Fix unsafe cast in linegen.py w/ await yield handling (#3533)

Fixes #3532.

CHANGES.md

@@ -42,6 +42,7 @@
 - Fix an invalid quote escaping bug in f-string expressions where it produced invalid
   code. Implicitly concatenated f-strings with different quotes can now be merged or
   quote-normalized by changing the quotes used in expressions. (#3509)
+- Fix crash on `await (yield)` when Black is compiled with mypyc (#3533)
 
 ### Configuration
 

src/black/linegen.py

@@ -1223,7 +1223,8 @@ def remove_await_parens(node: Node) -> None:
             # N.B. We've still removed any redundant nested brackets though :)
             opening_bracket = cast(Leaf, node.children[1].children[0])
             closing_bracket = cast(Leaf, node.children[1].children[-1])
-            bracket_contents = cast(Node, node.children[1].children[1])
+            bracket_contents = node.children[1].children[1]
+            if isinstance(bracket_contents, Node):
                 if bracket_contents.type != syms.power:
                     ensure_visible(opening_bracket)
                     ensure_visible(closing_bracket)

tests/data/preview/remove_await_parens.py

@@ -77,6 +77,9 @@ async def main():
 async def main():
     await (await (await (await (await (asyncio.sleep(1))))))
 
+async def main():
+    await (yield)
+
 # output
 import asyncio
 
@@ -167,3 +170,7 @@ async def main():
 
 async def main():
     await (await (await (await (await asyncio.sleep(1)))))
+
+
+async def main():
+    await (yield)