py/runtime: Make import-all support non-modules via __dict__/__all__.

Prior to this fix, `mp_import_all()` assumed that its argument was exactly
a native module instance.  That would lead to a crash if something else was
passed in, eg a user class via a custom `__import__` implementation or by
writing to `sys.modules`.

MicroPython already supports injecting non-module objects into the import
machinery, so it makes sense to round out that implementation by supporting
`from x import *` where `x` is a non-module object.

Fixes issue micropython#18639.

Signed-off-by: Damien George <damien@micropython.org>

Author: dpgeorge

py/runtime.c

@@ -1592,28 +1592,39 @@ mp_obj_t mp_import_from(mp_obj_t module, qstr name) {
 void mp_import_all(mp_obj_t module) {
     DEBUG_printf("import all %p\n", module);
 
-    mp_map_t *map = &mp_obj_module_get_globals(module)->map;
+    mp_obj_t dest[2];
 
     #if MICROPY_MODULE___ALL__
-    mp_map_elem_t *elem = mp_map_lookup(map, MP_OBJ_NEW_QSTR(MP_QSTR___all__), MP_MAP_LOOKUP);
-    if (elem != NULL) {
+
+    mp_load_method_maybe(module, MP_QSTR___all__, dest);
+    if (dest[0] != MP_OBJ_NULL) {
         // When __all__ is defined, we must explicitly load all specified
         // symbols, possibly invoking the module __getattr__ function
         size_t len;
         mp_obj_t *items;
-        mp_obj_get_array(elem->value, &len, &items);
+        mp_obj_get_array(dest[0], &len, &items);
         for (size_t i = 0; i < len; i++) {
             qstr qname = mp_obj_str_get_qstr(items[i]);
-            mp_obj_t dest[2];
             mp_load_method(module, qname, dest);
             mp_store_name(qname, dest[0]);
         }
         return;
     }
     #endif
 
+    #if MICROPY_CPYTHON_COMPAT
+    // Load the dict from the module.  In MicroPython, if __dict__ is
+    // available then it always returns a native mp_obj_dict_t instance.
+    mp_load_method(module, MP_QSTR___dict__, dest);
+    #else
+    // Without MICROPY_CPYTHON_COMPAT __dict__ is not available, so just
+    // assume the given module is actually an mp_obj_module_t instance.
+    dest[0] = MP_OBJ_FROM_PTR(mp_obj_module_get_globals(module));
+    #endif
+
     // By default, the set of public names includes all names found in the module's
     // namespace which do not begin with an underscore character ('_')
+    mp_map_t *map = mp_obj_dict_get_map(dest[0]);
     for (size_t i = 0; i < map->alloc; i++) {
         if (mp_map_slot_is_filled(map, i)) {
             // Entry in module global scope may be generated programmatically

tests/basics/import_star_nonmodule.py

@@ -0,0 +1,65 @@
+# Test "from x import *" where x is something other than a module.
+
+import sys
+
+try:
+    next(iter([]), 42)
+except TypeError:
+    # Two-argument version of next() not supported.  We are probably not at
+    # MICROPY_CONFIG_ROM_LEVEL_BASIC_FEATURES which is needed for "import *".
+    print("SKIP")
+    raise SystemExit
+
+print("== test with a class as a module ==")
+
+
+class M:
+    x = "a1"
+
+    def __init__(self):
+        self.x = "a2"
+
+
+sys.modules["mod"] = M
+from mod import *
+
+print(x)
+
+sys.modules["mod"] = M()
+from mod import *
+
+print(x)
+
+print("== test with a class as a module that overrides __all__ ==")
+
+
+class M:
+    __all__ = ("y",)
+    x = "b1"
+    y = "b2"
+
+    def __init__(self):
+        self.__all__ = ("x",)
+        self.x = "b3"
+        self.y = "b4"
+
+
+sys.modules["mod"] = M
+x = None
+from mod import *
+
+print(x, y)
+
+sys.modules["mod"] = M()
+from mod import *
+
+print(x, y)
+
+print("== test with objects that don't have a __dict__ ==")
+
+sys.modules["mod"] = 1
+try:
+    from mod import *
+    # MicroPython raises AttributeError, CPython raises ImportError.
+except (AttributeError, ImportError):
+    print("ImportError")