refactor(derive): remove variant run_async state

[jdx]

Summary

• reject redundant variant-level run_async while parsing the attribute
• remove the private model field and downstream validation branches used only to carry that diagnostic
• preserve enum-level run_async dispatch behavior

Testing

• cargo test --all --all-features

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Note

Low Risk
Derive-only refactor of a redundant diagnostic path; no runtime or dispatch behavior change.

Overview
Stops carrying a private run_async flag on enum variants. Redundant #[usage(run_async)] on a variant is now rejected while parsing the attribute, with the same diagnostic as before.

Downstream validation no longer checks that stored flag. Enum-level run_async / run_async_with dispatch is unchanged.

^{Reviewed by Cursor Bugbot for commit ef4093d. Bugbot is set up for automated code reviews on this repo. Configure here.}

Summary by CodeRabbit

• Bug Fixes
  • Async execution settings on individual variants are now rejected immediately when unsupported.
  • Improved validation for external-subcommand and undispatched enum configurations.
  • Async enum dispatch now consistently awaits variants unless explicitly overridden by run.

[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: 71425399-8abe-40b1-907a-9bcc2b356f51

📥 Commits

Reviewing files that changed from the base of the PR and between 2a057ca and ef4093d.

📒 Files selected for processing (1)

• derive/src/model.rs

Included review availability: Your plan provides up to 4 included reviews per hour; 0 remain after this review.

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📝 Walkthrough

Walkthrough

The change removes stored per-variant run_async state. Variant-level run_async = true now produces an immediate diagnostic. Dispatch validation and variant construction use only run_sync and no_ctx.

Changes

Variant async dispatch validation

Layer / File(s)	Summary
Dispatch contract and validation derive/src/model.rs	Variant no longer stores run_async. Variant parsing rejects enabled run_async with a diagnostic. External-subcommand and undispatched-enum validation, plus variant construction, no longer reference the removed state.

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

Merge Risk: ⚪ Minimal · up to ef409

This localized derive refactor rejects redundant variant-level configuration earlier while preserving enum-level dispatch behavior; no actionable merge-blocking risk remains beyond normal checks and review.

Poem

A rabbit found async tucked away,
And cleared that field from the model today.
“Awaited by enums,” the new check will say,
While sync and context keep their place in the array.
Hop, hop—the dispatch paths are tidy and clear!

🚥 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 1 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 main change: removing variant-level run_async state.
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	▁▁▁▁▁▁▁▁▁▁▁▁█████████	286,216,149 → 286,170,478	-0.02%	25.42 → 25.48ms	+0.22%
startup	▁▁▁▁▁▁▂▂▂▂▂▂▃▃▃▃▃████	874,766 → 874,705	-0.01%	0.85 → 0.87ms	+3.14%

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	instructions, cold parse	vs usage
usage	8425	—
argh	6307	0.7x
clap	6315224	749x
bpaf	21909147	2600x

                                              min       p01       p10    median
usage-rs: argv -> struct                      423       427       431       438  ns
argh: argv -> struct                          270       278       282       288  ns
clap: build tree + parse -> struct         523239    523410    525131    530306  ns
bpaf: build parser + parse -> struct      1429988   1429988   1468243   1598084  ns

usage: argv -> struct                             449 ns      0.45 µs
clap: build tree + parse -> struct             529278 ns    529.28 µs
clap: parse -> struct, tree reused              23951 ns     23.95 µs
clap: build tree only                          324376 ns    324.38 µs

_{ef4093dbbaca vs 2a057ca19942 · measured on the runner, not pushed to the history.}