py/runtime: Add MICROPY_LAZY_LOAD_GLOBAL.

Jongy · Jongy · commit a3b787ae6623 · 2020-01-13T22:35:46.000+02:00
Allow ports to provide a lazy load function for undefined globals.
diff --git a/py/mpconfig.h b/py/mpconfig.h
@@ -757,6 +757,14 @@ typedef double mp_float_t;
 #define MICROPY_CAN_OVERRIDE_BUILTINS (0)
 #endif
 
+// Allow ports to provide a lazy load function for undefined globals
+// By enabling this, MicroPython will call mp_lazy_load_global() whenever an undefined
+// global is accessed.  Ports can return a non-MP_OBJ_NULL value which will be returned instead
+// of raising NameError.  It is also cached for faster future access.
+#ifndef MICROPY_LAZY_LOAD_GLOBAL
+#define MICROPY_LAZY_LOAD_GLOBAL (0)
+#endif
+
 // Whether to check that the "self" argument of a builtin method has the
 // correct type.  Such an explicit check is only needed if a builtin
 // method escapes to Python land without a first argument, eg
diff --git a/py/runtime.c b/py/runtime.c
@@ -184,6 +184,14 @@ mp_obj_t mp_load_global(qstr qst) {
         #endif
         elem = mp_map_lookup((mp_map_t*)&mp_module_builtins_globals.map, MP_OBJ_NEW_QSTR(qst), MP_MAP_LOOKUP);
         if (elem == NULL) {
+            #if MICROPY_LAZY_LOAD_GLOBAL
+            mp_obj_t obj = mp_lazy_load_global(qst);
+            if (obj != MP_OBJ_NULL) {
+                // cache it for faster access next time
+                mp_store_global(qst, obj);
+                return obj;
+            }
+            #endif
             if (MICROPY_ERROR_REPORTING == MICROPY_ERROR_REPORTING_TERSE) {
                 mp_raise_msg(&mp_type_NameError, "name not defined");
             } else {
diff --git a/py/runtime.h b/py/runtime.h
@@ -93,6 +93,9 @@ static inline void mp_globals_set(mp_obj_dict_t *d) { MP_STATE_THREAD(dict_globa
 
 mp_obj_t mp_load_name(qstr qst);
 mp_obj_t mp_load_global(qstr qst);
+#ifdef MICROPY_LAZY_LOAD_GLOBAL
+mp_obj_t mp_lazy_load_global(qstr qst);
+#endif
 mp_obj_t mp_load_build_class(void);
 void mp_store_name(qstr qst, mp_obj_t obj);
 void mp_store_global(qstr qst, mp_obj_t obj);
