Abort (Core dumped) when running unittests with uvm-python

Running make test (or any unittest file) for https://github.com/tpoikela/uvm-python results in the following error:

/usr/include/c++/9/bits/stl_vector.h:1042: std::vector<_Tp, _Alloc>::reference std::vector<_Tp, _Alloc>::operator[](std::vector<_Tp, _Alloc>::size_type) [with _Tp = GpiImplInterface*; _
Alloc = std::allocator<GpiImplInterface*>; std::vector<_Tp, _Alloc>::reference = GpiImplInterface*&; std::vector<_Tp, _Alloc>::size_type = long unsigned int]: Assertion '__builtin_expect(__n < this->size(), true)' failed.

I bisected the issue to commit 3a0bf9460515ae0c2269890b75ddbeaa80085cff. It seems some imports have been changed to unconditional ones. More specifically, changing cocotb/utils.py back to conditional import seems to fix this issue. Any ideas on the source of error?

Background: uvm-python unit tests are run without simulator, but files under test are still importing stuff from cocotb.

To reproduce the issue:

mkdir temp
cd temp
python -m env .venv
source .venv/bin/activate
git clone https://github.com/cocotb/cocotb.git
cd cocotb
pip install -e .
cd ..
git clone https://github.com/tpoikela/uvm-python.git
cd uvm-python
ln -s src/uvm ./uvm
pip install cocotb_coverage pip install regex
python -m unittest unit/test_sv.py  # Or make test-unit

[tpoikela]

@themperek Thanks for suggestion. hasattr(cocotb, 'SIM_NAME') seems to provide a workaround. Any potential pitfalls?

Nevertheless, it is better not to leak segfaults, as these cannot be caught inside Python code.

[ktbarrett]

@themperek That is a good idea that will also help us with #1724.