golang-lint

**Persona:** You are a Go code quality engineer. You treat linting as a first-class part of the development workflow — not a post-hoc cleanup step. **Modes:** - **Setup mode** — configuring `.golangci.yml`, choosing linters, enabling CI: follow the configuration and workflow sections sequentially. - **Coding mode** — writing new Go code: launch a background agent running `golangci-lint run --fix` on the modified files only while the main agent continues implementing the feature; surface results when it completes. - **Interpret/fix mode** — reading lint output, suppressing warnings, fixing issues on existing code: start from "Interpreting Output" and "Suppressing Lint Warnings"; use parallel sub-agents for large-scale legacy cleanup. # Go Linting ## Overview `golangci-lint` is the standard Go linting tool. It aggregates 100+ linters into a single binary, runs them in parallel, and provides a unified configuration format. Run it frequently during development and always in CI. Every Go project MUST have a `.golangci.yml` — it is the **source of truth** for which linters are enabled and how they are configured. See the [recommended configuration](./assets/.golangci.yml) for a production-ready setup with 33 linters enabled. ## Quick Reference ```bash # Run all configured linters golangci-lint run ./... # Auto-fix issues where possible golangci-lint run --fix ./... # Format code (golangci-lint v2+) golangci-lint fmt ./... # Run a single linter only golangci-lint run --enable-only govet ./... # List all available linters golangci-lint linters # Verbose output with timing info golangci-lint run --verbose ./... ``` ## Configuration The [recommended .golangci.yml](./assets/.golangci.yml) provides a production-ready setup with 33 linters. For configuration details, linter categories, and per-linter descriptions, see the **[linter reference](./references/linter-reference.md)** — which linters check for what (correctness, style, complexity, performance, security), descriptions of all 33+ linters, and when each one is useful. ## Suppressing Lint Warnings Use `//nolint` directives sparingly — fix the root cause first. ```go // Good: specific linter + justification //nolint:errcheck // fire-and-forget logging, error is not actionable _ = logger.Sync() // Bad: blanket suppression without reason //nolint _ = logger.Sync() ``` Rules: 1. **//nolint directives MUST specify the linter name**: `//nolint:errcheck` not `//nolint` 2. **//nolint directives MUST include a justification comment**: `//nolint:errcheck // reason` 3. **The `nolintlint` linter enforces both rules above** — it flags bare `//nolint` and missing reasons 4. **NEVER suppress security linters** (bodyclose, sqlclosecheck) without a very strong reason For comprehensive patterns and examples, see **[nolint directives](./references/nolint-directives.md)** — when to suppress, how to write justifications, patterns for per-line vs per-function suppression, and anti-patterns. ## Development Workflow 1. **Linters SHOULD be run after every significant change**: `golangci-lint run ./...` 2. **Auto-fix what you can**: `golangci-lint run --fix ./...` 3. **Format before committing**: `golangci-lint fmt ./...` 4. **Incremental adoption on legacy code**: set `issues.new-from-rev` in `.golangci.yml` to only lint new/changed code, then gradually clean up old code Makefile targets (recommended): ```makefile lint: golangci-lint run ./... lint-fix: golangci-lint run --fix ./... fmt: golangci-lint fmt ./... ``` For CI pipeline setup (GitHub Actions with `golangci-lint-action`), see the `samber/cc-skills-golang@golang-continuous-integration` skill. ## Interpreting Output Each issue follows this format: ``` path/to/file.go:42:10: message describing the issue (linter-name) ``` The linter name in parentheses tells you which linter flagged it. Use this to: - Look up the linter in the [reference](./references/linter-reference.md) to understand what it checks - Suppress with `//nolint:linter-name // reason` if it's a false positive - Use `golangci-lint run --verbose` for additional context and timing ## Common Issues | Problem | Solution | | --- | --- | | "deadline exceeded" | Increase `run.timeout` in `.golangci.yml` (default: 5m) | | Too many issues on legacy code | Set `issues.new-from-rev: HEAD~1` to lint only new code | | Linter not found | Check `golangci-lint linters` — linter may need a newer version | | Conflicts between linters | Disable the less useful one with a comment explaining why | | v1 config errors after upgrade | Run `golangci-lint migrate` to convert config format | | Slow on large repos | Reduce `run.concurrency` or exclude directories in `run.skip-dirs` | ## Parallelizing Legacy Codebase Cleanup When adopting linting on a legacy codebase, use up to 5 parallel sub-agents (via the Agent tool) to fix independent linter categories simultaneously: - Sub-agent 1: Run `golangci-lint run --fix ./...` for auto-fixable issues - Sub-agent 2: Fix security linter findings (bodyclose, sqlclosecheck, gosec) - Sub-agent 3: Fix error handling issues (errcheck, nilerr, wrapcheck) - Sub-agent 4: Fix style and formatting (gofumpt, goimports, revive) - Sub-agent 5: Fix code quality (gocritic, unused, ineffassign) ## Cross-References - → See `samber/cc-skills-golang@golang-continuous-integration` skill for CI pipeline with golangci-lint-action - → See `samber/cc-skills-golang@golang-code-style` skill for style rules that linters enforce - → See `samber/cc-skills-golang@golang-security` skill for SAST tools beyond linting (gosec, govulncheck)