fix: support recursive models in local scope

closes #567

pyflakes/checker.py

@@ -866,7 +866,6 @@ class Checker(object):
     offset = None
     traceTree = False
     _in_annotation = AnnotationState.NONE
-    _in_deferred = False
 
     builtIns = set(builtin_vars).union(_MAGIC_GLOBALS)
     _customBuiltIns = os.environ.get('PYFLAKES_BUILTINS')
@@ -898,7 +897,6 @@ def __init__(self, tree, filename='(none)', builtins=None,
         for builtin in self.builtIns:
             self.addBinding(None, Builtin(builtin))
         self.handleChildren(tree)
-        self._in_deferred = True
         self.runDeferred(self._deferredFunctions)
         # Set _deferredFunctions to None so that deferFunction will fail
         # noisily if called after we've run through the deferred functions.
@@ -1803,10 +1801,7 @@ def STR(self, node):
                 node.col_offset,
                 messages.ForwardAnnotationSyntaxError,
             )
-            if self._in_deferred:
-                fn()
-            else:
-                self.deferFunction(fn)
+            self.deferFunction(fn)
 
     if PY38_PLUS:
         def CONSTANT(self, node):

pyflakes/test/test_type_annotations.py

@@ -667,3 +667,22 @@ class C(Protocol):
                 def f():  # type: () -> int
                     pass
         """)
+
+    @skipIf(version_info < (3, 6), 'new in Python 3.6')
+    def test_recursive_global_scope(self):
+        self.flakes("""
+            from typing import Optional, Tuple
+
+            class NestedTuple:
+                x: Tuple[int, Optional['NestedTuple']]
+        """)
+
+    @skipIf(version_info < (3, 6), 'new in Python 3.6')
+    def test_recursive_local_scope(self):
+        self.flakes("""
+            from typing import Optional, Tuple
+
+            def test():
+                class NestedTuple:
+                    x: Tuple[int, Optional['NestedTuple']]
+        """)