Check for list emptiness before checking variants

src/lib/pythongen.ml

@@ -213,10 +213,12 @@ let rec typecheck : type a. a typ -> string -> t list =
  variants
  in
  let check_contents =
- List.fold_left
- (fun acc x -> List.concat [ acc; check false x ])
- (check true (List.hd variants_to_check))
- (List.tl variants_to_check)
+ match variants_to_check with
+ | [] -> []
+ | v :: vs ->
+ List.fold_left
+ (fun acc x -> List.concat [ acc; check false x ])
+ (check true v) vs
  in
  let all_tags = List.map (fun (BoxedTag t) -> t.tname) variants in
  let pylist =

tests/rpc/test_pythongen.ml

@@ -67,6 +67,50 @@ module Interface (R : Idl.RPC) = struct
 end
 
 module IfCode = Interface (Codegen.Gen ())
+module UnitVInterface (R : Idl.RPC) = struct
+ open R
+
+ type unit_variant =
+ | Empty
+ | Hollow
+ | Vacant
+ | Void
+ [@@deriving rpcty]
+
+ let unit_variant_p = Idl.Param.mk ~name:"unit_variant" unit_variant
+ let int_p = Idl.Param.mk Rpc.Types.int
+
+ let discard_v =
+ R.declare
+ "discard_v"
+ [ "constant function taking a unit variant and discards it by returning an integer"
+ ]
+ (unit_variant_p @-> returning int_p Idl.DefaultError.err)
+
+ let implementation =
+ implement
+ { Idl.Interface.name = "UnitVInterface"
+ ; namespace = Some "UnitVInterface"
+ ; description =
+ [ "Unit variant interface which does absolutely nothing. Only used to test \
+ whether the pythongen code can handle variants with zero argument \
+ constructors."
+ ]
+ ; version = 1, 0, 0
+ }
+end
+
+module UnitVCode : sig
+ val implementation : unit -> Codegen.Interface.t
+end =
+ UnitVInterface (Codegen.Gen ())
+
+let unitv_interface = 
+ Codegen.Interfaces.create
+ ~name:"unitv"
+ ~title:"Unit Variant"
+ ~description:[ "Interface for Unit variant" ]
+ ~interfaces:[ UnitVCode.implementation () ]
 
 let interfaces =
  Codegen.Interfaces.create
@@ -146,12 +190,15 @@ let check_exceptions () =
  gen_python_bindings "python/bindings.py";
  run_cmd "Exceptions should be correctly generated" "python python/exn_test.py"
 
+let check_unit_variants () =
+ Pythongen.of_interfaces interfaces |> Pythongen.string_of_ts |> ignore
 
 let tests =
  [ ( "Check generated test interface bindings with pylint & pycodestyle"
  , `Slow
  , lint_bindings )
  ; "Check generated commandline bindings", `Slow, test_commandline
  ; "Check generated test class with commandline bindings", `Slow, check_test_class
- ; "Cehck generated exceptions", `Slow, check_exceptions
+ ; "Check generated exceptions", `Slow, check_exceptions
+ ; "Check python generation on variants with zero-arg constructors", `Quick, check_unit_variants
  ]