ForgeLM/.agents/skills/code-review/languages/go.md

Go Anti-Patterns (Auto-Fail)

Load this file during code reviews of Go code. Patterns listed here are immediate findings — no judgment needed. If the pattern exists, it is a finding.

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Auto-Fail Table

Pattern	Severity	Tag	Correct Fix
defer X.Close() (bare)	Critical	[RES]	Error-checked closure with slog.Warn
//nolint:errcheck	Critical	[ERR]	Handle the error — use error-checked closure
defer tx.Rollback() (bare)	Critical	[RES]	Error-checked closure with sql.ErrTxDone guard
fmt.Printf / fmt.Println	Major	[OBS]	Replace with slog structured logging
log.Printf / log.Println	Major	[OBS]	Replace with slog structured logging
resp.Body.Close() without drain	Major	[RES]	io.Copy(io.Discard, resp.Body) then close
Empty if err != nil {} block	Critical	[ERR]	Handle, return, or log the error
_ = someFunc() (discarded error)	Major	[ERR]	Handle the error explicitly

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Detection Commands

Use these grep patterns to scan for anti-patterns before manual review:

# Bare defer Close/Rollback (no error check)
grep -rn 'defer.*\.Close()' --include='*.go'
grep -rn 'defer.*\.Rollback()' --include='*.go'

# nolint:errcheck suppression
grep -rn 'nolint:errcheck' --include='*.go'

# Unstructured logging in production code
grep -rn 'fmt\.Printf\|fmt\.Println\|log\.Printf\|log\.Println' --include='*.go' | grep -v '_test.go'

# Discarded errors
grep -rn '_ = ' --include='*.go' | grep -v '_test.go'

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Correct Patterns (Reference)

Resource Cleanup

// ✅ Rows / Statements / Connections
defer func() {
    if err := rows.Close(); err != nil {
        slog.Warn("failed to close rows", "error", err, "operation", "<operation>")
    }
}()

// ✅ Transaction Rollback
defer func() {
    if err := tx.Rollback(); err != nil && !errors.Is(err, sql.ErrTxDone) {
        slog.Error("failed to rollback transaction", "error", err, "operation", "<operation>")
    }
}()

// ✅ HTTP Response Body
defer func() {
    if _, err := io.Copy(io.Discard, resp.Body); err != nil {
        slog.Warn("failed to drain response body", "error", err)
    }
    if err := resp.Body.Close(); err != nil {
        slog.Warn("failed to close response body", "error", err)
    }
}()

Structured Logging

// ❌ fmt.Printf("User %s logged in from %s\n", userID, ip)
// ❌ log.Printf("User %s logged in from %s", userID, ip)

// ✅
slog.Info("user login", "userId", userID, "ip", ip)

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References

• Go Idioms and Patterns @go-idioms-and-patterns.md
• Logging and Observability Principles @logging-and-observability-principles.md
• Error Handling Principles @error-handling-principles.md
• Resources and Memory Management Principles @resources-and-memory-management-principles.md