Seomtiems we need to add "yield"...

in order to get the generator bit flag set, such as in 3.x where the
yield is optimized away.

uncompyle6/semantics/make_function2.py

@@ -1,4 +1,4 @@
-#  Copyright (c) 2015-2019 by Rocky Bernstein
+#  Copyright (c) 2015-2020 by Rocky Bernstein
 #  Copyright (c) 2000-2002 by hartmut Goebel <h.goebel@crazy-compilers.com>
 #
 #  This program is free software: you can redistribute it and/or modify
@@ -18,6 +18,7 @@ All the crazy things we have to do to handle Python functions in Python before 3
 The saga of changes continues in 3.0 and above and in other files.
 """
 from xdis.code import iscode, code_has_star_arg, code_has_star_star_arg
+from xdis.util import CO_GENERATOR
 from uncompyle6.scanner import Code
 from uncompyle6.parsers.treenode import SyntaxTree
 from uncompyle6 import PYTHON3
@@ -182,7 +183,6 @@ def make_function2(self, node, is_lambda, nested=1, code_node=None):
         # docstring exists, dump it
         print_docstring(self, indent, code.co_consts[0])
 
-    code._tokens = None  # save memory
     if not is_lambda:
         assert ast == "stmts"
 
@@ -203,5 +203,21 @@ def make_function2(self, node, is_lambda, nested=1, code_node=None):
     self.gen_source(
         ast, code.co_name, code._customize, is_lambda=is_lambda, returnNone=rn
     )
-    code._tokens = None
+
+    # In obscure cases, a function may be a generator but the "yield"
+    # was optimized away. Here, we need to put in unreachable code to
+    # add in "yield" just so that the compiler will mark
+    # the GENERATOR bit of the function. See for example
+    # Python 3.x's test_generator.py test program.
+    if code.co_flags & CO_GENERATOR:
+        need_bogus_yield = True
+        for token in scanner_code._tokens:
+            if token == "YIELD_VALUE":
+                need_bogus_yield = False
+                break
+            pass
+        if need_bogus_yield:
+            self.template_engine(("%|if False:\n%+%|yield None%-",), node)
+
+    code._tokens = None # save memory
     code._customize = None  # save memory