deprecate unpacking marks in parameter values and provide a clean alternative

[RonnyPfannschmidt]

the mechanism we use to makr parameter sets

like

import pytest
@pytest.mark.parametrize(("n", "expected"), [
  (1, 2),
  pytest.mark.foo((2, 3)),
  (3, 4),
])
def test_increment(n, expected):
    assert n + 1 == expected

means that we have to unpack mark decorator objects in a very error prone/messy way
and in addition we end up with the inability to safely use function that way

i propose replacing it with something like

import pytest
@pytest.mark.parametrize(("n", "expected"), [
  (1, 2),
  pytest.marked_value((2, 3)), marks=pytest.mark.foo)
  (3, 4),
])
def test_increment(n, expected):
    assert n + 1 == expected

[The-Compiler]

Assuming you mean pytest.marked_value((2, 3), marks=pytest.mark.foo) (without the extra )), that sounds like a good idea.

It'd also make using marks with arguments nicer IMHO:

before: pytest.mark.xfail(reason='...')((1, 2))
after: pytest.marked_value((1, 2), marks=pytest.mark.xfail(reason='...'))

[RonnyPfannschmidt]

laos a "fun detail" currently pytest.mark.xfail(reason='...')((1, 2)) is equivalent to pytest.mark.xfail((1, 2), reason='...')

which is just plain horror

[RonnyPfannschmidt]

fixed in #1921