Avoid specialized assert formatting when we detect that __eq__ is overridden

changelog/9326.bugfix.rst

@@ -0,0 +1 @@
+Pytest will now avoid specialized assert formatting when it is detected that the default __eq__ is overridden

src/_pytest/assertion/util.py

@@ -135,6 +135,27 @@ def isiterable(obj: Any) -> bool:
         return False
 
 
+def has_default_eq(
+    obj: object,
+) -> bool:
+    """Check if an instance of an object contains the default eq
+
+    First, we check if the object's __eq__ attribute has __code__,
+    if so, we check the equally of the method code filename (__code__.co_filename)
+    to the default onces generated by the dataclass and attr module
+    for dataclasses the default co_filename is <string>, for attrs class, the __eq__ should contain "attrs eq generated"
+    """
+    # inspired from https://github.com/willmcgugan/rich/blob/07d51ffc1aee6f16bd2e5a25b4e82850fb9ed778/rich/pretty.py#L68
+    if hasattr(obj.__eq__, "__code__") and hasattr(obj.__eq__.__code__, "co_filename"):
+        code_filename = obj.__eq__.__code__.co_filename
+
+        if isattrs(obj):
+            return "attrs generated eq" in code_filename
+
+        return code_filename == "<string>"  # data class
+    return True
+
+
 def assertrepr_compare(config, op: str, left: Any, right: Any) -> Optional[List[str]]:
     """Return specialised explanations for some operators/operands."""
     verbose = config.getoption("verbose")
@@ -427,6 +448,8 @@ def _compare_eq_dict(
 
 
 def _compare_eq_cls(left: Any, right: Any, verbose: int) -> List[str]:
+    if not has_default_eq(left):
+        return []
     if isdatacls(left):
         all_fields = left.__dataclass_fields__
         fields_to_check = [field for field, info in all_fields.items() if info.compare]

testing/example_scripts/dataclasses/test_compare_dataclasses_with_custom_eq.py

@@ -0,0 +1,17 @@
+from dataclasses import dataclass
+from dataclasses import field
+
+
+def test_dataclasses() -> None:
+    @dataclass
+    class SimpleDataObject:
+        field_a: int = field()
+        field_b: str = field()
+
+        def __eq__(self, __o: object) -> bool:
+            return super().__eq__(__o)
+
+    left = SimpleDataObject(1, "b")
+    right = SimpleDataObject(1, "c")
+
+    assert left == right

testing/test_assertion.py

@@ -899,6 +899,16 @@ def test_comparing_two_different_data_classes(self, pytester: Pytester) -> None:
         result = pytester.runpytest(p, "-vv")
         result.assert_outcomes(failed=0, passed=1)
 
+    @pytest.mark.skipif(sys.version_info < (3, 7), reason="Dataclasses in Python3.7+")
+    def test_data_classes_with_custom_eq(self, pytester: Pytester) -> None:
+        p = pytester.copy_example(
+            "dataclasses/test_compare_dataclasses_with_custom_eq.py"
+        )
+        # issue 9362
+        result = pytester.runpytest(p, "-vv")
+        result.assert_outcomes(failed=1, passed=0)
+        result.stdout.no_re_match_line(".*Differing attributes.*")
+
 
 class TestAssert_reprcompare_attrsclass:
     def test_attrs(self) -> None:
@@ -982,7 +992,6 @@ class SimpleDataObject:
         right = SimpleDataObject(1, "b")
 
         lines = callequal(left, right, verbose=2)
-        print(lines)
         assert lines is not None
         assert lines[2].startswith("Matching attributes:")
         assert "Omitting" not in lines[1]
@@ -1007,6 +1016,36 @@ class SimpleDataObjectTwo:
         lines = callequal(left, right)
         assert lines is None
 
+    def test_attrs_with_auto_detect_and_custom_eq(self) -> None:
+        @attr.s(
+            auto_detect=True
+        )  # attr.s doesn’t ignore a custom eq if auto_detect=True
+        class SimpleDataObject:
+            field_a = attr.ib()
+
+            def __eq__(self, other):  # pragma: no cover
+                return super().__eq__(other)
+
+        left = SimpleDataObject(1)
+        right = SimpleDataObject(2)
+        # issue 9362
+        lines = callequal(left, right, verbose=2)
+        assert lines is None
+
+    def test_attrs_with_custom_eq(self) -> None:
+        @attr.define
+        class SimpleDataObject:
+            field_a = attr.ib()
+
+            def __eq__(self, other):  # pragma: no cover
+                return super().__eq__(other)
+
+        left = SimpleDataObject(1)
+        right = SimpleDataObject(2)
+        # issue 9362
+        lines = callequal(left, right, verbose=2)
+        assert lines is None
+
 
 class TestAssert_reprcompare_namedtuple:
     def test_namedtuple(self) -> None: