Fix attribute writes after impossible narrowing

[cakeni]

Summary

Fix attribute writes in impossible narrowing branches to fall back to the receiver's unnarrowed declared path when the flow receiver has become Never. Normal receiver narrowing is preserved, and the assignment continues to invalidate stale attribute facets.

The regression test verifies both sides: a Container write is accepted and an incompatible Literal[1] write is still rejected against the declared Container type.

Fixes #4478

Test Plan

• cargo +stable-x86_64-pc-windows-gnu test -p pyrefly --lib test_attr_assignment_uses_declared_type_after_impossible_narrow -- --nocapture
• python test.py --no-test --no-tensor-shapes --no-conformance --no-jsonschema
• cargo fmt --all -- --check
• git diff --check

[meta-codesync]

This pull request has been imported. If you are a Meta employee, you can view this in D115588096. (Because this pull request was imported automatically, there will not be any future comments.)

[shobhitmehro]

Thanks for the PR! Could you review the mypy_primer diff above and confirm the new diagnostics are expected?

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

============================================================
SUMMARY
============================================================
Total: +12 new errors, -46 fixed errors

Projects with changes (21):
  cloud-init: +1 -3
  dulwich: +0 -3
  steam.py: +0 -1
  bokeh: +0 -1
  spark: +0 -1
  prefect: +0 -1
  colour: +2 -1
  freqtrade: +0 -2
  setuptools: +0 -6
  apprise: +0 -1
  manticore: +0 -2
  beartype: +0 -1
  pandera: +0 -1
  ibis: +6 -6
  hydpy: +0 -1
  meson: +0 -5
  werkzeug: +0 -1
  core: +1 -1
  paasta: +0 -2
  sphinx: +1 -5
  poetry: +1 -1
============================================================

FULL DIFF DETAILS
------------------------------------------------------------

cloud-init (https://github.com/canonical/cloud-init)
- ERROR cloudinit/sources/DataSourceHetzner.py:204:36-49: `Literal['_unset']` is not assignable to attribute `_network_config` with type `Never` [bad-assignment]
- ERROR cloudinit/sources/DataSourceScaleway.py:320:36-49: `Literal['_unset']` is not assignable to attribute `_network_config` with type `Never` [bad-assignment]
- ERROR cloudinit/sources/DataSourceSmartOS.py:205:34-38: `None` is not assignable to attribute `md_client` with type `Never` [bad-assignment]
+ ERROR cloudinit/sources/DataSourceSmartOS.py:205:34-38: `None` is not assignable to attribute `md_client` with type `str` [bad-assignment]

dulwich (https://github.com/dulwich/dulwich)
- ERROR dulwich/repo.py:1677:42-1679:22: `ObjectFormat` is not assignable to attribute `object_format` with type `Never` [bad-assignment]
- ERROR dulwich/repo.py:1681:42-63: `ObjectFormat` is not assignable to attribute `object_format` with type `Never` [bad-assignment]
- ERROR dulwich/repo.py:1683:38-59: `ObjectFormat` is not assignable to attribute `object_format` with type `Never` [bad-assignment]

steam.py (https://github.com/Gobot1234/steam.py)
- ERROR steam/ext/commands/commands.py:248:49-60: `dict[str, Any]` is not assignable to attribute `__annotations__` with type `Never` [bad-assignment]

bokeh (https://github.com/bokeh/bokeh)
- ERROR src/bokeh/layouts.py:679:32-43: `Literal['fixed', 'inherit', 'scale_both', 'scale_height', 'scale_width', 'stretch_both', 'stretch_height', 'stretch_width']` is not assignable to attribute `sizing_mode` with type `Never` [bad-assignment]

spark (https://github.com/apache/spark)
- ERROR python/pyspark/ml/connect/pipeline.py:78:27-33: `list[Unknown]` is not assignable to attribute `stages` with type `Never` [bad-assignment]

prefect (https://github.com/PrefectHQ/prefect)
- ERROR src/integrations/prefect-gcp/prefect_gcp/workers/cloud_run_v2.py:302:30-38: `str` is not assignable to attribute `_job_name` with type `Never` [bad-assignment]

