[PATCH] D12747: Implement [depr.c.headers]

Eric Fiselier via cfe-commits cfe-commits at lists.llvm.org
Fri Oct 9 15:48:48 PDT 2015


Regarding Patch #15.

1. Tests under 'test/std' shouldn't directly include <__config> or
depend on any libc++ implementation details. We are trying to make the
test suite generic so refrain from referencing libc++ symbols.
2. "static_assert" is C++11 only but this test should work in C++03.
Can you use "#if TEST_STD_VER >= 11" from "test_macros.h" to use
static assert in C++11 and just "assert" in C++03 (or something
similar)?
3. Could you throw the standarese that requires this behavior at the
top of the test?

LGTM after you address those points.

/Eric


On Fri, Oct 9, 2015 at 4:26 PM, Eric Fiselier <eric at efcs.ca> wrote:
> Patch #12 LGTM. Thanks for doing tho cwchar approach in this patch.
> One small nit. I would prefer a "negative" feature macro for
> "_LIBCPP_STRING_H_HAS_CONST_OVERLOADS" because correct defaults
> shouldn't need a macro definition to be selected. (ie
> _LIBCPP_STRING_H_HAS_NO_CONST_OVERLOAD.)
>
> /Eric
>
> On Fri, Oct 9, 2015 at 1:59 PM, Richard Smith <richard at metafoo.co.uk> wrote:
>> As of r249890, all committed other than patches 12 (string.h) and 15 (more
>> tests).
>>
>> On Thu, Oct 8, 2015 at 9:12 PM, Richard Smith <richard at metafoo.co.uk> wrote:
>>>
>>> On Thu, Oct 8, 2015 at 6:58 PM, Richard Smith <richard at metafoo.co.uk>
>>> wrote:
>>>>
>>>> On Thu, Oct 8, 2015 at 6:25 PM, Eric Fiselier <eric at efcs.ca> wrote:
>>>>>
>>>>> Patch #12 needs revision. A bunch of function definitions were moved
>>>>> out of the std namespace and into the global.
>>>>> That change is incorrect.
>>>>
>>>>
>>>> Slightly updated version attached. I should probably explain what's going
>>>> on here in more detail:
>>>>
>>>> Per [c.strings]p4-p13, we're supposed to replace C functions of the form
>>>>
>>>>   char *foo(const char*);
>>>>
>>>> with a pair of const-correct overloads of the form
>>>>
>>>>   char *foo(char *);
>>>>   const char *foo(const char*);
>>>>
>>>> Now, most C standard libraries will do this for us when included in C++
>>>> mode (because it's not possible for the C++ library to fix this up after the
>>>> fact). For the cases where we *don't* believe we have such a considerate C
>>>> library, we add one declaration to C's overload, to get:
>>>>
>>>>   char *foo(char*);
>>>>   char *foo(const char*)
>>>>
>>>> ... which doesn't really help much, but is the closest we can get to the
>>>> right set of declarations. The declarations we add just dispatch to the C
>>>> declarations.
>>>>
>>>> These new declarations *should* be in the global namespace when including
>>>> <string.h>, and it makes sense for us to put them in the global namespace
>>>> when including <cstring> (otherwise, that header leaves us with a broken
>>>> overload set in the global namespace, containing just one of the two
>>>> expected functions).
>>>>
>>>> Anyway, most of the above is a description of what we did before. What's
>>>> new here is that we attempt to fix the overload set for both <string.h> and
>>>> for <cstring>, not just for the latter. At the end of all these changes,
>>>> you'll see that all that the <cfoo> headers do is to include the <foo.h>
>>>> header and use using-declarations to pull the names into namespace std; this
>>>> is no exception to that pattern.
>>>
>>>
>>> Per Eric and my discussion on IRC, the pattern used by <cwchar> seems
>>> better here:
>>>
>>> If libc has left us with a bad overload set, don't try to fix the names in
>>> ::, just provide a complete set of overloads in namespace std.
>>>
>>> A patch for that approach is attached.
>>>
>>>>> On Thu, Oct 8, 2015 at 7:09 PM, Eric Fiselier <eric at efcs.ca> wrote:
>>>>> > Patch #11 LGTM. Any reason you removed the "#pragma diagnostic ignored
>>>>> > "-Wnonnull"" in test/std/depr/depr.c.headers/stdlib_h.pass.cpp?
>>>>> > I would like to leave it in so this test doesn't fail with older clang
>>>>> > versions.
>>>>> >
>>>>> > /Eric
>>>>> >
>>>>> > On Thu, Oct 8, 2015 at 6:47 PM, Eric Fiselier <eric at efcs.ca> wrote:
>>>>> >> Patch #10 LGTM.
>>>>> >>
>>>>> >> On Thu, Oct 8, 2015 at 4:28 PM, Richard Smith <richard at metafoo.co.uk>
>>>>> >> wrote:
>>>>> >>> On Thu, Oct 8, 2015 at 11:50 AM, Marshall Clow
>>>>> >>> <mclow.lists at gmail.com>
>>>>> >>> wrote:
>>>>> >>>>
>>>>> >>>> On Tue, Oct 6, 2015 at 3:57 PM, Richard Smith
>>>>> >>>> <richard at metafoo.co.uk>
>>>>> >>>> wrote:
>>>>> >>>>>
>>>>> >>>>> <stddef.h>. This one is tricky:
>>>>> >>>>>
>>>>> >>>>> 1) There's an (undocumented) interface between the C standard
>>>>> >>>>> library and
>>>>> >>>>> this header, where the macros __need_ptrdiff_t, __need_size_t,
>>>>> >>>>> __need_wchar_t, __need_NULL, __need_wint_t request just a piece of
>>>>> >>>>> this
>>>>> >>>>> header rather than the whole thing. If we see any of those, just
>>>>> >>>>> go straight
>>>>> >>>>> to the underlying header.
>>>>> >>>>
>>>>> >>>>
>>>>> >>>> Ok, but in that case we don't get nullptr.  I suspect that's OK.
>>>>> >>>>
>>>>> >>>>>
>>>>> >>>>> 2) We probably don't want <stddef.h> to include <cstddef> (for
>>>>> >>>>> consistency with other headers)
>>>>> >>>>
>>>>> >>>>
>>>>> >>>> No, we do not! :-)
>>>>> >>>>
>>>>> >>>>>
>>>>> >>>>> , but <stddef.h> must provide a ::nullptr_t (which we don't want
>>>>> >>>>> <cstddef> to provide). So neither header includes the other.
>>>>> >>>>> Instead, both
>>>>> >>>>> include <__nullptr> for std::nullptr_t, and we duplicate the
>>>>> >>>>> definition of
>>>>> >>>>> max_align_t between them, in the case where the compiler's
>>>>> >>>>> <stddef.h>
>>>>> >>>>> doesn't provide it.
>>>>> >>>>>
>>>>> >>>>> If you prefer, I could make <stddef.h> include <cstddef> to avoid
>>>>> >>>>> the
>>>>> >>>>> duplication of the max_align_t logic.
>>>>> >>>>
>>>>> >>>>
>>>>> >>>> No; this is a minor annoyance, and layer jumping (<stdXXX.h>
>>>>> >>>> including
>>>>> >>>> <cstdXXX>) is a major annoyance - and I'm pretty sure that that
>>>>> >>>> would come
>>>>> >>>> back to bite us in the future.
>>>>> >>>>
>>>>> >>>> Looks ok to me.
>>>>> >>>
>>>>> >>>
>>>>> >>> Thanks, everything up to and including patch 09 is now committed.
>>>>
>>>>
>>>
>>


More information about the cfe-commits mailing list