py/runtime: Add MP_BINARY_OP_CONTAINS as reverse of MP_BINARY_OP_IN.

Before this patch MP_BINARY_OP_IN had two meanings: coming from bytecode it
meant that the args needed to be swapped, but coming from within the
runtime meant that the args were already in the correct order.  This lead
to some confusion in the code and comments stating how args were reversed.
It also lead to 2 bugs: 1) containment for a subclass of a native type
didn't work; 2) the expression "{True} in True" would illegally succeed and
return True.  In both of these cases it was because the args to
MP_BINARY_OP_IN ended up being reversed twice.

To fix these things this patch introduces MP_BINARY_OP_CONTAINS which
corresponds exactly to the __contains__ special method, and this is the
operator that built-in types should implement.  MP_BINARY_OP_IN is now only
emitted by the compiler and is converted to MP_BINARY_OP_CONTAINS by
swapping the arguments.

extmod/modbtree.c

@@ -282,7 +282,7 @@ STATIC mp_obj_t btree_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
 STATIC mp_obj_t btree_binary_op(mp_binary_op_t op, mp_obj_t lhs_in, mp_obj_t rhs_in) {
     mp_obj_btree_t *self = MP_OBJ_TO_PTR(lhs_in);
     switch (op) {
-        case MP_BINARY_OP_IN: {
+        case MP_BINARY_OP_CONTAINS: {
             DBT key, val;
             key.data = (void*)mp_obj_str_get_data(rhs_in, &key.size);
             int res = __bt_get(self->db, &key, &val, 0);

py/objarray.c

@@ -269,8 +269,7 @@ STATIC mp_obj_t array_binary_op(mp_binary_op_t op, mp_obj_t lhs_in, mp_obj_t rhs
             return lhs_in;
         }
 
-        case MP_BINARY_OP_IN: {
-            /* NOTE `a in b` is `b.__contains__(a)` */
+        case MP_BINARY_OP_CONTAINS: {
             mp_buffer_info_t lhs_bufinfo;
             mp_buffer_info_t rhs_bufinfo;
 

py/objdict.c

@@ -115,7 +115,7 @@ STATIC mp_obj_t dict_unary_op(mp_unary_op_t op, mp_obj_t self_in) {
 STATIC mp_obj_t dict_binary_op(mp_binary_op_t op, mp_obj_t lhs_in, mp_obj_t rhs_in) {
     mp_obj_dict_t *o = MP_OBJ_TO_PTR(lhs_in);
     switch (op) {
-        case MP_BINARY_OP_IN: {
+        case MP_BINARY_OP_CONTAINS: {
             mp_map_elem_t *elem = mp_map_lookup(&o->map, rhs_in, MP_MAP_LOOKUP);
             return mp_obj_new_bool(elem != NULL);
         }
@@ -485,7 +485,7 @@ STATIC mp_obj_t dict_view_binary_op(mp_binary_op_t op, mp_obj_t lhs_in, mp_obj_t
     if (o->kind != MP_DICT_VIEW_KEYS) {
         return MP_OBJ_NULL; // op not supported
     }
-    if (op != MP_BINARY_OP_IN) {
+    if (op != MP_BINARY_OP_CONTAINS) {
         return MP_OBJ_NULL; // op not supported
     }
     return dict_binary_op(op, o->dict, rhs_in);

py/objint_mpz.c

@@ -207,7 +207,7 @@ mp_obj_t mp_obj_int_binary_op(mp_binary_op_t op, mp_obj_t lhs_in, mp_obj_t rhs_i
         return mp_obj_new_float(flhs / frhs);
 #endif
 
-    } else if (op >= MP_BINARY_OP_INPLACE_OR) {
+    } else if (op >= MP_BINARY_OP_INPLACE_OR && op < MP_BINARY_OP_CONTAINS) {
         mp_obj_int_t *res = mp_obj_int_new_mpz();
 
         switch (op) {

py/objset.c

@@ -461,7 +461,7 @@ STATIC mp_obj_t set_binary_op(mp_binary_op_t op, mp_obj_t lhs, mp_obj_t rhs) {
     #else
     bool update = true;
     #endif
-    if (op != MP_BINARY_OP_IN && !is_set_or_frozenset(rhs)) {
+    if (op != MP_BINARY_OP_CONTAINS && !is_set_or_frozenset(rhs)) {
         // For all ops except containment the RHS must be a set/frozenset
         return MP_OBJ_NULL;
     }
@@ -507,7 +507,7 @@ STATIC mp_obj_t set_binary_op(mp_binary_op_t op, mp_obj_t lhs, mp_obj_t rhs) {
             return set_issubset(lhs, rhs);
         case MP_BINARY_OP_MORE_EQUAL:
             return set_issuperset(lhs, rhs);
-        case MP_BINARY_OP_IN: {
+        case MP_BINARY_OP_CONTAINS: {
             mp_obj_set_t *o = MP_OBJ_TO_PTR(lhs);
             mp_obj_t elem = mp_set_lookup(&o->set, rhs, MP_MAP_LOOKUP);
             return mp_obj_new_bool(elem != MP_OBJ_NULL);

py/objstr.c

@@ -384,8 +384,7 @@ mp_obj_t mp_obj_str_binary_op(mp_binary_op_t op, mp_obj_t lhs_in, mp_obj_t rhs_i
             return mp_obj_new_str_from_vstr(lhs_type, &vstr);
         }
 
