Fix unindented comments being corrupted in indented blocks

[worksbyfriday]

Summary

When an unindented comment appears before an indented import block, isort corrupts the comment by stripping len(indent) characters from the start of every line—even lines that don't begin with that indent.

Before fix:

# Input
if True:
# this will get cut off
    import os

# Output (corrupted)
if True:
is will get cut off
    import os

After fix: The comment is preserved correctly.

Root cause

In isort/core.py line 422, the indent-stripping logic:

line[len(indent):] for line in import_section.splitlines(keepends=True)

blindly slices every line without checking if it actually starts with the indent prefix.

Fix

Added a line.startswith(indent) guard so only properly indented lines get stripped:

line[len(indent):] if line.startswith(indent) else line

Test plan

• Added test_unindented_comment_in_indented_block_issue_1899 to tests/unit/test_ticketed_features.py
• Verified existing unit tests still pass (283 passed, 1 pre-existing failure unrelated to this change)

Fixes #1899

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.24%. Comparing base (b0f2dab) to head (fd2514b).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2459   +/-   ##
=======================================
  Coverage   99.24%   99.24%           
=======================================
  Files          39       39           
  Lines        3057     3057           
  Branches      675      675           
=======================================
  Hits         3034     3034           
  Misses         13       13           
  Partials       10       10           

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[DanielNoord]

Thanks!