fix(all): fix super call in multi-level generic class hierarchy using wrong mangled name

src/Fable.Transforms/FSharp2Fable.Util.fs

@@ -2947,7 +2947,7 @@ module Util =
             // When calling `super` in an override, it may happen the method is not originally declared
             // by the immediate parent, so we need to go through the hierarchy until we find the original declaration
             // (this is important to get the correct mangled name)
-            let entity =
+            let entity, memb =
                 match memb.IsOverrideOrExplicitInterfaceImplementation, callInfo.ThisArg with
                 | true, Some(Fable.Value(Fable.BaseValue _, _)) ->
                     // Only compare param types for overloads (single curried parameter group)
@@ -2960,13 +2960,24 @@ module Util =
                         else
                             None
 
-                    entity
-                    |> tryFindBaseEntity (fun ent ->
-                        tryFindAbstractMember com ent memb.CompiledName memb.IsInstanceMember paramTypes
-                        |> Option.isSome
-                    )
-                    |> Option.defaultValue entity
-                | _ -> entity
+                    let baseEntity =
+                        entity
+                        |> tryFindBaseEntity (fun ent ->
+                            tryFindAbstractMember com ent memb.CompiledName memb.IsInstanceMember paramTypes
+                            |> Option.isSome
+                        )
+                        |> Option.defaultValue entity
+
+                    // Also find the member from the base entity so the overload hash is computed
+                    // with matching generic parameter names. When 'memb' is an override from a
+                    // subclass with different generic param names than the base entity, the hash
+                    // would be wrong if we use the override member with the base entity. (#3895)
+                    let baseMember =
+                        tryFindAbstractMember com baseEntity memb.CompiledName memb.IsInstanceMember paramTypes
+                        |> Option.defaultValue memb
+
+                    baseEntity, baseMember
+                | _ -> entity, memb
 
             callAttachedMember com ctx r typ callInfo entity memb
 

src/Fable.Transforms/Python/Fable2Python.Transforms.fs

@@ -3996,6 +3996,24 @@ let transformAttachedMethod (com: IPythonCompiler) ctx (info: Fable.MemberFuncti
     let args, body, returnType =
         getMemberArgsAndBody com ctx (Attached isStatic) info.HasSpread memb.Args memb.Body
 
+    let args =
+        let declaredAsGenericSingleArg =
+            List.isEmpty args.Defaults
+            && List.length args.Args = 1
+            && (
+                match info.CurriedParameterGroups |> List.collect id with
+                | [ p ] ->
+                    match p.Type with
+                    | Fable.GenericParam _ -> true
+                    | _ -> false
+                | _ -> false
+            )
+
+        if declaredAsGenericSingleArg then
+            { args with Defaults = [ libValue com ctx "util" "UNIT" ] }
+        else
+            args
+
     let self = Arg.arg "self"
 
     let arguments =

tests/Js/Main/TypeTests.fs

@@ -670,6 +670,30 @@ type AbstractClassWithResizeArrayProp() =
 type ConcreteClass1() =
     inherit MangledAbstractClass5(2)
 
+// See #3895 - super call with generic class hierarchy uses wrong overload hash
+type IGenericAttach3895<'C> =
+    abstract Attach: 'C -> unit
+
+[<AbstractClass>]
+type GenericAttachBase3895<'C>(log: ResizeArray<string>) =
+    abstract Attach: 'C -> unit
+    default _.Attach(_owner: 'C) = log.Add("Base")
+
+    interface IGenericAttach3895<'C> with
+        member this.Attach(owner: 'C) = this.Attach(owner)
+
+type GenericAttachMid3895<'Container>(log: ResizeArray<string>) =
+    inherit GenericAttachBase3895<'Container>(log)
+    override this.Attach(owner) =
+        base.Attach(owner)
+        log.Add("Mid")
+
+type GenericAttachLeaf3895(log: ResizeArray<string>) =
+    inherit GenericAttachMid3895<string>(log)
+    override this.Attach(owner) =
+        base.Attach(owner)
+        log.Add("Leaf")
+
 type IndexedProps(v: int) =
     let mutable v = v
     member _.Item with get (v2: int) = v + v2 and set v2 (s: string) = v <- v2 + int s
@@ -1552,6 +1576,14 @@ let tests =
         let c = ConcreteClass1()
         c.MyMethod(4) |> equal 58
 