-        case MP_BINARY_OP_IN:
-            /* NOTE `a in b` is `b.__contains__(a)` */
+        case MP_BINARY_OP_CONTAINS:
             return mp_obj_new_bool(find_subbytes(lhs_data, lhs_len, rhs_data, rhs_len, 1) != NULL);
 
         //case MP_BINARY_OP_NOT_EQUAL: // This is never passed here

py/objtype.c

@@ -424,7 +424,7 @@ const byte mp_binary_op_method_name[MP_BINARY_OP_NUM_RUNTIME] = {
     [MP_BINARY_OP_LESS_EQUAL] = MP_QSTR___le__,
     [MP_BINARY_OP_MORE_EQUAL] = MP_QSTR___ge__,
     // MP_BINARY_OP_NOT_EQUAL, // a != b calls a == b and inverts result
-    [MP_BINARY_OP_IN] = MP_QSTR___contains__,
+    [MP_BINARY_OP_CONTAINS] = MP_QSTR___contains__,
 
     // All inplace methods are optional, and normal methods will be used
     // as a fallback.

py/opmethods.c

@@ -47,6 +47,6 @@ MP_DEFINE_CONST_FUN_OBJ_2(mp_op_delitem_obj, op_delitem);
 
 STATIC mp_obj_t op_contains(mp_obj_t lhs_in, mp_obj_t rhs_in) {
     mp_obj_type_t *type = mp_obj_get_type(lhs_in);
-    return type->binary_op(MP_BINARY_OP_IN, lhs_in, rhs_in);
+    return type->binary_op(MP_BINARY_OP_CONTAINS, lhs_in, rhs_in);
 }
 MP_DEFINE_CONST_FUN_OBJ_2(mp_op_contains_obj, op_contains);

py/runtime.c

@@ -523,30 +523,12 @@ mp_obj_t mp_binary_op(mp_binary_op_t op, mp_obj_t lhs, mp_obj_t rhs) {
         }
     }
 
-    /* deal with `in`
-     *
-     * NOTE `a in b` is `b.__contains__(a)`, hence why the generic dispatch
-     * needs to go below with swapped arguments
-     */
+    // Convert MP_BINARY_OP_IN to MP_BINARY_OP_CONTAINS with swapped args.
     if (op == MP_BINARY_OP_IN) {
-        mp_obj_type_t *type = mp_obj_get_type(rhs);
-        if (type->binary_op != NULL) {
-            mp_obj_t res = type->binary_op(op, rhs, lhs);
-            if (res != MP_OBJ_NULL) {
-                return res;
-            }
-        }
-
-        // final attempt, walk the iterator (will raise if rhs is not iterable)
-        mp_obj_iter_buf_t iter_buf;
-        mp_obj_t iter = mp_getiter(rhs, &iter_buf);
-        mp_obj_t next;
-        while ((next = mp_iternext(iter)) != MP_OBJ_STOP_ITERATION) {
-            if (mp_obj_equal(next, lhs)) {
-                return mp_const_true;
-            }
-        }
-        return mp_const_false;
+        op = MP_BINARY_OP_CONTAINS;
+        mp_obj_t temp = lhs;
+        lhs = rhs;
+        rhs = temp;
     }
 
     // generic binary_op supplied by type
@@ -575,6 +557,20 @@ generic_binary_op:
     }
 #endif
 
+    if (op == MP_BINARY_OP_CONTAINS) {
+        // If type didn't support containment then explicitly walk the iterator.
+        // mp_getiter will raise the appropriate exception if lhs is not iterable.
+        mp_obj_iter_buf_t iter_buf;
+        mp_obj_t iter = mp_getiter(lhs, &iter_buf);
+        mp_obj_t next;
+        while ((next = mp_iternext(iter)) != MP_OBJ_STOP_ITERATION) {
+            if (mp_obj_equal(next, rhs)) {
+                return mp_const_true;
+            }
+        }
+        return mp_const_false;
+    }
+
 unsupported_op:
     if (MICROPY_ERROR_REPORTING == MICROPY_ERROR_REPORTING_TERSE) {
         mp_raise_TypeError("unsupported type for operator");

py/runtime0.h

@@ -131,6 +131,10 @@ typedef enum {
         #endif
     ,
 
+    // The runtime will convert MP_BINARY_OP_IN to this operator with swapped args.
+    // A type should implement this containment operator instead of MP_BINARY_OP_IN.
+    MP_BINARY_OP_CONTAINS,
+
     MP_BINARY_OP_NUM_RUNTIME,
 
     // These 2 are not supported by the runtime and must be synthesised by the emitter

tests/micropython/viper_error.py.exp

@@ -18,7 +18,7 @@ ViperTypeError('must raise an object',)
 ViperTypeError('unary op __pos__ not implemented',)
 ViperTypeError('unary op __neg__ not implemented',)
 ViperTypeError('unary op __invert__ not implemented',)
-ViperTypeError('binary op __contains__ not implemented',)
+ViperTypeError('binary op  not implemented',)
 NotImplementedError('native yield',)
 NotImplementedError('native yield from',)
 NotImplementedError('conversion to object',)