clean argument for runner

[vborchsh]

The argument might be used for 100% pure rebuild the testbench and delete any previous results such as build artifacts, simulator libraries and so on.

Actually, simple copy-paste of cocotb-test with minor editing, because cocotb runner knows exact path to the building directory thanks to build_dir argument.

Not sure about tests, it could be something like:

1. create build_dir before runner.build() call
2. put some file into folder
3. run runner.build()
4. assert file in the folder. Must be false for clean build, true for non-clean build.

Looks a bit poor, but still... Feedback is welcome :)

[themperek]

I am OK with this. Maybe should also take the COCOTB_CLEAN environmental variable if set?

Could we just "clean" when always is set?

Maybe add runner.clean() instead?

The question would be should we have a command like cocotb-clean command? Since build_dir can be set it will only work on the default.

[vborchsh]

I am OK with this. Maybe should also take the COCOTB_CLEAN environmental variable if set?

If I get it right, you're going to leave Makefiles flow for back compatibility only. So, this case I'd leave it as is.

Could we just "clean" when always is set?
Maybe add runner.clean() instead?

This is the idea I thought about. But I think, clean + always is more flexible. You can keep any libs and artifacts in the folder in case always. And purge everything in case clean.

The question would be should we have a command like cocotb-clean command? Since build_dir can be set it will only work on the default.

I used to use the command with cocotb-test before. And we can do the same, plus couple keys: --recursive, --buildir. In the other PR, I guess.

[ktbarrett]

I think this is fine as is. Just needs a newsfragement. See instructions here.

[vborchsh]

Are there any ideas about failed MacOS icarus test? There is a timeout in the tests but I didn't touch them... And test_runner is passed:

tests/pytest/test_runner.py::test_runner[False-parameters0] PASSED       [ 66%]
tests/pytest/test_runner.py::test_runner[False-parameters1] PASSED       [ 75%]
tests/pytest/test_runner.py::test_runner[True-parameters0] PASSED        [ 83%]
tests/pytest/test_runner.py::test_runner[True-parameters1] PASSED        [ 91%]

[vborchsh]

Everything is merged into single commit. Thanks @imphil for advice.