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fix(changelog): Prevent IndexError for empty paragraphs#1446

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Open

fix(changelog): Prevent IndexError for empty paragraphs#1446
soyamigo wants to merge 2 commits into
python-semantic-release:masterfrom
soyamigo:master

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@soyamigo

@soyamigo soyamigo commented Jun 12, 2026 •
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Purpose

Fixes an IndexError crash in autofit_text_width when a commit body contains whitespace-only lines. When PSR parses such a commit and splits the body into paragraphs, a whitespace-only line produces an empty words list after filtering. The subsequent line = words[0] then raises IndexError: list index out of range, aborting changelog generation entirely.

This is the full stacktrace:

IndexError: list index out of range

Traceback (most recent call last):
  File "~/.venv/lib/python3.11/site-packages/semantic_release/__main__.py", line 16, in main
    cli_main(args=sys.argv[1:])
  File "~/.venv/lib/python3.11/site-packages/click/core.py", line 1161, in __call__
    return self.main(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "~/.venv/lib/python3.11/site-packages/click/core.py", line 1082, in main
    rv = self.invoke(ctx)
         ^^^^^^^^^^^^^^^^
  File "~/.venv/lib/python3.11/site-packages/click/core.py", line 1697, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "~/.venv/lib/python3.11/site-packages/click/core.py", line 1443, in invoke
    return ctx.invoke(self.callback, **ctx.params)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "~/.venv/lib/python3.11/site-packages/click/core.py", line 788, in invoke
    return __callback(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "~/.venv/lib/python3.11/site-packages/click/decorators.py", line 45, in new_func
    return f(get_current_context().obj, *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "~/.venv/lib/python3.11/site-packages/semantic_release/cli/commands/version.py", line 647, in version
    write_changelog_files(
  File "~/.venv/lib/python3.11/site-packages/semantic_release/cli/changelog_writer.py", line 214, in write_changelog_files
    write_default_changelog(
  File "~/.venv/lib/python3.11/site-packages/semantic_release/cli/changelog_writer.py", line 154, in write_default_changelog
    changelog_text = render_default_changelog_file(
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "~/.venv/lib/python3.11/site-packages/semantic_release/cli/changelog_writer.py", line 82, in render_default_changelog_file
    changelog_content = template.render().rstrip()
                        ^^^^^^^^^^^^^^^^^
  File "~/.venv/lib/python3.11/site-packages/jinja2/environment.py", line 1295, in render
    self.environment.handle_exception()
  File "~/.venv/lib/python3.11/site-packages/jinja2/environment.py", line 942, in handle_exception
    raise rewrite_traceback_stack(source=source)
  File "~/.venv/lib/python3.11/site-packages/semantic_release/data/templates/conventional/md/CHANGELOG.md.j2", line 18, in top-level template code
    %}{%    include ".components/changelog_update.md.j2"
    ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "~/.venv/lib/python3.11/site-packages/semantic_release/data/templates/conventional/md/.components/changelog_update.md.j2", line 57, in top-level template code
    }}{%-       include "versioned_changes.md.j2"
    ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "~/.venv/lib/python3.11/site-packages/semantic_release/data/templates/conventional/md/.components/versioned_changes.md.j2", line 19, in top-level template code
    %}{%  include "changes.md.j2"
    ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "~/.venv/lib/python3.11/site-packages/semantic_release/data/templates/conventional/md/.components/changes.md.j2", line 51, in top-level template code
    %}{%      set description = description | autofit_text_width(max_line_width, hanging_indent)
    ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "~/.venv/lib/python3.11/site-packages/semantic_release/changelog/context.py", line 173, in autofit_text_width
    line = words[0]
           ~~~~~^^^

::ERROR:: list index out of range

Rationale

The words list is already constructed with a filter(None, ...) call to strip empty strings, so an empty result after that filter means the paragraph itself was blank or whitespace-only. The correct behavior is to skip such paragraphs entirely, which is consistent with what the surrounding split("\n\n") loop is trying to do — process meaningful paragraph blocks. A simple if not words: continue guard before accessing words[0] is the minimal, safe fix.

How did you test?

Reproduced the crash locally by running semantic-release version against a repository containing commits with whitespace-only lines in their bodies (e.g. a line containing only spaces or tabs). Confirmed the IndexError occurred before the fix and that changelog generation completed successfully after applying it.

Edge cases considered:

  • Paragraph that is entirely whitespace; skipped cleanly
  • Paragraph with leading/trailing blank lines but valid content; unaffected, strip() handles it upstream
  • Normal single and multi-paragraph commit bodies; behavior unchanged

How to Verify

  1. Create a git repo with at least one conventional commit whose body contains a line of only whitespace (e.g. )
  2. Run semantic-release version - observe the IndexError: list index out of range crash
  3. Apply this patch
  4. Run semantic-release version again to make sure changelog generates successfully

PR Completion Checklist

  • Reviewed & followed the Contributor Guidelines

  • Changes Implemented & Validation pipeline succeeds

  • Commits follow the Conventional Commits standard
    and are separated into the proper commit type and scope (recommended order: test, build, feat/fix, docs)

  • Appropriate Unit tests added/updated

  • Appropriate End-to-End tests added/updated

  • Appropriate Documentation added/updated and syntax validated for sphinx build (see Contributor Guidelines)

@soyamigo

soyamigo commented Jun 12, 2026

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FWIW, ran the CI(manual) workflow in my fork: https://github.com/soyamigo/python-semantic-release/actions/runs/27431762140

Seems to be okay.

chore: release v1.0.0
3181496 
Automatically generated by python-semantic-release
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