1}", path, timestamp)
 
+    member this.GetFcsIlType(t: IType) =
+        mkType t
+
     interface IProjectFcsModuleReader with
         member this.ILModuleDef =
             FSharpAsyncUtil.CheckAndThrow()

ReSharper.FSharp/src/FSharp/FSharp.Common/src/Util/FSharpAttributesUtil.fs

@@ -3,25 +3,33 @@ namespace JetBrains.ReSharper.Plugins.FSharp.Util
 open System.Collections.Generic
 open FSharp.Compiler.Symbols
 open JetBrains.Metadata.Reader.API
+open JetBrains.Metadata.Reader.Impl
+open JetBrains.ReSharper.Psi.ExtensionsAPI
 open JetBrains.Util
 
-[<Extension; Sealed; AbstractClass>]
+[<Sealed; AbstractClass>]
 type FcsAttributeUtil =
     [<Extension>]
-    static member GetClrName(attr: FSharpAttribute) = attr.AttributeType.BasicQualifiedName
+    static member GetClrNameFullName(attr: FSharpAttribute) =
+        attr.AttributeType.BasicQualifiedName
+        |> Option.defaultValue SharedImplUtil.MISSING_DECLARATION_NAME
+
+    [<Extension>]
+    static member GetClrName(attr: FSharpAttribute) =
+        ClrTypeName(attr.GetClrNameFullName())
 
     [<Extension>]
     static member HasAttributeInstance(attrs: IList<FSharpAttribute>, clrName: string) =
-        attrs |> Seq.exists (fun a -> a.GetClrName() = clrName)
+        attrs |> Seq.exists (fun a -> a.GetClrNameFullName() = clrName)
 
     [<Extension>]
     static member GetAttributes(attrs: IList<FSharpAttribute>, clrName: string) =
-        let filteredAttributes = attrs |> Seq.filter (fun a -> a.GetClrName() = clrName)
+        let filteredAttributes = attrs |> Seq.filter (fun a -> a.GetClrNameFullName() = clrName)
         filteredAttributes.AsIList()
 
     [<Extension>]
     static member TryFindAttribute(attrs: IList<FSharpAttribute>, clrName: string) =
-        attrs |> Seq.tryFind (fun a -> a.GetClrName() = clrName)
+        attrs |> Seq.tryFind (fun a -> a.GetClrNameFullName() = clrName)
 
     [<Extension>]
     static member HasAttributeInstance(attrs: IList<FSharpAttribute>, clrTypeName: IClrTypeName) =

ReSharper.FSharp/src/FSharp/FSharp.Common/src/Util/FSharpPredefinedType.fs

@@ -1,9 +1,7 @@
-[<AutoOpen; Extension>]
+[<AutoOpen>]
 module JetBrains.ReSharper.Plugins.FSharp.Util.FSharpPredefinedType
 
-open System
 open System.Collections.Generic
-open FSharp.Compiler.Symbols
 open JetBrains.Metadata.Reader.API
 open JetBrains.Metadata.Reader.Impl
 open JetBrains.ReSharper.Psi
@@ -132,41 +130,3 @@ let predefinedAbbreviations =
 [<Extension; CompiledName("TryGetPredefinedAbbreviations")>]
 let tryGetPredefinedAbbreviations(clrTypeName: IClrTypeName, names: outref<string[]>) =
     predefinedAbbreviations.TryGetValue(clrTypeName, &names)
-
-
-let isOption (fcsType: FSharpType) =
-    fcsType.ErasedType.BasicQualifiedName = fsOptionTypeName.FullName
-
-let isValueOption (fcsType: FSharpType) =
-    fcsType.ErasedType.BasicQualifiedName = fsValueOptionTypeName.FullName
-
-let isChoice (fcsType: FSharpType) =
-    fcsType.ErasedType.BasicQualifiedName.StartsWith("Microsoft.FSharp.Core.FSharpChoice`", StringComparison.Ordinal)
-
-[<Extension; CompiledName("IsUnit")>]
-let isUnit (fcsType: FSharpType) =
-    try fcsType.ErasedType.BasicQualifiedName = unitTypeName.FullName
-    with _ -> false
-
-let isFSharpList (fcsType: FSharpType) =
-    if isNull fcsType then false else
-
-    let erasedType = fcsType.ErasedType
-    if not erasedType.HasTypeDefinition then false else
-
-    let fcsEntity = erasedType.TypeDefinition
-    if fcsEntity.IsArrayType then false else
-
-    fcsEntity.BasicQualifiedName = "Microsoft.FSharp.Collections.FSharpList`1"
-
-[<Extension; CompiledName("IsNativePtr")>]
-let isNativePtr (fcsType: FSharpType) =
-    try fcsType.ErasedType.BasicQualifiedName = StandardTypeNames.IntPtr
-    with _ -> false
-
-let isReadOnly (fcsType: FSharpType) =
-    if fcsType.HasTypeDefinition && fcsType.TypeDefinition.IsArrayType then false else
-
-    let name = fcsType.ErasedType.BasicQualifiedName
-    startsWith "Microsoft.FSharp.Collections.FSharpList`" name ||
-    startsWith "System.String" name

