fix(colang): raise ValueError for unbalanced closing bracket in split_args

[vidigoat]

Fixes #2144

Description

split_args reads closing_char[stack[-1]] for every closing character, but when a ), ], or } appears with an empty bracket stack, stack[-1] raises an uncaught IndexError. (Quote characters are unaffected — they are treated as openers on an empty stack.) This adds an explicit empty-stack guard that raises the same ValueError the function already uses to report malformed input, so callers get a consistent, catchable error instead of an IndexError.

Steps to reproduce (before this fix)

from nemoguardrails.colang.v1_0.lang.utils import split_args
split_args("x=1, y)")   # IndexError: list index out of range

Also affected: ")", "a)b", "foo]", "}".

Test plan

• Added a parametrized regression test in tests/test_parser_utils.py covering ")", "a)b", "foo]", "x=1, y)", "}"; each now asserts ValueError.
• Verified the new test fails before the fix (IndexError) and passes after; existing split_args tests and the mismatched-bracket ValueError path are unchanged.

AI disclosure

This change was drafted with the assistance of an AI coding assistant; I reproduced the bug and verified the fix and tests before submitting.

Summary by CodeRabbit

• Bug Fixes
  • Improved argument parsing to handle unexpected closing brackets more gracefully.
  • Replaced an internal crash case with a clear error message when bracket or quote characters are unbalanced.
  • Added coverage for several malformed input examples to prevent regressions.

[coderabbitai]

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 89df3de and d78589e.

📒 Files selected for processing (2)

• nemoguardrails/colang/v1_0/lang/utils.py
• tests/test_parser_utils.py

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📝 Walkthrough

Walkthrough

The split_args function in nemoguardrails now raises ValueError when encountering a closing quote or bracket character with an empty stack, replacing the previous unhandled IndexError. A parametrized test was added to verify this behavior across multiple unbalanced input cases.

Changes

split_args bracket validation fix

Layer / File(s)	Summary
Empty-stack validation and regression test nemoguardrails/colang/v1_0/lang/utils.py, tests/test_parser_utils.py	split_args now raises ValueError when a closing character appears with no matching opener (empty stack) instead of raising IndexError; a new parametrized test validates ValueError is raised for inputs like ")", "a)b", "foo]", "x=1, y)", and "}".

Estimated code review effort: 1 (Trivial) | ~5 minutes

🚥 Pre-merge checks | ✅ 6

✅ Passed checks (6 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly states the main fix: split_args now raises ValueError for unbalanced closing brackets.
Linked Issues check	✅ Passed	The code and regression test match issue #2144 by converting stray closing brackets from IndexError to ValueError.
Out of Scope Changes check	✅ Passed	The changes stay focused on split_args and its regression test, with no unrelated edits.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Test Results For Major Changes	✅ Passed	PASS: This is a small bug fix, and the PR description includes a Test plan plus before/after verification for the new regression test.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

⚔️ Resolve merge conflicts

• Resolve merge conflict in branch fix/split-args-unbalanced-closing-bracket

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