Avoid false positives on generic aliases with nested classes (#624)

quora · May 12, 2023 · 36ef3d2 · 36ef3d2
1 parent dfd534c
commit 36ef3d2
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diff --git a/docs/changelog.md b/docs/changelog.md
@@ -1,5 +1,10 @@
 # Changelog
 
+## Unreleased
+
+- Fix false positive error when annotations refer to classes defined
+  inside functions (#624)
+
 ## Version 0.10.0 (May 10, 2023)
 
 - Infer the signature for built-in static methods, such as `dict.fromkeys` (#619)

diff --git a/pyanalyze/name_check_visitor.py b/pyanalyze/name_check_visitor.py
@@ -225,6 +225,13 @@ class ExceptionGroup:
         pass
 
 
+try:
+    from types import GenericAlias
+except ImportError:
+    # 3.8 and lower
+    GenericAlias = None
+
+
 T = TypeVar("T")
 U = TypeVar("U")
 AwaitableValue = GenericValue(collections.abc.Awaitable, [TypeVarValue(T)])
@@ -4467,6 +4474,17 @@ def _composite_from_subscript_no_mvv(
                         return_value = self.check_call(
                             node.value, cgi, [index_composite], allow_call=True
                         )
+                        # Special case to avoid "Unrecognized annotation types.GenericAlias" later;
+                        # ideally we'd be more precise.
+                        if GenericAlias is not None and return_value == TypedValue(
+                            GenericAlias
+                        ):
+                            return_value = self.check_call(
+                                node.value,
+                                cgi,
+                                [Composite(KnownValue(Any))],
+                                allow_call=True,
+                            )
 
                 if (
                     self._should_use_varname_value(return_value)

diff --git a/pyanalyze/test_annotations.py b/pyanalyze/test_annotations.py
@@ -705,6 +705,19 @@ def capybara(
                 ),
             )
 
+    @skip_before((3, 9))
+    @assert_passes()
+    def test_genericalias_nested_class(self):
+        def capybara():
+            class Base:
+                pass
+
+            class Child:
+                attrs: list[Base]
+
+            # Ideally should not be Any, but this is better than throwing a false positive error.
+            assert_is_value(Child().attrs, AnyValue(AnySource.from_another))
+
 
 class TestCallable(TestNameCheckVisitorBase):
     @assert_passes()