Function decorated with [<NamedParams>] without arguments provided sh…

…ould take an empty object Fix #3480
fable-compiler · Aug 9, 2023 · 3662dfc · 3662dfc
1 parent f7196af
commit 3662dfc
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Showing 5 changed files with 44 additions and 6 deletions.
diff --git a/src/Fable.AST/Fable.fs b/src/Fable.AST/Fable.fs
@@ -31,10 +31,15 @@ type EntityRef =
         | PrecompiledLib(p,_) -> Some p
         | AssemblyPath _ | CoreAssemblyName _ -> None
 
+type Attribute =
+    abstract Entity: EntityRef
+    abstract ConstructorArgs: obj list
+
 type MemberRefInfo =
     { IsInstance: bool
       CompiledName: string
-      NonCurriedArgTypes: Type list option }
+      NonCurriedArgTypes: Type list option
+      Attributes : Attribute seq }
 
 type MemberRef =
     | MemberRef of declaringEntity: EntityRef * info: MemberRefInfo
@@ -44,10 +49,6 @@ type DeclaredType =
     abstract Entity: EntityRef
     abstract GenericArgs: Type list
 
-type Attribute =
-    abstract Entity: EntityRef
-    abstract ConstructorArgs: obj list
-
 type Field =
     abstract Name: string
     abstract FieldType: Type

diff --git a/src/Fable.Cli/RELEASE_NOTES.md b/src/Fable.Cli/RELEASE_NOTES.md
@@ -1,3 +1,7 @@
+### Unreleased
+
+* Fix #3480: Function decorated with `[<NamedParams>]` without arguments provided should take an empty object
+
 ### 4.1.4
 
 * Fix #3438: Source maps

diff --git a/src/Fable.Transforms/FSharp2Fable.Util.fs b/src/Fable.Transforms/FSharp2Fable.Util.fs
@@ -1694,10 +1694,14 @@ module Util =
                      |> Seq.mapToList (fun p -> makeType Map.empty p.Type)
                      |> Some
                  else None
+
+            let fableMemberFunctionOrValue = FsMemberFunctionOrValue(memb) :> Fable.MemberFunctionOrValue
+
             Fable.MemberRef(FsEnt.Ref(ent), {
                 CompiledName = memb.CompiledName
                 IsInstance = memb.IsInstanceMember
                 NonCurriedArgTypes = nonCurriedArgTypes
+                Attributes = fableMemberFunctionOrValue.Attributes
             })
         | ent ->
             let entRef = ent |> Option.map FsEnt.Ref
@@ -1712,10 +1716,13 @@ module Util =
         match memb.DeclaringEntity with
         // We cannot retrieve compiler generated members from the entity
         | Some ent when not memb.IsCompilerGenerated ->
+            let fableMemberFunctionOrValue = FsMemberFunctionOrValue(memb) :> Fable.MemberFunctionOrValue
+
             Fable.MemberRef(FsEnt.Ref(ent), {
                 CompiledName = memb.CompiledName
                 IsInstance = memb.IsInstanceMember
                 NonCurriedArgTypes = None
+                Attributes = fableMemberFunctionOrValue.Attributes
             })
         | ent ->
             let entRef = ent |> Option.map FsEnt.Ref

diff --git a/src/Fable.Transforms/Fable2Babel.fs b/src/Fable.Transforms/Fable2Babel.fs
@@ -1534,7 +1534,26 @@ module Util =
             |> Option.map (splitNamedArgs args)
             |> function
             | None -> args, None
-            | Some(args, []) -> args, None
+            | Some(args, []) ->
+                // Detect if the method has a ParamObject attribute
+                // If yes and no argument is passed, pass an empty object
+                // See https://github.com/fable-compiler/Fable/issues/3480
+                match callInfo.MemberRef with
+                | Some (Fable.MemberRef (_, info)) ->
+                    let hasParamObjectAttribute =
+                        info.Attributes
+                        |> Seq.tryFind (fun attr ->
+                            attr.Entity.FullName = Atts.paramObject
+                        )
+                        |> Option.isSome
+
+                    if hasParamObjectAttribute then
+                        args, Some (makeJsObject [])
+                    else
+                        args, None
+                | _ ->
+                    // Here detect empty named args
+                    args, None
             | Some(args, namedArgs) ->
                 let objArg =
                     namedArgs

diff --git a/tests/Js/Main/OptionTests.fs b/tests/Js/Main/OptionTests.fs
@@ -62,6 +62,12 @@ type VeryOptionalClass () =
 type StaticClass =
     [<NamedParams>]
     static member NamedParams(foo: string, ?bar: int) = int foo + (defaultArg bar -3)
+    [<NamedParams>]
+    static member NamedParams(?name : string, ?age: int) =
+        let name = defaultArg name "John"
+        let age = defaultArg age 30
+
+        $"%s{name} is %d{age} years old"
     static member FSharpOptionalParam(?value: bool) = defaultArg value true
     static member FSharpOptionalParam2(?value: unit) = Option.isSome value
     static member DefaultParam([<Optional; DefaultParameterValue(true)>] value: bool) = value
@@ -142,6 +148,7 @@ let tests =
         StaticClass.NamedParams(foo="5", bar=4) |> equal 9
         StaticClass.NamedParams(foo="3", ?bar=Some 4) |> equal 7
         StaticClass.NamedParams(foo="14") |> equal 11
+        StaticClass.NamedParams() |> equal "John is 30 years old"
 
     testCase "F# optional param works" <| fun () ->
         let mutable f1 = fun (v: bool) ->