tagparse.go

// Log custom tags used by running go root, and the files where they
// are used, so you can quickly see which tags can be used for
// specific behavior or just see, for example, which modules are CGo.

package main

import (
	"fmt"
	"go/scanner"
	"go/token"
	"io/fs"
	"os"
	"path/filepath"
	"regexp"
	"runtime"
	"sort"
	"strings"
)

type Token struct {
	pos token.Position
	tok token.Token
	lit string
}

func main() {
	root := runtime.GOROOT() + "/src"
	grouped := make(map[string][]string)
	isTag := regexp.MustCompile("[a-z0-9._]+")

	known := make(map[string]bool)
	for _, tkn := range scan(root+"/go/build/syslist.go", token.STRING) {
		for _, tag := range strings.Fields(strings.TrimSpace(strings.Trim(tkn.lit, `"`))) {
			known[tag] = true
		}
	}
	if len(known) == 0 {
		panic("parser: unable to find known tags")
	}

	var filenames []string
	err := filepath.WalkDir(root, func(path string, d fs.DirEntry, err error) error {
		if err == nil && !d.IsDir() && filepath.Ext(path) == ".go" {
			if !strings.Contains(path, "/vendor/") && !strings.Contains(path, "/testdata/") {
				filenames = append(filenames, path)
			}
		}
		return err
	})
	if err != nil {
		panic(err)
	}

	for _, filename := range filenames {
		for _, tkn := range scan(filename, token.COMMENT) {
			lit := tkn.lit
			var build string
			if strings.HasPrefix(lit, "//go:build") {
				build = lit[11:]
			}
			if strings.HasPrefix(lit, "// +build") {
				build = lit[10:]
			}
			if build == "" {
				continue
			}
			for _, tag := range isTag.FindAllString(build, -1) {
				if !known[tag] {
					grouped[tag] = append(grouped[tag], tkn.pos.String())
				}
			}
		}
	}

	tags := make([]string, 0, len(grouped))
	for tag, _ := range grouped {
		tags = append(tags, tag)
	}
	sort.Strings(tags)

	for _, tag := range tags {
		fmt.Println(tag + ":")
		for _, filename := range grouped[tag] {
			fmt.Println(filename)
		}
		fmt.Println()
	}
}

func scan(filename string, what token.Token) (tokens []Token) {
	src, err := os.ReadFile(filename)
	if err != nil {
		return
	}
	var s scanner.Scanner
	fset := token.NewFileSet()
	file := fset.AddFile(filename, fset.Base(), len(src))
	s.Init(file, src, nil, scanner.ScanComments)
	for {
		pos, tok, lit := s.Scan()
		if tok == token.EOF {
			break
		}
		if tok == what {
			tokens = append(tokens, Token{fset.Position(pos), tok, lit})
		}
	}
	return
}