Fix warnings with attrs 19.2 and fix object assertions (#5902)

Fix warnings with attrs 19.2 and fix object assertions

src/_pytest/assertion/util.py

@@ -8,6 +8,7 @@ from typing import Optional
 import _pytest._code
 from _pytest import outcomes
 from _pytest._io.saferepr import saferepr
+from _pytest.compat import ATTRS_EQ_FIELD
 
 # The _reprcompare attribute on the util module is used by the new assertion
 # interpretation code and assertion rewriter to detect this plugin was
@@ -375,7 +376,9 @@ def _compare_eq_cls(left, right, verbose, type_fns):
         fields_to_check = [field for field, info in all_fields.items() if info.compare]
     elif isattrs(left):
         all_fields = left.__attrs_attrs__
-        fields_to_check = [field.name for field in all_fields if field.cmp]
+        fields_to_check = [
+            field.name for field in all_fields if getattr(field, ATTRS_EQ_FIELD)
+        ]
 
     same = []
     diff = []

src/_pytest/compat.py

@@ -354,3 +354,9 @@ if sys.version_info < (3, 5, 2):  # pragma: no cover
 
     def overload(f):  # noqa: F811
         return f
+
+
+if getattr(attr, "__version_info__", ()) >= (19, 2):
+    ATTRS_EQ_FIELD = "eq"
+else:
+    ATTRS_EQ_FIELD = "cmp"

src/_pytest/mark/structures.py

@@ -8,6 +8,7 @@ from typing import Set
 import attr
 
 from ..compat import ascii_escaped
+from ..compat import ATTRS_EQ_FIELD
 from ..compat import getfslineno
 from ..compat import NOTSET
 from _pytest.outcomes import fail
@@ -367,7 +368,8 @@ class NodeKeywords(MutableMapping):
         return "<NodeKeywords for node {}>".format(self.node)
 
 
-@attr.s(cmp=False, hash=False)
+# mypy cannot find this overload, remove when on attrs>=19.2
+@attr.s(hash=False, **{ATTRS_EQ_FIELD: False})  # type: ignore
 class NodeMarkers:
     """
     internal structure for storing marks belonging to a node

testing/test_assertion.py

@@ -9,6 +9,7 @@ import pytest
 from _pytest import outcomes
 from _pytest.assertion import truncate
 from _pytest.assertion import util
+from _pytest.compat import ATTRS_EQ_FIELD
 
 
 def mock_config():
@@ -687,7 +688,7 @@ class TestAssert_reprcompare_attrsclass:
         @attr.s
         class SimpleDataObject:
             field_a = attr.ib()
-            field_b = attr.ib(cmp=False)
+            field_b = attr.ib(**{ATTRS_EQ_FIELD: False})
 
         left = SimpleDataObject(1, "b")
         right = SimpleDataObject(1, "b")