Implement default type param skipping

Author: kLabz

src/syntax/grammar.ml

@@ -710,6 +710,8 @@ and parse_complex_type_inner allow_named s = match%parser s with
 		in
 		let p = punion p1 p2 in
 		CTPath (make_ptp (mk_type_path ~params:[TPType hint] (["haxe"],"Rest")) p),p
+	| [ (Kwd Default,p) ] ->
+		CTPath (make_ptp (mk_type_path (["$"],"_hx_default")) p),p
 	| [ dollar_ident as n ] ->
 		(match%parser s with
 		| [ (DblDot,_); parse_complex_type as t ] when allow_named->

src/typing/typeload.ml

@@ -303,9 +303,9 @@ let rec load_params ctx info params p =
 	let is_rest = info.build_kind = BuildGenericBuild && (match info.build_params with [{ttp_name="Rest"}] -> true | _ -> false) in
 	let is_java_rest = ctx.com.platform = Jvm && info.build_extern in
 	let is_rest = is_rest || is_java_rest in
-	let load_param t =
-		match t with
-		| TPExpr e ->
+	let load_param t def =
+		match (t, def) with
+		| TPExpr e, _ ->
 			let name = (match fst e with
 				| EConst (String(s,_)) -> "S" ^ s
 				| EConst (Int (_,_) as c) -> "I" ^ s_constant c
@@ -318,14 +318,18 @@ let rec load_params ctx info params p =
 			let c = mk_class ctx.m.curmod ([],name) p (pos e) in
 			c.cl_kind <- KExpr e;
 			TInst (c,[]),pos e
-		| TPType t ->
+		| TPType (CTPath({ path = { tpackage = ["$"]; tname = "_hx_default" }}),p), None ->
+			raise_typing_error "Cannot apply default type parameter on non-default type parameter" p
+		| TPType (CTPath({ path = { tpackage = ["$"]; tname = "_hx_default" }}),p), Some def ->
+			def,p
+		| TPType t, _ ->
 			load_complex_type ctx true LoadNormal t,pos t
 	in
 	let checks = DynArray.create () in
 	let rec loop tl1 tl2 is_rest = match tl1,tl2 with
 		| t :: tl1,ttp:: tl2 ->
 			let name = ttp.ttp_name in
-			let t,pt = load_param t in
+			let t,pt = load_param t ttp.ttp_default in
 			let check_const c =
 				let is_expression = (match t with TInst ({ cl_kind = KExpr _ },_) -> true | _ -> false) in
 				let expects_expression = name = "Const" || Meta.has Meta.Const c.cl_meta in
@@ -364,7 +368,7 @@ let rec load_params ctx info params p =
 					t :: loop [] tl is_rest
 			end
 		| t :: tl,[] ->
-			let t,pt = load_param t in
+			let t,pt = load_param t None in
 			if is_rest then
 				t :: loop tl [] true
 			else if ignore_error ctx.com then
@@ -443,6 +447,7 @@ and load_complex_type' ctx allow_display mode (t,p) =
 	match t with
 	| CTParent t -> load_complex_type ctx allow_display mode t
 	| CTPath { path = {tpackage = ["$"]; tname = "_hx_mono" }} -> spawn_monomorph ctx p
+	| CTPath { path = {tpackage = ["$"]; tname = "_hx_default" }} -> raise_typing_error "Invalid type : default" p
 	| CTPath ptp -> load_instance ~allow_display ctx ptp ParamNormal mode
 	| CTOptional _ -> raise_typing_error "Optional type not allowed here" p
 	| CTNamed _ -> raise_typing_error "Named type not allowed here" p