Keep the multiline layout of a sorted literal that has a trailing comment

[youdie006]

#2605 and #2647 (both merged 2026-09-21) interact. #2605 keeps a multiline, trailing-comma literal in its layout when --sort-reexports runs under a trailing-comma profile, deciding with _has_trailing_comma(literal). Since #2647, literal also holds whatever follows the closing bracket, so a comment there hides the comma:

isort.code('__all__ = [\n    "b",\n    "a",\n]\n', profile="black", sort_reexports=True)
# '__all__ = [\n    "a",\n    "b",\n]\n'

isort.code('__all__ = [\n    "b",\n    "a",\n]  # noqa: F405\n', profile="black", sort_reexports=True)
# '__all__ = ["a", "b"]  # noqa: F405\n'

The trailing comma goes too, so Black does not expand it back. This moves #2647's end-position computation above the check and passes literal[:value_end]; the block and its comment are moved, not rewritten.

Verification

Base 13758cf5. New test next to #2605's in tests/unit/test_regressions.py.

row	isort/literal.py md5	result
main	cecdbba24c4f	new test fails
this PR	147208bf4bf5	passes
literal[:value_end - 1]	1087b8373008	also fails #2605's two _issue_2578 tests and four of #2669's tests

Following continuous-integration.yml: uv sync --all-extras --frozen, then uv run --with tox-uv tox -e py,coverage_report-ci: 660 passed, 1 skipped, isort/literal.py at 100%. tox -e lint passes mypy, isort, flake8 and ruff; it reports one bandit B101 at isort/parse.py:411, identical on main, in a file this does not touch. Not run: the integration job, other Python versions, Windows and macOS.

Written with AI assistance (Claude); the measurements above were run locally and I have reviewed the change.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.41%. Comparing base (9c00c1f) to head (f467420).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2686   +/-   ##
=======================================
  Coverage   99.41%   99.41%           
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  Files          41       41           
  Lines        3231     3231           
  Branches      690      690           
=======================================
  Hits         3212     3212           
  Misses         12       12           
  Partials        7        7           

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[Copilot]

Copilot review overview

🟡 Changes recommended

AST byte offsets are incorrectly used as character indices, potentially corrupting comments after non-ASCII literals.

Review effort: Balanced
Findings: 1

Open (1)

• Convert UTF-8 byte offsets before slicing non-ASCII values · New

What changed in this PR

Fixes multiline literal layout preservation when a trailing comment follows the closing bracket.

Changes:

• Detects trailing commas only within the parsed literal.
• Adds regression coverage for commented multiline reexports.

File	Description
isort/​literal.py	Uses the literal boundary for trailing-comma detection.
tests/​unit/​test_regressions.py	Tests multiline layout with a trailing comment.

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