Complete error signature of _InValidator

changelog.d/951.change.rst

@@ -0,0 +1,3 @@
+The error signature of _InValidator has been completed,
+it now includes the attribute,
+options and value as proclaimed in the docstring of _in().

src/attr/validators.py

@@ -299,7 +299,10 @@ def __call__(self, inst, attr, value):
             raise ValueError(
                 "'{name}' must be in {options!r} (got {value!r})".format(
                     name=attr.name, options=self.options, value=value
-                )
+                ),
+                attr,
+                self.options,
+                value,
             )
 
     def __repr__(self):

tests/test_validators.py

@@ -471,7 +471,12 @@ def test_fail(self):
         a = simple_attr("test")
         with pytest.raises(ValueError) as e:
             v(None, a, None)
-        assert ("'test' must be in [1, 2, 3] (got None)",) == e.value.args
+        assert (
+            "'test' must be in [1, 2, 3] (got None)",
+            a,
+            [1, 2, 3],
+            None,
+        ) == e.value.args
 
     def test_fail_with_string(self):
         """
@@ -482,7 +487,12 @@ def test_fail_with_string(self):
         a = simple_attr("test")
         with pytest.raises(ValueError) as e:
             v(None, a, None)
-        assert ("'test' must be in 'abc' (got None)",) == e.value.args
+        assert (
+            "'test' must be in 'abc' (got None)",
+            a,
+            "abc",
+            None,
+        ) == e.value.args
 
     def test_repr(self):
         """