type argument bug fix

src/fsharp/typrelns.fs

@@ -1735,10 +1735,11 @@ type CalledMeth<'T>
                         match epinfos with 
                         | [pinfo] when pinfo.HasSetter && not pinfo.IsIndexer -> 
                             let pminfo = pinfo.SetterMethod
-                            let pminst = freshenMethInfo m pminfo
+                            let pminst = match minfo with
+                                         | MethInfo.FSMeth(_,TType.TType_app(_,types),_,_) -> types
+                                         | _ -> freshenMethInfo m pminfo
                             Choice1Of2(AssignedItemSetter(id,AssignedPropSetter(pinfo,pminfo, pminst), e))
-                        |  _ ->
-
+                        |  _ ->    
                             match infoReader.GetILFieldInfosOfType(Some(nm),ad,m,returnedObjTy) with
                             | finfo :: _ -> 
                                 Choice1Of2(AssignedItemSetter(id,AssignedILFieldSetter(finfo), e))

tests/fsharpqa/Source/Conformance/DeclarationElements/MemberDefinitions/NamedArguments/PropertySetterAfterConstruction02NamedExtensions.fs

@@ -0,0 +1,40 @@
+// #Regression #Conformance #DeclarationElements #MemberDefinitions #NamedArguments 
+#light
+
+// FSB 1368, named arguments implicitly using property setters for generic class do not typecheck correctly
+
+module GenericClass =
+    type S<'a,'b> =
+        class
+           val mutable x : 'a
+           val mutable y : 'b
+           member obj.X with set(v) = obj.x <- v
+           member obj.Y with set(v) = obj.y <- v
+           new(a,b) = { x=a; y=b }
+        end
+    type S<'a,'b> with
+        member x.XProxyIntrinsic with set (v:'a) = x.X  <- v
+        member x.YProxyIntrinsic with set (v:'b) = x.Y  <- v
+    module Extensions =
+        type S<'a,'b> with
+            member x.XProxyOptional with set (v:'a) = x.X  <- v
+            member x.YProxyOptional with set (v:'b) = x.Y  <- v
+
+    open Extensions
+
+    // Standard construction
+    let x1 = S<int,string>(1,"1", XProxyIntrinsic = 42, YProxyIntrinsic = "42")
+    if x1.x <> 42   then exit 1
+    if x1.y <> "42" then exit 1
+
+    let x2 = S<_,_>(1,"1")
+    x2.XProxyOptional <- 43
+    x2.YProxyOptional <- "43"
+    if x2.x <> 43   then exit 1
+    if x2.y <> "43" then exit 1
+
+    let x3 = S<_,_>(1,"1", XProxyOptional = 44, YProxyOptional = "44")
+    if x3.x <> 44   then exit 1
+    if x3.y <> "44" then exit 1
+    exit 0
+