fix runnign on 3.7

IPython/core/async_helpers.py

@@ -1,88 +1,90 b''
 """
 Async helper function that are invalid syntax on Python 3.5 and below.
 
 Known limitation and possible improvement.
 
 Top level code that contain a return statement (instead of, or in addition to
 await) will be detected as requiring being wrapped in async calls. This should
 be prevented as early return will not work.
 """
 
 
 
 import ast
 import sys
 import inspect
 from textwrap import dedent, indent
 from types import CodeType
 
 
 def _asyncio_runner(coro):
     """
     Handler for asyncio autoawait
     """
     import asyncio
     return asyncio.get_event_loop().run_until_complete(coro)
 
 
 def _curio_runner(coroutine):
     """
     handler for curio autoawait
     """
     import curio
     return curio.run(coroutine)
 
 
 if sys.version_info > (3, 5):
     # nose refuses to avoid this file and async def is invalidsyntax
     s = dedent('''
     def _trio_runner(function):
         import trio
         async def loc(coro):
             """
             We need the dummy no-op async def to protect from
             trio's internal. See https://github.com/python-trio/trio/issues/89
             """
             return await coro
         return trio.run(loc, function)
     ''')
     exec(s, globals(), locals())
 
 
 def _asyncify(code: str) -> str:
     """wrap code in async def definition.
 
     And setup a bit of context to run it later.
     """
     res = dedent("""
         async def __wrapper__():
             try:
                 {usercode}
             finally:
                 locals()
     """).format(usercode=indent(code, ' ' * 8)[8:])
     return res
 
 
 def _should_be_async(cell: str) -> bool:
     """Detect if a block of code need to be wrapped in an `async def`
 
     Attempt to parse the block of code, it it compile we're fine.
     Otherwise we  wrap if and try to compile.
 
     If it works, assume it should be async. Otherwise Return False.
 
     Not handled yet: If the block of code has a return statement as  the top
     level, it will be seen as async. This is a know limitation.
     """
 
     try:
-        ast.parse(cell)
+        # we can't limit ourself to ast.parse, as it __accepts__ to parse on
+        # 3.7+, but just does not _compile_
+        compile(cell, '<>', 'exec')
         return False
     except SyntaxError:
         try:
             ast.parse(_asyncify(cell))
         except SyntaxError:
             return False
         return True
     return False