ReSharper.FSharp/src/FSharp/FSharp.Psi.Daemon/src/Analyzers/LambdaAnalyzer.fs

@@ -13,7 +13,6 @@ open JetBrains.ReSharper.Plugins.FSharp.Psi.Impl
 open JetBrains.ReSharper.Plugins.FSharp.Psi.PsiUtil
 open JetBrains.ReSharper.Plugins.FSharp.Psi.Tree
 open JetBrains.ReSharper.Plugins.FSharp.Psi.Util
-open JetBrains.ReSharper.Plugins.FSharp.Util.FSharpPredefinedType
 open JetBrains.ReSharper.Plugins.FSharp.Util.FSharpSymbolUtil
 open JetBrains.ReSharper.Psi
 open JetBrains.ReSharper.Psi.ExtensionsAPI
@@ -225,7 +224,7 @@ type LambdaAnalyzer() =
 
         let typeIsReadOnly (expr: IFSharpExpression) =
             let fcsType = expr.TryGetFcsType()
-            isNotNull fcsType && isReadOnly fcsType
+            isNotNull fcsType && (fcsType.IsFSharpList || fcsType.IsStringType)
 
         let processor =
             { new IRecursiveElementProcessor with

ReSharper.FSharp/src/FSharp/FSharp.Psi.Daemon/src/Stages/FcsErrorsStageProcessBase.fs

@@ -230,7 +230,7 @@ type FcsErrorsStageProcessBase(fsFile, daemonProcess) =
                 let node = nodeSelectionProvider.GetExpressionInRange(fsFile, range, false, null) |> getResultNode
                 if isNull node then
                     null
-                elif isUnit data.ExpectedType then
+                elif data.ExpectedType.IsUnitType then
                     createHighlightingFromNodeWithMessage UnitTypeExpectedError range error
                 else
                     createTypeMismatchHighlighting TypeEquationError range error
@@ -556,7 +556,7 @@ type FcsErrorsStageProcessBase(fsFile, daemonProcess) =
                 createHighlightingFromParentNodeWithMessage FieldNotContainedTypesDifferError range error
 
             | Some (:? TypeMismatchDiagnosticExtendedData as data) ->
-                if isUnit data.ExpectedType then
+                if data.ExpectedType.IsUnitType then
                     createHighlightingFromMappedExpression getResultNode UnitTypeExpectedError range error else
 
                 createTypeMismatchHighlighting TypeConstraintMismatchError range error

ReSharper.FSharp/src/FSharp/FSharp.Psi.Daemon/src/Stages/PipeChainTypeHintStage.fs

