[JS/TS] Initial support for Nullable Reference Types (fable-compiler#4159)

Co-authored-by: Maxime Mangel <[email protected]>

Author: ncave

src/Fable.AST/CHANGELOG.md

@@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+* [All] Support for Nullable Reference Types (by @ncave and @MangelMaxime)
+
 ## 5.0.0-beta.1 - 2025-02-16
 
 ### Added

src/Fable.AST/Fable.fs

@@ -191,18 +191,20 @@ type Type =
     | String
     | Regex
     | Number of kind: NumberKind * info: NumberInfo
-    | Option of genericArg: Type * isStruct: bool
-    | Tuple of genericArgs: Type list * isStruct: bool
-    | Array of genericArg: Type * kind: ArrayKind
-    | List of genericArg: Type
+    | Option of genArg: Type * isStruct: bool
+    | Tuple of genArg: Type list * isStruct: bool
+    | Array of genArg: Type * kind: ArrayKind
+    | List of genArg: Type
     | LambdaType of argType: Type * returnType: Type
     | DelegateType of argTypes: Type list * returnType: Type
     | GenericParam of name: string * isMeasure: bool * constraints: Constraint list
-    | DeclaredType of ref: EntityRef * genericArgs: Type list
-    | AnonymousRecordType of fieldNames: string[] * genericArgs: Type list * isStruct: bool
+    | DeclaredType of ref: EntityRef * genArgs: Type list
+    | AnonymousRecordType of fieldNames: string[] * genArgs: Type list * isStruct: bool
+    | Nullable of genArg: Type * isStruct: bool
 
     member this.Generics =
         match this with
+        | Nullable(gen, _)
         | Option(gen, _)
         | Array(gen, _)
         | List gen -> [ gen ]
@@ -225,6 +227,7 @@ type Type =
 
     member this.MapGenerics f =
         match this with
+        | Nullable(gen, isStruct) -> Nullable(f gen, isStruct)
         | Option(gen, isStruct) -> Option(f gen, isStruct)
         | Array(gen, kind) -> Array(f gen, kind)
         | List gen -> List(f gen)

src/Fable.Cli/CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 
 * [JS/TS] Fix #3533: Add directives prologues supports (by @MangelMaxime)
+* [JS/TS] Support for Nullable Reference Types (by @ncave and @MangelMaxime)
 
 ### Changed
 

src/Fable.Cli/Main.fs

@@ -737,7 +737,7 @@ and FableCompiler(checker: InteractiveChecker, projCracked: ProjectCracked, fabl
             let fableProj =
                 Project.From(
                     projCracked.ProjectFile,
-                    projCracked.ProjectOptions.SourceFiles,
+                    projCracked.ProjectOptions,
                     [],
                     assemblies,
                     Log.log,

src/Fable.Compiler/CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 
 * [JS/TS] Fix #3533: Add directives prologues supports (by @MangelMaxime)
+* [JS/TS] Support for Nullable Reference Types (by @ncave and @MangelMaxime)
 
 ### Changed
 

src/Fable.Compiler/Library.fs

@@ -164,7 +164,7 @@ module CodeServices =
             let fableProj =
                 Project.From(
                     cliArgs.ProjectFile,
-                    crackerResponse.ProjectOptions.SourceFiles,
+                    crackerResponse.ProjectOptions,
                     checkProjectResult.AssemblyContents.ImplementationFiles,
                     assemblies,
                     Log.log,
@@ -205,7 +205,7 @@ module CodeServices =
             let fableProj =
                 Project.From(
                     cliArgs.ProjectFile,
-                    crackerResponse.ProjectOptions.SourceFiles,
+                    crackerResponse.ProjectOptions,
                     typeCheckProjectResult.ProjectCheckResults.AssemblyContents.ImplementationFiles,
                     typeCheckProjectResult.Assemblies,
                     Log.log,
@@ -298,7 +298,7 @@ module CodeServices =
             let fableProj =
                 Project.From(
                     cliArgs.ProjectFile,
-                    crackerResponse.ProjectOptions.SourceFiles,
+                    crackerResponse.ProjectOptions,
                     checkProjectResult.AssemblyContents.ImplementationFiles,
                     assemblies,
                     Log.log,

src/Fable.Transforms/Dart/Fable2Dart.fs

@@ -194,6 +194,9 @@ module Util =
         let tup = List.length genArgs |> getTupleTypeIdent com ctx
         Type.reference (tup, genArgs)
 
+    let transformNullableType com ctx genArg =
+        transformType com ctx genArg |> Nullable
+
     let transformOptionType com ctx genArg =
         let genArg = transformType com ctx genArg
 
