Re: Making -Wmissing-include-dirs an error?
On Tue, 10 Oct 2023 at 12:17, Ian McInerney via devel
<devel(a)lists.fedoraproject.org> wrote:
On Tue, Oct 10, 2023 at 11:59 AM Neal Gompa <ngompa13(a)gmail.com> wrote:
>
> Hey all,
>
> Recently, one of the folks working on packaging stuff in Fedora KDE
> nearly missed an issue caused by GCC emitting a warning about missing
> include dirs:
>
> > cc1plus: warning: /usr/include/qt6/QtCore/6.5.3: No such file or directory
[-Wmissing-include-dirs]
> > cc1plus: warning: /usr/include/qt6/QtCore/6.5.3/QtCore: No such file or
directory [-Wmissing-include-dirs]
>
> I did manage to figure out this meant we needed an additional build
> dependency (qt6-qtbase-private-devel, FYI), but it made me think if
> there's a reason this shouldn't be an error.
>
> If it's an error, then at least we can evaluate these things and
> ensure we have the right build inputs...
Missing an include directory isn't necessarily the problem though, it is the missing
headers that aren't present when they are included that would be - and that should
trigger a build error for the missing file. What advantage does failing on this warning
provide that the failure on the include file missing doesn't?
Typically, yes, I'd expect a failure. But it's possible for code to do:
#if __has_include(<foo.h>)
# include <foo.h>
// use features in that header
#else
// roll your own inferior version
#endif
And so the code could compile either way, but with results that differ
depending on whether <foo.h> is found or not. The extra -I include dir
could be given to the compiler so that if <foo.h> is present in that
dir, it will be found and used. If it's not present, there's no harm.
I don't expect this to be a very widely used pattern though.
The above doesn't necessarily argue for or against making it an error.
There are arguments either way. Making it an error might give some
maintainers a heads up that something's missing, but for other
packages it would break a valid use case.