bug#42392: GCC includes ordering issue? g++: error: 'round' is not a member of 'std'

["Ludovic Courtès" <ludo@gnu.org>]

Hi!

Maxim Cournoyer <maxim.cournoyer@gmail.com> skribis:

>> configure:19948:  /tmp/guix-build-gcc-10.1.0.drv-0/build/./gcc/xgcc -shared-libgcc -B/tmp/guix-build-gcc-10.1.0.drv-0/build/./gcc -nostdinc++ -L/tmp/guix-build-gcc-10.1.0.drv-0/build/x86_64-unknown-linux-gnu/libstdc++-v3/src -L/tmp/guix-build-gcc-10.1.0.drv-0/build/x86_64-unknown-linux-gnu/libstdc++-v3/src/.libs -L/tmp/guix-build-gcc-10.1.0.drv-0/build/x86_64-unknown-linux-gnu/libstdc++-v3/libsupc++/.libs -B/gnu/store/jrzxs91zhpf6yr5fxisn3jjj7xai8zlk-gcc-10.1.0/x86_64-unknown-linux-gnu/bin/ -B/gnu/store/jrzxs91zhpf6yr5fxisn3jjj7xai8zlk-gcc-10.1.0/x86_64-unknown-linux-gnu/lib/ -isystem /gnu/store/jrzxs91zhpf6yr5fxisn3jjj7xai8zlk-gcc-10.1.0/x86_64-unknown-linux-gnu/include -isystem /gnu/store/jrzxs91zhpf6yr5fxisn3jjj7xai8zlk-gcc-10.1.0/x86_64-unknown-linux-gnu/sys-include   -fno-checking -c -fno-builtin -D_GNU_SOURCE  conftest.cpp >&5
>> In file included from /gnu/store/rn75fm7adgx3pw5j8pg3bczfqq1y17lk-gcc-7.5.0/include/c++/math.h:36,
>>                  from conftest.cpp:122:
>> /gnu/store/rn75fm7adgx3pw5j8pg3bczfqq1y17lk-gcc-7.5.0/include/c++/cmath:41:10: fatal error: bits/c++config.h: No such file or directory
>>    41 | #include <bits/c++config.h>
>>       |          ^~~~~~~~~~~~~~~~~~
>> compilation terminated.
>> configure:19948: $? = 1
>> configure: failed program was:
>
> Eh! I fail to see what changed between 7.5 and 8.1, that would have
> caused such a change in behavior.

Nothing: the difference is between ‘gcc-final’ and the GCCs exported
from (gnu packages gcc).

‘gcc-final’ has ‘libstdc++’ (a separate package) has an input, like I
wrote.  And thus <bits/c++config.h> is found in this case.

Does that make sense?

Thanks,
Ludo’.