[libcamera-devel] [PATCH] lc-compliance: Only download a gtest subproject as a fallback

[Hirokazu Honda]

Hi Javier, thank you for the patch.

On Thu, Feb 3, 2022 at 2:32 AM Laurent Pinchart
<laurent.pinchart at ideasonboard.com> wrote:
>
> Hi Javier,
>
> Thank you for the patch.
>
> On Wed, Feb 02, 2022 at 03:31:40PM +0100, Javier Martinez Canillas wrote:
> > Currently, a subproject is used to fetch gtest dependency unconditionally
> > for any Linux distribution besides ChromeOS. But it leads to a regression
> > in distros whose builders are not allowed to download files during build.
> >
> > This change was introduced by commit 0d50a04cc918 ("lc-compliance: Build
> > with gtest in subprojects") and the rationale is that some distros, such
> > as Debian ship libgtest-dev as a static library. And this could be built
> > with a different toolchain than the one used to build libcamera itself.
> >
> > But this seems to be a corner case, usually users will either build both
> > libcamera and all its dependencies using the same toolchain or build it
> > using both the libgtest library and toolchain as provided by the distro.
> >
> > If someone doesn't want for meson to pick up the non-compatible static
> > library provided by the distro, then instead should make sure that their
> > build root does not have the package providing this installed.
> >
> > Let's simplify the logic to find the dependency and just use the built-in
> > support in dependency() function to fallback to a subproject if not found.
> >
> > This covers to common case of attempting to use the gtest provided by the
> > system or pulling from source if not found or is not preferred.
> >
> > Fixes: commit 0d50a04cc918 ("lc-compliance: Build with gtest in subprojects")
> > Reported-by: Eric Curtin <ecurtin at redhat.com>
> > Signed-off-by: Javier Martinez Canillas <javierm at redhat.com>

The fallback option happens if there is no libgtest in a system.
https://mesonbuild.com/Dependencies.html#building-dependencies-as-subprojects
It is at linking time that we find the libgtest doesn't work.
So I think the problem happens in an environment where libgtest is
installed and a different compiler from one building the libgtest is
used for libcamera.
If I understand correctly, the built-in libgest is compiled always with gcc?
 I am not sure how edge case it is to build libcamera with a different compiler.

Best Regards,
-Hiro
>
> As discussed on IRC, this breaks the build when compiling libcamera with
> clang + libc++ on a system providing a gtest package compiled with g++ +
> libstdc++. Compilation also breaks with gcc 7 and gcc 8, due to the
> corresponding libstdc++ having different versions of some symbols:
>
> /usr/lib/gcc/x86_64-pc-linux-gnu/7.4.0/../../../../x86_64-pc-linux-gnu/bin/ld: /usr/lib64/libgtest.so: undefined reference to `std::__cxx11::basic_ostringstream<char, std::char_traits<char>, std::allocator<char> >::basic_ostringstream()@GLIBCXX_3.4.26'
>
> Such "cross" compilation isn't expected in most cases, but can be useful
> for CI to test multiple compilers on a host system without a fully
> separate build root. Setting the meson force_fallback_for option to
> gtest fixes the CI compilation tests, so
>
> Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
>
> > ---
> >
> >  src/lc-compliance/meson.build | 17 +++--------------
> >  1 file changed, 3 insertions(+), 14 deletions(-)
> >
> > diff --git a/src/lc-compliance/meson.build b/src/lc-compliance/meson.build
> > index 130ddbb55916..8b57474be2b2 100644
> > --- a/src/lc-compliance/meson.build
> > +++ b/src/lc-compliance/meson.build
> > @@ -1,25 +1,14 @@
> >  # SPDX-License-Identifier: CC0-1.0
> >
> >  libevent = dependency('libevent_pthreads', required : get_option('lc-compliance'))
> > +libgtest = dependency('gtest', required : get_option('lc-compliance'),
> > +                      fallback : ['gtest', 'gtest_dep'])
> >
> > -if not libevent.found()
> > +if not (libevent.found() and libgtest.found())
> >      lc_compliance_enabled = false
> >      subdir_done()
> >  endif
> >
> > -if get_option('android_platform') == 'cros'
> > -    libgtest = dependency('gtest', required : get_option('lc-compliance'))
> > -
> > -    if not libgtest.found()
> > -        lc_compliance_enabled = false
> > -        subdir_done()
> > -    endif
> > -
> > -else
> > -    libgtest_sp = subproject('gtest')
> > -    libgtest = libgtest_sp.get_variable('gtest_dep')
> > -endif
> > -
> >  lc_compliance_enabled = true
> >
> >  lc_compliance_sources = files([
>
> --
> Regards,
>
> Laurent Pinchart