Set the right path for `PODIO_SIOBLOCK_PATH` and add an error message

[jmcarcell]

BEGINRELEASENOTES

• Set the right path for PODIO_SIOBLOCK_PATH, fixing unit tests that read and write SIO files (there aren't any at the moment)
• Add an error message when PODIO_SIOBLOCK_PATH is set but none of the SioBlock libraries are found.

ENDRELEASENOTES

Adding a simple test that writes a frame to a SIO file won't work when ran with ctest. It looks like the environment is not correctly set because when running the test manually it will work fine. I don't know why but using LD_LIBRARY_PATH instead of DL_PATHS fixes this. This is the test

+#if PODIO_ENABLE_SIO
+
+TEST_CASE("SIO writing a frame", "[relations]") {
+  auto frame = podio::Frame();
+  auto emptyColl = ExampleClusterCollection();
+  frame.put(std::move(emptyColl), "emptyClusters");
+  auto writer = podio::SIOWriter("unittests_frame_sio.sio");
+  writer.writeFrame(frame, podio::Category::Event);
+  writer.finish();
+}
+
+#endif

Here I don't think we need a unittest to simply test the environment, but for running with sanitizers, since all the ROOT ones fail then it's useful to have the SIO ones run from the unit tests.

[jmcarcell]

I noticed but since it works fine without PODIO_SIOBLOCK_PATH didn't give it much thought. Actually, based on https://github.com/catchorg/Catch2/issues/2424, it's possible to set several variables at the same time. But when doing that and setting both LD_LIBRARY_PATH and PODIO_SIOBLOCK_PATH the unittest crashes. So actually that tells us that the problem is not with LD_LIBRARY_PATH but with PODIO_SIOBLOCK_PATH, and indeed removing both also makes this new unittest pass (and all the others). Why do we need PODIO_SIOBLOCK_PATH? What do we want to do here? Since all the test pass without PODIO_SIOBLOCK_PATH I would just remove it.

[jmcarcell]

So having a look I think the options are:

• Remove PODIO_SIOBLOCK_PATH and just use LD_LIBRARY_PATH. From the release notes it seems it was introduced when having multiple installations but then LD_LIBRARY_PATH also needs to be changed anyway.
• If PODIO_SIOBLOCK_PATH is not removed, a check should be added to not crash when the library is not found. Then the path can be modified since the current one is wrong and both PODIO_SIOBLOCK_PATH and LD_LIBRARY_PATH are set.

[tmadlener]

PODIO_SIOBLOCK_PATH was introduced to have the possibility to choose which SioBlocks libraries to actually. If we just have them on LD_LIBRARY_PATH that is much harder to do and in the past test regularly broke simply because we couldn't get a clean test environment to run the SIO backend tests, because we could not clean up the LD_LIBRARY_PATH (e.g. LCG stacks, where this usually pulls in a complete <stack-prefix>/lib). It's far eaiser (also for users) to hand-pick things into a PODIO_SIOBLOCK_PATH and adjust that to only load what they want than it is to try and play with the LD_LIBRARY_PATH.

I am not sure I understand how the failure appears with one but not the other. We first check if PODIO_SIOBLOCK_PATH is set and if not we see if we can find LD_LIBRARY_PATH. In case neither is set, we don't try to load any libraries and otherwise the library loading just continues exactly the same for both:

https://github.com/AIDASoft/podio/blob/82814a8800e246af71077982e270672b71ed6531/src/SIOBlock.cc#L141-L168

[jmcarcell]

The issue is that PODIO_SIOBLOCK_PATH is set but not to the correct path for unittests, and this isn't a problem because there isn't yet a test that triggers it. Then the library isn't found but it doesn't fall back to LD_LIBRARY_PATH as this only happens when PODIO_SIOBLOCK_PATH isn't set. I added an error message for this case, which would be triggered with the current set up. Then, the changes in CMakeLists.txt make it point to the right directory.

[tmadlener]

We even get the fine grained list for unittests in the sanitizer builds with this. Very nice. Thanks :)