go script to minimize gitignore rules for those super hairy repos

minignore.go

// minignore.go
// John Kelley <john@kelley.ca>
// January 2019
// Covered by BSD license
//
// minignore parses all of the rules in your gitignore files and omits those rules which are covered by others
// (including duplicate lines). The output is written to the given path with '.new' appended to the filename
//
// Usage: go run minignore.go .gitignore

package main

import  (
	"bufio"
	"bytes"
	"fmt"
	"log"
	"os"
	"io/ioutil"
	"github.com/sabhiram/go-gitignore"
	"strings"
)

func main() {
	new_data := bytes.NewBuffer(nil)
	lines := make(map[string]bool)
  if len(os.Args) != 2 {
    fmt.Println("Usage: go run minignore.go <gitignore path>")
    return
  }
	data,err := ioutil.ReadFile(os.Args[1])
	if err != nil {
		fmt.Println("Could not read file:", os.Args[1])
		return
	}


	{
		scanner := bufio.NewScanner(bytes.NewReader(data))
		for scanner.Scan() {
			lines[scanner.Text()] = true
		}
	}
	scanner1 := bufio.NewScanner(bytes.NewReader(data))

	for scanner1.Scan() {
//		log.Println("Matching ", scanner1.Text())
		filt, err := ignore.CompileIgnoreLines(scanner1.Text())

		if err != nil {
			log.Fatal(err)
		}
		scanner2 := bufio.NewScanner(bytes.NewReader(data))
		for scanner2.Scan() {
			if 0 == strings.Compare(scanner1.Text(), scanner2.Text()) {
				continue
			}
			if filt.MatchesPath(scanner2.Text()) {
				log.Printf("	Deleting %s (matches %s)\n", scanner2.Text(), scanner1.Text())
				delete(lines, scanner2.Text())
			}
		}
		if err := scanner2.Err(); err != nil {
			log.Fatal(err)
		}
	}

	if err := scanner1.Err(); err != nil {
		log.Fatal(err)
	}

	{
		scanner := bufio.NewScanner(bytes.NewReader(data))
		for scanner.Scan() {
			if lines[scanner.Text()] {
				new_data.WriteString(scanner.Text()+"\n")
			}
		}
	}

	if new_data.Len() > 0 {
		err := ioutil.WriteFile(os.Args[1] + ".new", new_data.Bytes(), 0644)
		if err != nil {
			log.Fatal(err)
		}
	}
}