Report one bad-context-manager error per broken with-item

[nitishagar]

Fixes #5079

Problem

A context manager that fails both protocol halves produced two bad-context-manager errors with an identical header and range:

from contextlib import asynccontextmanager

@asynccontextmanager
async def async_context():
    yield

with async_context():  # TWO identical errors appear here
    print("This will cause an error at runtime")

Both errors read "Cannot use _AsyncGeneratorContextManager[None] as a context manager"; they differ only in the detail line (__enter__ vs __exit__ missing). The error collector intentionally does not merge diagnostics whose details differ, so the pair always displayed.

Change

context_value checks the protocol in two halves (enter, exit), each attributing failures to the with-item's range under the shared bad-context-manager context. Each half's diagnostics are now collected in their own delayed collector, and only the first failing half's errors are forwarded:

• enter broken → the enter error survives (it carries the actionable "Did you mean __aenter__?" hint, which is exactly the fix a user needs for the issue's case);
• enter fine → exit errors forwarded byte-for-byte as before, including the existing two-call consolidation for bad __exit__ signatures;
• the exit half is still fully evaluated so its return type keeps feeding the bool | None check.

An object failing only one half still yields exactly one error naming that half; async with on async context managers is unaffected.

Test plan

• New testcase! reproducing the issue (async CM in sync with → exactly 1 error) — written first and verified failing ("expected 1 errors, but got 2") before the fix
• Tests pinning the old two-error shape updated deliberately (with-item with 42 case + LSP diagnostics snapshot) — the PR changes that pinned shape, hence the edits
• cargo test -p pyrefly --lib -- --skip test::lsp: 7741 passed, 0 failed (the two missing-source LSP interaction failures also fail on unmodified main)
• Formatting and linting clean

[meta-codesync]

This pull request has been imported. If you are a Meta employee, you can view this in D123266669. (Because this pull request was imported automatically, there will not be any future comments.)

[github-actions]

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

============================================================
SUMMARY
============================================================
Total: +0 new errors, -68 fixed errors
By preset: +0/-68 (default), +0/-68 (strict)

Projects with changes (6):
  prefect: +0 -2
  scikit-learn: +0 -60
  streamlit: +0 -2
  core: +0 -1
  xarray: +0 -1
  spack: +0 -2
============================================================

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

prefect (https://github.com/PrefectHQ/prefect)
- ERROR src/integrations/prefect-gcp/prefect_gcp/workers/cloud_run_v2.py:806:14-59: Cannot use `ResourceWarning` as a context manager [bad-context-manager]
- ERROR src/integrations/prefect-gcp/prefect_gcp/workers/cloud_run_v2.py:1417:14-45: Cannot use `ResourceWarning` as a context manager [bad-context-manager]

scikit-learn (https://github.com/scikit-learn/scikit-learn)
- ERROR sklearn/cluster/tests/test_hierarchical.py:110:14-31: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/cluster/tests/test_hierarchical.py:118:18-35: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/decomposition/tests/test_dict_learning.py:257:14-58: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/decomposition/tests/test_fastica.py:453:14-58: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/ensemble/tests/test_forest.py:1153:10-27: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/ensemble/tests/test_iforest.py:43:10-27: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/ensemble/tests/test_stacking.py:476:10-54: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/ensemble/tests/test_stacking.py:480:10-54: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/ensemble/tests/test_stacking.py:486:10-54: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/linear_model/tests/test_logistic.py:1167:10-54: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/linear_model/tests/test_logistic.py:1667:10-54: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/linear_model/tests/test_logistic.py:1700:10-54: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/linear_model/tests/test_logistic.py:1710:10-54: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/linear_model/tests/test_logistic.py:2637:10-54: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/linear_model/tests/test_logistic.py:2698:10-49: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/linear_model/tests/test_logistic.py:2709:10-49: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/metrics/tests/test_classification.py:3165:10-27: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/metrics/tests/test_common.py:843:10-27: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/metrics/tests/test_common.py:923:10-27: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/metrics/tests/test_common.py:1240:10-27: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/metrics/tests/test_common.py:1293:10-27: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/metrics/tests/test_dist_metrics.py:114:14-58: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/metrics/tests/test_dist_metrics.py:223:14-58: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/metrics/tests/test_pairwise.py:293:10-57: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/metrics/tests/test_score_objects.py:709:10-27: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/neural_network/tests/test_mlp.py:75:14-58: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/neural_network/tests/test_mlp.py:351:14-58: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/neural_network/tests/test_mlp.py:435:14-58: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/neural_network/tests/test_mlp.py:535:10-54: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/neural_network/tests/test_mlp.py:558:10-54: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/neural_network/tests/test_mlp.py:672:10-54: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/preprocessing/tests/test_discretization.py:89:10-47: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/svm/tests/test_sparse.py:499:10-54: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/svm/tests/test_sparse.py:502:10-54: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/tests/test_common.py:118:10-120:6: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/tests/test_common.py:262:14-55: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/tests/test_common.py:297:10-51: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/tests/test_common.py:354:14-55: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/tests/test_common.py:378:14-55: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/tests/test_docstring_parameters.py:312:14-53: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/tree/tests/test_tree.py:1619:10-27: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/utils/discovery.py:94:10-49: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/utils/discovery.py:176:10-49: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/utils/discovery.py:234:10-49: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/utils/estimator_checks.py:1660:10-49: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/utils/estimator_checks.py:1666:14-53: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/utils/estimator_checks.py:1690:18-57: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/utils/estimator_checks.py:2729:14-53: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/utils/estimator_checks.py:3030:10-49: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/utils/estimator_checks.py:4184:10-49: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/utils/tests/test_estimator_checks.py:936:14-58: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/utils/tests/test_estimator_checks.py:946:14-58: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/utils/tests/test_show_versions.py:16:10-27: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/utils/tests/test_show_versions.py:32:10-27: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/utils/tests/test_testing.py:146:14-31: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/utils/tests/test_testing.py:150:14-73: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/utils/tests/test_testing.py:154:14-58: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/utils/tests/test_testing.py:158:14-51: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/utils/tests/test_testing.py:162:14-58: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]
- ERROR sklearn/utils/tests/test_testing.py:166:14-51: Cannot use `(*args: Unknown, **kwargs: Unknown) -> Unknown` as a context manager [bad-context-manager]

streamlit (https://github.com/streamlit/streamlit)
- ERROR lib/tests/streamlit/components/v2/test_component_path_utils.py:233:10-48: Cannot use `object` as a context manager [bad-context-manager]
- ERROR lib/tests/streamlit/components/v2/test_component_path_utils.py:244:10-51: Cannot use `object` as a context manager [bad-context-manager]

core (https://github.com/home-assistant/core)
- ERROR homeassistant/components/nmap_tracker/__init__.py:291:20-35: Cannot use `None` as a context manager [bad-context-manager]

xarray (https://github.com/pydata/xarray)
- ERROR xarray/tests/test_distributed.py:310:14-18: Cannot use `None` as a context manager [bad-context-manager]

spack (https://github.com/spack/spack)
- ERROR lib/spack/spack/test/cmd/buildcache.py:1326:10-17: Cannot use `list[Unknown]` as a context manager [bad-context-manager]
- ERROR lib/spack/spack/test/cmd/buildcache.py:1351:10-17: Cannot use `list[Unknown]` as a context manager [bad-context-manager]