Fix Regression with quotations of List.sum on non-primitive type

src/fsharp/MethodCalls.fs

@@ -1864,13 +1864,21 @@ let GenWitnessExpr amap g m (traitInfo: TraitConstraintInfo) argExprs =
             let argTypes =
                 minfo.GetParamTypes(amap, m, methArgTys) 
                 |> List.concat 
+
             // do not apply coercion to the 'receiver' argument
             let receiverArgOpt, argExprs = 
                 if minfo.IsInstance then
                     match argExprs with
                     | h :: t -> Some h, t
                     | argExprs -> None, argExprs
                 else None, argExprs
+
+            // For methods taking no arguments, 'argExprs' will be a single unit expression here
+            let argExprs = 
+                 match argTypes, argExprs with
+                 | [], [_] -> []
+                 | _ -> argExprs
+
             let convertedArgs = (argExprs, argTypes) ||> List.map2 (fun expr expectedTy -> mkCoerceIfNeeded g expectedTy (tyOfExpr g expr) expr)
             match receiverArgOpt with
             | Some r -> r :: convertedArgs

tests/fsharp/core/quotes/test.fsx

@@ -3864,6 +3864,24 @@ module TestInlineQuotationOfAbsOperator  =
          | _ -> false)
 
 
+module TestQuotationOfListSum =
+    type Point =
+        { x: int; y: int }
+        static member Zero = { x=0; y=0 }
+        static member (+) (p1, p2) = { x= p1.x + p2.x; y = p1.y + p2.y }
+    let points = [{x=1; y=10}]
+
+    let q = <@ List.sum points @>
+
+    test "check List.sum" 
+       (match q with 
+         | CallWithWitnesses(None, minfo1, minfo2, [Value(f1,_); Value(f2,_)], [Value (v,_)]) ->
+             minfo1.Name = "Sum" &&
+             minfo2.Name = "Sum$W" &&
+             ((v :?> Point list) = points) &&
+             (((f1 :?> (unit -> Point)) ()) = Point.Zero) &&
+             (((f2 :?> (Point -> Point -> Point)) {x=1;y=1} {x=1;y=2}) = {x=2;y=3})
+         | _ -> false)
 
 #endif