Fix yield inference on inherited classes.

ChangeLog

@@ -12,6 +12,11 @@ What's New in astroid 2.6.3?
 ============================
 Release date: TBA
 
+
+* Fix a bad inferenece type for yield values inside of a derived class.
+
+  Closes PyCQA/astroid#1090
+
 * Fix a crash when the node is a 'Module' in the brain builtin inference
 
   Closes PyCQA/pylint#4671

astroid/bases.py

@@ -26,7 +26,7 @@
 import collections
 
 from astroid import context as contextmod
-from astroid import util
+from astroid import decorators, util
 from astroid.const import BUILTINS, PY310_PLUS
 from astroid.exceptions import (
     AstroidTypeError,
@@ -543,9 +543,14 @@ class Generator(BaseInstance):
 
     special_attributes = util.lazy_descriptor(objectmodel.GeneratorModel)
 
-    def __init__(self, parent=None):
+    def __init__(self, parent=None, generator_initial_context=None):
         super().__init__()
         self.parent = parent
+        self._call_context = contextmod.copy_context(generator_initial_context)
+
+    @decorators.cached
+    def infer_yield_types(self):
+        yield from self.parent.infer_yield_result(self._call_context)
 
     def callable(self):
         return False

astroid/protocols.py

@@ -489,22 +489,8 @@ def _infer_context_manager(self, mgr, context):
             # It doesn't interest us.
             raise InferenceError(node=func)
 
-        # Get the first yield point. If it has multiple yields,
-        # then a RuntimeError will be raised.
+        yield next(inferred.infer_yield_types())
 
-        possible_yield_points = func.nodes_of_class(nodes.Yield)
-        # Ignore yields in nested functions
-        yield_point = next(
-            (node for node in possible_yield_points if node.scope() == func), None
-        )
-        if yield_point:
-            if not yield_point.value:
-                const = nodes.Const(None)
-                const.parent = yield_point
-                const.lineno = yield_point.lineno
-                yield const
-            else:
-                yield from yield_point.value.infer(context=context)
     elif isinstance(inferred, bases.Instance):
         try:
             enter = next(inferred.igetattr("__enter__", context=context))

astroid/scoped_nodes.py

@@ -1708,6 +1708,21 @@ def is_generator(self):
         """
         return bool(next(self._get_yield_nodes_skip_lambdas(), False))
 
+    def infer_yield_result(self, context=None):
+        """Infer what the function yields when called
+
+        :returns: What the function yields
+        :rtype: iterable(NodeNG or Uninferable) or None
+        """
+        for yield_ in self.nodes_of_class(node_classes.Yield):
+            if yield_.value is None:
+                const = node_classes.Const(None)
+                const.parent = yield_
+                const.lineno = yield_.lineno
+                yield const
+            elif yield_.scope() == self:
+                yield from yield_.value.infer(context=context)
+
     def infer_call_result(self, caller=None, context=None):
         """Infer what the function returns when called.
 
@@ -1719,7 +1734,7 @@ def infer_call_result(self, caller=None, context=None):
                 generator_cls = bases.AsyncGenerator
             else:
                 generator_cls = bases.Generator
-            result = generator_cls(self)
+            result = generator_cls(self, generator_initial_context=context)
             yield result
             return
         # This is really a gigantic hack to work around metaclass generators

tests/unittest_inference.py

@@ -6154,5 +6154,26 @@ def test_issue926_binop_referencing_same_name_is_not_uninferable():
     assert inferred[0].value == 3
 
 
+def test_issue_1090_infer_yield_type_base_class():
+    code = """
+import contextlib
+
+class A:
+    @contextlib.contextmanager
+    def get(self):
+        yield self
+
+class B(A):
+    def play():
+        pass
+
+with B().get() as b:
+    b
+b
+    """
+    node = extract_node(code)
+    assert next(node.infer()).pytype() == ".B"
+
+
 if __name__ == "__main__":
     unittest.main()