py/makemoduledefs.py: Avoid empty extensible module lists.

An empty array is a C extension supported by clang & GCC but not MSVC.

This also saves a bit of code size if there are no extensible modules.

Fixes issue #18141.

Signed-off-by: Jeff Epler <jepler@unpythonic.net>

py/builtinhelp.c

@@ -79,7 +79,9 @@ static void mp_help_print_modules(void) {
     mp_obj_t list = mp_obj_new_list(0, NULL);
 
     mp_help_add_from_map(list, &mp_builtin_module_map);
+    #if MICROPY_HAVE_REGISTERED_EXTENSIBLE_MODULES
     mp_help_add_from_map(list, &mp_builtin_extensible_module_map);
+    #endif
 
     #if MICROPY_MODULE_FROZEN
     extern const char mp_frozen_names[];

py/builtinimport.c

@@ -403,6 +403,7 @@ static mp_obj_t process_import_at_level(qstr full_mod_name, qstr level_mod_name,
         // all the locations in sys.path.
         stat = stat_top_level(level_mod_name, &path);
 
+        #if MICROPY_HAVE_REGISTERED_EXTENSIBLE_MODULES
         // If filesystem failed, now try and see if it matches an extensible
         // built-in module.
         if (stat == MP_IMPORT_STAT_NO_EXIST) {
@@ -411,6 +412,7 @@ static mp_obj_t process_import_at_level(qstr full_mod_name, qstr level_mod_name,
                 return module_obj;
             }
         }
+        #endif
     } else {
         DEBUG_printf("Searching for sub-module\n");
 
@@ -646,11 +648,13 @@ mp_obj_t mp_builtin___import___default(size_t n_args, const mp_obj_t *args) {
     if (module_obj != MP_OBJ_NULL) {
         return module_obj;
     }
+    #if MICROPY_HAVE_REGISTERED_EXTENSIBLE_MODULES
     // Now try as an extensible built-in (e.g. `time`).
     module_obj = mp_module_get_builtin(module_name_qstr, true);
     if (module_obj != MP_OBJ_NULL) {
         return module_obj;
     }
+    #endif
 
     // Couldn't find the module, so fail
     #if MICROPY_ERROR_REPORTING <= MICROPY_ERROR_REPORTING_TERSE

py/makemoduledefs.py

@@ -85,19 +85,25 @@ def generate_module_table_header(modules):
             )
         )
 
+    # There should always be at least one module (__main__ in runtime.c)
+    assert mod_defs
+
     print("\n#define MICROPY_REGISTERED_MODULES \\")
 
     for mod_def in sorted(mod_defs):
         print("    {mod_def} \\".format(mod_def=mod_def))
-
     print("// MICROPY_REGISTERED_MODULES")
 
-    print("\n#define MICROPY_REGISTERED_EXTENSIBLE_MODULES \\")
+    # There are not necessarily any extensible modules (e.g., bare-arm or minimal x86)
+    print("\n#define MICROPY_HAVE_REGISTERED_EXTENSIBLE_MODULES ", len(extensible_mod_defs))
 
-    for mod_def in sorted(extensible_mod_defs):
+    if extensible_mod_defs:
-        print("    {mod_def} \\".format(mod_def=mod_def))
+        print("\n#define MICROPY_REGISTERED_EXTENSIBLE_MODULES \\")
 
-    print("// MICROPY_REGISTERED_EXTENSIBLE_MODULES")
+        for mod_def in sorted(extensible_mod_defs):
+            print("    {mod_def} \\".format(mod_def=mod_def))
+
+        print("// MICROPY_REGISTERED_EXTENSIBLE_MODULES")
 
 
 def generate_module_delegations(delegations):

py/objmodule.c

@@ -152,11 +152,13 @@ static const mp_rom_map_elem_t mp_builtin_module_table[] = {
 };
 MP_DEFINE_CONST_MAP(mp_builtin_module_map, mp_builtin_module_table);
 
