codex/tools/argument-comment-lint

argument-comment-lint

Isolated Dylint library for enforcing Rust argument comments in the exact /*param*/ shape.

Prefer self-documenting APIs over comment-heavy call sites when possible. If a call site would otherwise read like foo(false) or bar(None), consider an enum, named helper, newtype, or another idiomatic Rust API shape first, and use an argument comment only when a smaller compatibility-preserving change is more appropriate.

It provides two lints:

• argument_comment_mismatch (warn by default): validates that a present /*param*/ comment matches the resolved callee parameter name.
• uncommented_anonymous_literal_argument (allow by default): flags anonymous literal-like arguments such as None, true, false, and numeric literals when they do not have a preceding /*param*/ comment.

String and char literals are exempt because they are often already self-descriptive at the callsite.

Behavior

Given:

fn create_openai_url(base_url: Option<String>, retry_count: usize) -> String {
    let _ = (base_url, retry_count);
    String::new()
}

This is accepted:

create_openai_url(/*base_url*/ None, /*retry_count*/ 3);

This is warned on by argument_comment_mismatch:

create_openai_url(/*api_base*/ None, 3);

This is only warned on when uncommented_anonymous_literal_argument is enabled:

create_openai_url(None, 3);

Development

Install the required tooling once:

cargo install cargo-dylint dylint-link
rustup toolchain install nightly-2025-09-18 \
  --component llvm-tools-preview \
  --component rustc-dev \
  --component rust-src

Run the lint crate tests:

cd tools/argument-comment-lint
cargo test

GitHub releases also publish a DotSlash file named argument-comment-lint for macOS arm64, Linux arm64, Linux x64, and Windows x64. The published package contains a small runner executable, a bundled cargo-dylint, and the prebuilt lint library.

The package is not a full Rust toolchain. Running the prebuilt path still requires the pinned nightly toolchain to be installed via rustup:

rustup toolchain install nightly-2025-09-18 \
  --component llvm-tools-preview \
  --component rustc-dev \
  --component rust-src

The checked-in DotSlash file lives at tools/argument-comment-lint/argument-comment-lint. run-prebuilt-linter.py resolves that file via dotslash and is the path used by targeted package runs such as just argument-comment-lint -p codex-core. Repo-wide runs now go through a native Bazel aspect that invokes a custom rustc_driver and reuses Bazel-managed Rust dependency metadata instead of spawning cargo dylint once per crate. The source-build path remains available in run.py for people iterating on the lint crate itself.

The Unix archive layout is:

argument-comment-lint/
  bin/
    argument-comment-lint
    cargo-dylint
  lib/
    libargument_comment_lint@nightly-2025-09-18-<target>.dylib|so

On Windows the same layout is published as a .zip, with .exe and .dll filenames instead.

DotSlash resolves the package entrypoint to argument-comment-lint/bin/argument-comment-lint (or .exe on Windows). That runner finds the sibling bundled cargo-dylint binary and the single packaged Dylint library under lib/, normalizes the host-qualified nightly filename to the plain nightly-2025-09-18 channel when needed, and then invokes cargo-dylint dylint --lib-path <that-library> with the repo's default DYLINT_RUSTFLAGS and CARGO_INCREMENTAL=0 settings.

The checked-in run-prebuilt-linter.py wrapper uses the fetched package contents directly so the current checked-in alpha artifact works the same way. It also makes sure the rustup shims stay ahead of any direct toolchain cargo binary on PATH, and sets RUSTUP_HOME from rustup show home when the environment does not already provide it. That extra RUSTUP_HOME export is required for the current Windows Dylint driver path.

If you are changing the lint crate itself, use the source-build wrapper:

./tools/argument-comment-lint/run.py -p codex-core

Run the lint against codex-rs from the repo root:

just argument-comment-lint
bazel build --config=argument-comment-lint -- //codex-rs/...
./tools/argument-comment-lint/run-prebuilt-linter.py -p codex-core
just argument-comment-lint -p codex-core

If no package selection is provided, just argument-comment-lint now defaults to the Bazel aspect path over //codex-rs/.... The Python wrappers remain the package-scoped escape hatch and still default the underlying Cargo invocation to --all-targets unless you explicitly narrow the target set, so targeted wrapper runs cover test-only call sites by default.

Repo runs also promote uncommented_anonymous_literal_argument to an error by default:

./tools/argument-comment-lint/run-prebuilt-linter.py -p codex-core

The wrapper does that by setting DYLINT_RUSTFLAGS, and it leaves an explicit existing setting alone. It also defaults CARGO_INCREMENTAL=0 unless you have already set it, because the current nightly Dylint flow can otherwise hit a rustc incremental compilation ICE locally. To override that behavior for an ad hoc run:

DYLINT_RUSTFLAGS="-A uncommented-anonymous-literal-argument" \
CARGO_INCREMENTAL=1 \
  ./tools/argument-comment-lint/run.py -p codex-core

To override an explicitly narrow target selection, or to be explicit in scripts:

./tools/argument-comment-lint/run-prebuilt-linter.py -p codex-core -- --all-targets