colour (https://github.com/colour-science/colour)
- ERROR colour/io/fichet2021.py:843:36-845:10: `list[Image_Specification_Attribute]` is not assignable to attribute `attributes` with type `Never` [bad-assignment]
+ ERROR colour/io/fichet2021.py:843:36-845:10: `list[Image_Specification_Attribute]` is not assignable to attribute `attributes` with type `tuple[Unknown, ...]` [bad-assignment]
+ ERROR colour/io/fichet2021.py:848:13-44: Object of class `tuple` has no attribute `extend` [missing-attribute]

freqtrade (https://github.com/freqtrade/freqtrade)
- ERROR freqtrade/freqtradebot.py:1933:46-94: `str` is not assignable to attribute `ft_cancel_reason` with type `Never` [bad-assignment]
- ERROR freqtrade/freqtradebot.py:2027:46-94: `str` is not assignable to attribute `ft_cancel_reason` with type `Never` [bad-assignment]

setuptools (https://github.com/pypa/setuptools)
- ERROR setuptools/_distutils/command/build_ext.py:198:33-69: `list[@_]` is not assignable to attribute `include_dirs` with type `Never` [bad-assignment]
- ERROR setuptools/_distutils/command/build_ext.py:219:30-32: `list[@_]` is not assignable to attribute `libraries` with type `Never` [bad-assignment]
- ERROR setuptools/_distutils/command/build_ext.py:221:33-35: `list[@_]` is not assignable to attribute `library_dirs` with type `Never` [bad-assignment]
- ERROR setuptools/_distutils/command/build_ext.py:226:26-28: `list[@_]` is not assignable to attribute `rpath` with type `Never` [bad-assignment]
- ERROR setuptools/_distutils/command/build_ext.py:293:30-32: `list[@_]` is not assignable to attribute `swig_opts` with type `Never` [bad-assignment]
- ERROR setuptools/_vendor/wheel/_bdist_wheel.py:272:30-63: `LiteralString` is not assignable to attribute `bdist_dir` with type `Never` [bad-assignment]

apprise (https://github.com/caronc/apprise)
- ERROR tests/test_config_http.py:311:26-54: `int` is not assignable to attribute `max_buffer_size` with type `Never` [bad-assignment]

manticore (https://github.com/trailofbits/manticore)
- ERROR tests/native/test_cpu_manual.py:195:18-24: `Literal[43690]` is not assignable to attribute `SI` with type `Never` [bad-assignment]
- ERROR tests/native/test_cpu_manual.py:472:18-22: `Literal[221]` is not assignable to attribute `CL` with type `Never` [bad-assignment]

beartype (https://github.com/beartype/beartype)
- ERROR beartype/_check/code/codemain.py:1469:40-1472:14: `str` is not assignable to attribute `func_curr_code` with type `Never` [bad-assignment]

pandera (https://github.com/pandera-dev/pandera)
- ERROR tests/base/test_config.py:49:35-70: `ValidationDepth | None` is not assignable to attribute `validation_depth` with type `Never` [bad-assignment]

ibis (https://github.com/ibis-project/ibis)
- ERROR ibis/common/tests/test_grounds.py:302:11-12: `Literal[3]` is not assignable to attribute `a` with type `Never` [bad-assignment]
+ ERROR ibis/common/tests/test_grounds.py:302:11-12: `Literal[3]` is not assignable to attribute `a` with type `InstanceOf` [bad-assignment]
- ERROR ibis/common/tests/test_grounds.py:701:15-16: `Literal[1]` is not assignable to attribute `a` with type `Never` [bad-assignment]
+ ERROR ibis/common/tests/test_grounds.py:701:15-16: `Literal[1]` is not assignable to attribute `a` with type `Attribute` [bad-assignment]
- ERROR ibis/common/tests/test_grounds.py:869:11-12: `Literal[2]` is not assignable to attribute `j` with type `Never` [bad-assignment]
+ ERROR ibis/common/tests/test_grounds.py:869:11-12: `Literal[2]` is not assignable to attribute `j` with type `Attribute` [bad-assignment]
- ERROR ibis/common/tests/test_grounds.py:882:11-12: `Literal[2]` is not assignable to attribute `j` with type `Never` [bad-assignment]
+ ERROR ibis/common/tests/test_grounds.py:882:11-12: `Literal[2]` is not assignable to attribute `j` with type `Attribute` [bad-assignment]
- ERROR ibis/common/tests/test_grounds.py:943:19-20: `Literal[3]` is not assignable to attribute `double_a` with type `Never` [bad-assignment]
+ ERROR ibis/common/tests/test_grounds.py:943:19-20: `Literal[3]` is not assignable to attribute `double_a` with type `Attribute` [bad-assignment]
- ERROR ibis/common/tests/test_grounds.py:1034:21-23: `Literal[11]` is not assignable to attribute `value` with type `Never` [bad-assignment]
+ ERROR ibis/common/tests/test_grounds.py:1034:21-23: `Literal[11]` is not assignable to attribute `value` with type `InstanceOf` [bad-assignment]

