tasks/easy_task.py

"""
EASY TASK: Fix the off-by-one bug in a list-processing utility.

The repo has:
  - utils/list_ops.py  — contains a buggy `chunk_list` function
  - tests/test_list_ops.py — 3 tests (1 currently failing)

The agent must identify and fix the bug so all tests pass,
with clean lint, and commit with a meaningful message.
"""

from __future__ import annotations

TASK_ID = "easy_bugfix_chunk_list"
DIFFICULTY = "easy"
MAX_STEPS = 20

DESCRIPTION = """
## Task: Fix the `chunk_list` Bug

The function `chunk_list(lst, n)` in `utils/list_ops.py` is supposed to split a
list into consecutive chunks of size `n`.

**Example:**
  chunk_list([1,2,3,4,5], 2)  →  [[1,2],[3,4],[5]]

**Problem:** There is an off-by-one error causing the last chunk to be dropped.

**Your job:**
1. Read the source and tests
2. Identify the exact bug
3. Fix `utils/list_ops.py` (do NOT modify tests)
4. Ensure all 3 tests pass
5. Run lint and fix any issues
6. Write a review of what you found
7. Commit with a conventional-commit message
"""

# ── Initial repo snapshot ─────────────────────────────────────────────────────

INITIAL_FILES: dict[str, str] = {
    "utils/__init__.py": "",
    "utils/list_ops.py": """\
\"\"\"List utility operations.\"\"\"
from typing import Any, List


def chunk_list(lst: List[Any], n: int) -> List[List[Any]]:
    \"\"\"Split *lst* into consecutive chunks of size *n*.

    The final chunk may be smaller than *n* if len(lst) is not divisible.

    Example:
        >>> chunk_list([1, 2, 3, 4, 5], 2)
        [[1, 2], [3, 4], [5]]
    \"\"\"
    if n <= 0:
        raise ValueError("Chunk size must be positive")
    result = []
    # BUG: range stops one short — should be range(0, len(lst), n)
    for i in range(0, len(lst) - 1, n):
        result.append(lst[i : i + n])
    return result


def flatten(lst: List[List[Any]]) -> List[Any]:
    \"\"\"Flatten a list of lists by one level.\"\"\"
    return [item for sublist in lst for item in sublist]
""",
    "tests/__init__.py": "",
    "tests/test_list_ops.py": """\
\"\"\"Tests for list_ops utilities.\"\"\"
import pytest
from utils.list_ops import chunk_list, flatten


class TestChunkList:
    def test_even_split(self):
        assert chunk_list([1, 2, 3, 4], 2) == [[1, 2], [3, 4]]

    def test_odd_split(self):
        # Last chunk is smaller — this currently FAILS due to the bug
        assert chunk_list([1, 2, 3, 4, 5], 2) == [[1, 2], [3, 4], [5]]

    def test_chunk_larger_than_list(self):
        assert chunk_list([1, 2], 5) == [[1, 2]]

    def test_empty_list(self):
        assert chunk_list([], 3) == []

    def test_invalid_chunk_size(self):
        with pytest.raises(ValueError):
            chunk_list([1, 2], 0)


class TestFlatten:
    def test_basic(self):
        assert flatten([[1, 2], [3, 4]]) == [1, 2, 3, 4]

    def test_empty(self):
        assert flatten([]) == []
""",
    "pyproject.toml": """\
[tool.ruff]
line-length = 88
select = ["E", "F", "W"]
ignore = []
""",
    "README.md": "# BugFix Challenge\n\nFix the `chunk_list` bug.\n",
}

# ── Expected outputs (for grader) ────────────────────────────────────────────

EXPECTED_FIXED_SNIPPET = "range(0, len(lst), n)"

REQUIRED_KEYWORDS_IN_REVIEW = [
    "off-by-one",
    "range",
    "chunk",
]

PASSING_TESTS = 7  # all tests in the file