+#if MICROPY_HAVE_REGISTERED_EXTENSIBLE_MODULES
 static const mp_rom_map_elem_t mp_builtin_extensible_module_table[] = {
     // built-in modules declared with MP_REGISTER_EXTENSIBLE_MODULE()
     MICROPY_REGISTERED_EXTENSIBLE_MODULES
 };
 MP_DEFINE_CONST_MAP(mp_builtin_extensible_module_map, mp_builtin_extensible_module_table);
+#endif
 
 #if MICROPY_MODULE_ATTR_DELEGATION && defined(MICROPY_MODULE_DELEGATIONS)
 typedef struct _mp_module_delegation_entry_t {
@@ -173,7 +175,13 @@ static const mp_module_delegation_entry_t mp_builtin_module_delegation_table[] =
 // Attempts to find (and initialise) a built-in, otherwise returns
 // MP_OBJ_NULL.
 mp_obj_t mp_module_get_builtin(qstr module_name, bool extensible) {
-    mp_map_elem_t *elem = mp_map_lookup((mp_map_t *)(extensible ? &mp_builtin_extensible_module_map : &mp_builtin_module_map), MP_OBJ_NEW_QSTR(module_name), MP_MAP_LOOKUP);
+    #if MICROPY_HAVE_REGISTERED_EXTENSIBLE_MODULES
+    const mp_map_t *map = extensible ? &mp_builtin_extensible_module_map : &mp_builtin_module_map;
+    #else
+    const mp_map_t *map = &mp_builtin_module_map;
+    #endif
+    mp_map_elem_t *elem = mp_map_lookup((mp_map_t *)map, MP_OBJ_NEW_QSTR(module_name), MP_MAP_LOOKUP);
+
     if (!elem) {
         #if MICROPY_PY_SYS
         // Special case for sys, which isn't extensible but can always be
@@ -183,6 +191,7 @@ mp_obj_t mp_module_get_builtin(qstr module_name, bool extensible) {
         }
         #endif
 
+        #if MICROPY_HAVE_REGISTERED_EXTENSIBLE_MODULES
         if (extensible) {
             // At this point we've already tried non-extensible built-ins, the
             // filesystem, and now extensible built-ins. No match, so fail
@@ -204,6 +213,8 @@ mp_obj_t mp_module_get_builtin(qstr module_name, bool extensible) {
             return MP_OBJ_NULL;
         }
         elem = mp_map_lookup((mp_map_t *)&mp_builtin_extensible_module_map, MP_OBJ_NEW_QSTR(qstr_from_strn(module_name_str + 1, module_name_len - 1)), MP_MAP_LOOKUP);
+        #endif
+
         if (!elem) {
             return MP_OBJ_NULL;
         }

py/objmodule.h

@@ -35,7 +35,10 @@
 #endif
 
 extern const mp_map_t mp_builtin_module_map;
+
+#if MICROPY_HAVE_REGISTERED_EXTENSIBLE_MODULES
 extern const mp_map_t mp_builtin_extensible_module_map;
+#endif
 
 mp_obj_t mp_module_get_builtin(qstr module_name, bool extensible);
 

py/repl.c

@@ -162,8 +162,11 @@ static bool test_qstr(mp_obj_t obj, qstr name) {
         return dest[0] != MP_OBJ_NULL;
     } else {
         // try builtin module
-        return mp_map_lookup((mp_map_t *)&mp_builtin_module_map, MP_OBJ_NEW_QSTR(name), MP_MAP_LOOKUP) ||
+        return mp_map_lookup((mp_map_t *)&mp_builtin_module_map, MP_OBJ_NEW_QSTR(name), MP_MAP_LOOKUP)
-               mp_map_lookup((mp_map_t *)&mp_builtin_extensible_module_map, MP_OBJ_NEW_QSTR(name), MP_MAP_LOOKUP);
+               #if MICROPY_HAVE_REGISTERED_EXTENSIBLE_MODULES
+               || mp_map_lookup((mp_map_t *)&mp_builtin_extensible_module_map, MP_OBJ_NEW_QSTR(name), MP_MAP_LOOKUP)
+               #endif
+        ;
     }
 }