@@ -215,7 +218,6 @@ module Util =
         | Types.array, _ -> List Dynamic
         | "System.Tuple`1", _ -> transformTupleType com ctx genArgs
         | Types.valueType, _ -> Object
-        | Types.nullable, [ genArg ]
         | "Fable.Core.Dart.DartNullable`1", [ genArg ] -> Nullable genArg
         | Types.regexGroup, _ -> Nullable String
         | Types.regexMatch, _ -> makeTypeRefFromName "Match" []
@@ -650,6 +652,7 @@ module Util =
             | BigInt
             | NativeInt
             | UNativeInt -> Dynamic // TODO
+        | Fable.Nullable(genArg, _isStruct) -> transformNullableType com ctx genArg
         | Fable.Option(genArg, _isStruct) -> transformOptionType com ctx genArg
         | Fable.Array(TransformType com ctx genArg, _) -> List genArg
         | Fable.List(TransformType com ctx genArg) -> Type.reference (getFSharpListTypeIdent com ctx, [ genArg ])

src/Fable.Transforms/FSharp2Fable.Util.fs

@@ -1557,6 +1557,8 @@ module TypeHelpers =
             | Types.string -> Fable.String
             | Types.regex -> Fable.Regex
             | Types.type_ -> Fable.MetaType
+            | Types.nullable ->
+                Fable.Nullable(makeTypeGenArgsWithConstraints withConstraints ctxTypeArgs genArgs |> List.head, true)
             | Types.valueOption ->
                 Fable.Option(makeTypeGenArgsWithConstraints withConstraints ctxTypeArgs genArgs |> List.head, true)
             | Types.option ->
@@ -1632,12 +1634,12 @@ module TypeHelpers =
             else
                 Fable.Any // failwithf "Unexpected non-declared F# type: %A" t
 
-        // TODO:
-        // if not t.IsGenericParameter && t.HasNullAnnotation // || t.IsNullAmbivalent
-        // then
-        //     makeRuntimeType [ typ ] Types.nullable // represent it as Nullable<T>
-        // else typ
-        typ
+        if
+            Compiler.CheckNulls && t.HasNullAnnotation // || t.IsNullAmbivalent
+        then
+            Fable.Nullable(typ, false)
+        else
+            typ
 
     let makeType (ctxTypeArgs: Map<string, Fable.Type>) t =
         makeTypeWithConstraints true ctxTypeArgs t
@@ -1672,15 +1674,21 @@ module TypeHelpers =
         | FSharpXmlDoc.FromXmlText(xmlDoc) -> xmlDoc.GetXmlText() |> Some
         | _ -> None
 
-    let tryGetInterfaceTypeFromMethod (meth: FSharpMemberOrFunctionOrValue) =
-        if meth.ImplementedAbstractSignatures.Count > 0 then
-            nonAbbreviatedType meth.ImplementedAbstractSignatures[0].DeclaringType |> Some
+    let tryGetInterfaceTypeFromMethod (memb: FSharpMemberOrFunctionOrValue) =
+        if
+            memb.IsOverrideOrExplicitInterfaceImplementation
+            && memb.ImplementedAbstractSignatures.Count > 0
+        then
+            nonAbbreviatedType memb.ImplementedAbstractSignatures[0].DeclaringType |> Some
         else
             None
 
-    let tryGetInterfaceDefinitionFromMethod (meth: FSharpMemberOrFunctionOrValue) =
-        if meth.ImplementedAbstractSignatures.Count > 0 then
-            let t = nonAbbreviatedType meth.ImplementedAbstractSignatures[0].DeclaringType
+    let tryGetInterfaceDefinitionFromMethod (memb: FSharpMemberOrFunctionOrValue) =
+        if
+            memb.IsOverrideOrExplicitInterfaceImplementation
+            && memb.ImplementedAbstractSignatures.Count > 0
+        then
+            let t = nonAbbreviatedType memb.ImplementedAbstractSignatures[0].DeclaringType
 
             if t.HasTypeDefinition then
                 Some t.TypeDefinition
@@ -2380,6 +2388,7 @@ module Util =
         entityName + "." + memberName + overloadHash
 
     let getAbstractMemberInfo com (ent: FSharpEntity) (memb: FSharpMemberOrFunctionOrValue) =
+        let ent = tryGetInterfaceDefinitionFromMethod memb |> Option.defaultValue ent
         let isMangled = isMangledAbstractEntity com ent
         let isGetter = FsMemberFunctionOrValue.IsGetter(memb)
         let isSetter = not isGetter && FsMemberFunctionOrValue.IsSetter(memb)

