Use get_protocol_members in protocol checking

docs/versionhistory.rst

@@ -4,6 +4,11 @@ Version history
 This library adheres to
 `Semantic Versioning 2.0 <https://semver.org/#semantic-versioning-200>`_.
 
+**UNRELEASED**
+
+- Fixed basic support for intersection protocols
+  (`#490 <https://github.com/agronholm/typeguard/pull/490>`_; PR by @antonagestam)
+
 **4.3.0** (2024-05-27)
 
 - Added support for checking against static protocols

src/typeguard/_checkers.py

@@ -654,19 +654,13 @@ def check_protocol(
             else:
                 return
 
-    # Collect a set of methods and non-method attributes present in the protocol
-    ignored_attrs = set(dir(typing.Protocol)) | {
-        "__annotations__",
-        "__non_callable_proto_members__",
-    }
     expected_methods: dict[str, tuple[Any, Any]] = {}
     expected_noncallable_members: dict[str, Any] = {}
-    for attrname in dir(origin_type):
-        # Skip attributes present in typing.Protocol
-        if attrname in ignored_attrs:
-            continue
+    origin_annotations = typing.get_type_hints(origin_type)
+
+    for attrname in typing_extensions.get_protocol_members(origin_type):
+        member = getattr(origin_type, attrname, None)
 
-        member = getattr(origin_type, attrname)
         if callable(member):
             signature = inspect.signature(member)
             argtypes = [
@@ -681,10 +675,10 @@ def check_protocol(
             )
             expected_methods[attrname] = argtypes, return_annotation
         else:
-            expected_noncallable_members[attrname] = member
-
-    for attrname, annotation in typing.get_type_hints(origin_type).items():
-        expected_noncallable_members[attrname] = annotation
+            try:
+                expected_noncallable_members[attrname] = origin_annotations[attrname]
+            except KeyError:
+                expected_noncallable_members[attrname] = member
 
     subject_annotations = typing.get_type_hints(subject)
 

tests/test_checkers.py

@@ -16,14 +16,17 @@
     Dict,
     ForwardRef,
     FrozenSet,
+    Iterable,
     Iterator,
     List,
     Literal,
     Mapping,
     MutableMapping,
     Optional,
+    Protocol,
     Sequence,
     Set,
+    Sized,
     TextIO,
     Tuple,
     Type,
@@ -995,6 +998,86 @@ def test_text_real_file(self, tmp_path: Path):
             check_type(f, TextIO)
 
 
+class TestIntersectingProtocol:
+    SIT = TypeVar("SIT", covariant=True)
+
+    class SizedIterable(
+        Sized,
+        Iterable[SIT],
+        Protocol[SIT],
+    ): ...
+
+    @pytest.mark.parametrize(
+        "subject, predicate_type",
+        (
+            pytest.param(
+                (),
+                SizedIterable,
+                id="empty_tuple_unspecialized",
+            ),
+            pytest.param(
+                range(2),
+                SizedIterable,
+                id="range",
+            ),
+            pytest.param(
+                (),
+                SizedIterable[int],
+                id="empty_tuple_int_specialized",
+            ),
+            pytest.param(
+                (1, 2, 3),
+                SizedIterable[int],
+                id="tuple_int_specialized",
+            ),
+            pytest.param(
+                ("1", "2", "3"),
+                SizedIterable[str],
+                id="tuple_str_specialized",
+            ),
+        ),
+    )
+    def test_valid_member_passes(self, subject: object, predicate_type: type) -> None:
+        for _ in range(2):  # Makes sure that the cache is also exercised
+            check_type(subject, predicate_type)
+
+    xfail_nested_protocol_checks = pytest.mark.xfail(
+        reason="false negative due to missing support for nested protocol checks",
+    )
+
+    @pytest.mark.parametrize(
+        "subject, predicate_type",
+        (
+            pytest.param(
+                (1 for _ in ()),
+                SizedIterable,
+                id="generator",
+            ),
+            pytest.param(
+                range(2),
+                SizedIterable[str],
+                marks=xfail_nested_protocol_checks,
+                id="range_str_specialized",
+            ),
+            pytest.param(
+                (1, 2, 3),
+                SizedIterable[str],
+                marks=xfail_nested_protocol_checks,
+                id="int_tuple_str_specialized",
+            ),
+            pytest.param(
+                ("1", "2", "3"),
+                SizedIterable[int],
+                marks=xfail_nested_protocol_checks,
+                id="str_tuple_int_specialized",
+            ),
+        ),
+    )
+    def test_raises_for_non_member(self, subject: object, predicate_type: type) -> None:
+        with pytest.raises(TypeCheckError):
+            check_type(subject, predicate_type)
+
+
 @pytest.mark.parametrize(
     "instantiate, annotation",
     [