copy var flags when duplicating

Also don't unroll loops that have static vars
closes #11800

src/core/texpr.ml

@@ -328,6 +328,7 @@ let duplicate_tvars f_this e =
 		let v2 = alloc_var v.v_kind v.v_name v.v_type v.v_pos in
 		v2.v_meta <- v.v_meta;
 		v2.v_extra <- v.v_extra;
+		v2.v_flags <- v.v_flags;
 		Hashtbl.add vars v.v_id v2;
 		v2;
 	in

src/typing/forLoop.ml

@@ -412,6 +412,8 @@ let is_cheap_enough ctx e2 i =
 	let rec loop e = match fst e with
 		| EContinue | EBreak ->
 			raise Exit
+		| EVars vl when (List.exists (fun ev -> ev.ev_static) vl) ->
+			raise Exit
 		| _ ->
 			incr num_expr;
 			Ast.map_expr loop e

tests/unit/src/unit/issues/Issue11800.hx

@@ -0,0 +1,21 @@
+package unit.issues;
+
+class Issue11800 extends unit.Test {
+	public function test() {
+		static var a = 0; // Works.
+		var buf = new StringBuf();
+		function append(v:Int) {
+			buf.add(Std.string(v));
+		}
+		for (i in 0...3) {
+			switch i {
+				case n if (n < 2):
+					append(++a);
+					static var b = 0; // Not static.
+					append(++b); // Always `1`.
+				case _:
+			}
+		}
+		eq("1122", buf.toString());
+	}
+}