Support the --accelerate_config=<name> equals-sign CLI syntax

[amanyagami]

What does this PR do?

trl.cli.accelerate_config.resolve_accelerate_config_argument() is responsible for turning
--accelerate_config <name_or_path> on the trl <command> CLI into the --config_file <path> argument that gets
forwarded to accelerate launch. It only recognized the two-token form
(--accelerate_config single_gpu): it looks up "--accelerate_config" as a standalone element of launch_args
with launch_args.index("--accelerate_config") and reads the following element as the value.

The equals-sign form that argparse-style CLIs commonly support, --accelerate_config=single_gpu, doesn't match
that lookup at all. Because "--accelerate_config" not in launch_args is true in that case, the function returns
launch_args unchanged, --accelerate_config=single_gpu gets passed straight through to accelerate launch
(which has no idea what to do with it) instead of being resolved to --config_file .../single_gpu.yaml, and the
requested config is silently ignored.

Root cause

resolve_accelerate_config_argument() assumed --accelerate_config and its value are always two separate argv
elements, with no handling for the --flag=value form.

Fix

Before doing the existing lookup, scan launch_args for an element starting with "--accelerate_config=", and if
found, split it into the two-token form (["--accelerate_config", "<value>"]) and rebuild launch_args with that
substitution. The rest of the function is untouched and now only ever has to deal with the two-token form, so both
syntaxes resolve identically (same --config_file <path> output and remaining args preserved).

Tests

Added tests/test_cli_accelerate_config.py with regression tests for:

• the two-token form still works,
• the new --accelerate_config=<name> form resolves correctly,
• both forms produce the exact same output for the same input,
• --accelerate_config absent from args is a no-op,
• missing value after --accelerate_config still raises ValueError,
• an invalid config name still raises ValueError, for both syntaxes.

I confirmed these tests fail on main (3 of the 6 fail: the equals-form test, the equivalence test, and the
invalid-name-for-equals-form test) and pass after the fix.

Test output (after fix)

$ python -m pytest tests/test_cli_accelerate_config.py -v
============================= test session starts ==============================
platform linux -- Python 3.12.12, pytest-9.1.1, pluggy-1.6.0
collected 6 items

tests/test_cli_accelerate_config.py::TestResolveAccelerateConfigArgument::test_two_token_form PASSED [ 16%]
tests/test_cli_accelerate_config.py::TestResolveAccelerateConfigArgument::test_equals_form PASSED [ 33%]
tests/test_cli_accelerate_config.py::TestResolveAccelerateConfigArgument::test_equals_form_matches_two_token_form PASSED [ 50%]
tests/test_cli_accelerate_config.py::TestResolveAccelerateConfigArgument::test_no_accelerate_config_argument PASSED [ 66%]
tests/test_cli_accelerate_config.py::TestResolveAccelerateConfigArgument::test_missing_value_raises PASSED [ 83%]
tests/test_cli_accelerate_config.py::TestResolveAccelerateConfigArgument::test_invalid_config_name_raises PASSED [100%]

============================== 6 passed in 7.95s ===============================

Also ran the full existing CLI test suite to check for regressions:

$ python -m pytest tests/test_cli_utils.py tests/test_cli_accelerate_config.py -q
.........................................                                [100%]
41 passed in 41.92s

pre-commit run --files trl/cli/accelerate_config.py tests/test_cli_accelerate_config.py passes (ruff check, ruff
format, doc-builder style check all green).

Fixes #6874

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline, Pull Request section?
• Was this discussed/approved via a GitHub issue? Please add a link to it if that's the case.
• Did you make sure to update the documentation with your changes?
• Did you write any new necessary tests?

AI writing disclosure

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Who can review?

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---

Note

Low Risk
Small, localized CLI argument parsing change with dedicated tests; no auth, data, or training logic touched.

Overview
Fixes a bug where --accelerate_config=single_gpu was passed through to accelerate launch unchanged instead of being rewritten to --config_file with the bundled YAML path.

resolve_accelerate_config_argument now normalizes any --accelerate_config=<value> argv token into the existing two-token form before lookup, so both CLI styles behave the same and the rest of the resolver is unchanged.

Adds tests/test_cli_accelerate_config.py with regression coverage for both forms, equivalence, no-op when the flag is absent, missing values, and invalid config names (including equals form).

^{Reviewed by Cursor Bugbot for commit deb6ae0. Bugbot is set up for automated code reviews on this repo. Configure here.}

[DaoyuanLi2816]

Correction to my earlier overlap note: the earliest implementation is #6875, opened on August 23 for #6874. It already covers both CLI spellings, empty-value validation, trailing arguments, and CLI integration. Linking the canonical earlier PR so the implementations can be consolidated rather than reviewed independently.

[amanyagami]

Closing in favor of #6875, which was opened earlier (Aug 23) and covers the same fix (both CLI spellings, empty-value validation, trailing arguments, CLI integration tests). Thanks @DaoyuanLi2816 for the pointer — apologies for the duplicate effort.