Update a buildpack.toml file. For automating changes across many buildpacks.

main.go

package main

import (
	"bytes"
	"fmt"
	"os"
	"path/filepath"
	"strings"

	"github.com/BurntSushi/toml"
)

func main() {
	if len(os.Args) != 2 {
		fmt.Println("USAGE:")
		fmt.Println("  update-buildpack-toml <bp-path>")
		os.Exit(1)
	}

	buildpackRoot := os.Args[1]

	file := filepath.Join(buildpackRoot, "buildpack.toml")
	c, err := os.ReadFile(file)
	if err != nil && !os.IsNotExist(err) {
		panic(fmt.Errorf("unable to read %s\n%w", file, err))
	}

	comments := []byte{}
	for i, line := range bytes.SplitAfter(c, []byte("\n")) {
		if bytes.HasPrefix(line, []byte("#")) || (i > 0 && len(bytes.TrimSpace(line)) == 0) {
			comments = append(comments, line...)
		} else {
			break // stop on first comment
		}
	}

	md := make(map[string]interface{})
	if err := toml.Unmarshal(c, &md); err != nil {
		panic(fmt.Errorf("unable to decode buildpack\n%w", err))
	}

	md["targets"] = []map[string]string{
		{
			"os":   "linux",
			"arch": "amd64",
		},
		{
			"os":   "linux",
			"arch": "arm64",
		},
	}

	metadata, ok := md["metadata"].(map[string]interface{})
	if !ok {
		panic(fmt.Errorf("unable to find metadata key"))
	}

	include_files_raw, ok := metadata["include-files"]
	if !ok {
		panic(fmt.Errorf("unable to find include-files key"))
	}

	include_files, ok := include_files_raw.([]interface{})
	if !ok {
		panic(fmt.Errorf("unable to cast include-files to []string: %v", include_files_raw))
	}

	alreadyUpdated := false
	new_include_files := []string{}
	for _, f := range include_files {
		if strings.HasPrefix(f.(string), "linux/") {
			alreadyUpdated = true
			break
		}
		if strings.HasPrefix(f.(string), "bin/") {
			continue
		}
		new_include_files = append(new_include_files, f.(string))
	}

	if !alreadyUpdated {
		new_include_files = append(new_include_files, []string{
			"linux/amd64/bin/build",
			"linux/amd64/bin/detect",
			"linux/amd64/bin/main",
			"linux/arm64/bin/build",
			"linux/arm64/bin/detect",
			"linux/arm64/bin/main",
		}...)
	}

	metadata["include-files"] = new_include_files

	buf := &bytes.Buffer{}
	encoder := toml.NewEncoder(buf)
	if err := encoder.Encode(md); err != nil {
		panic(fmt.Errorf("unable to encode buildpack\n%w", err))
	}

	if err := os.WriteFile(file, append(comments, buf.Bytes()...), 0644); err != nil {
		panic(fmt.Errorf("unable to write out %s\n%w", file, err))
	}
}