Try to detect worktree (currently not working)

detect_dirty_worktree.go

package main

import (
        "fmt"
        "io/ioutil"
        "os"
        "os/user"
        "path/filepath"
        "strings"

        "gopkg.in/src-d/go-git.v4"
        "gopkg.in/src-d/go-git.v4/config"
        "gopkg.in/src-d/go-git.v4/plumbing/format/gitignore"
)

func main() {
        if len(os.Args) < 2 {
                fmt.Println("specify repository path.")
                return
        }

        cfg, err := parseGitIgnore()
        if err != nil {
                fmt.Fprintln(os.Stderr, "Could not read ~/.gitconfig: "+err.Error())
                return
        }

        excludesfile := getExcludesFile(cfg)
        if excludesfile == "" {
                fmt.Fprintln(os.Stderr, "Could not get core.excludesfile from ~/.gitconfig")
                return
        }

        ps, err := parseExcludesFile(excludesfile)
        if err != nil {
                fmt.Fprintln(os.Stderr, "Could not parse core.excludesfile: "+excludesfile+": "+err.Error())
                return
        }

        fmt.Println("dirty?:", isDirtyWorktree(os.Args[1], ps))
}

const globalGitConfig = "/home/tyru/.gitconfig"

func parseGitIgnore() (*config.Config, error) {
        cfg := config.NewConfig()

        b, err := ioutil.ReadFile(globalGitConfig)
        if err != nil {
                return nil, err
        }

        if err := cfg.Unmarshal(b); err != nil {
                return nil, err
        }

        return cfg, err
}

func getExcludesFile(cfg *config.Config) string {
        for _, sec := range cfg.Raw.Sections {
                if sec.Name == "core" {
                        for _, opt := range sec.Options {
                                if opt.Key == "excludesfile" {
                                        return opt.Value
                                }
                        }
                }
        }
        return ""
}

func parseExcludesFile(excludesfile string) ([]gitignore.Pattern, error) {
        excludesfile, err := expandTilde(excludesfile)
        if err != nil {
                return nil, err
        }

        data, err := ioutil.ReadFile(excludesfile)
        if err != nil {
                return nil, err
        }

        var ps []gitignore.Pattern
        for _, s := range strings.Split(string(data), "\n") {
                if !strings.HasPrefix(s, "#") && len(strings.TrimSpace(s)) > 0 {
                        ps = append(ps, gitignore.ParsePattern(s, nil))
                }
        }

        return ps, nil
}

// "~/.gitignore" -> "/home/tyru/.gitignore"
func expandTilde(path string) (string, error) {
        var paths []string
        u, err := user.Current()
        if err != nil {
                return "", err
        }
        for _, p := range strings.Split(path, string(filepath.Separator)) {
                if p == "~" {
                        paths = append(paths, u.HomeDir)
                } else {
                        paths = append(paths, p)
                }
        }
        return filepath.Join(paths...), nil
}

func isDirtyWorktree(fullpath string, ps []gitignore.Pattern) bool {
        repos, err := git.PlainOpen(fullpath)
        if err != nil {
                return true
        }
        wt, err := repos.Worktree()
        if err != nil {
                return true
        }
        st, err := wt.Status()
        if err != nil {
                return true
        }

        // Instead of using IsClean(), check each file with ignored patterns
        // return !st.IsClean()

        paths := make([]string, 0, len(st))
        for path := range st {
                paths = append(paths, path)
        }

        fmt.Println("paths:", paths)

        m := gitignore.NewMatcher(ps)
        return !m.Match(paths, false)
}

I managed to get it working in my version of your gist here. Thanks!