Support ValueOption module

Author: alfonsogarciacaro

src/Fable.Transforms/Replacements.fs

@@ -1687,11 +1687,11 @@ let options isStruct (com: ICompiler) (_: Context) r (t: Type) (i: CallInfo) (th
     | "get_IsNone", Some c -> Test(c, OptionTest false, r) |> Some
     | _ -> None
 
-let optionModule (com: ICompiler) (ctx: Context) r (t: Type) (i: CallInfo) (_: Expr option) (args: Expr list) =
+let optionModule isStruct (com: ICompiler) (ctx: Context) r (t: Type) (i: CallInfo) (_: Expr option) (args: Expr list) =
     let toArray r t arg =
         Helper.LibCall(com, "Option", "toArray", Array(t, MutableArray), [arg], ?loc=r)
     match i.CompiledName, args with
-    | "None", _ -> NewOption(None, t, false) |> makeValue r |> Some
+    | "None", _ -> NewOption(None, t, isStruct) |> makeValue r |> Some
     | "GetValue", [c] ->
         Helper.LibCall(com, "Option", "value", t, args, ?loc=r) |> Some
     | ("OfObj" | "OfNullable"), _ ->
@@ -2900,7 +2900,8 @@ let private replacedModules =
     Types.option, options false
     Types.valueOption, options true
     "System.Nullable`1", nullables
-    "Microsoft.FSharp.Core.OptionModule", optionModule
+    "Microsoft.FSharp.Core.OptionModule", optionModule false
+    "Microsoft.FSharp.Core.ValueOption", optionModule true
     "Microsoft.FSharp.Core.ResultModule", results
     Types.bigint, bigints
     "Microsoft.FSharp.Core.NumericLiterals.NumericLiteralI", bigints

tests/Dart/src/OptionTests.fs

@@ -74,6 +74,14 @@ let tests() =
         Option.isNone o2 |> equal false
         Option.isSome o2 |> equal true
 
+    testCase "ValueOption.isSome/isNone works" <| fun () ->
+        let o1: int voption = ValueNone
+        let o2 = ValueSome 5
+        ValueOption.isNone o1 |> equal true
+        ValueOption.isSome o1 |> equal false
+        ValueOption.isNone o2 |> equal false
+        ValueOption.isSome o2 |> equal true
+
     testCase "Option.IsSome/IsNone works" <| fun () ->
         let o1: int option = None
         let o2 = Some 5
@@ -82,6 +90,14 @@ let tests() =
         o2.IsNone |> equal false
         o2.IsSome |> equal true
 
+    testCase "ValueOption.IsSome/IsNone works" <| fun () ->
+        let o1: int voption = ValueNone
+        let o2 = Some 5
+        o1.IsNone |> equal true
+        o1.IsSome |> equal false
+        o2.IsNone |> equal false
+        o2.IsSome |> equal true
+
     testCase "Option.iter works" <| fun () -> // See #198
         let mutable res = false
         let getOnlyOnce =