[ybai08]

Fixes #2010

This is the second part of #2010 that @Eljees described: the else: imports are not combined, even without lines_before_imports.

import sys

if sys.version_info >= (3, 11):
    from typing import LiteralString, Never
else:
    from typing_extensions import LiteralString
    from typing_extensions import Never

import third_party_library

On main, isort leaves the two from typing_extensions import ... lines as they are. If you remove the last line, they are combined.

Cause

When an import with less indentation ends an indented import block, process() sets indent to the new indentation before it sorts the block it has collected so far. So that block is sorted as if it were not indented, and it comes out unchanged.

Change

• The new indentation is stored in next_indent and applied once the current block has been written. This only happens when the block already holds imports. When the block holds only comments or blank lines, indent still switches right away, as before.
• That block is now sorted as an indented section. Its output is the same as when code follows the block. For example, def f():\n import os\n import a\n import os\n sorts to the same lines whether x = 1 or import b comes next. The two places that used to read indent after the early switch now read the next section's indentation:
  • the separator line written before a following top-level section (lines_before_imports == -1);
  • the trailing blank lines of the block. They are left to the next section, which already writes its own blank lines (or exactly lines_before_imports of them).

These are the four tests @Eljees mentioned (test_nested_comment_handling, test_autofix_mixed_indent_imports_1575, test_unindented_comment_in_indented_block_issue_1899, test_isort_should_leave_non_import_from_lines_alone_issue_1488), plus test_lines_before_imports_keeps_import_after_indented_block. All of them pass unchanged.

Tests

New test_indented_imports_followed_by_less_indented_import_issue_2010 in tests/unit/test_regressions.py. It covers:

• the example from the issue;
• a function body followed by a top-level import, with and without lines_before_imports;
• a dedent from two levels to one.

Each case also checks that the output is stable on a second run. The test fails on main and passes with the change.

What was run (Python 3.14, uv sync --all-extras --frozen):

• pytest tests/unit: 695 passed, 1 skipped.
• pytest tests/integration/test_hypothesmith.py tests/integration/test_literal.py tests/integration/test_setting_combinations.py tests/integration/test_ticketed_features.py: 3 passed.
• The tox -e lint commands, run one by one: mypy, isort --profile hug --check --diff isort/ tests/ scripts/, flake8 isort/ tests/, ruff check, ruff format --check, bandit -r isort/. All clean.
• A differential check: 9,000 random snippets of nested blocks with imports, comments and code, under seven option sets, run through main and through this branch.
  • The output differs on 535 of them. Every one has an indented import followed by a less indented import.
  • On every snippet that parses, the set of imported names is unchanged.
  • The new output is stable on a second run except in one case. main gives the same second-run result there: with lines_before_imports=1, it adds a blank line between # comment and the import below it.

Not run: tests/integration/test_projects_using_isort.py, which clones other projects.

[Copilot]

🟡 Changes recommended

Partial dedents discard existing blank-line separators that the following indented section does not restore.

1 open issue

• Preserve blank lines when resetting indentation for partial dedents · New

What changed in this PR

Fixes the sorting issue in #2010 by preserving an import block’s indentation until sorting is complete.

Changes:

• Defers indentation changes until the next import section.
• Adjusts spacing between sections.
• Adds regression tests for top-level and nested dedents, including output stability.

File	Description
tests/​unit/​test_regressions.py	Adds coverage for indented imports followed by less-indented imports.
isort/​core.py	Preserves indentation during sorting and adjusts section spacing.

_{Review effort: Balanced}

[Copilot]

🟢 Approved

The focused indentation fix has regression coverage and no unresolved findings.

No open issues 🎉

1 resolved since last review

• Preserve blank lines when resetting indentation for partial dedents

_{Review effort: Balanced}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.38%. Comparing base (5a6aaf5) to head (9fdf9d2).
⚠️ Report is 20 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2730   +/-   ##
=======================================
  Coverage   99.37%   99.38%           
=======================================
  Files          40       40           
  Lines        3224     3272   +48     
  Branches      689      706   +17     
=======================================
+ Hits         3204     3252   +48     
  Misses         12       12           
  Partials        8        8           

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