fix-rust-lints

name	fix-rust-lints
description	Classify clippy/compiler failures by lint family and apply canonical idiomatic fixes.
argument-hint	[lint output | --scan]
user-invocable	true
allowed-tools	Bash, Read, Edit, Grep
truth_contract	{"canonical_sources":["ops/state/config/repo-map.json"],"live_load_required":["cargo clippy --workspace --all-targets -- -D warnings 2>&1","git diff --name-only $(git merge-base HEAD origin/main)..HEAD"],"examples_only":[],"never_hardcode":["toolchain version (read from rust-toolchain.toml)","branch name or changed file list (always live-query)"]}

Turn recurring Rust lint failures into known remediation classes. Never debug clippy from scratch.

The Problem This Solves

The transcript discovered two lint patterns mid-run and fixed them ad hoc. Those same patterns will recur. This skill pre-encodes them as named classes with canonical fix shapes so the model stops relearning under pressure.

Steps

1. Collect failures: If $ARGUMENTS is empty, run:

   cargo clippy --workspace --all-targets -- -D warnings 2>&1 | grep "^error"
   

   Or read from provided output.

2. Classify each error by lint name (appears in brackets after error:):

   cargo clippy ... 2>&1 | grep -E "^error\[|^\s+-->"
   

3. Apply canonical fix from the playbook below.

4. Scan for recurrences of the same anti-pattern in nearby code:

   grep -rn "<pattern>" crates/ apps/ bins/
   

5. Verify: Re-run the scoped clippy command to confirm the fix.

---

Lint Remediation Playbook

field_reassign_with_default

Trigger: let mut x = T::default(); x.field = value;

Canonical fix: Struct update syntax

// BEFORE
let mut cfg = FooConfig::default();
cfg.some_field = new_value;

// AFTER
let cfg = FooConfig {
    some_field: new_value,
    ..Default::default()
};

Why: Removes the mut binding, signals intent at construction, eliminates post-init mutation.

Scan for recurrences:

grep -rn "let mut .* = .*::default();" crates/ apps/ bins/ --include="*.rs"

---

Deprecated item in --all-targets (test code)

Trigger: use of deprecated ... in test modules when compiling with --all-targets -D warnings

Root cause: #[deprecated] is transitive. CI uses --all-targets, which compiles test code. A deprecated constant marked in a library still fires as an error wherever test code references it, even if the non-test code is clean.

Canonical fix: Replace deprecated references with the recommended replacement, even in tests. Do NOT use #[allow(deprecated)] unless the replacement doesn't exist yet.

// BEFORE (in test)
membership_age_secs: MIN_MEMBERSHIP_AGE_SECS + 1,

// AFTER
membership_age_secs: AttestationThresholds::default().min_membership_age_secs + 1,

Scan for recurrences:

# Find uses of deprecated constants in test modules
grep -rn "MIN_MEMBERSHIP_AGE_SECS\|MAX_ATTESTATIONS_PER_PERIOD\|MIN_TRUST_TO_ATTEST" \
  crates/ apps/ --include="*.rs" | grep -v "pub const\|#\[deprecated"

Re-export workaround: When a module re-exports deprecated items for backward compat, add #[allow(deprecated)] on the pub use block only, not on callers:

#[allow(deprecated)]
pub use attestation::{LEGACY_CONST, old_function};

---

clippy::unwrap_used / clippy::expect_used in tests

Trigger: error: used unwrap() on a Result value in test code

Canonical fix: Add workspace-level test allowance or use #![cfg_attr(test, allow(...))] in the crate root. Do NOT sprinkle #[allow] throughout test functions.

// In lib.rs crate root:
#![cfg_attr(test, allow(clippy::unwrap_used, clippy::expect_used))]

---

clippy::too_many_arguments

Trigger: Function has 8+ parameters.

Canonical fix: Either group related params into a config struct, or accept the lint suppression if the function is a one-off constructor:

// Group into struct when params are logically related
pub fn build_policy(config: PolicyConfig) -> Policy { ... }

// Or suppress if it's an internal constructor unlikely to be called repeatedly
#[allow(clippy::too_many_arguments)]
pub fn new_internal(a: T, b: U, ...) -> Self { ... }

ICN note: Prefer the config struct approach for any function that appears in lifecycle.rs, since those wire multiple values from config objects.

---

clippy::missing_errors_doc / clippy::missing_panics_doc

Trigger: Public function lacks # Errors / # Panics doc section.

Canonical fix: Add the section, or suppress at crate level with #![allow(missing_docs)] if the crate already has that allowance:

/// Does the thing.
///
/// # Errors
/// Returns `Err` if the configuration is invalid.
pub fn do_thing(&self) -> Result<(), String> { ... }

---

Overflow / underflow in time arithmetic

Trigger: SystemTime subtraction that can underflow, or u64::checked_mul missing.

Canonical fix:

// BEFORE (panics on underflow in debug mode)
let cutoff = now - duration;

// AFTER
let cutoff = now.checked_sub(duration).unwrap_or(SystemTime::UNIX_EPOCH);

// For u64 multiplication that might overflow:
let secs = days.checked_mul(SECONDS_PER_DAY).unwrap_or(u64::MAX);

---

Guardrails

• Never suppress a lint without understanding its class. Find the canonical fix first.
• Prefer fixing the anti-pattern to suppressing the warning.
• After fixing, scan for the same pattern in nearby code before committing.
• A fix that passes local cargo clippy -p <crate> may still fail CI --workspace --all-targets. Always scope-check with --all-targets before declaring victory.