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, 4 insertions, 4 deletions

diff --git a/py/obj.c b/py/obj.c
index 024de3c96..51f6d85de 100644
--- a/py/obj.c
+++ b/py/obj.c
@@ -304,7 +304,7 @@ mp_int_t mp_obj_get_int(mp_const_obj_t arg) {
         return 1;
     } else if (mp_obj_is_small_int(arg)) {
         return MP_OBJ_SMALL_INT_VALUE(arg);
-    } else if (mp_obj_is_type(arg, &mp_type_int)) {
+    } else if (mp_obj_is_exact_type(arg, &mp_type_int)) {
         return mp_obj_int_get_checked(arg);
     } else {
         mp_obj_t res = mp_unary_op(MP_UNARY_OP_INT, (mp_obj_t)arg);
@@ -330,7 +330,7 @@ bool mp_obj_get_int_maybe(mp_const_obj_t arg, mp_int_t *value) {
         *value = 1;
     } else if (mp_obj_is_small_int(arg)) {
         *value = MP_OBJ_SMALL_INT_VALUE(arg);
-    } else if (mp_obj_is_type(arg, &mp_type_int)) {
+    } else if (mp_obj_is_exact_type(arg, &mp_type_int)) {
         *value = mp_obj_int_get_checked(arg);
     } else {
         return false;
@@ -349,7 +349,7 @@ bool mp_obj_get_float_maybe(mp_obj_t arg, mp_float_t *value) {
     } else if (mp_obj_is_small_int(arg)) {
         val = (mp_float_t)MP_OBJ_SMALL_INT_VALUE(arg);
     #if MICROPY_LONGINT_IMPL != MICROPY_LONGINT_IMPL_NONE
-    } else if (mp_obj_is_type(arg, &mp_type_int)) {
+    } else if (mp_obj_is_exact_type(arg, &mp_type_int)) {
         val = mp_obj_int_as_float_impl(arg);
     #endif
     } else if (mp_obj_is_float(arg)) {
@@ -389,7 +389,7 @@ bool mp_obj_get_complex_maybe(mp_obj_t arg, mp_float_t *real, mp_float_t *imag)
         *real = (mp_float_t)MP_OBJ_SMALL_INT_VALUE(arg);
         *imag = 0;
     #if MICROPY_LONGINT_IMPL != MICROPY_LONGINT_IMPL_NONE
-    } else if (mp_obj_is_type(arg, &mp_type_int)) {
+    } else if (mp_obj_is_exact_type(arg, &mp_type_int)) {
         *real = mp_obj_int_as_float_impl(arg);
         *imag = 0;
     #endif