code-quality

Reference content for naming and addressing structural and hygiene problems in code. Consumers cite the relevant pattern or rule by name.

Discipline

When citing any pattern or rule from this catalog:

• Name the pattern (e.g. "Feature Envy", "Premature Abstraction"); cite Fowler or Evans where applicable.
• Refactoring direction — propose a concrete move (e.g. "Move Method to X", "Replace Conditional with Polymorphism", "Extract Policy object").
• Severity — blocker if the change entrenches a pre-existing scattered pattern by adding a callsite; suggestion if it introduces a new pattern or a prerequisite refactor would simplify the work.

Pre-existing pattern rule

"Make the change easy, then make the easy change." — Kent Beck. When working with code that has pre-existing problems:

• Doesn't worsen it (reads, passes through, no new callsite): skip — never flag ambient patterns the work doesn't interact with.
• Adds another callsite to a scattered pattern: flag as blocker — stop and extract.
• Depends on it (would be simpler if fixed first): flag as suggestion — "Consider extracting [X] first as a prerequisite." Suggest a separate issue.

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System-level anti-patterns

For evaluating a proposed approach before code exists.

• Premature abstraction — interface/layer before 2+ concrete implementations.
• Wrong layer — business logic in DB, presentation in service layer, persistence in domain.
• Leaky abstraction — forces callers to know its internals.
• Distributed monolith — services that must deploy together or share a database.
• Config as code — logic that belongs in code lives in feature flags or env vars.
• Speculative generality — building for scale or flexibility not needed yet.

Code-level smells

For scanning a concrete diff for structural problems.

Tell, Don't Ask / Feature Envy

Callsites pulling state out of an object to make a decision the object should make itself.

Signals: multiple files checking the same attribute chain (record.status == :locked, record.full_lock?); same conditional duplicated across services/controllers/views/helpers; new method replicating a check already in another layer.

When found: name the violated object, list every callsite, suggest where the logic belongs (policy, model method, service). Adding another callsite to an already-scattered pattern is a blocker.

Scattered Enforcement

A specific Tell-Don't-Ask: authorization or validation enforced in multiple places independently. Access decisions in controller AND service AND view; policy methods partially redundant with service-layer guards; lock/state checks in helpers and views duplicating service rules.

Flag: "Enforced in N places — [list]. Any new callsite should go through [central point]."

Shotgun Surgery

One logical change requires edits across 5+ unrelated files. The rule isn't encapsulated.

Primitive Obsession / Data Clumps

Primitives passed together repeatedly where a value object would clarify intent. Domain concepts as raw strings or magic numbers. A parameter hash that grows beyond 3-4 keys and always travels together.

Layering Violations

Business logic in a view or controller. Persistence logic in domain objects (queries in presenters/helpers). View conditionals encoding business rules.

Anemic Domain Model

Rich service classes doing all the work, model is a data bag. Methods that only do self.field = value; save. New service files reconstructing domain knowledge already implicit in the model. Only flag when the diff adds to this pattern.

Anti-Extensibility Conditionals

New if/elsif/case on type/state/role where polymorphism or strategy would eliminate future N+1 branching. Existing case extended with another arm — flag "this case has N arms now; consider a table or strategy pattern."

Coupling Introduced

New cross-module dependency where modules had no prior relationship. New parameter threaded through multiple layers. New shared mutable structure (global config, class-level state) creating hidden coupling.

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Hygiene rules

For diff review beyond named patterns.

• Single responsibility — flag functions/classes doing too many things.
• Method placement — method with one call site in a different domain belongs closer to caller.
• Naming — flag imprecise (data, info, handle, process, temp) or domain-opaque (internal, app, type, status without qualification).
• Dead code — for every new function, method, scope, constant, or route in the diff, search for callers; zero callers = dead.
• Orphaned code — for every call the diff REMOVES, check if the target still has other callers; last caller removed = dead.
• DRY violations — duplicated logic where existing patterns could be extended. Confirm the pattern exists elsewhere via code search before flagging.
• UX pattern drift — different interactions than established patterns on similar pages (inline vs. modal editing, URL-synced vs. non-synced filters).
• Job granularity — N individual jobs in a loop where one batch job would work, or vice versa.
• Propagation — when the diff renames, removes, or semantically changes a column, attribute, enum, scope, association, route, or method, search the entire codebase (source, views, JS, JSON, YAML, fixtures, exports, serializers, mailers, jobs, seed files, admin pages, marketing pages). Any surviving reference not updated by the diff is a blocker.
• Caching correctness — when the diff reads from caches (in-process memoization, Redis, framework cache stores), verify the cached value can't be stale relative to the operation's requirements, especially after writes.
• Minimize diff — unnecessary whitespace changes (blank lines added/removed, trailing whitespace, re-indentation), unnecessary formatting changes, unrelated refactors, scope creep.

Tests

• Test coverage — every changed behavior has tests. Missing coverage on a happy path or a documented edge case is a finding.
• Test validity — stubs/mocks must target methods actually called in the code path being tested. A stub on a method outside the execution path means the test asserts nothing.
• Testing pyramid — tests sit at the right tier. Most coverage is unit (fast, isolated, exercises one module). Integration tests are for cross-module contracts. End-to-end tests are sparse, expensive, used for critical user flows. Flag when:
  • Logic that could be unit-tested is only exercised through integration or end-to-end tests (slow feedback, hides regressions).
  • Logic that needs real component interaction is only unit-tested with mocks (false confidence).
  • Pyramid is inverted: many e2e tests, few unit tests.
• Test placement — a test belongs at the lowest tier that can validate the behavior. If a unit test covers the requirement, an integration or e2e test for the same logic is duplication.

Auditing pre-existing issues

Check version-control history to confirm an issue is from the current diff, not pre-existing. Apply the pre-existing pattern rule above.