bpo-34616: add flags to allow top-level-await

Doc/library/functions.rst

@@ -257,6 +257,12 @@ are always available. They are listed here in alphabetical order.
  can be found as the :attr:`~__future__._Feature.compiler_flag` attribute on
  the :class:`~__future__._Feature` instance in the :mod:`__future__` module.
 
+ The optional argument *flags* also controls whether the compiled source is
+ allowed to contain top-level ``await``, ``async for`` and ``async with``.
+ When the bit ``ast.PyCF_ALLOW_TOP_LEVEL_AWAIT`` is set, the return code
+ object has ``CO_COROUTINE`` set in ``co_code``, and can be interactively
+ executed via ``await eval(code_object)``.
+
  The argument *optimize* specifies the optimization level of the compiler; the
  default value of ``-1`` selects the optimization level of the interpreter as
  given by :option:`-O` options. Explicit levels are ``0`` (no optimization;
@@ -290,6 +296,10 @@ are always available. They are listed here in alphabetical order.
  Previously, :exc:`TypeError` was raised when null bytes were encountered
  in *source*.
 
+ .. versionadded:: 3.8
+ ``ast.PyCF_ALLOW_TOP_LEVEL_AWAIT`` can now be passed in flags to enable
+ support for top-level ``await``, ``async for``, and ``async with``.
+
 
 .. class:: complex([real[, imag]])
 

Include/compile.h

@@ -23,6 +23,7 @@ PyAPI_FUNC(PyCodeObject *) PyNode_Compile(struct _node *, const char *);
 #define PyCF_ONLY_AST 0x0400
 #define PyCF_IGNORE_COOKIE 0x0800
 #define PyCF_TYPE_COMMENTS 0x1000
+#define PyCF_ALLOW_TOP_LEVEL_AWAIT 0x2000
 
 #ifndef Py_LIMITED_API
 typedef struct {

Lib/test/test_builtin.py

@@ -1,6 +1,7 @@
 # Python test set -- built-in functions
 
 import ast
+import asyncio
 import builtins
 import collections
 import decimal
@@ -18,9 +19,14 @@
 import unittest
 import warnings
 from contextlib import ExitStack
+from inspect import CO_COROUTINE
+from itertools import product
+from textwrap import dedent
+from types import AsyncGeneratorType, FunctionType
 from operator import neg
 from test.support import (
- EnvironmentVarGuard, TESTFN, check_warnings, swap_attr, unlink)
+ EnvironmentVarGuard, TESTFN, check_warnings, swap_attr, unlink,
+ maybe_get_event_loop_policy)
 from test.support.script_helper import assert_python_ok
 from unittest.mock import MagicMock, patch
 try:
@@ -358,6 +364,71 @@ def f(): """doc"""
  rv = ns['f']()
  self.assertEqual(rv, tuple(expected))
 
+ def test_compile_top_level_await(self):
+ """Test whether code some top level await can be compiled.
+
+ Make sure it compiles only with the PyCF_ALLOW_TOP_LEVEL_AWAIT flag set,
+ and make sure the generated code object has the CO_COROUTINE flag set in
+ order to execute it with `await eval(.....)` instead of exec, or via a
+ FunctionType.
+ """
+
+ # helper function just to check we can run top=level async-for
+ async def arange(n):
+ for i in range(n):
+ yield i
+
+ modes = ('single', 'exec')
+ code_samples = ['''a = await asyncio.sleep(0, result=1)''',
+ '''async for i in arange(1):
+ a = 1''',
+ '''async with asyncio.Lock() as l:
+ a = 1''']
+ policy = maybe_get_event_loop_policy()
+ try:
+ for mode, code_sample in product(modes,code_samples):
+ source = dedent(code_sample)
+ with self.assertRaises(SyntaxError, msg=f"{source=} {mode=}"):
+ compile(source, '?' , mode)
+
+ co = compile(source,
+ '?',
+ mode,
+ flags=ast.PyCF_ALLOW_TOP_LEVEL_AWAIT)
+
+ self.assertEqual(co.co_flags & CO_COROUTINE, CO_COROUTINE,
+ msg=f"{source=} {mode=}")
+
+
+ # test we can create and advance a function type
+ globals_ = {'asyncio': asyncio, 'a':0, 'arange': arange}
+ async_f = FunctionType(co, globals_)
+ asyncio.run(async_f())
+ self.assertEqual(globals_['a'], 1)
+
+ # test we can await-eval,
+ globals_ = {'asyncio': asyncio, 'a':0, 'arange': arange}
+ asyncio.run(eval(co, globals_))
+ self.assertEqual(globals_['a'], 1)
+ finally:
+ asyncio.set_event_loop_policy(policy)
+
+ def test_compile_async_generator(self):
+ """
+ With the PyCF_ALLOW_TOP_LEVEL_AWAIT flag added in 3.8, we want to
+ make sure AsyncGenerators are still properly not marked with CO_COROUTINE
+ """
+ code = dedent("""async def ticker():
+ for i in range(10):
+ yield i
+ await asyncio.sleep(0)""")
+
+ co = compile(code, '?', 'exec', flags=ast.PyCF_ALLOW_TOP_LEVEL_AWAIT)
+ glob = {}
+ exec(co, glob)
+ self.assertEqual(type(glob['ticker']()), AsyncGeneratorType)
+
+
  def test_delattr(self):
  sys.spam = 1
  delattr(sys, 'spam')

