Lang Go

Activate this skill when the user mentions any of:

File Extensions: .go, go.mod, go.sum

Go Core: Golang, Go language, goroutine, channel, sync.WaitGroup, sync.Mutex, context.Context, errgroup, defer, panic/recover, go mod, go build, go test

Web Frameworks: Fiber, Gin, Echo, Chi, net/http, http.Handler, middleware, router, REST API

Database/ORM: GORM, sqlc, pgx, database/sql, sql.DB, migrations, query builder

CLI: Cobra, Viper, CLI tool, command-line, flags, subcommands

Concurrency: worker pool, semaphore, select statement, buffered channel, fan-out/fan-in, rate limiting

Cloud Native: Docker, Kubernetes, containerized, microservice, gRPC, protobuf

⛔ Forbidden Patterns

1. NO Ignoring Errors: Never write _ = func() if it returns an error. Always check if err != nil.
2. NO Global State: Avoid mutable global variables. Use dependency injection (pass structs/interfaces).
3. NO Panic: Do not use panic() in application code. Use it only for unrecoverable startup errors. Return errors instead.
4. NO interface{} Abuse: Avoid interface{}/any unless absolutely necessary. Use specific interfaces or generics.
5. NO Naked Returns: Avoid named return parameters with naked return statements in non-trivial functions. It hurts readability.

🤖 Agent Tool Strategy

1. Dependency Management: Run go mod tidy after adding imports or dependencies.
2. Testing: Use go test -v ./... or just test if available.
3. Formatting: Run gofmt -w . or goimports -w . before submitting code.
4. Discovery: Check for justfile first. If it exists, use just -l to list recipes and prefer just commands over language-specific CLIs (npm, cargo, poetry, etc.). Then, read go.mod to check the Go version and dependencies.
5. Build: Use go build -v . to verify compilation.

Quick Reference (30 seconds)

Go 1.23+ Development Expert for high-performance backend systems and CLI applications.

Auto-Triggers: .go, go.mod, go.sum, goroutines, channels, Fiber, Gin, GORM, Echo, Chi

Core Use Cases:

• High-performance REST APIs and microservices
• Concurrent and parallel processing systems
• CLI tools and system utilities
• Cloud-native containerized services

Quick Patterns:

Fiber API:

app := fiber.New()
app.Get("/api/users/:id", func(c fiber.Ctx) error {
    return c.JSON(fiber.Map{"id": c.Params("id")})
})
app.Listen(":3000")

Gin API:

r := gin.Default()
r.GET("/api/users/:id", func(c *gin.Context) {
    c.JSON(200, gin.H{"id": c.Param("id")})
})
r.Run(":3000")

Goroutine with Error Handling:

g, ctx := errgroup.WithContext(context.Background())
g.Go(func() error { return processUsers(ctx) })
g.Go(func() error { return processOrders(ctx) })
if err := g.Wait(); err != nil { log.Fatal(err) }

Implementation Guide (5 minutes)

Go 1.23 Language Features

New Features:

• Range over integers: for i := range 10 { fmt.Println(i) }
• Profile-Guided Optimization (PGO) 2.0
• Improved generics with better type inference

Generics:

func Map[T, U any](slice []T, fn func(T) U) []U {
    result := make([]U, len(slice))
    for i, v := range slice { result[i] = fn(v) }
    return result
}

Web Framework: Fiber v3

app := fiber.New(fiber.Config{ErrorHandler: customErrorHandler, Prefork: true})
app.Use(recover.New())
app.Use(logger.New())
app.Use(cors.New())

api := app.Group("/api/v1")
api.Get("/users", listUsers)
api.Get("/users/:id", getUser)
api.Post("/users", createUser)
api.Put("/users/:id", updateUser)
api.Delete("/users/:id", deleteUser)
app.Listen(":3000")

Web Framework: Gin

r := gin.Default()
r.Use(cors.Default())

api := r.Group("/api/v1")
api.GET("/users", listUsers)
api.GET("/users/:id", getUser)
api.POST("/users", createUser)
r.Run(":3000")

Request Binding:

type CreateUserRequest struct {
    Name  string `json:"name" binding:"required,min=2"`
    Email string `json:"email" binding:"required,email"`
}

func createUser(c *gin.Context) {
    var req CreateUserRequest
    if err := c.ShouldBindJSON(&req); err != nil {
        c.JSON(400, gin.H{"error": err.Error()})
        return
    }
    c.JSON(201, gin.H{"id": 1, "name": req.Name})
}

Web Framework: Echo

e := echo.New()
e.Use(middleware.Logger())
e.Use(middleware.Recover())
e.Use(middleware.CORS())

api := e.Group("/api/v1")
api.GET("/users", listUsers)
api.POST("/users", createUser)
e.Logger.Fatal(e.Start(":3000"))

Web Framework: Chi

r := chi.NewRouter()
r.Use(middleware.Logger)
r.Use(middleware.Recoverer)

r.Route("/api/v1", func(r chi.Router) {
    r.Route("/users", func(r chi.Router) {
        r.Get("/", listUsers)
        r.Post("/", createUser)
        r.Get("/{id}", getUser)
    })
})
http.ListenAndServe(":3000", r)

