licensepack

licensepack generates Go source files containing licensing information for all dependencies used by your Go project. This should help distributors of your software follow the terms of most open source licenses.

Usage

licensepack is intended to be run as a go-generate script. Start by adding licensepack to your go.mod file:

go get -d github.com/paulhammond/licensepack

Then add a go-generate line to your code, along with a variable definition. By default licensepack uses a variable called licenses:

//go:generate go run github.com/paulhammond/licensepack ./path/to/main
var licenses string

Then run go generate:

go generate ./...

A file called licenses.go will be created with contents looking something like this:

// Code generated by licensepack; DO NOT EDIT.
package main

func init() {
	licenses = "## github.com/your/package\n" +
		"\n" +
		"LICENSE:\n" +
		"\n" +
		"Copyright (c) 2021 Your Name. All rights reserved.\n" +
		…
}

Then you can add some code to output the contents of the licenses variable, perhaps if a command line flag is provided:

func main(){
	…
	var credits = flag.Bool("credits", false, "show open source credits")

	flag.Parse()
	if *credits {
		fmt.Println(licenses)
		os.Exit(0)
	}
	…
}

A complete example is available in examples/hello.

By default licensepack generates code wrapped in an init() function so that you can avoid committing the generated file without complaints from the Go tooling. By recreating the file every time your project is compiled you ensure the license information is always kept up to date, at the cost of adding go generate to your build scripts. This is customizable, see below for details.

Adjusting the generated code

Simple changes, including package name, variable name and the output filename can be adjusted with command line flags:

//go:generate go run github.com/paulhammond/licensepack -pkg cmd -var Credits -file path/to/credits.go .
var Credits string

Built in templates

licensepack uses text/template to generate code, allowing you to customize the output to meet your needs. A few built in templates are provided, including one that creates a struct instead of a string:

//go:generate go run github.com/paulhammond/licensepack -tmpl struct .

A complete example of using this template is provided in examples/struct.

If you believe that init() functions are always bad or would prefer to commit the generated file, then templates that generate a variable, const or function declaration are also provided with the -var, -const, and -func suffixes. For example:

//go:generate go run github.com/paulhammond/licensepack -tmpl struct-func .
//go:generate go run github.com/paulhammond/licensepack -tmpl string-const .

If you’d prefer to generate plain text output, perhaps because you’d like to embed licensing information using a different mechanism, there is a plain text template available. To use this you’ll need to disable gofmt. For example:

//go:generate go run github.com/paulhammond/licensepack -file licenses.txt -nofmt -tmpl text .

Custom templates

If you’d like to customize the template you can provide the path to a template file. For example:

//go:generate go run github.com/paulhammond/licensepack -tmpl ./licenses.tmpl .

A complete example is provided in examples/custom. The built in templates can be used as a starting point and hopefully demonstrate usage of the available template helper functions. By default the generated code is formatted before being written to a file so you can be lax with your whitespace.

Keeping licensepack in go.mod

If you follow the instructions above, then run go mod tidy, you will find that licensepack has been removed from your go.mod file. To prevent this from happening make a tools.go file. For example:

// +build tools

package tools

import (
	_ "github.com/paulhammond/licensepack"
)

Alternatives

go-licence-detector also generates license notices. It has many options not available in licensepack, but invocation is more complex and, at the time of writing, includes indirect dependencies that are not actually linked into the compiled binary.

Credits/License

Run licensepack -credits for license information.