fix(toolshed): accept // seals so C/C++ generated files can be sealed

[LeSingh1]

Problem

toolshed/check_generated_file_seals.py declares three comment styles for the seal line, one per generated-file family:

_COMMENT_CHARS = {
    ".py": b"#", ".pxd": b"#", ".pxi": b"#", ".pyx": b"#",
    ".pyx.in": b"#", ".pxd.in": b"#", ".pxi.in": b"#",
    ".rst": b"..",
    ".c": b"//", ".cpp": b"//", ".h": b"//",
}

and validate_generated_file_seal deliberately compares the seal's captured prefix against expected_comment_prefix(filepath), so a .rst file cannot be sealed with a #:

if match.group("prefix") != expected_prefix:
    print(f"INVALID generated-file seal comment prefix in {filepath!r}")

But the marker regex only accepts two of the three declared prefixes:

_MARKER_REGEX = re.compile(
    rb"^(?P<prefix>#|\.\.) "        # no //
    + re.escape(_TOKEN_BYTES)
    + rb" format=(?P<format>[0-9]+); content-sha256=(?P<digest>[0-9a-f]{64})\n$"
)

// can never be captured, so fullmatch returns None for a sealed .c/.cpp/.h file and it is rejected as MALFORMED generated-file seal before the prefix comparison ever runs. The b"//" entries in _COMMENT_CHARS — and the branch that would validate them — are dead.

Reproduced by writing one identical seal three ways and calling validate_generated_file_seal directly:

gen.c      prefix=b'//'  regex_match=False  ->  MALFORMED generated-file seal in '.../gen.c'   False
gen.pyx    prefix=b'#'   regex_match=True   ->  True
gen.rst    prefix=b'..'  regex_match=True   ->  True

Only the prefix differs; the token, format, digest, and body are byte-identical.

The hook runs over ^cuda_bindings/ with types: [text], which already contains C headers (cuda_bindings/cuda/bindings/_lib/param_packer.h), so the first generated .h or .cpp to be sealed would be rejected with a message that points at the file rather than at the checker.

Fix

Add // to the alternation, with a comment tying it to _COMMENT_CHARS so the two do not drift apart again. One line of behavior change; no other logic touched.

Tests

This script had no tests. Added toolshed/tests/test_check_generated_file_seals.py covering the seal round-trip for every entry in _COMMENT_CHARS (parametrized off the dict itself, so a future entry the regex cannot match fails immediately rather than silently becoming dead code), plus the wrong-prefix-for-extension rejection, the tampered-content rejection, the unsupported-extension rejection, and the never-sealed passthrough. They call validate_generated_file_seal(path, set()) directly, so no git subprocess and no CUDA are involved.

The new directory is wired into the existing nightly tooling job next to ci/tools/tests:

python -m pytest -v --noconftest ci/tools/tests toolshed/tests

Verification

All of this was actually executed (pure Python, no GPU):

# with the fix
18 passed

# with toolshed/check_generated_file_seals.py restored from upstream/main
FAILED test_every_declared_comment_prefix_validates[.c-//]
FAILED test_every_declared_comment_prefix_validates[.cpp-//]
FAILED test_every_declared_comment_prefix_validates[.h-//]
FAILED test_marker_regex_accepts_every_declared_prefix[//]
FAILED test_edited_content_is_rejected
5 failed, 13 passed

Combined pytest --noconftest ci/tools/tests toolshed/tests: 74 passed. ruff check / ruff format --check clean on both changed Python files (no new findings vs. an upstream/main baseline), toolshed/check_spdx.py clean on the new file, python -m py_compile clean.

Verified index-safely (cp aside, git show upstream/main:<path> >, run, restore) — no staged reverts.

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[mdboom]

Seems fine (except tests at this level are unnecessary).

[mdboom]

Remove this test file. We have no infra to run tests in toolshed/tests anyway.

[mdboom]

Revert this change.

[LeSingh1]

Done in a80e43c — dropped the test file and reverted the ci-nightly.yml change, so this is now just the one-line fix in check_generated_file_seals.py.

[mdboom]

/ok to test a80e43c

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