Fix single-line Array losing its closing bracket after a trailing comment

[afonsojanu]

Summary

Array.as_string() for a non-multiline array renders by concatenating the raw text of each item, including any comment attached through add_line(). Since a # comment runs to the end of its physical line, if that comment happens to be the last thing rendered before the closing ], the bracket gets swallowed into the comment text and the array stops being valid TOML:

>>> import tomlkit
>>> a = tomlkit.array()
>>> a.add_line("foo", comment="bar")
>>> a.as_string()
'[\n    "foo", # bar]'
>>> doc = tomlkit.document()
>>> doc.add("array", a)
>>> tomlkit.loads(doc.as_string())
tomlkit.exceptions.UnexpectedCharError: Unexpected character: '\x00' at line 2 col 0

This matches #580: the existing workaround is to always finish with a manual add_line(indent="") call to supply the missing newline yourself, which is easy to forget and produces a document that silently fails to round-trip.

Fix

In the non-multiline branch of Array.as_string(), if the rendered content ends with a comment and isn't already terminated by a newline, a newline (plus the array's indent) is appended before the closing bracket. This only changes output for the specific case that was broken; arrays without a trailing comment, and the already-documented workaround, render exactly as before.

Testing

Added test_array_add_line_with_comment_on_last_line_round_trips in tests/test_items.py, which reproduces the issue and asserts the array parses back correctly. Ran the full suite (pytest tests/ --ignore=tests/test_toml_tests.py, the ignored module needs a submodule I didn't have checked out) plus ruff check / ruff format --check on the touched files; everything passes.

Fixes #580.

Agent Drafting Metadata

• Agent: Claude Code
• Model: Claude (Sonnet 5)
• Notes: I used Claude Code to investigate the issue, write the fix in tomlkit/items.py, and add the regression test. I reviewed the diff, ran the test suite and linters myself, and wrote this description.