@@ -17,8 +17,7 @@ open JetBrains.ReSharper.Plugins.FSharp.Psi.Tree
 open JetBrains.ReSharper.Plugins.FSharp.Psi.Impl
 open JetBrains.ReSharper.Plugins.FSharp.Psi.Util
 open JetBrains.ReSharper.Plugins.FSharp.Settings
-open JetBrains.ReSharper.Plugins.FSharp.Util.FSharpPredefinedType
-open JetBrains.ReSharper.Plugins.FSharp.Util.FSharpSymbolUtil
+open JetBrains.ReSharper.Plugins.FSharp.Util
 open JetBrains.ReSharper.Psi.Tree
 
 [<RequireQualifiedAccess>]
@@ -98,7 +97,7 @@ type PipeChainHighlightingProcess(fsFile, settings: IContextBoundSettingsStore,
         | :? IDotLambdaExpr -> skipFunArgs exprType = pipeResultType
         | _ ->
         if not exprType.IsFunctionType || exprType.GenericArguments[1] <> pipeResultType then false else
-        if not (isUnit pipeResultType) then true else
+        if not (pipeResultType.IsUnitType) then true else
 
         let invokedRefExpr =
             match expr with
@@ -114,9 +113,8 @@ type PipeChainHighlightingProcess(fsFile, settings: IContextBoundSettingsStore,
         | Some t ->
             // We know that the result of the pipe is unit.
             // We want to get the very last returned value and make sure that it is not generic, but strictly unit.
-            skipFunArgs t
-            |> isUnit
-            |> not
+            let t = skipFunArgs t
+            not t.IsUnitType
         | None -> false
 
     let adornExprs (exprs : (IReferenceExpr * ITreeNode * bool) ICollection) =

ReSharper.FSharp/src/FSharp/FSharp.Psi.Features/src/CodeCompletion/Rules/NameSuggestionRule.fs

@@ -16,7 +16,6 @@ open JetBrains.ReSharper.Plugins.FSharp.Psi.Resolve
 open JetBrains.ReSharper.Plugins.FSharp.Psi.Services.Util.FSharpCompletionUtil
 open JetBrains.ReSharper.Plugins.FSharp.Psi.Tree
 open JetBrains.ReSharper.Plugins.FSharp.Psi.Util
-open JetBrains.ReSharper.Plugins.FSharp.Util
 open JetBrains.ReSharper.Psi
 open JetBrains.ReSharper.Psi.Tree
 open JetBrains.Util
@@ -151,7 +150,7 @@ type NameSuggestionFromTypeRule() =
             | valueType -> Option.toList valueType.FcsType
 
         let tryReplaceWithParameterBaseTypes (fcsType: FSharpType) =
-            if isUnit fcsType then [] else
+            if fcsType.IsUnitType then [] else
             if not fcsType.IsGenericParameter then [fcsType] else
 
             match fcsType.BaseType with

ReSharper.FSharp/src/FSharp/FSharp.Psi.Features/src/CodeCompletion/Rules/UnionCasePatternRule.fs

@@ -258,7 +258,7 @@ type UnionCasePatternRule() =
             match lookupItem.FcsSymbol with
             | :? FSharpUnionCase as fcsUnionCase ->
                 let returnType = fcsUnionCase.ReturnType
-                if not (matchesType returnType || isFSharpList returnType) then
+                if not (matchesType returnType || returnType.IsFSharpList) then
                     let text = fcsUnionCase.Name
                     let fcsEntityInstance = FcsEntityInstance.create returnType
                     let item = createUnionCaseItem fcsEntityInstance returnType text fcsUnionCase false
@@ -282,8 +282,8 @@ type UnionCasePatternRule() =
 
         match expectedType with
         | None -> ()
-        | Some(fcsEntityInstance, fcsType, displayContext) ->
-            if isNull expectedTypeElement || isFSharpList fcsType then () else
+        | Some(fcsEntityInstance, fcsType, _) ->
+            if isNull expectedTypeElement || fcsType.IsFSharpList then () else
 
             let fcsEntity = fcsEntityInstance.Entity
             let typeName = expectedTypeElement.GetSourceName()

ReSharper.FSharp/src/FSharp/FSharp.Psi.Features/src/LanguageService/FSharpDeclaredElementIconProvider.fs