+    // See #3895 - super call in generic class hierarchy was using wrong mangled name
+    testCase "Super call works correctly in multi-level generic class hierarchy" <| fun () ->
+        let log = ResizeArray<string>()
+        let obj = GenericAttachLeaf3895(log)
+        obj.Attach("hello")
+        // Each override delegates to base before logging, so the chain unwinds Base -> Mid -> Leaf
+        log |> List.ofSeq |> equal [ "Base"; "Mid"; "Leaf" ]
+
     // See #3328
     testCase "SRTP works with byref" <| fun () ->
       let result = doubleIntByRef (TypeWithByRefMember()) 7

tests/Python/TestType.fs

@@ -607,9 +607,33 @@
     override _.MapAToB(a: int) = string a
     override _.SomeProp = 42
 
+// See #3895 - super call in multi-level generic class hierarchy used wrong mangled name
+type IGenericAttach3895<'C> =
+    abstract Attach: 'C -> unit
+
+[<AbstractClass>]
+type GenericAttachBase3895<'C>(log: ResizeArray<string>) =
+    abstract Attach: 'C -> unit
+    default _.Attach(_owner: 'C) = log.Add("Base")
+
+    interface IGenericAttach3895<'C> with
+        member this.Attach(owner: 'C) = this.Attach(owner)
+
+type GenericAttachMid3895<'Container>(log: ResizeArray<string>) =
+    inherit GenericAttachBase3895<'Container>(log)
+    override this.Attach(owner) =
+        base.Attach(owner)
+        log.Add("Mid")
+
+type GenericAttachLeaf3895(log: ResizeArray<string>) =
+    inherit GenericAttachMid3895<string>(log)
+    override this.Attach(owner) =
+        base.Attach(owner)
+        log.Add("Leaf")
+
 type IndexedProps(v: int) =
     let mutable v = v
     member _.Item with get (v2: int) = v + v2 and set v2 (s: string) = v <- v2 + int s
     member _.Item with get (v2: float) = float v + v2 / 2.
 
 [<Interface>]
@@ -1831,3 +1855,12 @@
     reader.Warnings.Add("Warning 2")
 
     reader.Warnings.Count |> equal 2
+
+// See #3895 - super call in generic class hierarchy was using wrong mangled name
+[<Fact>]
+let ``test Super call works correctly in multi-level generic class hierarchy`` () =
+    let log = ResizeArray<string>()
+    let obj = GenericAttachLeaf3895(log)
+    obj.Attach("hello")
+    // Each override delegates to base before logging, so the chain unwinds Base -> Mid -> Leaf
+    log |> List.ofSeq |> equal [ "Base"; "Mid"; "Leaf" ]

tests/Rust/tests/src/TypeTests.fs

@@ -512,9 +512,33 @@
 type ConcreteClass1() =
     inherit MangledAbstractClass5(2)
 
+// See #3895 - super call in multi-level generic class hierarchy used wrong mangled name
+type IGenericAttach3895<'C> =
+    abstract Attach: 'C -> unit
+
+[<AbstractClass>]
+type GenericAttachBase3895<'C>(log: ResizeArray<string>) =
+    abstract Attach: 'C -> unit
+    default _.Attach(_owner: 'C) = log.Add("Base")
+
+    interface IGenericAttach3895<'C> with
+        member this.Attach(owner: 'C) = this.Attach(owner)
+
+type GenericAttachMid3895<'Container>(log: ResizeArray<string>) =
+    inherit GenericAttachBase3895<'Container>(log)
+    override this.Attach(owner) =
+        base.Attach(owner)
+        log.Add("Mid")
+
+type GenericAttachLeaf3895(log: ResizeArray<string>) =
+    inherit GenericAttachMid3895<string>(log)
+    override this.Attach(owner) =
+        base.Attach(owner)
+        log.Add("Leaf")
+
 type IndexedProps(v: int) =
     let mutable v = v
     member _.Item with get (v2: int) = v + v2 and set v2 (s: string) = v <- v2 + int s
     member _.Item with get (v2: float) = float v + v2 / 2.
 
 [<Interface>]
@@ -1372,3 +1396,12 @@
 let ``Can call the base version of a mangled abstract method that was declared above in the hierarchy`` () =
     let c = ConcreteClass1()
     c.MyMethod(4) |> equal 58
+
+// See #3895 - super call in generic class hierarchy was using wrong mangled name
+[<Fact>]
+let ``Super call works correctly in multi-level generic class hierarchy`` () =
+    let log = ResizeArray<string>()
+    let obj = GenericAttachLeaf3895(log)
+    obj.Attach("hello")
+    // Each override delegates to base before logging, so the chain unwinds Base -> Mid -> Leaf
+    List.ofSeq log |> equal [ "Base"; "Mid"; "Leaf" ]