Fix --sort-reexports crash when __all__ is immediately followed by another assignment

[Copilot]

When sort_reexports=True, a multi-line __all__ followed immediately by another assignment (e.g. __version__) without a blank line caused a ValueError: too many values to unpack because the collector kept consuming lines past the end of the __all__ block.

__all__ = [
    "FooType",
    "BarType",
]
__version__ = importlib.metadata.version("my-package")  # was incorrectly absorbed into __all__ section

Changes

• isort/core.py: Added _net_open_brackets(line) helper that counts net open brackets while correctly ignoring brackets inside string literals and comments. Tracks reexport_bracket_depth across collected lines; when depth reaches 0 the section is processed immediately rather than waiting for a blank line or EOF. Also fixed split("=", 1) in __all__ detection to handle values containing =.
• isort/literal.py: Defensive fix — code.split("=", 1) instead of code.split("=").
• tests/unit/test_isort.py: Added tests for both multi-line and single-line __all__ immediately followed by another assignment with no blank line.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>--sort-reexports results in isort not being able to parse file</issue_title>
<issue_description>Python version 3.12
isort version: 5.13.2

Test file test.py:

#!/usr/bin/env python
import importlib.metadata

__all__ = [
    "FooType",
    "BarType",
    "some_method",
]
__version__ = importlib.metadata.version("my-package")

Calling isort --srx test.py results in:

isort/main.py:105: UserWarning: Unable to parse file test.py due to too many values to unpack (expected 2)

The exception is actually triggered here - somehow, both assignments to __all__ and __version__ end up in code.

It works if an empty line between both assignments is introduced (or any other code, for that matter).</issue_description>

Comments on the Issue (you are @copilot in this section)

@DanielNoord Traceback is as follows: ``` Traceback (most recent call last): File "/home/daniel-vannoord/Documents/github/isort/.venv/bin/isort", line 10, in sys.exit(main()) ~~~~^^ File "/home/daniel-vannoord/Documents/github/isort/isort/main.py", line 1236, in main for sort_attempt in attempt_iterator: ^^^^^^^^^^^^^^^^ File "/home/daniel-vannoord/Documents/github/isort/isort/main.py", line 1220, in sort_imports( # type: ignore ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^ file_name, ^^^^^^^^^^ ...<6 lines>... config_trie=config_trie, ^^^^^^^^^^^^^^^^^^^^^^^^ ) ^ File "/home/daniel-vannoord/Documents/github/isort/isort/main.py", line 96, in sort_imports incorrectly_sorted = not api.sort_file( ~~~~~~~~~~~~~^ file_name, ^^^^^^^^^^ ...<3 lines>... **kwargs, ^^^^^^^^^ ) ^ File "/home/daniel-vannoord/Documents/github/isort/isort/api.py", line 435, in sort_file changed = sort_stream( input_stream=source_file.stream, ...<4 lines>... extension=extension, ) File "/home/daniel-vannoord/Documents/github/isort/isort/api.py", line 212, in sort_stream changed = core.process( input_stream, ...<3 lines>... raise_on_skip=raise_on_skip, ) File "/home/daniel-vannoord/Documents/github/isort/isort/core.py", line 142, in process isort.literal.assignment( ~~~~~~~~~~~~~~~~~~~~~~~~^ code_sorting_section, ^^^^^^^^^^^^^^^^^^^^^ ...<2 lines>... config=_indented_config(config, indent), ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ), ^ File "/home/daniel-vannoord/Documents/github/isort/isort/literal.py", line 51, in assignment variable_name, literal = code.split("=") ^^^^^^^^^^^^^^^^^^^^^^ ValueError: too many values to unpack (expected 2, got 3) ```

• Fixes --sort-reexports results in isort not being able to parse file #2286

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[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 99.03%. Comparing base (ad2dfe9) to head (acfc59d).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2473      +/-   ##
==========================================
- Coverage   99.25%   99.03%   -0.22%     
==========================================
  Files          40       40              
  Lines        3079     3117      +38     
  Branches      671      684      +13     
==========================================
+ Hits         3056     3087      +31     
- Misses         13       17       +4     
- Partials       10       13       +3     

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