py/obj: Add static safety checks to mp_obj_is_type().

Commit d96cfd13e3a464862c introduced a regression by breaking existing
users of mp_obj_is_type(.., &mp_obj_bool).  This function (and associated
helpers like mp_obj_is_int()) have some specific nuances, and mistakes like
this one can happen again.

This commit adds mp_obj_is_exact_type() which behaves like the the old
mp_obj_is_type().  The new mp_obj_is_type() has the same prototype but it
attempts to statically assert that it's not called with types which should
be checked using mp_obj_is_type().  If called with any of these types: int,
str, bool, NoneType - it will cause a compilation error.  Additional
checked types (e.g function types) can be added in the future.

Existing users of mp_obj_is_type() with the now "invalid" types, were
translated to use mp_obj_is_exact_type().

The use of MP_STATIC_ASSERT() is not bulletproof - usually GCC (and other
compilers) can't statically check conditions that are only known during
link-time (like variables' addresses comparison).  However, in this case,
GCC is able to statically detect these conditions, probably because it's
the exact same object - `&mp_type_int == &mp_type_int` is detected.
Misuses of this function with runtime-chosen types (e.g:
`mp_obj_type_t *x = ...; mp_obj_is_type(..., x);` won't be detected.  MSC
is unable to detect this, so we use MP_STATIC_ASSERT_NOT_MSC().

Compiling with this commit and without the fix for d96cfd13e3a464862c shows
that it detects the problem.

Signed-off-by: Yonatan Goldschmidt <yon.goldschmidt@gmail.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/py/map.c b/py/map.c
index b194250cb..7a6f2233e 100644
--- a/py/map.c
+++ b/py/map.c
@@ -174,7 +174,7 @@ mp_map_elem_t *MICROPY_WRAP_MP_MAP_LOOKUP(mp_map_lookup)(mp_map_t * map, mp_obj_
     if (compare_only_ptrs) {
         if (mp_obj_is_qstr(index)) {
             // Index is a qstr, so can just do ptr comparison.
-        } else if (mp_obj_is_type(index, &mp_type_str)) {
+        } else if (mp_obj_is_exact_type(index, &mp_type_str)) {
             // Index is a non-interned string.
             // We can either intern the string, or force a full equality comparison.
             // We chose the latter, since interning costs time and potentially RAM,