@@ -36,14 +36,14 @@ type FSharpDeclaredElementIconProvider() =
             match declaredElement with
             | :? IFSharpModule -> FSharpIcons.FSharpModule.Id
 
-            | :? IUnionCase as unionCase ->
+            | :? IFSharpUnionCase as unionCase ->
                 canApplyExtensions <- false
                 match unionCase.RepresentationAccessRights with
                 | AccessRights.PRIVATE -> privateCase
                 | AccessRights.INTERNAL -> internalCase
                 | _ -> PsiSymbolsThemedIcons.EnumMember.Id
 
-            | :? IRecordField as field ->
+            | :? IFSharpRecordField as field ->
                 canApplyExtensions <- false
                 if field.IsMutable then
                     match field.RepresentationAccessRights with

ReSharper.FSharp/src/FSharp/FSharp.Psi.Features/src/LanguageService/FSharpLanguageService.fs

@@ -71,7 +71,7 @@ type FSharpLanguageService(languageType, constantValueService, cacheProvider: FS
     member x.GetDefaultAccessType(declaredElement: IDeclaredElement) =
         // todo: invocations, partial applications
         match declaredElement with
-        | :? IUnionCase ->
+        | :? IFSharpUnionCase ->
             ReferenceAccessType.OTHER
 
         | :? IField

ReSharper.FSharp/src/FSharp/FSharp.Psi.Features/src/ParameterInfo/FSharpParameterInfo.fs

@@ -297,12 +297,12 @@ type FcsParameterInfoCandidateBase<'TSymbol, 'TParameter when 'TSymbol :> FSharp
                         let fcsParameterType = this.GetParamType(fcsParameter)
                         if not (this.IsOptionalParam(fcsParameter)) then fcsParameterType else
 
-                        match tryGetAbbreviatedTypeEntity fcsParameterType with
-                        | Some entity when entity.BasicQualifiedName = FSharpPredefinedType.fsOptionTypeName.FullName ->
+                        if fcsParameterType.IsFSharpOption then
                             fcsParameterType.GenericArguments
                             |> Seq.tryExactlyOne
                             |> Option.defaultValue fcsParameterType
-                        | _ -> fcsParameterType
+                        else
+                            fcsParameterType
 
                     text.Append(fcsParameterType.FormatLayout(displayContext) |> richText) |> ignore
 
@@ -444,16 +444,16 @@ type FcsActivePatternMfvParameterInfoCandidate(apc: FSharpActivePatternCase, mfv
             match activePatternGroup.IsTotal with
             | true when
                     names.Count > 1 && apc.Index < names.Count &&
-                    apc.Index < mfvReturnType.GenericArguments.Count && FSharpPredefinedType.isChoice mfvReturnType ->
+                    apc.Index < mfvReturnType.GenericArguments.Count && mfvReturnType.IsFSharpChoice ->
                 Some mfvReturnType.GenericArguments[apc.Index]
 
             | false when
-                    FSharpPredefinedType.isOption mfvReturnType ||
+                    mfvReturnType.IsFSharpOption ||
 
-                    FSharpPredefinedType.isValueOption mfvReturnType &&
+                    mfvReturnType.IsFSharpValueOption &&
                     mfv.ReturnParameter.Attributes.HasAttributeInstance(FSharpPredefinedType.structAttrTypeName) ->
                 let optionArgType = mfvReturnType.GenericArguments[0]
-                if FSharpPredefinedType.isUnit optionArgType.ErasedType then None else Some optionArgType
+                if optionArgType.IsUnitType then None else Some optionArgType
 
             | _ -> Some mfvReturnType
 

ReSharper.FSharp/src/FSharp/FSharp.Psi.Features/src/Parsing/FSharpTreeBuilderBase.fs

@@ -68,6 +68,9 @@ type FSharpTreeBuilderBase(lexer: ILexer, document: IDocument, warnDirectives: W
 
     member x.AdvanceLexer() =
         if nextDirectiveOffset <> -1 && x.CurrentOffset = nextDirectiveOffset then
+            while (isNotNull x.TokenType && x.TokenType.IsWhitespace) && not x.Eof do
+                x.Builder.AdvanceLexer() |> ignore
+
             let (WarningDirectiveRange directiveRange) = warnDirectives.Head
             setWarnDirectives warnDirectives.Tail
 

