blankParam_checker.go

package checkers

import (
	"go/ast"

	"github.com/go-lintpack/lintpack"
	"github.com/go-lintpack/lintpack/astwalk"
)

func init() {
	var info lintpack.CheckerInfo
	info.Name = "blankParam"
	info.Tags = []string{"style", "opinionated", "experimental"}
	info.Summary = "Detects unused params and suggests to name them as `_` (blank)"
	info.Before = `func f(a int, b float64) // b isn't used inside function body`
	info.After = `func f(a int, _ float64) // everything is cool`

	collection.AddChecker(&info, func(ctx *lintpack.CheckerContext) lintpack.FileWalker {
		return astwalk.WalkerForFuncDecl(&blankParamChecker{ctx: ctx})
	})
}

type blankParamChecker struct {
	astwalk.WalkHandler
	ctx *lintpack.CheckerContext
}

func (c *blankParamChecker) VisitFuncDecl(decl *ast.FuncDecl) {
	params := decl.Type.Params
	if decl.Body == nil || params == nil || params.NumFields() == 0 {
		return
	}

	// collect all params to map
	objToIdent := make(map[*ast.Object]*ast.Ident)
	for _, p := range params.List {
		if len(p.Names) == 0 {
			c.warnUnnamed(p)
			return
		}
		for _, id := range p.Names {
			if id.Name != "_" {
				objToIdent[id.Obj] = id
			}
		}
	}

	// remove used params
	// TODO(cristaloleg): we might want to have less iterations here.
	for id := range c.ctx.TypesInfo.Uses {
		if _, ok := objToIdent[id.Obj]; ok {
			delete(objToIdent, id.Obj)
			if len(objToIdent) == 0 {
				return
			}
		}
	}

	// all params that are left are unused
	for _, id := range objToIdent {
		c.warn(id)
	}
}

func (c *blankParamChecker) warn(param *ast.Ident) {
	c.ctx.Warn(param, "rename `%s` to `_`", param)
}

func (c *blankParamChecker) warnUnnamed(n ast.Node) {
	c.ctx.Warn(n, "consider to name parameters as `_`")
}