[core] Move TClass tests to core/meta

[hahnjo]

The test in core/clingutils is meant for unit testing of TClingUtils and statically links ClingUtils and Cling/Clang/LLVM libraries. Calling Cling, TInterpreter, or TClass results in two copies of the functions being around (in libCling.so and the test binary) with not much guarantees which ones are called at which moment.

(causes a test failure with the upgrade to LLVM 20)

[devajithvs]

LGTM! Thanks.

[pcanal]

(causes a test failure with the upgrade to LLVM 20)

Having twice the same symbols is indeed bad. What was the symptoms in the failures?

[pcanal]

Thanks. (and indeed a test using TClass belongs to core/meta).

[github-actions]

Test Results

    20 files      20 suites   3d 4h 24m 20s ⏱️
 3 257 tests  3 257 ✅ 0 💤 0 ❌
63 502 runs  63 502 ✅ 0 💤 0 ❌

Results for commit 44e5bb2.

♻️ This comment has been updated with latest results.

[hahnjo]

(causes a test failure with the upgrade to LLVM 20)

Having twice the same symbols is indeed bad. What was the symptoms in the failures?

There were two symptoms with LLVM 20, depending on your "luck":

1. Without JITLink, target machines & triples were registered in the static copy of the symbols and then libCling.so could not find them. This was "caused" by a change in symbol visibility in LLVM 20 and left us confused for quite some time.
2. When hacking around this (for example by reverting that symbol visibility change), llvm::Module destruction would fail at the end of the test execution because hash values were different. That's because of a second change that now uses a process-specific seed for hashing. That is implemented by taking the address of a known function (install_fatal_error_handler) and relying on address space layout randomization (ASLR) to load code at different virtual addresses every time. The problem here is that we have two install_fatal_error_handler, one in the static binary and one in libCling.so.

We focused on the second point and eventually I guessed what is going on when seeing the size of coreclingutilstestUnit.