chore: lower published crate msrv to 1.91

[jdx]

Summary

• lower usage-lib, usage-dynamic, clap_usage, and usage-cli from Rust 1.95 to 1.91
• consolidate the MSRV matrix so every published crate is checked at Rust 1.91
• keep the manifest-to-matrix guard that prevents the declared floor from drifting

Why

The 1.95 floor came from the external kdl dependency. The parser is now vendored and the published crates build successfully at the fleet's existing Rust 1.91 floor. This lets usage-cli install on runner images currently providing Rust 1.94.

A new usage release will be required before crates.io consumers receive the lower MSRV metadata.

Validation

• all published crates: cargo +1.91 check --locked -p <crate> --all-features
• cargo +1.91 install --path cli --locked
• mise run lint
• git diff --check

AI-assisted — Tool: Codex; model: openai/unavailable; version: unavailable.

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Note

Low Risk
Mostly manifest and CI policy plus equivalent slice chunking; consumers need a new release for crates.io MSRV metadata, and dropping Windows clippy may reduce cfg-specific lint coverage unless intentional.

Overview
Lowers the published crates’ MSRV from 1.95 to 1.91 so metadata matches the fleet toolchain (e.g. usage-cli on runners with Rust 1.94). rust-version is updated in usage-lib, usage-dynamic, clap_usage, and usage-cli.

CI MSRV checks move from a split matrix (1.91 vs 1.95) to a single 1.91 row that runs cargo check on every published crate, with the existing manifest↔matrix guard kept so declared floors cannot drift.

KDL parsing for required_if_eq / required_if_eq_all pairs switches from chunks_exact(2) to as_chunks::<2>() in arg.rs and flag.rs as part of building cleanly at 1.91.

Workflow comments are updated to drop the old “KDL needs 1.95” story; conformance crate comment is tweaked to past tense. The diff also removes the Windows job’s mise r lint:clippy step while nearby comments still argue for platform-specific clippy there.

^{Reviewed by Cursor Bugbot for commit f9861e1. Bugbot is set up for automated code reviews on this repo. Configure here.}

Summary by CodeRabbit

• New Features

  • Expanded compatibility to support Rust 1.91 across the project’s packages.

• Chores

  • Updated automated validation to consistently check the Rust 1.91 minimum supported version.
  • Refined related version-floor documentation and comments.
  • Improved internal argument-pair processing without changing application behavior.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Central YAML (base), Organization UI (inherited)

Review profile: CHILL

Plan: Pro Plus

Run ID: 17765cb8-80a6-4246-a25b-965182b64ce7

📥 Commits

Reviewing files that changed from the base of the PR and between f7cf2f1 and f9861e1.

📒 Files selected for processing (2)

• lib/src/spec/arg.rs
• lib/src/spec/flag.rs

Included review availability: Your plan provides up to 4 included reviews per hour; 1 remains after this review.

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📝 Walkthrough

Walkthrough

The change lowers five crate manifests from Rust 1.95 to 1.91, aligns the MSRV workflow with the shared floor, and uses fixed-size pair iteration in two parsing paths.

Changes

MSRV alignment

Layer / File(s)	Summary
Lower crate version floors clap_usage/Cargo.toml, cli/Cargo.toml, lib/Cargo.toml, usage-dynamic/Cargo.toml, conformance/Cargo.toml	Five manifests declare Rust 1.91 instead of 1.95. A related version comment is updated.
Align MSRV workflow checks .github/workflows/test.yml	The workflow uses one Rust 1.91 matrix row, updates its documentation, and detects any manifest floor mismatch.
Use fixed-size pair iteration lib/src/spec/arg.rs, lib/src/spec/flag.rs	Two parsing paths use as_chunks::<2>() instead of chunks_exact(2) for selector/value pairs. Pairing behavior remains unchanged.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to f9861

The change lowers the published MSRV and updates the corresponding checks without any actionable merge-blocking risk remaining after normal checks and review.

Poem

A rabbit checks the Rust floor,
Ninety-one guards every door.
Workflow rows now match the plan,
Pair chunks fit their arrays well.
Hop, hop—the checks align!

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the primary change: lowering the published crates' MSRV to Rust 1.91.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[github-actions]

Instruction counts

benchmark	trend	instructions	Δ	wall (min)	Δ
markdown	▄▄▆▆▇█▅▆▆▁▂▁▂▃▃▂▃	336,861,274 → 337,877,640	+0.30%	28.87 → 38.44ms	+33.16%
startup	▄▄▃▃▃▄▁▁▁▃▃▃▃████	910,478 → 910,390	-0.01%	0.90 → 0.98ms	+7.98%

No instruction-count regression above 1%.

_{Only instruction counts gate. Wall clock is shown for context — on identical hardware it moves 4-20% run to run.}

_{Measured by tak — instruction-counted CLI benchmarks, stored in this repository's git notes.}

Shadow comparison

Parsing mise use -g node@20 against a shadow of mise's committed spec.
Reported, not gated: the shadow grows as the derive learns to express more, so
what to watch is the ratio rather than either column.

framework	stripped binary, bytes
usage	1321264
bpaf	2493280
clap	3101832

framework	instructions, cold parse	vs usage
usage	8309	—
clap	6315228	760x
bpaf	21909141	2636x

                                              min       p01       p10    median
usage-rs: argv -> struct                      419       426       435       451  ns
clap: build tree + parse -> struct         554167    557090    572232    649566  ns
bpaf: build parser + parse -> struct      1668272   1668272   1678652   1705192  ns

usage: argv -> struct                             469 ns      0.47 µs
clap: build tree + parse -> struct             542528 ns    542.53 µs
clap: parse -> struct, tree reused              24632 ns     24.63 µs
clap: build tree only                          333266 ns    333.27 µs

_{f9861e17d091 vs 3d69594373f9 · measured on the runner, not pushed to the history.}