[jvm] drop functional_interface_lut; compute SAM field on demand

The LUT memoized get_singular_interface_field per class, populated by
typeloadFields.check_functional_interface and re-checked lazily by
AbstractCast (#11549, for display-mode flows where init_class hadn't
run yet by the time a SAM conversion was queried). It was a global
mutable hashtbl on common.context whose only reader was AbstractCast.

The cached computation is a walk over a SAM interface's field list —
typically under 10 entries, and short-circuits on the second non-default
method, so the perf delta from recomputing is well below noise. Doing
that directly in AbstractCast collapses the two load paths into one and
removes the field from common.context.

Also drops the now-no-op typeloadFields.check_functional_interface
(its only effect was populating the LUT) and the bridge call that
re-invoked it from init_class when the flag was set via @:functionalInterface
meta in typeloadModule.

Author: kLabz

src/context/abstractCast.ml

@@ -88,14 +88,9 @@ and do_check_cast ctx uctx tleft eright p =
 						loop2 a.a_to
 					end
 				| TInst(c,tl), TFun _ when has_class_flag c CFunctionalInterface ->
-					let cf = try
-						snd (ctx.com.functional_interface_lut#find c.cl_path)
-					with Not_found -> match TClass.get_singular_interface_field c.cl_ordered_fields with
-						| None ->
-							raise Not_found
-						| Some cf ->
-							ctx.com.functional_interface_lut#add c.cl_path (c,cf);
-							cf
+					let cf = match TClass.get_singular_interface_field c.cl_ordered_fields with
+						| None -> raise Not_found
+						| Some cf -> cf
 					in
 					let map = apply_params c.cl_params tl in
 					let monos = Monomorph.spawn_constrained_monos map cf.cf_params in

src/context/common.ml

@@ -345,7 +345,6 @@ and context = {
 	mutable modules : Type.module_def list;
 	mutable types : Type.module_type list;
 	mutable resources : (string,string) Hashtbl.t;
-	functional_interface_lut : (path,(tclass * tclass_field)) lookup;
 	(* target-specific *)
 	mutable flash_version : float;
 	mutable neko_lib_paths : string list;
@@ -810,7 +809,6 @@ let create sctx request_scope part_scope display_mode =
 		parser_cache = new hashtbl_lookup;
 		overload_cache = new hashtbl_lookup;
 		is_macro_context = false;
-		functional_interface_lut = new Lookup.hashtbl_lookup;
 		hxb_reader_api = None;
 		hxb_reader_stats = HxbReader.create_hxb_reader_stats ();
 		hxb_writer_config = None;
@@ -935,7 +933,6 @@ let clone com is_macro_context =
 		parser_cache = new hashtbl_lookup;
 		overload_cache = new hashtbl_lookup; (* ! *)
 		is_macro_context = is_macro_context;
-		functional_interface_lut = new Lookup.hashtbl_lookup;
 		hxb_reader_api = None;
 		hxb_reader_stats = HxbReader.create_hxb_reader_stats ();
 	}

src/typing/typeloadFields.ml

@@ -1644,14 +1644,6 @@ let finalize_class cctx =
 		| Some r -> delay ctx.g PTypeField (fun() -> ignore(lazy_type r)))
 	) cctx.delayed_expr
 
-let check_functional_interface ctx c =
-	match TClass.get_singular_interface_field c.cl_ordered_fields with
-	| None ->
-		()
-	| Some cf ->
-		add_class_flag c CFunctionalInterface;
-		ctx.com.functional_interface_lut#add c.cl_path (c,cf)
-
 let create_class_field cctx f  =
 	let cf = {(mk_field (fst f.cff_name) ~public:(is_public cctx f.cff_access None) t_dynamic f.cff_pos (pos f.cff_name)) with
 		cf_doc = f.cff_doc;
@@ -1793,7 +1785,7 @@ let init_class ctx_c cctx c p herits fields =
 			a.a_unops <- List.rev a.a_unops;
 			a.a_array <- List.rev a.a_array;
 		| None ->
-			if (has_class_flag c CFunctionalInterface) && com.platform = Jvm then check_functional_interface ctx_c c;
+			()
 	end;
 	c.cl_ordered_statics <- List.rev c.cl_ordered_statics;
 	c.cl_ordered_fields <- List.rev c.cl_ordered_fields;