Fix #376: argparse conflicting option string: --file

[idevasena]

Fix #376: argparse "conflicting option string: --file" by removing duplicate declaration

Fixes #376.

Root cause

--file / --object are declared in two places in mlpstorage_py/cli/common_args.py:

• add_universal_arguments() — line ~198
• add_storage_type_arguments() — line ~323

Every benchmark subparser builder (add_training_arguments, add_checkpointing_arguments, add_vectordb_arguments, add_kvcache_arguments) calls both functions on the same parser, so argparse raises

argparse.ArgumentError: argument --file: conflicting option string: --file

at parser-construction time — which fires on the very first mlpstorage --help invocation, before any user arg is parsed. This is also why --debug appeared not to work in the report: the parser never finishes being built, so no flag gets evaluated.

How the regression was introduced

Two commits, in sequence:

1. PR Bug fixes and performance enhancements: object storage, checkpointing, Parquet loading #359 (39e657d, May 8 2026) — Correctly extracted --file/--object out of add_universal_arguments into a new add_storage_type_arguments(). After this commit --file lived in one place.

2. PR Fix: Issue 349 open flag recognition #352 (258483b, May 13 2026) — Fix for Running training with --open doesn't seem to be recognized #349 --open recognition. The substantive change was rewriting the --open/--closed mutex group inside add_universal_arguments, but the diff also re-introduced the --file/--object mutex block (with required=True) — most likely a merge-conflict resolution against a pre-Bug fixes and performance enhancements: object storage, checkpointing, Parquet loading #359 base. From that commit onward, --file exists in both functions and every benchmark subparser builder crashes.

Verifiable from git show 258483b -- mlpstorage_py/cli/common_args.py: the diff adds back an access_proto.add_argument("--file", ...) block that PR #359 had explicitly removed eight days earlier.

Fix

Remove the duplicate --file/--object block from add_universal_arguments. Replace with a comment that pins the invariant so a future merge can't silently re-introduce it. Restores PR #359's intent: declare those flags once, in add_storage_type_arguments, attached only to benchmark subparsers (training, checkpointing, vectordb, kvcache).

Utility subparsers (reports, history, lockfile) that only call add_universal_arguments no longer carry --file/--object, which is the correct behavior — they don't need storage-type selection.

Tests

New file: mlpstorage_py/tests/test_issue_376_file_arg_conflict.py — seven cases pinning the invariant:

• Direct reproduction: both adders on one parser no longer raise
• --file/--object declared in exactly one adder (add_storage_type_arguments)
• All four benchmark builders (add_training_arguments, add_checkpointing_arguments, add_vectordb_arguments, add_kvcache_arguments) construct cleanly when invoked the same way cli_parser.py invokes them
• --debug parses correctly post-fix

Updated: mlpstorage_py/tests/test_open_closed_flag_recognition.py — _build_parser now also calls add_storage_type_arguments, mirroring how real benchmark subparsers are built, so the open/closed CLI tests keep working.

Validation

Check	Pre-fix	Post-fix
mlpstorage --help	ArgumentError: --file conflict	clean SystemExit(0)
mlpstorage training --help	crash	clean SystemExit(0)
mlpstorage checkpointing --help	crash	clean SystemExit(0)
mlpstorage vectordb --help	crash	clean SystemExit(0)
mlpstorage kvcache --help	crash	clean SystemExit(0)
mlpstorage --debug --help	crash	clean SystemExit(0)
tests/unit/test_cli.py::TestAddUniversalArguments (8 tests)	7 failed, 1 passed	8 passed
mlpstorage_py/tests/test_open_closed_flag_recognition.py::TestOpenClosedCLIFlags (4 tests)	crash	4 passed
mlpstorage_py/tests/test_issue_376_file_arg_conflict.py (7 tests, new)	—	7 passed

The 7 pre-existing unit-test failures in TestAddUniversalArguments were caused by the same regression (the required=True re-introduction made every parse_args call without --file exit with code 2) — they likely went unnoticed because CI wasn't running them on PR #352.

Diff stats

 mlpstorage_py/cli/common_args.py                          | 21 +++++--------------
 mlpstorage_py/tests/test_open_closed_flag_recognition.py  |  9 +++++++-
 mlpstorage_py/tests/test_issue_376_file_arg_conflict.py   | 131 +++++++++++++++ (new)
 3 files changed, 145 insertions(+), 16 deletions(-)

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[FileSystemGuy]

Please review (and merge if appropriate): @russfellows