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fix: refactor sem analysis of the await-not-async on generators and list comprehension #18152

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fix: refactor sem analysis of the await-not-async on generators and list comprehension #18152

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d3b2d9d
fix: refactor sem analysis of the await-not-async on generators and l…
josetapadas Nov 13, 2024
ed2937a
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Nov 13, 2024
c97bce7
chore: added unit test
josetapadas Nov 13, 2024
ada4720
chore: refactor to remove function for simple check
josetapadas Nov 13, 2024
43fc65a
fix: fixed the await outside coroutine within list comprehensions error
josetapadas Nov 13, 2024
e3004a1
chore: error type is not syntax but await-not-async
josetapadas Nov 13, 2024
e7ef1f6
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Nov 13, 2024
0c82fb9
fix: added await-outside-coroutine checks also to list and dict compr…
josetapadas Nov 14, 2024
8e8298e
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Nov 14, 2024
0fee8d6
chore: remove artefact from update data
josetapadas Nov 18, 2024
95c5730
chore: fail consistently for the new case also on the set comprehension
josetapadas Nov 18, 2024
48148ac
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Nov 18, 2024
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2 changes: 2 additions & 0 deletions mypy/message_registry.py
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Original file line number Diff line number Diff line change
Expand Up @@ -80,6 +80,8 @@ def with_additional_msg(self, info: str) -> ErrorMessage:
ASYNC_FOR_OUTSIDE_COROUTINE: Final = '"async for" outside async function'
ASYNC_WITH_OUTSIDE_COROUTINE: Final = '"async with" outside async function'

AWAIT_WITH_OUTSIDE_COROUTINE: Final = '"await" outside coroutine ("async def")'

INCOMPATIBLE_TYPES_IN_YIELD: Final = ErrorMessage('Incompatible types in "yield"')
INCOMPATIBLE_TYPES_IN_YIELD_FROM: Final = ErrorMessage('Incompatible types in "yield from"')
INCOMPATIBLE_TYPES_IN_STR_INTERPOLATION: Final = "Incompatible types in string interpolation"
Expand Down
30 changes: 26 additions & 4 deletions mypy/semanal.py
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Expand Up @@ -228,6 +228,7 @@
set_callable_name as set_callable_name,
)
from mypy.semanal_typeddict import TypedDictAnalyzer
from mypy.traverser import has_await_expression
from mypy.tvar_scope import TypeVarLikeScope
from mypy.typeanal import (
SELF_TYPE_NAMES,
Expand Down Expand Up @@ -6076,7 +6077,20 @@ def visit_type_application(self, expr: TypeApplication) -> None:
def visit_list_comprehension(self, expr: ListComprehension) -> None:
if any(expr.generator.is_async):
if not self.is_func_scope() or not self.function_stack[-1].is_coroutine:
self.fail(message_registry.ASYNC_FOR_OUTSIDE_COROUTINE, expr, code=codes.SYNTAX)
self.fail(
message_registry.ASYNC_FOR_OUTSIDE_COROUTINE,
expr,
code=codes.SYNTAX,
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@sterliakov sterliakov Nov 14, 2024

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I don't really like the use of codes.SYNTAX vs codes.AWAIT_NOT_ASYNC here. Prior to this PR AWAIT_NOT_ASYNC was only used once.

As far as I understand, the purpose of using a special code was to support "specific" environments: e.g. IPython allows top-level awaits, so it should be easy to disable such a check when checking IPython snippets.

I see two possible resolutions here:

  1. Declare that we only type-check true python code. Then codes.AWAIT_NOT_ASYNC can be safely removed altogether and replaced with codes.SYNTAX
  2. Declare that we want to support such environments. Then all these checks become more complicated: when at module scope (note it isn't same as not self.is_func_scope()), produce codes.AWAIT_NOT_ASYNC, otherwise produce codes.SYNTAX. This can also be extracted into a helper like def require_async_scope(self, message). This logic is close to what visit_await_expr was doing before.

I somewhat prefer 2 as that isn't that much work to do, but can live with 1 either.

Disclaimer: please note I'm not a mypy maintainer and just try to help sometimes. You'd better ask for a maintainer's opinion here: @brianschubert do you have any preference?

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@sterliakov sterliakov Nov 14, 2024 •
edited
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OTOH 2 can also be misleading and deserves an explicit mention in the docs.

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@josetapadas josetapadas Nov 18, 2024

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Thank you for the review and explanation, I understand your point so thank you for clarifying it. Will then wait for any guidance on how to proceed on any of these two options.

