Fix nested classes in stubs

docs/changelog.md

@@ -2,6 +2,8 @@
 
 ## Unreleased
 
+- Fix crash with nested classes in stubs. For now, `Any` is
+  inferred for such classes (#647)
 - Add `disallowed_imports` configuration option to disallow
   imports of specific modules (#645, #646)
 - Consider an annotated assignment without a value to be

pyanalyze/stubs/_pyanalyze_tests-stubs/nested.pyi

@@ -0,0 +1,3 @@
+class Outer:
+    class Inner:
+        def __init__(self, x: int) -> None: ...

pyanalyze/test_typeshed.py

@@ -786,3 +786,33 @@ def capybara():
             assert_is_value(
                 itertools.count(1), GenericValue(itertools.count, [TypedValue(int)])
             )
+
+
+class TestNestedClass(TestNameCheckVisitorBase):
+    @assert_passes()
+    def test_nested(self):
+        def capybara() -> None:
+            from _pyanalyze_tests.nested import Outer
+
+            Outer.Inner(1)
+
+    @assert_passes()
+    def test_with_runtime_object(self):
+        import sys
+        import types
+
+        class Inner:
+            def __init__(self, arg: int) -> None:
+                pass
+
+        # The bug here only reproduces if a class that exists at runtime contains
+        # a nested class in a stub. So we simulate that by creating a fake runtime
+        # module.
+        Outer = type("Outer", (), {"Inner": Inner})
+        Outer.__module__ = "_pyanalyze_tests.nested"
+        mod = types.ModuleType("_pyanalyze_tests.nested")
+        mod.Outer = Outer
+        sys.modules["_pyanalyze_tests.nested"] = mod
+
+        def capybara() -> None:
+            Outer.Inner(1)

pyanalyze/typeshed.py

@@ -492,6 +492,7 @@ def _get_attribute_from_info(
                             mod,
                             is_typeddict=is_typeddict,
                             on_class=on_class,
+                            parent_name=info.ast.name,
                         )
                     assert False, repr(child_info)
                 return UNINITIALIZED_VALUE
@@ -514,6 +515,7 @@ def _get_value_from_child_info(
         *,
         is_typeddict: bool,
         on_class: bool,
+        parent_name: str,
     ) -> Value:
         if isinstance(node, ast.AnnAssign):
             return self._parse_type(node.annotation, mod, is_typeddict=is_typeddict)
@@ -530,12 +532,21 @@ def _get_value_from_child_info(
                 return AnyValue(AnySource.inference)
             else:
                 return CallableValue(sig)
+        elif isinstance(node, ast.ClassDef):
+            # should be
+            # SubclassValue(TypedValue(f"{mod}.{parent_name}.{node.name}"), exactly=True)
+            # but that doesn't currently work well
+            return AnyValue(AnySource.inference)
         elif isinstance(node, ast.Assign):
             return UNINITIALIZED_VALUE
         elif isinstance(node, typeshed_client.OverloadedName):
             vals = [
                 self._get_value_from_child_info(
-                    subnode, mod, is_typeddict=is_typeddict, on_class=on_class
+                    subnode,
+                    mod,
+                    is_typeddict=is_typeddict,
+                    on_class=on_class,
+                    parent_name=parent_name,
                 )
                 for subnode in node.definitions
             ]
@@ -1204,7 +1215,8 @@ def _value_from_info_inner(
 
 def _obj_from_qualname_is(module_name: str, qualname: str, obj: object) -> bool:
     try:
-        __import__(module_name)
+        if module_name not in sys.modules:
+            __import__(module_name)
         mod = sys.modules[module_name]
         actual = mod
         for piece in qualname.split("."):