[matcher[ don't drop `var = null` bindings

closes #6724

src/typing/matcher.ml

@@ -1028,18 +1028,18 @@ module Compile = struct
 			let unguarded = ConTable.create 0 in
 			let null = ref [] in
 			List.iter (fun (case,bindings,patterns) ->
-				let rec loop pat = match fst pat with
+				let rec loop bindings pat = match fst pat with
 					| PatConstructor(ConConst TNull,_) ->
 						null := (case,bindings,List.tl patterns) :: !null;
 					| PatConstructor(con,_) ->
 						if case.case_guard = None then ConTable.replace unguarded con true;
 						ConTable.replace sigma con true;
-					| PatBind(_,pat) -> loop pat
+					| PatBind(v,pat) -> loop ((v,pos pat,subject) :: bindings) pat
 					| PatVariable _ | PatAny -> ()
 					| PatExtractor _ -> raise Extractor
 					| _ -> error ("Unexpected pattern: " ^ (Pattern.to_string pat)) case.case_pos;
 				in
-				loop (List.hd patterns)
+				loop bindings (List.hd patterns)
 			) cases;
 			let sigma = ConTable.fold (fun con _ acc -> (con,ConTable.mem unguarded con) :: acc) sigma [] in
 			sigma,List.rev !null

tests/unit/src/unit/issues/Issue6724.hx

@@ -0,0 +1,11 @@
+package unit.issues;
+
+class Issue6724 extends unit.Test {
+	function test() {
+		var v = switch (null) {
+			case v = null: v;
+			case _: throw false;
+		}
+		eq(null, v);
+	}
+}