hydpy (https://github.com/hydpy-dev/hydpy)
- ERROR hydpy/core/importtools.py:821:35-50: `dict[str, Any]` is not assignable to attribute `_namespace` with type `Never` [bad-assignment]

meson (https://github.com/mesonbuild/meson)
- ERROR mesonbuild/build.py:2145:44-46: `list[@_]` is not assignable to attribute `extra_args` with type `Never` [bad-assignment]
- ERROR mesonbuild/build.py:2151:57-59: `list[@_]` is not assignable to attribute `extra_depends` with type `Never` [bad-assignment]
- ERROR mesonbuild/build.py:2750:27-33: `str` is not assignable to attribute `prefix` with type `Never` [bad-assignment]
- ERROR mesonbuild/build.py:2752:27-33: `str` is not assignable to attribute `suffix` with type `Never` [bad-assignment]
- ERROR mesonbuild/build.py:3620:27-76: `list[@_]` is not assignable to attribute `rename` with type `Never` [bad-assignment]

werkzeug (https://github.com/pallets/werkzeug)
- ERROR tests/test_utils.py:173:14-48: `datetime` is not assignable to attribute `date` with type `Never` [bad-assignment]

core (https://github.com/home-assistant/core)
- ERROR homeassistant/helpers/entity.py:1033:42-46: `Literal[True]` is not assignable to attribute `_no_platform_reported` with type `Never` [bad-assignment]
+ ERROR homeassistant/helpers/entity_platform.py:887:73-74: Unused `# type: ignore` comment [unused-type-ignore]

paasta (https://github.com/yelp/paasta)
- ERROR paasta_tools/paasta_service_config_loader.py:86:30-89: `list[str]` is not assignable to attribute `_clusters` with type `Never` [bad-assignment]
- ERROR paasta_tools/paasta_service_config_loader.py:146:38-148:14: `DeploymentsJsonV2` is not assignable to attribute `_deployments_json` with type `Never` [bad-assignment]

sphinx (https://github.com/sphinx-doc/sphinx)
- ERROR sphinx/directives/patches.py:54:32-44: `int` is not assignable to attribute `line` with type `Never` [bad-assignment]
- ERROR sphinx/environment/__init__.py:278:28-280:14: `_DomainsContainer` is not assignable to attribute `domains` with type `Never` [bad-assignment]
- ERROR sphinx/util/nodes.py:184:27-48: `str` is not assignable to attribute `source` with type `Never` [bad-assignment]
- ERROR sphinx/util/nodes.py:778:32-58: `str` is not assignable to attribute `source` with type `Never` [bad-assignment]
- ERROR sphinx/util/nodes.py:780:30-54: `str` is not assignable to attribute `line` with type `Never` [bad-assignment]
+ ERROR sphinx/util/nodes.py:780:30-54: `str` is not assignable to attribute `line` with type `int` [bad-assignment]

poetry (https://github.com/python-poetry/poetry)
- ERROR src/poetry/console/commands/init.py:548:26-42: `RepositoryPool` is not assignable to attribute `_pool` with type `Never` [bad-assignment]
+ ERROR src/poetry/console/commands/init.py:550:13-75: Result of call expression is of type `RepositoryPool` and is not used; assign to `_` if this is intentional [unused-call-result]