Cython 3.3.0 compiler crash when compiling _websocket/reader_c.py

[tom--pollard]

Describe the bug

Hi,

We're upgrading Cython from 3.2.9 to 3.3.0 in the freedesktop-sdk project (https://gitlab.com/freedesktop-sdk/freedesktop-sdk/-/merge_requests/34031) and found that aiohttp no longer compiles with the new version.

The failure is in aiohttp/_websocket/reader_c.py on this line:

ALLOWED_CLOSE_CODES: Final[set[int]] = {int(i) for i in WSCloseCode}

Cython 3.3.0 crashes with:

Compiler crash in AnalyseDeclarationsTransform

and eventually:

AttributeError: 'NoneType' object has no attribute 'assignable_from'

The relevant part of the traceback is:

File ".../Cython/Compiler/ExprNodes.py", line 2377, in _analyse_target_declaration
  if not (annotation_type.assignable_from(entry_type) or entry_type.assignable_from(annotation_type)):
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'assignable_from'

Cython 3.2.9 compiles the same source successfully.

We're seeing this with Python 3.14 (but can also produce on 3.13 & 3.12) and Cython 3.3.0.

For reference, this is the command being used to regenerate the C files:

python3 -m cython -3 -I aiohttp aiohttp/_websocket/reader_c.py

It looks like this may be related to the type inference for the set comprehension and/or the Final[set[int]] annotation.

I noticed that ALLOWED_CLOSE_CODES has also been discussed recently in #12918, although that appears to be for a different issue.

You can view a failing pipeline at https://gitlab.com/freedesktop-sdk/freedesktop-sdk/-/jobs/16049983973#L3941

To Reproduce

See above, try and build the latest version of the aiohttp source dist 3.14.3 with cython 3.3.0

Expected behavior

The compilation is successful

Logs/tracebacks

Error compiling Cython file:
------------------------------------------------------------
...
    WSMessage,
    WSMessageTextBytes,
    WSMsgType,
)

ALLOWED_CLOSE_CODES: Final[set[int]] = {int(i) for i in WSCloseCode}
^
------------------------------------------------------------
aiohttp/_websocket/reader_c.py:22:0: Compiler crash in AnalyseDeclarationsTransform

File 'ModuleNode.py', line 297, in analyse_declarations: ModuleNode(reader_c.py:1:0,
    doc = 'Reader for WebSocket protocol versions 13 and 8.',
    full_module_name = 'aiohttp._websocket.reader_c')
File 'Nodes.py', line 426, in analyse_declarations: StatListNode(reader_c.py:3:0)
File 'Nodes.py', line 426, in analyse_declarations: StatListNode(reader_c.py:22:39)
File 'Nodes.py', line 6380, in analyse_declarations: SingleAssignmentNode(reader_c.py:22:39,
    first = True)
File 'ExprNodes.py', line 2345, in analyse_target_declaration: NameNode(reader_c.py:22:0,
    cf_maybe_null = True,
    is_name = True,
    is_target = True,
    module_state_lookup = '',
    name = 'ALLOWED_CLOSE_CODES',
    result_is_used = True,
    use_managed_ref = True)
File 'ExprNodes.py', line 2377, in _analyse_target_declaration: NameNode(reader_c.py:22:0,
    cf_maybe_null = True,
    is_name = True,
    is_target = True,
    module_state_lookup = '',
    name = 'ALLOWED_CLOSE_CODES',
    result_is_used = True,
    use_managed_ref = True)

Compiler crash traceback from this point on:
  File "/usr/lib/python3.14/site-packages/Cython/Compiler/ExprNodes.py", line 2377, in _analyse_target_declaration
    if not (annotation_type.assignable_from(entry_type) or entry_type.assignable_from(annotation_type)):
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'assignable_from'
Command 'for filename in $(grep -rl '/\* Generated by Cython'); do
  rm -v ${filename}
  basefile=$(echo ${filename} | cut -d"." -f1)
  python3 -m cython -3 -I aiohttp ${basefile}.py*
done' failed with exitcode 1

Python Version

3.14.7

aiohttp Version

3.14.3

multidict Version

6.7.1

propcache Version

0.5.2

yarl Version

1.24.5

OS

Freedesktop-sdk based linux toolchain

Related component

Client

Additional context

No response

Code of Conduct

• I agree to follow the aio-libs Code of Conduct

[tom--pollard]

Thanks @Georgefifth @bdraco !

[Dreamsorcerer]

I'm a little confused, because it's still failing in CI with the same error:
#13547