Proposed patch converts some dynamic assert to static asserts (Py_BUILD_ASSERT_EXPR). This allows to check static invariants at compile time.

+    (void)Py_BUILD_ASSERT_EXPR(INT_MAX <= _PyTime_MAX / SEC_TO_NS);

Hum, maybe the existing macro should be renamed to Py_BUILD_ASSERT_EXPR and a new Py_BUILD_ASSERT_EXPR macro should add the (void) to ignore the result? It would avoid to have to repeat (void) everywhere.

What do you think?

This is a public name and can be used in third-party code.

> This is a public name and can be used in third-party code.

Do you mean that a library can really rely on the result!? It would be insane :-)

Hum, maybe I wasn't clear: I propose attached macro.patch.

A library can follow the example in the comment.

   #define foo_to_char(foo)  \
       ((char *)(foo)        \
        + Py_BUILD_ASSERT_EXPR(offsetof(struct foo, string) == 0))

Serhiy, could you please not change stuff that I maintain?  I know
you have the best intentions, but I really don't like these kinds
of changes (just like you don't like trailing whitespace :).

OK, I'll exclude Modules/_decimal/_decimal.c.

Thank you!

New changeset ad44d551c13c by Serhiy Storchaka in branch '3.5':
Issue #25558: Refactoring OrderedDict iteration.
https://hg.python.org/cpython/rev/ad44d551c13c

New changeset 51f3547da99c by Serhiy Storchaka in branch 'default':
Issue #25558: Refactoring OrderedDict iteration.
https://hg.python.org/cpython/rev/51f3547da99c

Wrong issue. The correct one is issue24726.

Oh, no, the correct one is issue25410.

use_Py_BUILD_ASSERT_EXPR.patch looks good to me. But you should revert the change on decimal, as asked by Stefan, and I suggested to move an assertion inside the related function (see my comment on Rietveld).

"""
A library can follow the example in the comment.

   #define foo_to_char(foo)  \
       ((char *)(foo)        \
        + Py_BUILD_ASSERT_EXPR(offsetof(struct foo, string) == 0))
"""

Hum ok, I know understand the "_EXPR" suffix of the macro name. Maybe it's worth to add a new #define Py_BUILD_ASSERT(expr) (void)Py_BUILD_ASSERT_EXPR(expr)" macro?

By the way, I don't know what happens if you pass a variable to Py_BUILD_ASSERT_EXPR() rather than a constant. Maybe we could use __builtin_constant_p() on GCC? Maybe it's overcomplexicated :-)

New changeset 45a404d33c2d by Serhiy Storchaka in branch 'default':
Issue #25558: Use compile-time asserts.
https://hg.python.org/cpython/rev/45a404d33c2d

> By the way, I don't know what happens if you pass a variable to Py_BUILD_ASSERT_EXPR() rather than a constant.

If the compiler can't calculate it at compile time (e.g. int_var <= INT_MAX), your are out of luck.

> Maybe we could use __builtin_constant_p() on GCC?

Don't know if it will help.

This issue can now be closed, no?

(I don't think that it's worth to add a new macro and make the existing macro more strict.)