Fix internal assert failure regression in 5.3.4

[bluetech]

This reverts commit 930a158 (pr #6511).

Fixes #6517.

The assert is failing on a real test suite. Basically, I was sure the assert was safe because the _node_location_to_relpath cache that the value is passed into is only designed to work with py.path.locals, not strs, and code-wise if given an str, it would fail. Or so I thought. Turns out several less-than-nice things combined to mislead me:

1. The py.path.local function bestrelpath is wrapped in a giant try...except AttributeError which masks any wrong types.
2. py.path.local has an __eq__ implementation that can compare true with an str: py.path.local('/foo') == '/foo' is true.
3. The cache seems to always be warmed up with a py.path.local, so the bestrelpath code actually does run with py.path.locals. When an str comes in which compares true with a previous py.path.local, it seems like everything's fine.

Anyway, can look into these things later 😨 , but for now, better to just revert the offending commit to fix people's tests.

[nicoddemus]

Awesome @bluetech, thanks for the lightning fast response!

And ouch, indeed py.path.local comparing with str is misleading... good thing that pathlib doesn't do that.

I managed to reproduce the issue with this:

from nose.tools import raises

@raises(RuntimeError)
def test_fail_without_tcp():
    raise RuntimeError

I don't think we need to release this in a hurry, few test suites will be affected (only those mixing nose and pytest). Perhaps we should keep your original patch and just fix the assertion? The test above passes for me when I apply this:

diff --git a/src/_pytest/nodes.py b/src/_pytest/nodes.py
index fc951d2bc..64363662a 100644
--- a/src/_pytest/nodes.py
+++ b/src/_pytest/nodes.py
@@ -462,7 +462,7 @@ class Item(Node):
     @cached_property
     def location(self) -> Tuple[str, Optional[int], str]:
         location = self.reportinfo()
-        assert isinstance(location[0], py.path.local), location[0]
+        assert isinstance(location[0], (py.path.local, str)), location[0]
         fspath = self.session._node_location_to_relpath(location[0])
         assert type(location[2]) is str
         return (fspath, location[1], location[2])

(It is a shame we don't have a test for that nose feature in the first place actually)

[bluetech]

I prefer to revert the entire commit, because all of the changes related to this cache and the type of reportinfo() need a deeper look now. So I prefer to have a clean master reintroduce the changes with more consideration.

I'll add the regression test to this PR, thanks!

[bluetech]

I added the regression test. Verified that it crashes before/passes after. Will merge once CI passes.

[nicoddemus]

Awesome, thanks again. 👍