lib/utils/pyexec: Allow behaviour of SystemExit to be configurable.

Setting the pyexec_system_exit variable to PYEXEC_FORCED_EXT allows
SystemExit exceptions to terminate the pyexec functions.

lib/utils/pyexec.c

@@ -45,6 +45,7 @@
 #include "genhdr/mpversion.h"
 
 pyexec_mode_kind_t pyexec_mode_kind = PYEXEC_MODE_FRIENDLY_REPL;
+int pyexec_system_exit = 0;
 STATIC bool repl_display_debugging_info = 0;
 
 #define EXEC_FLAG_PRINT_EOF (1)
@@ -61,6 +62,9 @@ STATIC int parse_compile_execute(void *source, mp_parse_input_kind_t input_kind,
     int ret = 0;
     uint32_t start = 0;
 
+    // by default a SystemExit exception returns 0
+    pyexec_system_exit = 0;
+
     nlr_buf_t nlr;
     if (nlr_push(&nlr) == 0) {
         mp_obj_t module_fun;
@@ -99,7 +103,7 @@ STATIC int parse_compile_execute(void *source, mp_parse_input_kind_t input_kind,
         // check for SystemExit
         if (mp_obj_is_subclass_fast(mp_obj_get_type((mp_obj_t)nlr.ret_val), &mp_type_SystemExit)) {
             // at the moment, the value of SystemExit is unused
-            ret = 0;
+            ret = pyexec_system_exit;
         } else {
             mp_obj_print_exception(&mp_plat_print, (mp_obj_t)nlr.ret_val);
             ret = 0;

lib/utils/pyexec.h

@@ -33,6 +33,11 @@ typedef enum {
 
 extern pyexec_mode_kind_t pyexec_mode_kind;
 
+// Set this to the value (eg PYEXEC_FORCED_EXIT) that will be propagated through
+// the pyexec functions if a SystemExit exception is raised by the running code.
+// It will reset to 0 at the start of each execution (eg each REPL entry).
+extern int pyexec_system_exit;
+
 #define PYEXEC_FORCED_EXIT (0x100)
 #define PYEXEC_SWITCH_MODE (0x200)