func (w *walker) init() {
	var ignoredPaths []string
	if w.root.Type == RootModuleCache {
		ignoredPaths = []string{"cache"}
	}
	if !w.opts.ModulesEnabled && w.root.Type == RootGOPATH {
		ignoredPaths = w.getIgnoredDirs(w.root.Path)
		ignoredPaths = append(ignoredPaths, "v", "mod")
	}
	for _, p := range ignoredPaths {
		full := filepath.Join(w.root.Path, p)
		if fi, err := os.Stat(full); err == nil {
			w.ignoredDirs = append(w.ignoredDirs, fi)
			if w.opts.Debug {
				log.Printf("Directory added to ignore list: %s", full)
			}
		} else if w.opts.Debug {
			log.Printf("Error statting ignored directory: %v", err)
		}
	}
}
init initializes the walker based on its Options.
package gopathwalk
import (
	"bufio"
	"bytes"
	"fmt"
	"go/build"
	"io/ioutil"
	"log"
	"os"
	"path/filepath"
	"strings"
	"github.com/henrylee2cn/aster/internal/fastwalk"
)
type Options struct {
	Debug          bool  
	ModulesEnabled bool  
}
type RootType int
const (
	RootUnknown RootType = iota
	RootGOROOT
	RootGOPATH
	RootCurrentModule
	RootModuleCache
	RootOther
)
type Root struct {
	Path string
	Type RootType
}
func SrcDirsRoots(ctx *build.Context) []Root {
	var roots []Root
	roots = append(roots, Root{filepath.Join(ctx.GOROOT, "src"), RootGOROOT})
	for _, p := range filepath.SplitList(ctx.GOPATH) {
		roots = append(roots, Root{filepath.Join(p, "src"), RootGOPATH})
	}
	return roots
}
func Walk(roots []Root, add func(root Root, dir string), opts Options) {
	for _, root := range roots {
		walkDir(root, add, opts)
	}
}
func walkDir(root Root, add func(Root, string), opts Options) {
	if _, err := os.Stat(root.Path); os.IsNotExist(err) {
		if opts.Debug {
			log.Printf("skipping nonexistant directory: %v", root.Path)
		}
		return
	}
	if opts.Debug {
		log.Printf("scanning %s", root.Path)
	}
	w := &walker{
		root: root,
		add:  add,
		opts: opts,
	}
	w.init()
	if err := fastwalk.Walk(root.Path, w.walk); err != nil {
		log.Printf("gopathwalk: scanning directory %v: %v", root.Path, err)
	}
	if opts.Debug {
		log.Printf("scanned %s", root.Path)
	}
}
type walker struct {
	root Root                
	add  func(Root, string)  
	opts Options             
	ignoredDirs []os.FileInfo  
}