revive/rule/useless-break.go

package rule

import (
	"go/ast"
	"go/token"

	"github.com/mgechev/revive/lint"
)

// UselessBreak lint rule.
type UselessBreak struct{}

// Apply applies the rule to given file.
func (r *UselessBreak) Apply(file *lint.File, _ lint.Arguments) []lint.Failure {
	var failures []lint.Failure

	onFailure := func(failure lint.Failure) {
		failures = append(failures, failure)
	}

	astFile := file.AST
	w := &lintUselessBreak{onFailure, false}
	ast.Walk(w, astFile)
	return failures
}

// Name returns the rule name.
func (r *UselessBreak) Name() string {
	return "useless-break"
}

type lintUselessBreak struct {
	onFailure  func(lint.Failure)
	inLoopBody bool
}

func (w *lintUselessBreak) Visit(node ast.Node) ast.Visitor {
	switch v := node.(type) {
	case *ast.ForStmt:
		w.inLoopBody = true
		ast.Walk(w, v.Body)
		w.inLoopBody = false
		return nil
	case *ast.CommClause:
		for _, n := range v.Body {
			w.inspectCaseStatement(n)
		}
		return nil
	case *ast.CaseClause:
		for _, n := range v.Body {
			w.inspectCaseStatement(n)
		}
		return nil
	}
	return w
}

func (w *lintUselessBreak) inspectCaseStatement(n ast.Stmt) {
	switch s := n.(type) {
	case *ast.BranchStmt:
		if s.Tok != token.BREAK {
			return // not a break statement
		}
		if s.Label != nil {
			return // labeled break statement, usually affects a nesting loop
		}
		msg := "useless break in case clause"
		if w.inLoopBody {
			msg += " (WARN: this break statement affects this switch or select statement and not the loop enclosing it)"
		}
		w.onFailure(lint.Failure{
			Confidence: 1,
			Node:       s,
			Failure:    msg,
		})
	}
}