py/objgenerator: Check stack before resuming a generator.

This turns a hard crash in a recursive generator into a 'maximum recursion
depth exceeded' exception.

py/objgenerator.c

@@ -32,6 +32,7 @@
 #include "py/bc.h"
 #include "py/objgenerator.h"
 #include "py/objfun.h"
+#include "py/stackctrl.h"
 
 /******************************************************************************/
 /* generator wrapper                                                          */
@@ -92,6 +93,7 @@ STATIC void gen_instance_print(const mp_print_t *print, mp_obj_t self_in, mp_pri
 }
 
 mp_vm_return_kind_t mp_obj_gen_resume(mp_obj_t self_in, mp_obj_t send_value, mp_obj_t throw_value, mp_obj_t *ret_val) {
+    MP_STACK_CHECK();
     mp_check_self(MP_OBJ_IS_TYPE(self_in, &mp_type_gen_instance));
     mp_obj_gen_instance_t *self = MP_OBJ_TO_PTR(self_in);
     if (self->code_state.ip == 0) {

tests/run-tests

@@ -367,6 +367,7 @@ def run_tests(pyb, tests, args, base_path="."):
         skip_tests.add('micropython/heapalloc_iter.py') # requires generators
         skip_tests.add('micropython/schedule.py') # native code doesn't check pending events
         skip_tests.add('stress/gc_trace.py') # requires yield
+        skip_tests.add('stress/recursive_gen.py') # requires yield
 
     for test_file in tests:
         test_file = test_file.replace('\\', '/')

tests/stress/recursive_gen.py

@@ -0,0 +1,9 @@
+# test deeply recursive generators
+
+def gen():
+    yield from gen()
+
+try:
+    list(gen())
+except RuntimeError:
+    print('RuntimeError')