deps.go

// Prints dependent packages (including test ones) of the given package.
// $ deps github.com/foo/bar/baz
// net
// net/http
// net/http/httptrace
// net/http/httputil
// net/http/internal
// net/textproto
// net/url
// os
// os/exec
// os/user
// path
// path/filepath
package main

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"os"
	"os/exec"
	"sort"
)

func main() {
	if len(os.Args) != 2 {
		fmt.Printf("usage: %s <pkg>\n", os.Args[0])
		os.Exit(-1)
	}

	cmd := exec.Command("go", "list", "-json", os.Args[1])
	var stdout bytes.Buffer
	cmd.Stdout = &stdout
	cmd.Stderr = os.Stderr
	if err := cmd.Run(); err != nil {
		os.Exit(1)
	}

	pkgs := []pkg{}
	stack := 0
	var buf bytes.Buffer
	for {
		c, err := stdout.ReadByte()
		if err == io.EOF {
			break
		}
		if err != nil {
			os.Exit(1)
		}
		buf.WriteByte(c)

		switch c {
		case 123: // '{'
			stack++
		case 125: // '}'
			stack--
			if stack == 0 {
				var pkg pkg
				dec := json.NewDecoder(&buf)
				if err := dec.Decode(&pkg); err != nil {
					fmt.Println(err)
					os.Exit(-1)
				}
				pkgs = append(pkgs, pkg)
			}
		}
	}

	deps := []string{}
	for _, p := range pkgs {
		deps = append(deps, p.ImportPath)
		deps = append(deps, p.Deps...)
	}

	var curr string
	sort.Strings(deps)
	for _, d := range deps {
		if curr != d {
			fmt.Println(d)
			curr = d
		}
	}
}

// taken from "go list -h"
type pkg struct {
	ImportPath string   // import path of package in dir
	Deps       []string // all (recursively) imported dependencies
}