Go Quality - Quick Reference

When NOT to Use This Skill

• SonarQube setup - Use sonarqube skill

• Security scanning - Use go-security skill

• Testing - Use Go testing skills

Deep Knowledge: Use mcp__documentation__fetch_docs with technology: go for comprehensive documentation.

Tool Overview

Tool Focus Included In

go fmt Formatting Go toolchain

go vet Bug detection Go toolchain

staticcheck Advanced analysis golangci-lint

golangci-lint Meta-linter Standalone

gofumpt Stricter formatting golangci-lint

Recommendation: Use golangci-lint - it runs 100+ linters in parallel.

golangci-lint Setup

Installation

Binary installation (recommended)

curl -sSfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh | sh -s -- -b $(go env GOPATH)/bin v1.56.0

Go install

go install github.com/golangci/golangci-lint/cmd/golangci-lint@latest

macOS

brew install golangci-lint

.golangci.yml

run: timeout: 5m tests: true go: "1.22"

linters: enable: # Bugs - bodyclose - durationcheck - errcheck - exportloopref - gosec - nilerr - sqlclosecheck

# Performance
- prealloc

# Style
- gofumpt
- goimports
- misspell

# Complexity
- cyclop
- gocognit
- gocyclo
- funlen
- nestif

# Best Practices
- goconst
- gocritic
- godot
- ineffassign
- revive
- staticcheck
- unconvert
- unparam
- unused

linters-settings: cyclop: max-complexity: 10

gocognit: min-complexity: 15

gocyclo: min-complexity: 10

funlen: lines: 60 statements: 40

nestif: min-complexity: 4

goconst: min-len: 3 min-occurrences: 3

gocritic: enabled-tags: - diagnostic - style - performance disabled-checks: - hugeParam

revive: rules: - name: blank-imports - name: context-as-argument - name: context-keys-type - name: dot-imports - name: error-naming - name: error-return - name: error-strings - name: exported - name: increment-decrement - name: indent-error-flow - name: package-comments - name: range - name: receiver-naming - name: time-naming - name: unexported-return - name: var-declaration - name: var-naming

issues: exclude-rules: # Exclude some linters from tests - path: _test.go linters: - funlen - gocognit

# Exclude generated files
- path: \.pb\.go
  linters:
    - all

max-same-issues: 0 max-issues-per-linter: 0

Commands

Run all linters

golangci-lint run

Run on specific path

golangci-lint run ./pkg/...

Fix auto-fixable issues

golangci-lint run --fix

Show enabled linters

golangci-lint linters

Run specific linter

golangci-lint run --enable=gosec --disable-all

Verbose output

golangci-lint run -v

Built-in Go Tools

go fmt / gofmt

Format file

go fmt ./...

Check without changing

gofmt -l .

Simplify code

gofmt -s -w .

go vet

Run vet

go vet ./...

Specific checks

go vet -printf ./...

gofumpt (Stricter Formatting)

Install

go install mvdan.cc/gofumpt@latest

Format

gofumpt -w .

Common Linter Errors

errcheck - Unhandled Errors

// BAD - Error ignored file, _ := os.Open("file.txt")

// GOOD - Error handled file, err := os.Open("file.txt") if err != nil { return fmt.Errorf("failed to open file: %w", err) } defer file.Close()

bodyclose - Unclosed Response Body

// BAD - Body not closed resp, err := http.Get(url) if err != nil { return err } data, _ := io.ReadAll(resp.Body)

// GOOD - Body closed resp, err := http.Get(url) if err != nil { return err } defer resp.Body.Close() data, err := io.ReadAll(resp.Body)

gosec - Security Issues

// BAD - Hardcoded credentials (G101) const password = "secret123"

// GOOD - Environment variable password := os.Getenv("DB_PASSWORD") if password == "" { return errors.New("DB_PASSWORD not set") }

ineffassign - Ineffective Assignment

// BAD - Assignment overwritten x := 5 x = 10 // Previous value never used

// GOOD - Remove or use x := 10

cyclop/gocyclo - High Complexity

// BAD - Complex function func process(data Data) error { if data.Type == "A" { if data.Status == "active" { if data.Value > 0 { // deep nesting } } } // ... many more conditions }

// GOOD - Extract and simplify func process(data Data) error { if !data.isValid() { return ErrInvalidData }

switch data.Type {
case "A":
    return processTypeA(data)
case "B":
    return processTypeB(data)
default:
    return ErrUnknownType
}

}

Common Code Smells & Fixes

1. Error Handling

// BAD - Ignoring errors data, _ := json.Marshal(obj)

