test_parsing.py

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#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# tests/tests_core/test_parsing.py
 
"""
Purpose
-------
OI-509 / FS-505 regression tests — :func:`oct.core.parsing.header_boundary`
is the single implementation shared by the linter and the formatter for
locating the start of file content after an Option-C 4-line header
(shebang → encoding → file-identity → blank).
 
Also covers :func:`oct.core.parsing.safe_parse` — shared AST helper that
captures ``SyntaxWarning`` diagnostics instead of leaking them to stderr.
 
Responsibilities
----------------
- Full 4-line header → boundary is 4.
- Missing shebang → skips straight to encoding.
- No header at all → boundary is 0.
- Trailing blank is only consumed when at least one header element matched.
- Identity comment is matched via either the strict expected string or the
  path-basename fallback.
- ``safe_parse`` returns (None, []) on syntax error.
- ``safe_parse`` captures invalid-escape SyntaxWarnings without printing.
 
Diagnostics
-----------
Domain: CORE-TESTS
Levels:
    L2 — test lifecycle
    L3 — assertion details
    L4 — deep tracing
 
Contracts
---------
- Tests operate on in-memory strings; no files are created or read.
"""
 
from pathlib import Path
 
from oct.core.parsing import header_boundary, safe_parse
 
 
def _lines(text: str) -> list[str]:
    return text.splitlines()
 
 
def test_full_header_boundary_is_four():
    path = Path("oct/core/parsing.py")
    text = (
        "#!/usr/bin/env python3\n"
        "# -*- coding: utf-8 -*-\n"
        "# oct/core/parsing.py\n"
        "\n"
        "import os\n"
    )
    assert header_boundary(
        _lines(text), path, expected_identity="# oct/core/parsing.py"
    ) == 4
 
 
def test_missing_shebang_skips_to_encoding():
    path = Path("oct/core/parsing.py")
    text = (
        "# -*- coding: utf-8 -*-\n"
        "# oct/core/parsing.py\n"
        "\n"
        "import os\n"
    )
    assert header_boundary(
        _lines(text), path, expected_identity="# oct/core/parsing.py"
    ) == 3
 
 
def test_no_header_returns_zero():
    path = Path("foo.py")
    text = "import os\nprint('hi')\n"
    assert header_boundary(_lines(text), path) == 0
 
 
def test_trailing_blank_not_consumed_without_header():
    path = Path("foo.py")
    text = "\nimport os\n"
    assert header_boundary(_lines(text), path) == 0
 
 
def test_identity_fallback_matches_basename():
    """When no expected_identity is passed, any `# ...basename` qualifies."""
    path = Path("pkg/mod.py")
    text = (
        "#!/usr/bin/env python3\n"
        "# some/other/prefix mod.py\n"
        "\n"
        "x = 1\n"
    )
    assert header_boundary(_lines(text), path) == 3
 
 
def test_safe_parse_returns_none_on_syntax_error():
    tree, warns = safe_parse("def broken(:\n")
    assert tree is None
    assert warns == []
 
 
def test_safe_parse_captures_invalid_escape_warning():
    src = 's = "\\d+"\n'
    tree, warns = safe_parse(src)
    assert tree is not None
    assert any("invalid escape" in w for w in warns)