Misc/NEWS.d/next/Core and Builtins/2019-05-07-17-12-37.bpo-34616.0Y0_9r.rst

@@ -0,0 +1 @@
+The ``compile()`` builtin functions now support the ``ast.PyCF_ALLOW_TOP_LEVEL_AWAIT`` flag, which allow to compile sources that contains top-level ``await``, ``async with`` or ``async for``. This is useful to evaluate async-code from with an already async functions; for example in a custom REPL.

Parser/asdl_c.py

@@ -1000,6 +1000,8 @@ def visitModule(self, mod):
  self.emit("if (!m) return NULL;", 1)
  self.emit("d = PyModule_GetDict(m);", 1)
  self.emit('if (PyDict_SetItemString(d, "AST", (PyObject*)&AST_type) < 0) return NULL;', 1)
+ self.emit('if (PyModule_AddIntMacro(m, PyCF_ALLOW_TOP_LEVEL_AWAIT) < 0)', 1)
+ self.emit("return NULL;", 2)
  self.emit('if (PyModule_AddIntMacro(m, PyCF_ONLY_AST) < 0)', 1)
  self.emit("return NULL;", 2)
  self.emit('if (PyModule_AddIntMacro(m, PyCF_TYPE_COMMENTS) < 0)', 1)

Python/compile.c

@@ -2609,7 +2609,9 @@ static int
 compiler_async_for(struct compiler *c, stmt_ty s)
 {
  basicblock *start, *except, *end;
- if (c->u->u_scope_type != COMPILER_SCOPE_ASYNC_FUNCTION) {
+ if (c->c_flags->cf_flags & PyCF_ALLOW_TOP_LEVEL_AWAIT){
+ c->u->u_ste->ste_coroutine = 1;
+ } else if (c->u->u_scope_type != COMPILER_SCOPE_ASYNC_FUNCTION) {
  return compiler_error(c, "'async for' outside async function");
  }
 
@@ -4564,7 +4566,9 @@ compiler_async_with(struct compiler *c, stmt_ty s, int pos)
  withitem_ty item = asdl_seq_GET(s->v.AsyncWith.items, pos);
 
  assert(s->kind == AsyncWith_kind);
- if (c->u->u_scope_type != COMPILER_SCOPE_ASYNC_FUNCTION) {
+ if (c->c_flags->cf_flags & PyCF_ALLOW_TOP_LEVEL_AWAIT){
+ c->u->u_ste->ste_coroutine = 1;
+ } else if (c->u->u_scope_type != COMPILER_SCOPE_ASYNC_FUNCTION){
  return compiler_error(c, "'async with' outside async function");
  }
 
@@ -4773,12 +4777,16 @@ compiler_visit_expr1(struct compiler *c, expr_ty e)
  ADDOP(c, YIELD_FROM);
  break;
  case Await_kind:
- if (c->u->u_ste->ste_type != FunctionBlock)
- return compiler_error(c, "'await' outside function");
+ if (!(c->c_flags->cf_flags & PyCF_ALLOW_TOP_LEVEL_AWAIT)){
+ if (c->u->u_ste->ste_type != FunctionBlock){
+ return compiler_error(c, "'await' outside function");
+ }
 
- if (c->u->u_scope_type != COMPILER_SCOPE_ASYNC_FUNCTION &&
- c->u->u_scope_type != COMPILER_SCOPE_COMPREHENSION)
- return compiler_error(c, "'await' outside async function");
+ if (c->u->u_scope_type != COMPILER_SCOPE_ASYNC_FUNCTION && 
+ c->u->u_scope_type != COMPILER_SCOPE_COMPREHENSION){
+ return compiler_error(c, "'await' outside async function");
+ }
+ }
 
  VISIT(c, expr, e->v.Await.value);
  ADDOP(c, GET_AWAITABLE);
@@ -5712,6 +5720,12 @@ compute_code_flags(struct compiler *c)
  /* (Only) inherit compilerflags in PyCF_MASK */
  flags |= (c->c_flags->cf_flags & PyCF_MASK);
 
+ if ((c->c_flags->cf_flags & PyCF_ALLOW_TOP_LEVEL_AWAIT) &&
+ ste->ste_coroutine &&
+ !ste->ste_generator) {
+ flags |= CO_COROUTINE;
+ }
+
  return flags;
 }