[LuShadowX]

Description

Fixes #4036, the crash hug_parens_with_braces_and_square_brackets is parked in UNSTABLE_FEATURES for.

items = [  # type: ignore
    (  # type: ignore
        {"key1": "val1", "key2": "val2", "key3": "val3"}
        if some_var == "longstring"
        else {"key": "val"}
    )
]

$ black --enable-unstable-feature=hug_parens_with_braces_and_square_brackets file.py
INTERNAL ERROR: Black produced code that is not equivalent to the source.

Hugging pulls the inner opening bracket up onto the outer one, and the comments attached to both brackets come along:

items = [(  # type: ignore  # type: ignore

Merging comments like that is the intended hug style — preview_hug_parens_with_braces_and_square_brackets.py already expects func([ # a # b. But type: ignore is not an ordinary comment: CPython records one TypeIgnore per line in Module.type_ignores, so two of them on one line collapse into one and the AST safety check fails.

So the fix is narrow: keep hugging, but not when it would put a second type: ignore on a line. Black already treats these comments as load-bearing elsewhere — contains_unsplittable_type_ignore guards the rhs-oop choice a few hundred lines down — so the new guard fits the existing pattern.

Both examples in #4036 now format cleanly (the reporter's original one and the one @cobaltt7 added last October, which is the one that still reproduced).

Verification

• New case file, preview_hug_parens_with_type_ignore.py: fails on main (unequal output for the first two cases), passes with this change.
• pytest: 475 passed, 3 skipped — the baseline 474 plus the new case. black --check ., flake8, isort and mypy clean.
• Formatted 376 files from scrapy, pydantic and Pillow with --unstable before and after, comparing output hashes: zero differences, and no errors either way. The guard only fires on the pathological shape.

Checklist - did you ...

• Implement any code style changes under the --preview style, following the stability policy? — the feature is unstable-only, and the stable style is untouched
• Add an entry in CHANGES.md if necessary?
• Add / update tests if necessary?
• Add new / update outdated documentation? — no documented behaviour changes

[github-actions]

diff-shades results comparing this PR (8c317de) to main (c7801d9):

--preview style: no changes

--stable style: no changes

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What is this? | Workflow run | diff-shades documentation

[LuShadowX]

happy to help!😊