test_legacy_callbacks in test_compat.py is failing in pytest 3.1+

[segevfiner]

pytest 3.1+ added https://docs.pytest.org/en/latest/warnings.html. This causes test_legacy_callbacks to fail since the warning is not printed during the test as expected. This fails in Travis CI under the Python 3.6 environment.

=================================== FAILURES ===================================
____________________________ test_legacy_callbacks _____________________________
test_compat.py:17: in test_legacy_callbacks
    assert 'Invoked legacy parameter callback' in result.output
E   AssertionError: assert 'Invoked legacy parameter callback' in 'WAT\n'
E    +  where 'WAT\n' = <Result okay>.output
=============================== warnings summary ===============================
tests/test_basic.py::test_evaluation_order
  /home/travis/build/pallets/click/click/core.py:880: Warning: Invoked legacy parameter callback "<function test_evaluation_order.<locals>.memo at 0x2b06d4955f28>".  The new signature for such callbacks starting with click 2.0 is (ctx, param, value).
    value, args = param.handle_parse_result(ctx, opts, args)

tests/test_compat.py::test_legacy_callbacks
  /home/travis/build/pallets/click/click/core.py:880: Warning: Invoked legacy parameter callback "<function test_legacy_callbacks.<locals>.legacy_callback at 0x2b06d41781e0>".  The new signature for such callbacks starting with click 2.0 is (ctx, param, value).
    value, args = param.handle_parse_result(ctx, opts, args)

tests/test_options.py::test_custom_validation
  /home/travis/build/pallets/click/click/core.py:880: Warning: Invoked legacy parameter callback "<function test_custom_validation.<locals>.validate_pos_int at 0x2b06d4196e18>".  The new signature for such callbacks starting with click 2.0 is (ctx, param, value).
    value, args = param.handle_parse_result(ctx, opts, args)

-- Docs: http://doc.pytest.org/en/latest/warnings.html
========= 1 failed, 127 passed, 1 xfailed, 3 warnings in 0.85 seconds ==========

[aviau]

This also affects Debian: #868816

[FRidh]

I'm fixing Python packages for our NixOS 17.09 release, and encountered this issue. What is keeping #838 from being merged? cc @untitaker

[LokiHokie]

Fixed