regression: testdir fixture not found with pytester plugin loaded

[The-Compiler]

After #9208, this:

pytest_plugins = 'pytester'

def test_testdir(testdir):
    pass

fails with:

============================= test session starts ==============================
platform linux -- Python 3.9.7, pytest-7.0.0.dev294+g86446edc8, pluggy-1.0.0
rootdir: /home/florian/tmp/td
collected 1 item                                                               

test_td.py E                                                             [100%]

==================================== ERRORS ====================================
________________________ ERROR at setup of test_testdir ________________________
file /home/florian/tmp/td/test_td.py, line 3
  def test_testdir(testdir):
E       fixture 'testdir' not found
>       available fixtures: LineMatcher, _config_for_test, _pytest, _sys_snapshot, cache, capfd, capfdbinary, caplog, capsys, capsysbinary, doctest_namespace, linecomp, monkeypatch, pytestconfig, pytester, record_property, record_testsuite_property, record_xml_attribute, recwarn, tmp_path, tmp_path_factory, tmpdir, tmpdir_factory
>       use 'pytest --fixtures [testpath]' for help on them.

/home/florian/tmp/td/test_td.py:3
=========================== short test summary info ============================
ERROR test_td.py::test_testdir
=============================== 1 error in 0.01s ===============================

I bisected this to e6eac28.

Considering this as a showstopper for 7.0 given that this is a very common way of accessing the testdir fixture.

cc @bluetech

[bluetech]

Right, has_plugin("pytester") is not going to work at configure time when its loaded from a conftest, didn't think of that.

I'll send a PR to revert this commit, see this discussion on why I added it. Maybe @RonnyPfannschmidt has an idea how to salvage it though. Anyway it's not too bad without it.

[RonnyPfannschmidt]

Let's register pytester legacy in the pytest plugin registred hook so we auto enable when pytester gets activated

We need a condition on the plugin

[bluetech]

The idea is to eventually move the plugin to be standalone, so I prefer the approach to be compatible with that. Can you think of a trick that would keep it localized to the legacypath plugin? Hmm maybe use pytest_plugin_registered (in addition to configure)?

[RonnyPfannschmidt]

Exactly that 😅

[bluetech]

I should learn to read :) (I read it as loading the sub-plugin from the pytester plugin)