name: golang-senior-lead
description: "Expert Golang senior/lead developer dengan 20+ tahun pengalaman. Gunakan skill ini ketika bekerja dengan Go/Golang projects untuk membuat kode clean, maintainable, scalable, struktur folder production-grade, Docker containerization, debugging, mendeteksi celah crash/bug/race condition, code review standar senior engineer, testing strategies, performance optimization, dan library selection battle-tested. Trigger keywords include golang, go, docker, microservice, api, backend, clean code, refactor, debugging."

Golang Senior/Lead Developer Expertise

Skill ini mengandung accumulated wisdom dari 20+ tahun production experience. Setiap recommendation sudah battle-tested di high-traffic systems.

Core Philosophy

KISS (Keep It Stupid Simple) - Kode terbaik adalah kode yang tidak perlu ditulis. Setiap line of code adalah liability.

Less is More - Jangan over-engineer. Solve today's problem, not imaginary future problems. YAGNI (You Ain't Gonna Need It).

Explicit over Implicit - Go menghargai explicitness. Jangan gunakan magic. Kode harus readable tanpa documentation.

Fail Fast, Fail Loud - Error harus di-handle segera, jangan di-ignore. Panic early jika state tidak valid.

Project Structure (Production-Grade)

project-name/
├── cmd/                    # Entry points (main packages)
│   ├── api/               
│   │   └── main.go        # HTTP API server
│   └── worker/            
│       └── main.go        # Background worker
├── internal/               # Private packages (tidak bisa di-import external)
│   ├── domain/            # Business entities & interfaces (CORE)
│   │   ├── user.go        # Entity + Repository interface
│   │   └── order.go
│   ├── usecase/           # Business logic (orchestration)
│   │   └── user/
│   │       ├── service.go
│   │       └── service_test.go
│   ├── repository/        # Data access implementations
│   │   └── postgres/
│   │       └── user.go
│   ├── handler/           # HTTP/gRPC handlers
│   │   └── http/
│   │       └── user.go
│   └── pkg/               # Internal shared utilities
│       ├── validator/
│       └── logger/
├── pkg/                    # Public packages (bisa di-import external)
├── config/                 # Configuration files
├── migrations/             # Database migrations
├── scripts/                # Build/deploy scripts
├── docker/
│   ├── Dockerfile
│   └── docker-compose.yml
├── go.mod
├── go.sum
├── Makefile
└── .golangci.yml          # Linter config

Critical Rules:
- internal/ = private, tidak bisa di-import dari luar module
- domain/ = ZERO dependencies ke infrastructure. Pure business logic.
- Dependency flow: handler → usecase → repository. NEVER backwards.

Error Handling Golden Rules

// ❌ NEVER ignore errors
result, _ := someFunction()

// ✅ ALWAYS handle or propagate
result, err := someFunction()
if err != nil {
    return fmt.Errorf("someFunction failed: %w", err) // wrap with context
}

// ❌ NEVER use panic for expected errors
if user == nil {
    panic("user not found") // WRONG!
}

// ✅ Return error for expected failures
if user == nil {
    return nil, ErrUserNotFound
}

// Sentinel errors (define di package level)
var (
    ErrNotFound     = errors.New("not found")
    ErrUnauthorized = errors.New("unauthorized")
)

Concurrency Patterns (Race Condition Prevention)

Lihat references/concurrency.md untuk patterns lengkap.

Quick Rules:
- Selalu gunakan sync.Mutex untuk shared state
- Prefer channels untuk communication, mutex untuk state protection
- SELALU run go test -race ./... sebelum merge
- Gunakan context.Context untuk cancellation propagation

Docker Best Practices

Lihat references/docker.md untuk Dockerfile dan docker-compose templates.

Quick Rules:
- Multi-stage builds untuk minimal image size
- Non-root user untuk security
- .dockerignore wajib
- Health checks wajib untuk orchestration
- Pin specific versions, NEVER use latest

Recommended Libraries (Battle-Tested)

Lihat references/libraries.md untuk complete list dengan use cases.

Essential Stack:
| Category | Library | Reason |
|----------|---------|--------|
| HTTP Router | chi atau gin | Chi lebih Go-idiomatic, Gin lebih feature-rich |
| Database | sqlx + pgx | Raw SQL power + type safety |
| Validation | validator/v10 | De-facto standard |
| Config | viper atau envconfig | Viper untuk complex, envconfig untuk simple |
| Logging | zerolog atau zap | Structured, fast, production-ready |
| Testing | testify + testcontainers | Assertions + integration tests |

Debugging Workflow

Lihat references/debugging.md untuk advanced techniques.

Quick Commands:

# Race detector
go test -race ./...

# CPU profiling
go test -cpuprofile cpu.prof -bench .

# Memory profiling  
go test -memprofile mem.prof -bench .

# Deadlock detection
GODEBUG=schedtrace=1000 ./app

# Detailed stack traces
GOTRACEBACK=all ./app

Code Review Checklist

Sebelum approve PR, pastikan:

1. Error Handling - Semua error di-handle, tidak ada _ untuk error
2. Race Conditions - Shared state dilindungi, go test -race pass
3. Resource Leaks - Semua defer Close() ada, context digunakan
4. Tests - Unit tests ada, edge cases covered
5. Naming - Clear, Go conventions (MixedCaps, not snake_case)
6. Simplicity - Tidak over-engineered, KISS principle

Testing Strategy

// Table-driven tests (Go idiom)
func TestCalculatePrice(t *testing.T) {
    tests := []struct {
        name     string
        input    float64
        expected float64
        wantErr  bool
    }{
        {"normal price", 100, 110, false},
        {"zero price", 0, 0, false},
        {"negative price", -1, 0, true},
    }

    for _, tt := range tests {
        t.Run(tt.name, func(t *testing.T) {
            got, err := CalculatePrice(tt.input)
            if (err != nil) != tt.wantErr {
                t.Errorf("error = %v, wantErr %v", err, tt.wantErr)
            }
            if got != tt.expected {
                t.Errorf("got %v, want %v", got, tt.expected)
            }
        })
    }
}

Performance Quick Wins

1. Preallocate slices - make([]T, 0, expectedSize)
2. Avoid string concatenation in loops - Use strings.Builder
3. Sync.Pool untuk frequent allocations
4. Buffer channels - Prevent goroutine blocking
5. Index database queries - Explain analyze sebelum deploy

Common Pitfalls to Avoid

Additional References

• references/concurrency.md - Concurrency patterns lengkap
• references/docker.md - Docker templates dan best practices
• references/libraries.md - Complete library recommendations
• references/debugging.md - Advanced debugging techniques
• references/patterns.md - Design patterns untuk Go