[gmx-developers] issues with libxml detection issues with GMX_BUILD_UNITTESTS=ON

[Mark Abraham]

Hi,

Yes, perhaps that call to check_library_exists can be improved, e.g. by
setting CMAKE_REQUIRED_LIBRARIES for the check (see
https://cmake.org/cmake/help/v3.0/module/CheckLibraryExists.html). However,
it is awkward to do a good job here, because libxml2 only requires zlib if
the former was configured that way, so we have a fairly large number of
conditions to handle in constructing our handling (shared/static, whether
either was found, whether libxml2 needs zlib or not, whether test binaries
need to be built, etc.).

Roland suggested https://gerrit.gromacs.org/#/c/5630/2 but I am not sure if
it is related.

Alternatively/also, since currently the only use for XML handling in master
branch is for test reference data, I have uploaded
https://gerrit.gromacs.org/#/c/5653/ to replace this use of libxml2 with a
bundled copy of tinyxml2, as part of http://redmine.gromacs.org/issues/1908 so
that we get rid of such problematic external dependencies. These have been
causing grief lately for users on BG/Q machines. I suggest we keep libxml2
detection and handling present but inactive while the future of various
patches in Gerrit gets resolved.

Mark

On Wed, Feb 10, 2016 at 4:37 PM Szilárd Páll <pall.szilard at gmail.com> wrote:

> Hi,
>
> $ cmake -DGMX_PREFER_STATIC_LIBS=ON -DGMX_BUILD_UNITTESTS=ON
>
> [...]
> -- Looking for zlibVersion in /usr/lib/x86_64-linux-gnu/libz.a
> -- Looking for zlibVersion in /usr/lib/x86_64-linux-gnu/libz.a - found
> -- Found LibXml2: /usr/lib/x86_64-linux-gnu/libxml2.a (found version
> "2.9.1")
> -- Looking for xmlTextWriterEndAttribute in
> /usr/lib/x86_64-linux-gnu/libxml2.a
> -- Looking for xmlTextWriterEndAttribute in
> /usr/lib/x86_64-linux-gnu/libxml2.a - not found
> [...]
> CMake Error at CMakeLists.txt:562 (message):
>   Cannot build unit tests without libxml2.  Either set
>   GMX_BUILD_UNITTESTS=OFF or tell CMake how to find a working version of
>   libxml2.
>
> Even though both libz and libxml are detected, the
> xmlTextWriterEndAttribute lib test fails to link as the
> check_library_exists() does not pass -lz.
>
> I vaguely remember some discussion around it so I thought I'd ask
> whether this is a known issue before filing a report.
>
> Are there any simple workarounds for this? (I tried passing -lz in the
> linker flags, but that does not help).
> Could we provide a better hint in the error?
>
> Cheers,
> --
> Szilárd
> --
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