Make it possible to use generic/parametrised exceptions with pytest.raises

[dimaqq]

What's the problem this feature will solve?

Code I'd like to write:

        excinfo: pytest.ExceptionInfo[pebble.ExecError[str]]
        with pytest.raises(pebble.ExecError[str]) as excinfo:
            container.exec(['foo']).wait()
        assert excinfo.value.exit_code == 10

I'd like to write this so that it type-checks cleanly.

Alternatively, it could be:

        with pytest.raises(pebble.ExecError[str]) as excinfo:
            container.exec(['foo']).wait()
        # excinfo if of correct type here
        assert excinfo.value.exit_code == 10

Today, this fails with:

  File "/Users/runner/work/operator/operator/test/test_testing.py", line 6405, in test_register_with_result
    with pytest.raises(pebble.ExecError[str]) as excinfo:
  File "/Users/runner/work/operator/operator/.tox/py3.10-unit/lib/python3.10/site-packages/_pytest/raises.py", line 284, in raises
    return RaisesExc(expected_exception, **kwargs)
  File "/Users/runner/work/operator/operator/.tox/py3.10-unit/lib/python3.10/site-packages/_pytest/raises.py", line 635, in __init__
    self.expected_exceptions = tuple(
  File "/Users/runner/work/operator/operator/.tox/py3.10-unit/lib/python3.10/site-packages/_pytest/raises.py", line 636, in <genexpr>
    self._parse_exc(e, expected="a BaseException type")
  File "/Users/runner/work/operator/operator/.tox/py3.10-unit/lib/python3.10/site-packages/_pytest/raises.py", line 472, in _parse_exc
    raise TypeError(msg + repr(type(exc).__name__))
TypeError: expected exception must be a BaseException type, not '_GenericAlias'

P.S. my codebase supports py3.10 and later, so I can't use the newest Python language features.
(@james-garner-canonical commented about a work-around with TypeVars or something, which would require later Pythons)

Additional context

Refs
Similar ticker and PR for generic exception groups: #13115 #13134
Discussion: microsoft/pyright#10774