Typescript Bun Drizzle Quality

TypeScript Bun Drizzle Quality

Use this as an umbrella fullstack skill for Bun + TypeScript + Drizzle work.

For slop-reduction/refactor passes focused on deleting custom helpers/types/assertions, use ../desloppify/SKILL.md alongside this skill.

Deliver production-grade code by optimizing for:

• type safety and clarity
• predictable runtime behavior in Bun
• correct and reversible data changes with Drizzle
• clean contract boundaries between API, domain logic, and persistence

Repository Overrides (Required When Present)

Always follow repository-level agent rules (for example AGENTS.md) when they are stricter than this skill.

In this repository, enforce these defaults while using this skill:

• keep things in one function unless extraction is clearly reusable
• avoid try/catch where practical; prefer explicit control flow
• avoid else; prefer early returns
• avoid any and broad assertions
• prefer single-word names when possible
• avoid unnecessary destructuring; prefer dot access
• prefer functional array methods over loops when practical
• prefer Bun-native APIs like Bun.file() where practical
• run tests from package directories, not repository root, when root test is guarded

Track Selection

Choose the track before coding:

1. App/API logic track
   • Use when changing handlers, services, orchestration, auth, or domain rules.
2. Data layer track
   • Use when changing Drizzle schema, migrations, indexes, transactions, or query shape.
3. Fullstack integration track
   • Use when changes cross boundaries (API contract + domain behavior + database effects).

If multiple tracks apply, run App/API first, then Data layer, then Integration checks.

1) Define Constraints First

Before coding, pin down:

• runtime: Bun version and package manager commands
• database: SQL dialect (Postgres/MySQL/SQLite/Turso) and migration flow
• API shape: request/response contracts and error model
• compatibility: expected behavior changes vs strict backward compatibility

If context is missing, ask only for blocking details. Otherwise proceed with explicit assumptions.

2) Adapt to the Host Repository

Distill practices into the target repository instead of assuming fixed commands or structure.

Before implementation or review:

• inspect workspace scripts to discover quality gates (typecheck, lint/format, test)
• inspect CI workflows to confirm which checks are required in pull requests
• identify local test taxonomy and map commands to:
  • unit tests
  • integration tests
  • e2e tests
• run only the smallest relevant subset for touched code paths

Do not assume naming conventions like test:unit or test:e2e; infer from scripts and workflow usage.

3) Fullstack Testing with Bun (Required)

Treat test design and test execution as first-class implementation work.

Use this decision flow:

1. classify repository test commands by behavior into unit, integration, and e2e
2. map touched files/modules to the smallest package/service-local commands
3. if root test is guarded (for example intentionally fails), do not run tests from root
4. run required layers in order: unit -> integration -> e2e, based on scope/risk
5. ensure CI-required checks for pull requests are represented in local verification
6. if no explicit integration suite exists, treat boundary tests (API + real DB or equivalent) as integration coverage and call it out

Technical expectations for Bun repositories:

• use Bun test runner features intentionally (bun test, --watch, --preload, --timeout, path filters)
• keep unit tests deterministic and fast; avoid network and global time randomness
• for integration tests, run real migrations/schema setup and isolate test data
• for e2e, run realistic app wiring and capture artifacts on failure

Do not mark work complete unless one of these is true:

• relevant tests were executed and results were recorded
• execution was blocked by environment constraints and the block + residual risk were stated explicitly

For deeper guidance, read references/testing-patterns.md. For copyable boundary snippets, read references/examples/integration-boundary-test.md.

4) App/API Logic Track

Prefer:

• narrow, composable functions with explicit inputs and outputs
• inferred types where clear, explicit types at boundaries (public functions, adapters, exported utilities)
• discriminated unions for branching states
• unknown + schema validation for untrusted input
• early returns over deeply nested branching

Avoid:

• any unless unavoidable and scoped with justification
• broad as assertions that bypass type checks
• duplicated business logic between handlers, services, and tests

Use Zod (or equivalent) to enforce runtime contracts at process boundaries. For copyable handler patterns, read references/examples/api-boundary.md.

Use Bun-native patterns when they simplify runtime behavior:

• file I/O: Bun.file, Bun.write
• scripting and process execution: Bun shell APIs
• tests and fixtures: Bun test runner patterns

Keep Node compatibility shims only when required by dependencies or deployment targets.

5) Data Layer Track

When touching schema, models, or queries:

• keep naming stable and consistent across schema and code
• preserve backward compatibility unless migration plan explicitly breaks it
• create reversible migrations where possible
• include indexes/constraints intentionally, not implicitly
• validate nullability/default changes against existing data

For deeper patterns, read references/drizzle-patterns.md. For copyable transaction/query patterns, read references/examples/drizzle-transaction.md.

6) Fullstack Integration Track

When a change crosses boundaries, explicitly validate:

• API contract to domain mapping (validation, defaults, and error translation)
• domain rules to persistence behavior (transactions, consistency, rollback behavior)
• persistence results to API output shape (including empty and partial data cases)
• backward compatibility for clients and existing data
• corresponding test coverage across unit/integration/e2e layers where applicable

Use the review rubric in references/quality-checklist.md to structure findings. For end-to-end mapping examples, read references/examples/fullstack-flow.md.

Output Format

Use this as the canonical output template for this skill:

1. What changed and why
2. Risk assessment (behavioral, data, performance)
3. Verification performed or intentionally skipped
4. Required fixes vs optional improvements
5. Remaining gaps or follow-ups

Keep output concise and concrete. Avoid generic "looks good" conclusions without evidence.

Canonical Documentation

Use official docs when clarifying edge behavior:

• Bun docs: https://bun.sh/docs
• Drizzle ORM docs: https://orm.drizzle.team/docs/overview
• Drizzle migrations docs: https://orm.drizzle.team/docs/migrations
• Zod docs: https://zod.dev
• Turbo docs: https://turbo.build/repo/docs