py/modbuiltins: Simplify and generalise dir() by probing qstrs.

This patch improves the builtin dir() function by probing the target object
with all possible qstrs via mp_load_method_maybe.  This is very simple (in
terms of implementation), doesn't require recursion, and allows to list all
methods of user-defined classes (without duplicates) even if they have
multiple inheritance with a common parent.  The downside is that it can be
slow because it has to iterate through all the qstrs in the system, but
the "dir()" function is anyway mostly used for testing frameworks and user
introspection of types, so speed is not considered a priority.

In addition to providing a more complete implementation of dir(), this
patch is simpler than the previous implementation and saves some code
space:

   bare-arm:   -80
minimal x86:   -80
   unix x64:   -56
unix nanbox:   -48
      stm32:   -80
     cc3200:   -80
    esp8266:  -104
      esp32:   -64

2 files changed, 31 insertions, 34 deletions

diff --git a/py/modbuiltins.c b/py/modbuiltins.c
index 5461816af0..5d4ec8ffe4 100644
--- a/py/modbuiltins.c
+++ b/py/modbuiltins.c
@@ -173,46 +173,24 @@ STATIC mp_obj_t mp_builtin_chr(mp_obj_t o_in) {
 MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_chr_obj, mp_builtin_chr);
 
 STATIC mp_obj_t mp_builtin_dir(size_t n_args, const mp_obj_t *args) {
-    // TODO make this function more general and less of a hack
-
-    mp_obj_dict_t *dict = NULL;
-    mp_map_t *members = NULL;
-    if (n_args == 0) {
-        // make a list of names in the local name space
-        dict = mp_locals_get();
-    } else { // n_args == 1
-        // make a list of names in the given object
-        if (MP_OBJ_IS_TYPE(args[0], &mp_type_module)) {
-            dict = mp_obj_module_get_globals(args[0]);
-        } else {
-            mp_obj_type_t *type;
-            if (MP_OBJ_IS_TYPE(args[0], &mp_type_type)) {
-                type = MP_OBJ_TO_PTR(args[0]);
-            } else {
-                type = mp_obj_get_type(args[0]);
-            }
-            if (type->locals_dict != NULL && type->locals_dict->base.type == &mp_type_dict) {
-                dict = type->locals_dict;
-            }
-        }
-        if (mp_obj_is_instance_type(mp_obj_get_type(args[0]))) {
-            mp_obj_instance_t *inst = MP_OBJ_TO_PTR(args[0]);
-            members = &inst->members;
-        }
-    }
-
     mp_obj_t dir = mp_obj_new_list(0, NULL);
-    if (dict != NULL) {
+    if (n_args == 0) {
+        // Make a list of names in the local namespace
+        mp_obj_dict_t *dict = mp_locals_get();
         for (size_t i = 0; i < dict->map.alloc; i++) {
             if (MP_MAP_SLOT_IS_FILLED(&dict->map, i)) {
                 mp_obj_list_append(dir, dict->map.table[i].key);
             }
         }
-    }
-    if (members != NULL) {
-        for (size_t i = 0; i < members->alloc; i++) {
-            if (MP_MAP_SLOT_IS_FILLED(members, i)) {
-                mp_obj_list_append(dir, members->table[i].key);
+    } else { // n_args == 1
+        // Make a list of names in the given object
+        // Implemented by probing all possible qstrs with mp_load_method_maybe
+        size_t nqstr = QSTR_TOTAL();
+        for (size_t i = 1; i < nqstr; ++i) {
+            mp_obj_t dest[2];
+            mp_load_method_maybe(args[0], i, dest);
+            if (dest[0] != MP_OBJ_NULL) {
+                mp_obj_list_append(dir, MP_OBJ_NEW_QSTR(i));
             }
         }
     }
diff --git a/tests/basics/builtin_dir.py b/tests/basics/builtin_dir.py
index 16e7e669e4..c15a76f4c6 100644
--- a/tests/basics/builtin_dir.py
+++ b/tests/basics/builtin_dir.py
@@ -17,3 +17,22 @@ foo = Foo()
 print('__init__' in dir(foo))
 print('x' in dir(foo))
 
+# dir of subclass
+class A:
+    def a():
+        pass
+class B(A):
+    def b():
+        pass
+d = dir(B())
+print(d.count('a'), d.count('b'))
+
+# dir of class with multiple bases and a common parent
+class C(A):
+    def c():
+        pass
+class D(B, C):
+    def d():
+        pass
+d = dir(D())
+print(d.count('a'), d.count('b'), d.count('c'), d.count('d'))