py: Add protection against printing too nested or recursive data structures.

With a test which cannot be automatically validated so far.

py/obj.c

@@ -35,6 +35,7 @@
 #include "obj.h"
 #include "runtime0.h"
 #include "runtime.h"
+#include "stackctrl.h"
 
 mp_obj_type_t *mp_obj_get_type(mp_const_obj_t o_in) {
     if (MP_OBJ_IS_SMALL_INT(o_in)) {
@@ -59,6 +60,8 @@ void printf_wrapper(void *env, const char *fmt, ...) {
 }
 
 void mp_obj_print_helper(void (*print)(void *env, const char *fmt, ...), void *env, mp_obj_t o_in, mp_print_kind_t kind) {
+    // There can be data structures nested too deep, or just recursive
+    STACK_CHECK();
 #if !NDEBUG
     if (o_in == NULL) {
         print(env, "(nil)");

tests/misc/recursive_data.py_

@@ -0,0 +1,9 @@
+# This tests that printing recursive data structure doesn't lead to segfault.
+# Unfortunately, print() so far doesn't support "file "kwarg, so variable-len
+# output of this test cannot be redirected, and this test cannot be validated.
+l = [1, 2, 3, None]
+l[-1] = l
+try:
+    print(l)
+except RuntimeError:
+    print("RuntimeError")