Fix filter attribute identity matching

Author: Sean-Kenneth-Doherty

changelog.d/864.change.md

@@ -0,0 +1,2 @@
+`attrs.filters.include()` and `attrs.filters.exclude()` now match `attrs.Attribute` instances by identity.
+Passing a field returned by `attrs.fields()` therefore only matches that exact class's field; pass a string field name to match same-named fields across classes.

docs/examples.md

@@ -271,6 +271,7 @@ For the common case where you want to [`include`](attrs.filters.include) or [`ex
 Though using string names directly is convenient, mistyping attribute names will silently do the wrong thing and neither Python nor your type checker can help you.
 {func}`attrs.fields()` will raise an `AttributeError` when the field doesn't exist while literal string names won't.
 Using {func}`attrs.fields()` to get attributes is worth being recommended in most cases.
+String names match all fields with that name, while fields returned from {func}`attrs.fields()` only match that exact class's field.
 
 ```{doctest}
 >>> asdict(

src/attr/filters.py

@@ -9,15 +9,19 @@
 
 def _split_what(what):
     """
-    Returns a tuple of `frozenset`s of classes and attributes.
+    Returns a tuple of classes, names, and attributes to match.
     """
     return (
         frozenset(cls for cls in what if isinstance(cls, type)),
         frozenset(cls for cls in what if isinstance(cls, str)),
-        frozenset(cls for cls in what if isinstance(cls, Attribute)),
+        tuple(cls for cls in what if isinstance(cls, Attribute)),
     )
 
 
+def _matches_attribute(attribute, attrs):
+    return any(attribute is a for a in attrs)
+
+
 def include(*what):
     """
     Create a filter that only allows *what*.
@@ -39,7 +43,7 @@ def include_(attribute, value):
         return (
             value.__class__ in cls
             or attribute.name in names
-            or attribute in attrs
+            or _matches_attribute(attribute, attrs)
         )
 
     return include_
@@ -66,7 +70,7 @@ def exclude_(attribute, value):
         return not (
             value.__class__ in cls
             or attribute.name in names
-            or attribute in attrs
+            or _matches_attribute(attribute, attrs)
         )
 
     return exclude_

tests/test_filters.py

@@ -18,6 +18,11 @@ class C:
     b = attr.ib()
 
 
+@attr.s
+class D:
+    a = attr.ib()
+
+
 class TestSplitWhat:
     """
     Tests for `_split_what`.
@@ -30,7 +35,7 @@ def test_splits(self):
         assert (
             frozenset((int, str)),
             frozenset(("abcd", "123")),
-            frozenset((fields(C).a,)),
+            (fields(C).a,),
         ) == _split_what((str, "123", fields(C).a, int, "abcd"))
 
 
@@ -79,6 +84,15 @@ def test_drop_class(self, incl, value):
         i = include(*incl)
         assert i(fields(C).a, value) is False
 
+    def test_allow_attributes_by_identity(self):
+        """
+        Attributes with the same name on other classes are not included.
+        """
+        i = include(fields(C).a)
+
+        assert i(fields(C).a, 42) is True
+        assert i(fields(D).a, 42) is False
+
 
 class TestExclude:
     """
@@ -124,3 +138,12 @@ def test_drop_class(self, excl, value):
         """
         e = exclude(*excl)
         assert e(fields(C).a, value) is False
+
+    def test_drop_attributes_by_identity(self):
+        """
+        Attributes with the same name on other classes are not excluded.
+        """
+        e = exclude(fields(C).a)
+
+        assert e(fields(C).a, 42) is False
+        assert e(fields(D).a, 42) is True