ReSharper.FSharp/src/FSharp/FSharp.Psi.Features/src/PostfixTemplates/ForPostfixTemplate.fs

@@ -30,7 +30,7 @@ open JetBrains.Util
 
 module ForPostfixTemplate =
     let tryGetEnumerableTypeArg (contextExpr: IFSharpExpression) (fcsType: FSharpType) : FSharpType option =
-        let seenTypes = HashSet()
+        let seenTypes = HashSet<string>()
 
         let rec loop (fcsType: FSharpType) =
             let fcsType = FSharpSymbolUtil.getAbbreviatedType fcsType
@@ -44,7 +44,8 @@ module ForPostfixTemplate =
             let entity = fcsType.TypeDefinition
             if entity.IsArrayType then Some fcsType.GenericArguments[0] else
 
-            if not (seenTypes.Add(entity.BasicQualifiedName)) then None else
+            let qualifiedName = Option.defaultValue SharedImplUtil.MISSING_DECLARATION_NAME entity.BasicQualifiedName
+            if not (seenTypes.Add(qualifiedName)) then None else
 
             fcsType.BaseType
             |> Option.bind loop

ReSharper.FSharp/src/FSharp/FSharp.Psi.Intentions/src/Intentions/ToMutableAction.fs

@@ -1,7 +1,7 @@
 namespace JetBrains.ReSharper.Plugins.FSharp.Psi.Features.Intentions
 
 open JetBrains.ReSharper.Feature.Services.ContextActions
-open JetBrains.ReSharper.Plugins.FSharp.Psi.Impl.DeclaredElement
+open JetBrains.ReSharper.Plugins.FSharp.Psi
 open JetBrains.ReSharper.Plugins.FSharp.Psi.Tree
 open JetBrains.ReSharper.Psi.Tree
 open JetBrains.ReSharper.Resources.Shell
@@ -16,14 +16,14 @@ type ToMutableAction(dataProvider: FSharpContextActionDataProvider) =
         let decl = dataProvider.GetSelectedElement<IRecordFieldDeclaration>()
         if not (isValid decl && decl.GetNameRange().Contains(dataProvider.SelectedTreeRange)) then false else
 
-        let field = decl.DeclaredElement.As<IRecordField>()
+        let field = decl.DeclaredElement.As<IFSharpRecordField>()
         isValid field && field.CanBeMutable && not field.IsMutable
 
     override x.ExecutePsiTransaction _ =
         let fieldDecl = dataProvider.GetSelectedElement<IRecordFieldDeclaration>()
         use writeCookie = WriteLockCookie.Create(fieldDecl.IsPhysical())
 
-        let declaredElement = fieldDecl.DeclaredElement :?> IRecordField
+        let declaredElement = fieldDecl.DeclaredElement :?> IFSharpRecordField
         declaredElement.SetIsMutable(true)
 
 
@@ -42,12 +42,12 @@ type ToImmutableFieldAction(dataProvider: FSharpContextActionDataProvider) =
         let selectedRange = dataProvider.SelectedTreeRange
         if not (nameRange.Contains(selectedRange) || mutableRange.Contains(selectedRange)) then false else
 
-        let field = decl.DeclaredElement.As<IRecordField>()
+        let field = decl.DeclaredElement.As<IFSharpRecordField>()
         isValid field && field.IsMutable
 
     override x.ExecutePsiTransaction _ =
         let fieldDecl = dataProvider.GetSelectedElement<IRecordFieldDeclaration>()
         use writeCookie = WriteLockCookie.Create(fieldDecl.IsPhysical())
 
-        let declaredElement = fieldDecl.DeclaredElement :?> IRecordField
+        let declaredElement = fieldDecl.DeclaredElement :?> IFSharpRecordField
         declaredElement.SetIsMutable(false)