// BAD - Generic error message if err != nil { return errors.New("error occurred") }

// GOOD - Wrap with context data, err := json.Marshal(obj) if err != nil { return fmt.Errorf("failed to marshal user %d: %w", user.ID, err) }

2. Context Propagation

// BAD - No context func fetchUser(id int) (*User, error) { return db.Query("SELECT * FROM users WHERE id = ?", id) }

// GOOD - Context first parameter func fetchUser(ctx context.Context, id int) (*User, error) { return db.QueryContext(ctx, "SELECT * FROM users WHERE id = ?", id) }

3. Interface Pollution

// BAD - Interface with many methods type UserService interface { GetUser(id int) (*User, error) CreateUser(u *User) error UpdateUser(u *User) error DeleteUser(id int) error ListUsers() ([]*User, error) SearchUsers(q string) ([]*User, error) // ... 10 more methods }

// GOOD - Small, focused interfaces type UserGetter interface { GetUser(ctx context.Context, id int) (*User, error) }

type UserCreator interface { CreateUser(ctx context.Context, u *User) error }

// Compose when needed type UserService interface { UserGetter UserCreator }

4. Package Structure

// BAD - God package package app

func CreateUser() {} func CreateOrder() {} func SendEmail() {} func GeneratePDF() {}

// GOOD - Focused packages // user/service.go package user func Create(ctx context.Context, u *User) error {}

// order/service.go package order func Create(ctx context.Context, o *Order) error {}

5. Receiver Naming

// BAD - Long receiver names func (userService *UserService) GetUser(id int) {} func (this *UserService) CreateUser(u *User) {}

// GOOD - Short, consistent names func (s *UserService) GetUser(id int) {} func (s *UserService) CreateUser(u *User) {}

// Or even shorter for simple types func (u *User) FullName() string {}

Pre-commit Setup

.pre-commit-config.yaml

repos:

• repo: https://github.com/golangci/golangci-lint rev: v1.56.0 hooks:

  • id: golangci-lint

• repo: local hooks:

  • id: go-fmt name: go fmt entry: gofmt -w language: system types: [go]

  • id: go-vet name: go vet entry: go vet ./... language: system types: [go] pass_filenames: false

Makefile

.PHONY: lint fmt vet test quality

lint: golangci-lint run

fmt: gofumpt -w .

vet: go vet ./...

test: go test -race -cover ./...

quality: fmt vet lint test

VS Code Settings

// .vscode/settings.json { "go.lintTool": "golangci-lint", "go.lintFlags": ["--fast"], "go.formatTool": "gofumpt", "[go]": { "editor.formatOnSave": true, "editor.codeActionsOnSave": { "source.organizeImports": "explicit" } }, "gopls": { "staticcheck": true, "analyses": { "unusedparams": true, "shadow": true } } }

Quality Metrics Targets

Metric Target Linter

Cyclomatic Complexity < 10 cyclop, gocyclo

Cognitive Complexity < 15 gocognit

Function Lines < 60 funlen

Nesting Depth < 4 nestif

Test Coverage

80% go test

CI/CD Integration

GitHub Actions

name: Quality on: [push, pull_request]

jobs: quality: runs-on: ubuntu-latest steps: - uses: actions/checkout@v4

  - name: Set up Go
    uses: actions/setup-go@v5
    with:
      go-version: "1.22"

  - name: golangci-lint
    uses: golangci/golangci-lint-action@v4
    with:
      version: v1.56.0

  - name: Run tests
    run: go test -race -coverprofile=coverage.txt ./...

  - name: Upload coverage
    uses: codecov/codecov-action@v4
    with:
      files: coverage.txt

Anti-Patterns

Anti-Pattern Why It's Bad Correct Approach

_ = err (ignoring) Hides failures Handle or log errors

No context in functions Can't cancel/timeout Pass context as first param

Giant interfaces Hard to mock/test Small, focused interfaces

Package-level vars Global state Dependency injection

//nolint without reason Hides issues Add comment explaining why

init() abuse Hidden initialization Explicit setup functions

Quick Troubleshooting

Issue Likely Cause Solution

golangci-lint timeout Too many linters Increase timeout or use --fast

Conflicting linter rules Multiple formatters Disable duplicates

False positive Linter bug or edge case Add //nolint:linter with comment

Missing go.sum entries Incomplete module Run go mod tidy

Import grouping wrong goimports config Configure in .golangci.yml

Related Skills

• SonarQube

• Clean Code

• Go Security