src/Fable.Transforms/Fable2Babel.fs

@@ -334,6 +334,7 @@ module Reflection =
         | Fable.LambdaType(argType, returnType) -> genericTypeInfo "lambda" [ argType; returnType ]
         | Fable.DelegateType(argTypes, returnType) -> genericTypeInfo "delegate" [ yield! argTypes; yield returnType ]
         | Fable.Tuple(genArgs, _) -> genericTypeInfo "tuple" genArgs
+        | Fable.Nullable(genArg, isStruct) -> transformTypeInfoFor purpose com ctx r genMap genArg
         | Fable.Option(genArg, _) -> genericTypeInfo "option" [ genArg ]
         | Fable.Array(genArg, _) -> genericTypeInfo "array" [ genArg ]
         | Fable.List genArg -> genericTypeInfo "list" [ genArg ]
@@ -495,6 +496,7 @@ module Reflection =
         | Fable.MetaType -> jsInstanceof (libValue com ctx "Reflection" "TypeInfo") expr
         | Fable.Option _ -> warnAndEvalToFalse "options" // TODO
         | Fable.GenericParam _ -> warnAndEvalToFalse "generic parameters"
+        | Fable.Nullable(genArg, _isStruct) -> transformTypeTest com ctx range expr genArg
         | Fable.DeclaredType(ent, genArgs) ->
             match ent.FullName with
             | Types.idisposable ->
@@ -609,6 +611,7 @@ module Annotation =
         | Fable.Regex -> makeAliasTypeAnnotation com ctx "RegExp"
         | Fable.Number(BigInt, _) -> makeAliasTypeAnnotation com ctx "bigint"
         | Fable.Number(kind, _) -> makeNumericTypeAnnotation com ctx kind
+        | Fable.Nullable(genArg, _) -> makeNullableTypeAnnotation com ctx genArg
         | Fable.Option(genArg, _) -> makeOptionTypeAnnotation com ctx genArg
         | Fable.Tuple(genArgs, _) -> makeTupleTypeAnnotation com ctx genArgs
         | Fable.Array(genArg, kind) -> makeArrayTypeAnnotation com ctx genArg kind
@@ -693,7 +696,7 @@ module Annotation =
         makeFableLibImportTypeAnnotation com ctx [] moduleName typeName
 
     let makeNullableTypeAnnotation com ctx genArg =
-        makeFableLibImportTypeAnnotation com ctx [ genArg ] "Option" "Nullable"
+        makeFableLibImportTypeAnnotation com ctx [ genArg ] "Util" "Nullable"
 
     let makeOptionTypeAnnotation com ctx genArg =
         makeFableLibImportTypeAnnotation com ctx [ genArg ] "Option" "Option"
@@ -881,8 +884,6 @@ module Annotation =
 
     let makeEntityTypeAnnotation com ctx genArgs (ent: Fable.Entity) =
         match genArgs, ent with
-        | [ genArg ], EntFullName Types.nullable -> makeNullableTypeAnnotation com ctx genArg
-
         | _, Patterns.Try (tryNativeOrFableLibraryInterface com ctx genArgs) ta -> ta
 
         | _, Patterns.Try (Lib.tryJsConstructorFor Annotation com ctx) entRef ->
@@ -1978,6 +1979,16 @@ module Util =
                 | Fable.Value(Fable.Null _, _), e
                 | e, Fable.Value(Fable.Null _, _) ->
                     com.TransformAsExpr(ctx, e) |> makeNullCheck range (op = BinaryEqual)
+                | ExprType(Fable.Nullable _), ExprType(Fable.Nullable _) ->
+                    Replacements.Util.Helper.LibCall(
+                        com,
+                        "Util",
+                        "nullableEquals",
+                        Fable.Boolean,
+                        [ e1; e2 ],
+                        ?loc = range
+                    )
+                    |> transformAsExpr com ctx
                 | ExprType(Fable.MetaType), _ ->
                     let e =
                         Replacements.Util.Helper.LibCall(

src/Fable.Transforms/Global/Compiler.fs

@@ -124,15 +124,20 @@ module CompilerExt =
             false
 
     let private coreAssemblyNames = set Metadata.coreAssemblies
-    let mutable private _lang = JavaScript
+
+    let mutable private _language = JavaScript
+    let mutable private _checkNulls = false
 
     type Compiler with
 
         static member CoreAssemblyNames = coreAssemblyNames
 
-        static member Language = _lang
-        /// Use this only once at the start of the program
-        static member SetLanguageUnsafe lang = _lang <- lang
+        static member Language = _language
+        static member CheckNulls = _checkNulls
+
+        /// Set these only once at the start of the program
+        static member SetLanguageUnsafe language = _language <- language
+        static member SetCheckNullsUnsafe enabled = _checkNulls <- enabled
 
         member com.GetEntity(entityRef: Fable.EntityRef) =
             match com.TryGetEntity(entityRef) with