code-quality

name	code-quality
description	Shared clean-code / DRY / KISS / YAGNI standards and stack-specific smells for the React 19 + TypeScript + Rust (Tauri 2) monorepo. Library consumed by the code-quality-reviewer and code-quality-author agents.
disable-model-invocation	true

Code Quality Standards

Standards for a pnpm/Turbo monorepo: React 19 + TypeScript frontend, Rust (Tauri 2) backend. The reviewer reports violations against this; the author fixes against it. Both apply the judgment below — these are heuristics, not a linter.

Severity

• High — bugs in waiting: real logic duplication that will drift; a function doing >1 job over shared mutable state; any/unchecked casts hiding type holes; unwrap()/expect()/panic! on fallible paths in non-test Rust; swallowed errors.
• Medium — friction: functions >~50 lines or nesting >3; unclear names; magic numbers/strings; prop drilling; repeated literals; dead params.
• Low — polish: comment-as-deodorant, inconsistent ordering, minor naming, anything the formatter already owns.

Principles — and where they backfire (do NOT over-apply)

• DRY: dedupe knowledge, not coincidental similarity. Two blocks that look alike but change for different reasons stay separate — a wrong abstraction costs more than duplication. Don't unify before the third occurrence, and only when the rule is truly the same.
• KISS / YAGNI: prefer the boring direct solution. Strip speculative generality — flags, params, hooks, and layers with one caller. Never add abstraction "for later."
• Single responsibility, not dogmatic SOLID. Split when there are two reasons to change, not to hit a line count.
• Net result must be simpler. A change that adds indirection, interfaces, or files without removing real complexity is a regression — record it as "considered, rejected," don't ship it.

Stack smells

React/TS:

• A component doing fetch + state + formatting + render → extract a hook / presentational split.
• State derivable from props or other state (compute, don't store); effects syncing state that should be derived.
• Over-memoization (useMemo/useCallback with no measured need) as much as missing memo on a hot path.
• any, as assertions, stringly-typed unions → discriminated unions / generics. Enum where a union literal is simpler. Non-null ! masking a real nullable; // @ts-ignore.
• Prop drilling >2 levels → context or composition. Exported types/components with no consumer. Rust/Tauri:
• unwrap/expect/panic! on I/O, parse, lock, or command paths → Result + ? + a real error enum (thiserror).
• Clone-happy code where a borrow works; String params that should be &str.
• Fat command handlers → push logic into testable fns; keep #[tauri::command] thin. unsafe without a justifying comment. Cross-cutting: duplicated literals/config → one const/module; magic numbers → named; deep nesting → guard clauses / early returns; a boolean param gating two behaviors → split the function.

External standards & best-practices (verified 2026-06-19)

These are tensions to manage, not rules to obey.

• SOLID — SRP/OCP/LSP/ISP/DIP guide module boundaries; apply where they cut coupling, not reflexively. https://martinfowler.com/bliki/
• DRY — dedupe knowledge, not coincidentally-similar code; premature DRY couples unrelated call sites. https://martinfowler.com/bliki/BeckDesignRules.html
• KISS / YAGNI — simplest thing that works; DRY routinely collides with KISS → prefer the clearer code; add abstraction at the second real use (rule of three). https://martinfowler.com/bliki/Yagni.html
• AHA (Avoid Hasty Abstractions) — the current critique of over-abstraction: a wrong abstraction costs more than duplication; inline a leaky abstraction back before re-splitting. https://kentcdodds.com/blog/aha-programming · https://sandimetz.com/blog/2016/1/20/the-wrong-abstraction
• Smallest behavior-preserving diff; name the trade-off (coupling↔reuse, simplicity↔flexibility) rather than citing an acronym.

Common mistakes: citing DRY to justify a shared abstraction over two superficially-similar but semantically-unrelated blocks (premature coupling); treating SOLID/YAGNI as pass/fail gates → ceremony (interfaces with one impl, factories for one type).