[cppyy] Move libcppyy.so to <LIBDIR>/cppyy/libcppyy.so

[hageboeck]

When compiling ROOT in Gentoo, the following warning is issued:

 * Verifying compiled files for python3.13 *
 * QA Notice: The following unexpected files/directories were found
 * top-level in the site-packages directory: *
 *   /usr/lib/python3.13/site-packages/libcppyy.so.6.37.01
 *
 * This is most likely a bug in the build system.  More information
 * can be found in the Python Guide:
 * https://projects.gentoo.org/python/guide/qawarn.html#stray-top-level-files-in-site-packages

Similarly to #14917, this can be solved by moving it to /cppyy.

Fix #20015.

[guitargeek]

Great, thank you very much! Good for me once the install tree works 👍

[guitargeek]

Looking at the current test failure:

2025-09-30T14:28:11.7394805Z     Start 1: run-hsimple
2025-09-30T14:28:11.7403649Z     Start 3: python-import-root
2025-09-30T14:28:11.7410796Z     Start 4: python-create-histo
2025-09-30T14:28:11.7635281Z 1/4 Test #3: python-import-root ...............***Failed    0.02 sec
2025-09-30T14:28:11.7635773Z 2/4 Test #4: python-create-histo ..............***Failed  Required regular expression not found. Regex=[myHistoName
2025-09-30T14:28:11.7636194Z ]  0.02 sec
2025-09-30T14:28:12.7766475Z 3/4 Test #1: run-hsimple ......................   Passed    1.04 sec
2025-09-30T14:28:12.7766962Z     Start 2: read-hsimple
2025-09-30T14:28:13.0585817Z 4/4 Test #2: read-hsimple .....................   Passed    0.28 sec

Are we not running with --output-on-failue? If not, can we maybe do that? It would help to debug things going wrong in the install tree.

[github-actions]

Test Results

    22 files      22 suites   3d 22h 45m 57s ⏱️
 3 704 tests  3 703 ✅ 0 💤 1 ❌
79 537 runs  79 536 ✅ 0 💤 1 ❌

For more details on these failures, see this check.

Results for commit 669b59b.

♻️ This comment has been updated with latest results.

[guitargeek]

Thanks. I'll take care of the patch file later when I do the next cppyy sync

[pcanal]

Are we not running with --output-on-failue? If not, can we maybe do that? It would help to debug things going wrong in the install tree.

We indirect do. The individual logs can be found in the "Test Results": eg https://github.com/root-project/root/pull/20016/checks?check_run_id=51624533514
Is that not the case for the 'install-tree' testing?

[guitargeek]

I don't know. But we do --output-on-failure also for the build tree tests, so I'd say this change is not controversial.

Thanks, I was not aware of these individual logs! I forgot about them because I noticed that for me, Ctrl+F-ing through the full log was actually faster than clicking around in the web interface, so I started ignoring everything but the full log.

[guitargeek]

@hageboeck, if you want to make it also work on Windows, you can use this trick for example:
https://github.com/root-project/root/pull/15310/files#diff-99c1321adf45e1356a5dccb621001c5baf3a1f69f71ed4ba1f3ad60c1f79c23fR24

[guitargeek]

Thanks!

[guitargeek]

Maybe we need the help of @bellenot for Windows after all 🙁

[vepadulano]

Super nice to see that the install testing is preventing us from merging breaking changes! 😄

Another note: can we please also run the wheel building on this PR? It's enough to add the label from the GitHub UI

[ferdymercury]

Maybe related? https://root-forum.cern.ch/t/rootls-could-not-load-cppyy-backend-library/64339

[guitargeek]

Wow, you made it work!

Do I understand correctly that you install libcppyy.so in the subdirectory also on Windows now, but it needs to be imported as import cppyy anyway? That's unexpected 🙂

[hageboeck]

Wow, you made it work!

Do I understand correctly that you install libcppyy.so in the subdirectory also on Windows now, but it needs to be imported as import cppyy anyway? That's unexpected 🙂

Actually, no. Since the library is a .pyd dll on Windows, it's currently installed in the top-level directory, so we have to import it directly. I guess the (cmake) problem is that it doesn't fall in any category of Archive/DLL/Exe, so CMake doesn't update the path. We could probably override this manually, but I didn't think this was necessary for Windows at the moment.

Maybe we could do it in the future, to have all OS consistent ...
I will give it one more try today. If I don't find it, I would propose to fix it for linux/Mac, and defer the fix for Windows to the next root version.