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@jakkdl jakkdl Nov 27, 2024 •
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I don't think this is an important enough problem to change our stance on allowing top-level awaits, so you're probably safer to go ahead with option 2 for now. A bare await outside async has always been a syntax error in python, so whatever reason the original PR had for not making that use codes.SYNTAX should apply here as well.

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@A5rocks A5rocks Feb 24, 2025

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I think 2 is better, and there's precedent for switching around error codes with missing return statements. I also don't think anyone with authority is going to provide an opinion...

def f() -> str:  # E: Missing return statement  [empty-body]
    pass

def g() -> str:  # E: Missing return statement  [return]
    if True:
        pass

serious=True,
)
elif has_await_expression(expr):
if not self.is_func_scope() or not self.function_stack[-1].is_coroutine:
self.fail(
message_registry.AWAIT_WITH_OUTSIDE_COROUTINE,
expr,
code=codes.AWAIT_NOT_ASYNC,
serious=True,
)

expr.generator.accept(self)

Expand All @@ -6090,7 +6104,12 @@ def visit_set_comprehension(self, expr: SetComprehension) -> None:
def visit_dictionary_comprehension(self, expr: DictionaryComprehension) -> None:
if any(expr.is_async):
if not self.is_func_scope() or not self.function_stack[-1].is_coroutine:
self.fail(message_registry.ASYNC_FOR_OUTSIDE_COROUTINE, expr, code=codes.SYNTAX)
self.fail(
message_registry.ASYNC_FOR_OUTSIDE_COROUTINE,
expr,
code=codes.SYNTAX,
serious=True,
)

with self.enter(expr):
self.analyze_comp_for(expr)
Expand Down Expand Up @@ -6167,9 +6186,12 @@ def visit_await_expr(self, expr: AwaitExpr) -> None:
# This is not a blocker, because some enviroments (like ipython)
# support top level awaits.
self.fail('"await" outside function', expr, serious=True, code=codes.TOP_LEVEL_AWAIT)
elif not self.function_stack[-1].is_coroutine:
elif (
not self.function_stack[-1].is_coroutine
and self.scope_stack[-1] != SCOPE_COMPREHENSION
):
self.fail(
'"await" outside coroutine ("async def")',
message_registry.AWAIT_WITH_OUTSIDE_COROUTINE,
expr,
serious=True,
code=codes.AWAIT_NOT_ASYNC,
Expand Down
16 changes: 15 additions & 1 deletion test-data/unit/check-async-await.test
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Original file line number Diff line number Diff line change
Expand Up @@ -1013,13 +1013,17 @@ async def foo(x: int) -> int: ...

# These are allowed in some cases:
top_level = await foo(1) # E: "await" outside function [top-level-await]
crasher = [await foo(x) for x in [1, 2, 3]] # E: "await" outside function [top-level-await]
crasher = [await foo(x) for x in [1, 2, 3]] # E: "await" outside coroutine ("async def") [await-not-async] \
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@sterliakov sterliakov Nov 14, 2024

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More explicit tests would be really helpful here. Consider at least checking all of the following in different scopes (module level, non-async function body and async function body at least; the former two should produce the same errors and async function should allow all of those):

(await x for x in xs)  # OK
[await x for x in xs]  # E
{await x for x in xs}  # E
{0: await x for x in xs}  # E
{await x: 0 for x in xs}  # E

(x async for x in xs)  # OK
[x async for x in xs]  # E
{x async for x in xs}  # E
{x: 0 async for x in xs}  # E

(x for x in await xs)  # E
[x for x in await xs]  # E
{x for x in await xs}  # E
{x: 0 for x in await xs}  # E

There's already testAsyncForOutsideCoroutine for the 2nd block, the 3rd one is probably not interesting (follows regular rules), but the 1st one isn't exercised yet.

# E: "await" outside function [top-level-await]

def bad() -> None:
# These are always critical / syntax issues:
y = [await foo(x) for x in [1, 2, 3]] # E: "await" outside coroutine ("async def") [await-not-async]
async def good() -> None:
y = [await foo(x) for x in [1, 2, 3]] # OK



[builtins fixtures/async_await.pyi]
[typing fixtures/typing-async.pyi]

Expand Down Expand Up @@ -1080,3 +1084,13 @@ class Launcher(P):

[builtins fixtures/async_await.pyi]
[typing fixtures/typing-async.pyi]

[case testAwaitInsideGeneratorExpr]
def foo():
yield 0

def bar():
(await x for x in foo())

[builtins fixtures/async_await.pyi]
[typing fixtures/typing-async.pyi]
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