ORM: GORM 1.25

Model Definition:

type User struct {
    gorm.Model
    Name    string  `gorm:"uniqueIndex;not null"`
    Email   string  `gorm:"uniqueIndex;not null"`
    Posts   []Post  `gorm:"foreignKey:AuthorID"`
}

Query Patterns:

db.Preload("Posts", func(db *gorm.DB) *gorm.DB {
    return db.Order("created_at DESC").Limit(10)
}).First(&user, 1)

db.Transaction(func(tx *gorm.DB) error {
    if err := tx.Create(&user).Error; err != nil { return err }
    return tx.Create(&profile).Error
})

Type-Safe SQL: sqlc

# sqlc.yaml
version: "2"
sql:
  - engine: "postgresql"
    queries: "query.sql"
    schema: "schema.sql"
    gen:
      go:
        package: "db"
        out: "internal/db"
        sql_package: "pgx/v5"

-- name: GetUser :one
SELECT * FROM users WHERE id = $1;

-- name: CreateUser :one
INSERT INTO users (name, email) VALUES ($1, $2) RETURNING *;

Concurrency Patterns

Errgroup:

g, ctx := errgroup.WithContext(ctx)
g.Go(func() error { users, err = fetchUsers(ctx); return err })
g.Go(func() error { orders, err = fetchOrders(ctx); return err })
if err := g.Wait(); err != nil { return nil, err }

Worker Pool:

func workerPool(jobs <-chan Job, results chan<- Result, n int) {
    var wg sync.WaitGroup
    for i := 0; i < n; i++ {
        wg.Add(1)
        go func() {
            defer wg.Done()
            for job := range jobs { results <- processJob(job) }
        }()
    }
    wg.Wait()
    close(results)
}

Context with Timeout:

ctx, cancel := context.WithTimeout(r.Context(), 5*time.Second)
defer cancel()
result, err := fetchData(ctx)
if errors.Is(err, context.DeadlineExceeded) {
    http.Error(w, "timeout", http.StatusGatewayTimeout)
}

Testing Patterns

Table-Driven Tests:

tests := []struct {
    name    string
    input   CreateUserInput
    wantErr bool
}{
    {"valid", CreateUserInput{Name: "John"}, false},
    {"empty", CreateUserInput{Name: ""}, true},
}
for _, tt := range tests {
    t.Run(tt.name, func(t *testing.T) {
        _, err := svc.Create(tt.input)
        if tt.wantErr { require.Error(t, err) }
    })
}

HTTP Testing:

app := fiber.New()
app.Get("/users/:id", getUser)
req := httptest.NewRequest("GET", "/users/1", nil)
resp, _ := app.Test(req)
assert.Equal(t, 200, resp.StatusCode)

CLI: Cobra with Viper

var rootCmd = &cobra.Command{Use: "myapp", Short: "Description"}

func init() {
    rootCmd.PersistentFlags().StringVar(&cfgFile, "config", "", "config file")
    viper.BindPFlag("config", rootCmd.PersistentFlags().Lookup("config"))
    viper.SetEnvPrefix("MYAPP")
    viper.AutomaticEnv()
}

Advanced Patterns

Performance Optimization

PGO Build:

GODEBUG=pgo=1 ./myapp -cpuprofile=default.pgo
go build -pgo=default.pgo -o myapp

Object Pooling:

var bufferPool = sync.Pool{
    New: func() interface{} { return make([]byte, 4096) },
}
buf := bufferPool.Get().([]byte)
defer bufferPool.Put(buf)

Container Deployment (10-20MB)

FROM golang:1.23-alpine AS builder
WORKDIR /app
COPY go.mod go.sum ./
RUN go mod download
COPY . .
RUN CGO_ENABLED=0 go build -ldflags="-s -w" -o main .

FROM scratch
COPY --from=builder /app/main /main
ENTRYPOINT ["/main"]

Graceful Shutdown

go func() { app.Listen(":3000") }()
quit := make(chan os.Signal, 1)
signal.Notify(quit, syscall.SIGINT, syscall.SIGTERM)
<-quit
app.Shutdown()

Context7 Libraries

/air-verse/air    - Live reload for Go apps
/golang/go        - Go language and stdlib
/gofiber/docs     - Fiber web framework
/gin-gonic/gin    - Gin web framework
/labstack/echo    - Echo web framework
/go-chi/docs      - Chi router
/go-gorm/gorm     - GORM ORM
/sqlc-dev/sqlc    - Type-safe SQL
/jackc/pgx        - PostgreSQL driver
/spf13/cobra      - CLI framework
/spf13/viper      - Configuration
/stretchr/testify - Testing toolkit

Troubleshooting

Common Issues:

• Module errors: go mod tidy && go mod verify
• Version check: go version && go env GOVERSION
• Build issues: go clean -cache && go build -v

Performance Diagnostics:

• CPU profiling: go test -cpuprofile=cpu.prof -bench=.
• Memory profiling: go test -memprofile=mem.prof -bench=.
• Race detection: go test -race ./...

Additional Resources

See reference.md for complete framework reference, advanced patterns, and Context7 library mappings.

See examples.md for production-ready code including REST APIs, CLI tools, and deployment configurations.