main.go

// vfsgendev is a convenience tool for using vfsgen in a common development configuration.
package main

import (
	"bytes"
	"flag"
	"fmt"
	"go/build"
	"io"
	"io/ioutil"
	"log"
	"os"
	"os/exec"
	"path/filepath"
)

var (
	sourceFlag = flag.String("source", "", "Specifies the http.FileSystem variable to use as source.")
	tagFlag    = flag.String("tag", "dev", "Specifies a single build tag to use for source. The output will include a negated version.")
	nFlag      = flag.Bool("n", false, "Print the generated source but do not run it.")
)

func usage() {
	fmt.Fprintln(os.Stderr, `Usage: vfsgendev [flags] -source="import/path".VariableName`)
	flag.PrintDefaults()
}

func main() {
	flag.Usage = usage
	flag.Parse()
	if flag.NArg() != 0 {
		flag.Usage()
		os.Exit(2)
	}
	importPath, variableName, err := parseSourceFlag(*sourceFlag)
	if err != nil {
		fmt.Fprintln(os.Stderr, "-source flag has invalid value:", err)
		fmt.Fprintln(os.Stderr)
		flag.Usage()
		os.Exit(2)
	}
	tag, err := parseTagFlag(*tagFlag)
	if err != nil {
		fmt.Fprintln(os.Stderr, "-tag flag has invalid value:", err)
		fmt.Fprintln(os.Stderr)
		flag.Usage()
		os.Exit(2)
	}

	err = run(importPath, variableName, tag)
	if err != nil {
		log.Fatalln(err)
	}
}

func run(importPath, variableName, tag string) error {
	bctx := build.Default
	bctx.BuildTags = []string{tag}
	packageName, variableComment, err := lookupNameAndComment(bctx, importPath, variableName)
	if err != nil {
		return err
	}

	var buf bytes.Buffer
	err = generateTemplate.Execute(&buf, data{
		ImportPath:      importPath,
		PackageName:     packageName,
		BuildTags:       "!" + tag,
		VariableName:    variableName,
		VariableComment: variableComment,
	})
	if err != nil {
		return err
	}

	if *nFlag {
		io.Copy(os.Stdout, &buf)
		return nil
	}

	err = goRun(buf.String(), tag)
	return err
}

// goRun runs Go code src with build tags.
func goRun(src string, tags string) error {
	// Create a temp folder.
	tempDir, err := ioutil.TempDir("", "vfsgendev_")
	if err != nil {
		return err
	}
	defer func() {
		err := os.RemoveAll(tempDir)
		if err != nil {
			fmt.Fprintln(os.Stderr, "warning: error removing temp dir:", err)
		}
	}()

	// Write the source code file.
	tempFile := filepath.Join(tempDir, "generate.go")
	err = ioutil.WriteFile(tempFile, []byte(src), 0600)
	if err != nil {
		return err
	}

	// Compile and run the program.
	cmd := exec.Command("go", "run", "-tags="+tags, tempFile)
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr
	return cmd.Run()
}