Poetry: select olddeps using poetry

[DMRobertson]

There are a few moving parts here.

• Once we ditch setup.py we'll need to patch the dependencies in pyproject.toml to maintain this CI job.
• If we were using poetry-core as our PEP 517 build system, it would suffice to pip install .[all,test]. But we're gradually transitioning to that; setuptools remains the build system for now.
• Therefore use the "full" poetry to lock an olddeps environment and run using poetry run.

[DMRobertson]

Moved into the script file as an explicit argument rather than

I don't think TRIAL_FLAGS is something trial actually supports; I think we just hacked it into our tox config:

synapse/tox.ini

Line 83 in 50910da

/usr/bin/env COVERAGE_PROCESS_START={toxinidir}/.coveragerc "{envbindir}/trial" {env:TRIAL_FLAGS:} {posargs:tests} {env:TOXSUFFIX:}

[clokep]

I don't see these being moved into the new bits, but maybe that's OK?

[DMRobertson]

It should be okay.

• Automat isn't a direct dependency (it's not in python_dependencies,py nor pyproject.toml), so I don't think we have any business pinning it to a particular version anyway;
• lxml will be installed it's part of all, and in the config we install all extras
• markupsafe is also not a direct dependency.
• the base dependencies are pip, setuptools, and stuff related to coverage. We've stopped using coverage (and I suspect it'd need some config fiddling to have it work in poetry anyway).

[richvdh]

lgtm!

[DMRobertson]

I've just realised I missed some changes from the big PR; those are ported over in 695eb3c. Mind taking another quick look?

[richvdh]

lgtm otherwise

[richvdh]

this feels like a retrograde step.

[DMRobertson]

It is. Thanks.